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CT3 175 Runs Runs but then Doesn't


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You are of course correct. Heck, the rod take the force from repeated explosions above it and has no issues; but I'm sort of like the dog that just got bumped by a car crossing the road and then is scared to go near the curb for a while. I may return to reality before I actually do anything.

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In my hunt for a replacement basket I had also started looking around and was finding both ends of the spectrum as you saw as well - from a $155 new to $35 questionable condition. I had somehow not seen the $99 one.

The $99 is ebay item number


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Hi All.

First, thanks again for the suggestions and info.

I had most of the day off today, so was able to get some dip and completely disassembled the carb, let it soak, and once it was as clean I put it back on with a new fuel filter (which looks as ugly as sin itself)and fired it up. Seemed to run OK and drove around for about a half hour. The problem was that by the time I got on the road the sun was setting and the temp had dropped to about 80 or below, so I think it's still inconclusive as a fix. (Fact is, I was a bit of a coward and didn't want to to risk pushing it home several miles in the dark, so didn't stress it as much as I might have.)

I did however, find a few things in the total teardown that I missed before - while the main jet nozzle was always clear, I didn't take it out before and when I did this time I noted that there was some dirt in the space between the tube and the wall. The tiny pinholes that were spread up the length of the tube might have been partially blocked by that dirt.

Also, although the float needle and seat were clear, there was a little bit of dirt in there after I removed the seat.

Current situation: it didn't fail, but by next weekend I'll have had time to go on a long enough trip to give me more confidence.

Remaining issues:

The throttle slide isn't really smooth. I neither see nor feel any burrs on it and the carb throat feels clear in the space where it moves, but once in a blue moon it sticks (usually at wide open) which I must deal with somehow. It just doesn't move as freely as I think it should. Any suggestions appreciated.

I want to keep the inline fuel filter, but the one that I have is really too large. Problem is that I did a lot of searching just to find this ugly but serviceable one. All the small ones I saw were in on one end and out of the other, which would bring things too close to the exhaust pipe (plus curving the fuel line without kinking it is not especially easy). Any ideas for a source for one that others have used with a CT3 would be really helpful. The problem is that there isn't much space there and the inlet and outlet have to face almost the same way to get to the carb without issues.

The idle is beautiful, but certain throttle settings are uneven. With a gradual throttle increase it will go through periods of stumbling a little and then marvelous surges where everything works perfectly. It's got about 4.4k miles and the only obvious thing I can think of past the carb is points or timing. I haven't replaced the points because I don't have a dial gauge handy to set timing, but I may break down and buy one unless there's a good way to cheat that. My inability to accurately set the timing (at least with what I already know) also keeps me from removing the points to look them over closely. I did drag a business card through them and pulled out a little dirt the first time, but they show no evidence of arcing because I haven't seen anything there since (which should at least tell me the condenser is good). It's shocking what people want for a set of points these days, but it goes with the territory of restoring old toys, I guess. Any better ideas as to what might be causing the rough spots?

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Hi all.

When I first said hello in the bar a few weeks ago, I didn't think I'd be posting so soon, and I'll apologize in advance for rambling on.

I have a CT3 that I've shaken awake from about a 30 year nap in my garage, but it's doing something that is really frustrating and I'm hoping someone can help look into the future and tell me what I'll find.

I'll start by saying that I've chemically cleaned all rust from the tank (I believe) rebuilt the carb, replaced the air cleaner, new plug, changed all fluids.

It now starts easily, seems to run smoothly at low to medium RPM (5-6k) or so. The real high end isn't as good I remember when it was new, but I chalked that up to a need for minor tweaks and minor wear and tear (but now I'm starting to think that's a hint of what's really going on here).

I have the shop manual and am just scratching my head at this one so far. About the only think I haven't done yet is stop to replace the crank seals that I already bought because it seems to work OK to start.

Anyway, the story is this:

As I said, it starts and runs OK at first.

Once in a while it stumbles slightly at sustained acceleration after a few minutes. Maybe some scum found its way to the carb? It's only a slight stumble.

It will run fine for about 20 minutes at medium speeds.

Next, after running around the neighborhood for a while, I decided to go on a longer ride.

This requires speeding up quickly from 0-45 to get on a main road at one point because of where I live.

The first time I did this, I felt it miss/lug a bit, bit it straightened itself out and ran better.

However, at 3.5 miles from home, you'd have thought it ran out of gas or someone shut off the ignition, because the engine totally died.

I could then start it easily again and it would idle OK, but would not go above 3k without stalling. After trying multiple kicks with the throttle open a bit, it would sputter once through the exhaust once in a while (lean?) but wouldn't stay running at anything but idle.

I tried to pull the plug, but, idiot that I was, had forgotten to put the plug wrench back into the tool kit.

Now I had the enviable task of pushing 200 pounds of bike back home (mostly up small hills) in 90 deg heat - we're talking fun.

I got the bike home, took a cold shower, and went back outside pulled the plug and it was fouled with a mixture of gas and oil. I cleaned it and it ran fine again. OK, I'm thinking - if I just had a wrench, I wouldn't have had to tempt cardiac arrest that morning.

Next, after making sure I had tools, I went for another ride.

I drive around for a while, it seems OK, so I try yet another longer ride in widening circles around the neighborhood.

After a while I get brave and try the long ride I had tried earlier.

I get the same stumble after max acceleration onto the main road, but this time it dies completely 20 seconds after that.

Stupidly confident, I stop (like I have a choice) and pull the plug expecting to see it fouled.

It looks like it came out of a manual for descriptions of perfect heat range operation - tan color, no soot, no nothing wrong.

I see I have gas getting to carb (changed to clear fuel hose which helps).

I have spark just fine.

Pulling the started plunger makes it not run at all.

I can still run it at idle, but no high RPMs.

I call my daughter (the one I'm planning to ride this with) and she drives over a gallon of water to cool off the engine thinking I have some sort of heat related issue and I splash the engine are so that it's cool to the touch and try again.

No change.

Outside air temp still 90 degrees (ideal for exercise), so I push the bike 2.5 miles home and decide not to go to the gym that day.

Today I am convinced that when I go outside it will start fine, but I'll probably tear the carb apart looking for a clogged main jet maybe.

I could swear that I read about this happening to someone else in this or another forum, but I'll be darned if I can find it anywhere.

Any suggestions?


Of course when I tried to start it today it was as expected. I hadn't touched it since yesterday, it started fine and ran OK. Between 3-5k RPM it often isn't exactly right, but it's not bad either. (It sometimes seems to hesitate and then surges running extremely well.) I drove it around the neighborhood for about 20 minutes and opened it up almost all the way a few times where it ran fairly well. However, this time I wasn't foolish enough to go too far and sure enough, all at once it quit the same way as before, but less than 1/4 mile from home. It will idle OK, but other than a quick burst in neutral on starting if you crank the throttle it would never stay above 3K RPM for more than a second or two. I let it cool down to touch and it's still misbehaving. Spark seems to be OK still. I thought I had found something when the battery voltage was very low (<1V) and I found out that even though I had replaced the battery, the ground connection from the battery to the frame had enough rust on it to prevent charging. I charged the battery for 10 minutes while I cleaned the connection, sprayed the area with WD40 and used a star washer under the terminal, but no change to the situation - it still starts and stops.

I just pulled the carb and there was a small bit of dark brown granular residue in the bowl but no clogs in the main or pilot jet to be seen. I'll have to put an in line fuel filter in there, but finding one that fits comfortably has been a real issue because there's not much room. When I rebuilt the carb, I couldn't find a kit, so bought the main jet O ring and the gaskets individually but didn't replace the float valve and seat because they looked OK (as without a kit were pricey to buy). I was sure to check the float height, which was fine. Oh well. Off to buy some carb cleaner spray (and probably get an adult beverage) before reassembly and think some more...

Any ideas would still be most welcome.

Hi, Have you checked your float height? Many times I get bikes that the float height is set way too low. A lot of times people will go for the floats if the bike starts to spew gas from the carb when it's just time to clean it up. The bike will run ok untill there is a high demand for fuel, the bowl gets dry before anymore fuel can flow into the carb and it can show up as simply as a lean condition at hard accel or wide open throttle position to complete motor stall depending on how far out of whack they are? Just a thought, stu

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Thank for the suggestion.

In this particular case, I was careful to check the float height when I cleaned the carb after the first several mile walk home. It was exactly as per the spec in the manual, which didn't surprise me, since I've owned this since it was new and have never messed with it. Of course when I was in the Service in the 70s, it was home with my brother. Interestingly, for some reason, every single time I came home on leave there was a turn signal that needed to be replaced, a new scrape, or some other strange change (and also many more miles on the odometer). When I started working on this project a few weeks ago I told him I'd be tearing the engine down to replace a lot of things because of age, which caused him to inform me that the head bolts were slightly larger than standard now. Interesting how that little fact was never conveyed over the years. I would have been a bit more upset and looking for someone to blame for my current troubles were it not that my brother (then 19 to 22 years old) was then starting out and is now still an excellent professional mechanic. The bike ran many, many miles after whatever he did, but those little surprises could mean some other wear in places I didn't expect. (He seems to recall that he was removing carbon, but during those days it could have been exploratory surgery, knowing him).

So, in this case, I'm hoping that when I have replaced the crank seals (among others) and verified timing, etc, that I will have solved my problem. I'm still not convinced entirely that I'll have solved it, but finding that extra oil on top of the piston when I tore it down after the last failure and the strange carbon wear pattern on the head make me think a head gasket leak combine with a seal problem. We'll see. My shiny new clutch basket should arrive in a couple of days and I'm eager to give it another go. Vacation time is schedule starting tomorrow for two weeks, so I'll have a lot of time to figure this out.

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Aug 6 mid-day Update:

Received my new clutch basket in the mail today. :)

Using The OG's suggestion, put a 1/2" extension through the top of the connecting rod, padded things, and the it held everything easily while I removed the primary gear nut. THANKS!

Removing the right crank seal is proving to be difficult, however.

Unlike the left seal, there is no metal collar to easily put a screw into for removal. When I tried, it just tends to shred.

The space available is too small for any of my gear pullers to fit.

I'm considering heating things up with a heat gun or torch and then trying to pry it out, but before I risk damaging something, does anyone have any suggestions? I'm off to the store to see if some sort of seal removal tool to help, but if anyone happens to be at the computer and has done this I'd be much obliged.


Aug 6 Update 11:40PM

Spoke to my brother and one of the mechanics at his shop today and borrowed a few different seal pullers. We'll see what happens this weekend...however, first task will be to finally see if the 4 carbs I rebuilt this week for the FZR600 work as they are supposed to and finally allow it to rise above idle without stalling. That will be first in case it works and I can get it inspected before the shops close for the day on Saturday. I ran out of time after fitting them in today and had to stop to go out for the evening. Synchronizing them may prove to be lots of fun since I've never tried that before. I'll probably do a separate thread on that project later if I think it will be useful to anyone.


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Update Aug 7 10 PM

Using Seal pullers (one medium sized and one small)the right seal came out with only a minor amount of trouble. If I ever figure out how to solve my picture posting issue, I'll post some with the pullers I used. With the primary gear off and the collar pulled out, the seal puller is placed against the crankshaft and rapped with enough force to dig into the seal but not past it into the crankcase. For those that haven't used seal pullers before, note that you don't try to get it behind the seal, but actually dig slightly into the metal around its edge. Then the seal was pulled away with no damage to the case (I was very careful not to hit the puller too hard with a small hammer, but just enough to grab the seal). Then I spent quite a bit of time cleaning away all of the old crankcase gasket material in the area around the kickstart, clutch area, etc. I didn't have anything that was a good solvent for the old gasket cement lying around unfortunately. A small torch and a putty knife came in handy for some of that - just be careful to protect surrounding parts with something to deflect the heat. I used some scrap heavy aluminum flashing and a wet rag for that. It now looks all shiny and new and I'll work on the re-assembly tomorrow. We'll then see if my problems are really solved.

BTW, on my other project, I finished installing the 4 carbs I rebuilt for the FZR600. Syncing proved to be pretty simple using two soft drink bottles with 1/4" plastic tubing from them to the vacuum taps on the boots. I was surprised that it was so easy on a Saturday to locate 6mm MIG tips from a hardware to screw into the holes in the boots. I had seen descriptions of this method around the web for a while and understood the principles involved, but it was the first time I'd tried it, and it worked like a charm. It was readily apparent that there was some imbalance and it was easily corrected. My bottle construction was a little different from some I'd seen based on personal preferences (like making it impossible to get fluid into the cylinders) but nothing that anyone couldn't think up on their own in a short time. The only change I'd make doing this again would be to use plastic bottles that were larger (2 liter maybe?) and use some that were more rigid. At higher RPM, the bottles had a tendency to start to collapse, which was a little comical. Maybe even glass bottles with two hole stoppers on each, which would be more rugged and would stand up to much higher vacuum. It certainly would have been simpler/faster to have a 4 line vacuum gauge setup, but this was quick, effective, and only about $7 in parts. Plus, if I get to play mad scientist once in a while, it keeps me sane...and made a few curious neighbors suspect I wasn't quite sane, which was even better. Main parts of the FZR600 project are now completed. It will need a few tweaks here and there and a set of fork seals, but seems to be quite rideable in it's current form.

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Wel i'm impressed with all of that. I have never heard of seal pullers and would love to see them and hear how they work.

The carb syncronising too, pics and description would be good.

A man of your talents should have no problem with pics, we made it easy...see Forum Help > FAQ's ;)

As for the torch, could have used a hot air gun, just a little less severe. Funny though, there shouldnt be any gasket cement used...just a gasket? :rolleyes:

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Well, I'll give the photos another shot later on today when it's calm. Every time I think I have a few brain cells that still work, something like that comes up to put me in my place. ;)

I went to the FAQs originally when I tried to post a picture of my "rusty, then clean" tank in the Bar area and I thought I had everything all set. Got a Photobucket account, copied the pic "img" info into the body of the post, but all I got in the post was the address. However, when Vez replied, the picture was magically there. I'm sure it's just something stupid I've done, however, and I'll check it out later on.

Re the gasket, the heat gun would have been my first choice as well, but I'd loaned it to my brother to take some old window glazing off, and I was too lazy to go and fetch it.

I did think it was slightly odd to have gasket cement there, but some sections were sure stuck on there. I didn't really notice a huge amount, but they were practically welded in place in some sections, so figured it was cement.

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Well, OG, I have no idea what I'm doing differently now, but I now can post pictures just fine now (I'll chock it up to evil spirits).

Did a lot of bike work this weekend. I got the FZR running, which I'll post separately, and did a lot on the CT3, which I'll cover here.

Short story, everything's assembled, but I still have operational issues with the 175.

To summarize all the work since it was last running:

Replaced left and right crank seals.

Replaced a couple of clutch discs, but only because I sacrificed two to build the removal tool. The existing ones were fine.

Replaced the clutch basket because I was a dolt and broke the original trying to take off the primary drive nut before Mr. OG filled me in on a great way to hold the nut by using a 1/2" extension in the top of the connecting rod (thank you, thank you, again).

Replaced the kickstart seal.

Replaced several pan head case screws that had been distorted during removal.

Replaced the gasket at the bottom of the cylinder, the head gasket, the left and right case gaskets.

I was asked about some tools and procedures, which I'll describe here. (Apologies in advance, but my good camera wasn't around today, so I used my cell phone camera instead.)

First, alongside a ruler for scale, is a picture of the 3 seal pullers that I borrowed from the lead mechanic at my brother's shop.


If you've never used a seal puller, they make life much easier. They allow you to take a seal out of something with the shaft still in the way (and avoid splitting the cases). The one that looks like a miniature hammer has pointed ends that you continually sharpen with use. My mechanic friend uses this one a lot with transmissions, but it was great here as well. Keep in mine that a crankshaft is hardened steel so you're not going to easily hurt it. Place the head along the length of the shaft and the point toward the seal edge. Now hit the other side of the head with a hammer to embed the point into the seal (don't hit it too hard or you'll damage the aluminum case, of course). Once you have a grabbing point by doing this, you can pry the seal out. Sometimes (as in my case) I started with the big one and then used the smaller one to finish pulling it out just because of the tight spaces becasue the engine was still installed in the bike.

A few more pics are below:



As you can see, these tools aren't complicated, aren't expensive, and really come in handy. If the seal has a convenient metal collar, as in the magneto oil seal, a wood screw can take it out, but if it doesn't, like the right crank seal, a seal puller can be your best friend (it's only fault is that it will never buy you a beer - but it may keep you from needing one).

Back to today's work:

I completed the assembly, put in a little less than a quart of Yamalube (splurging on the mfr recommended stuff), torqued everything I could to factory spec from primary gear to clutch basket nut, to head bolts; turned on the key, saw the neutral light, and prepared to hear my future...

A couple of kicks with nothing because the carb was dry, but then if fired up.

It sounded pretty good. Hard to describe, but more even, solid combustion than before the work. I started to think I must have had a leaky head gasket or something because of how even it now sounded.

Then, a second or so later the smoke started.

Let's just say that if there were any mosquitoes in the area, they were gone now.

I was hoping that this was just because I had oil all over everything with the assembly process, but it sure was a lot of smoke.

I idled for a minute or so, then bounced the throttle a few times and it seemed much more responsive than before.

It was still smoking like it was trying to attract aircraft after a few minutes, so I shut it down to check things (I wondered if it was burning engine oil through a badly installed seal. The collar under the primary drive gear did have a small scratch on it that I had repaired with JB weld, but I thought it wasn't a real problem. I considered waiting for a new collar but decided to take my chances that I might have to do it all again later (summer only has a few more weeks left, which might be causing me to make bad decisions - I need to start these projects in mid winter).

After sitting a bit during dinner time, I tried it again. Less smoke, but still there. Checked the oil - it was OK.

Unfortunately it was getting dark so I couldn't do much troubleshooting that involved running the engine in deference to the neighbor kids' bedtimes, so I'll just talk about the other two problems that showed up at that point. I'll still be on vacation Monday, so I'll go into the breach yet again, but if anyone reads this and has a suggestions, I'm all ears.

The first problem that showed up was that the clutch was not a clutch. It was a constant connection to the engine. Not so efficient to have all those parts doing nothing important...

I shut things down and checked the cable play which wasn't right, and also the actual clutch adjustment next to the magneto, which was also off by about 2-3 turns of the screwdriver. I adjusted everything and tried again.

Still no clutch. Did I reassemble something incorrectly? The two new metal clutch discs were not exactly the same as the originals - they had a sort of a tab in one section on the outside, where the originals were perfectly round. I hoped it wouldn't make a difference. It didn't look like they would bind up anywhere. When I reinstalled the pressure plate screws, the manual said to make them just snug, which I thought was odd. They were really tight when I removed them, but I went by what the manual said. Maybe that is it? Also, I noticed that squeezing the clutch seems to put a lot of stress on the left side cover I hadn't tightened an allen screw quite all the way which made that apparent. There may be something just not lined up there. I hate to pull that right cover off, and I'll check the lineup on the left side first, but I'm probably going to have to pull the right side anyway. I hope the gasket will withstand another compression on that side. If I pull that side, I'm expecting that if I squeeze the clutch cable I should see movement there (which a good mechanic might have checked before buttoning things up *sigh*) but we'll see what develops.

The second problem was more disturbing. I seem to have a limit of run time. It was as if I was running out of gas after a few minutes each time it was started. The tank is on reserve right now but still has gas. However, I'll fill it and check again tomorrow. What bugs me is that this could be similar to my former troubles, which has me very worried.

In any case, tomorrow is another day. This will get figured out somehow...

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Well, I'll give the photos another shot later on today when it's calm. Every time I think I have a few brain cells that still work, something like that comes up to put me in my place. ;)

I went to the FAQs originally when I tried to post a picture of my "rusty, then clean" tank in the Bar area and I thought I had everything all set. Got a Photobucket account, copied the pic "img" info into the body of the post, but all I got in the post was the address. However, when Vez replied, the picture was magically there. I'm sure it's just something stupid I've done, however, and I'll check it out later on.

Re the gasket, the heat gun would have been my first choice as well, but I'd loaned it to my brother to take some old window glazing off, and I was too lazy to go and fetch it.

I did think it was slightly odd to have gasket cement there, but some sections were sure stuck on there. I didn't really notice a huge amount, but they were practically welded in place in some sections, so figured it was cement.

I shared your saga with my brother. He has reconstructed a number of vintage bikes. Here is his comment/suggestion:

"I had one just like this, I bet there is a restriction in the exhaust system, he should try running it without the exhaust system, I bet the back pressure is the issue. Perhaps a wasp next somewhere in the pipes. I had to cut mine open to find it." Might be worth a try. JW896

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I shared your saga with my brother. He has reconstructed a number of vintage bikes. Here is his comment/suggestion:

"I had one just like this, I bet there is a restriction in the exhaust system, he should try running it without the exhaust system, I bet the back pressure is the issue. Perhaps a wasp next somewhere in the pipes. I had to cut mine open to find it." Might be worth a try. JW896

Thats a good point there and worth a try, I would be more incined to barbecue the pipe if I thought it was blocked though. Try attaching a cylinder type vacuum cleaner the header pipe, you should get a strong suction at the other end, a blocked pipe would show poor suction and a racing motor in the cylinder vac.

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Yet another update:

Pretty much decided to do the work I was originally going to do before moving on, as I'm guessing I'm dealing with a seal issue.

Removed the cylinder, checked that it and piston were in remarkably good shape after cleaning the carbon off of the piston with a combination of a rounded hacksaw blade and some brake cleaner to finish things off. (Afterwards, of course, cleaned all chemical residue, oiled things up and loose fit things back together.) I may end up checking the timing with the head off - undecided as yet.

Replaced the left crank seal and checked the points closely and looked practically brand new. I have a vague memory of replacing them sometime in the mid to late 70s, but had no idea it was so soon before I parked it. The left seal was easy to replace after drilling a pilot hole and using a sheet metal screw to extract it, but needed to get a new Phillips bit for the impact driver to get the stator assembly out to access the thing (I think I ended up using a #2 for future reference after mashing one screw to oblivion with the wrong bit). If anyone knows an easy source for stator screw replacements it sure would save me time.

I started to do the left seal, but found out I don't have a long enough Phillips impact driver bit to take off the screws on the right case side. Those puppies are in there wicked tight and when I started to round one I decided to wait until I can get my hands on the correct tool so that I don't end up replacing every silly fastener on this engine.

Ah well. It will give me something to do over the weekend. I'd rather be riding all weekend, but without doing this work I might end up pushing instead and I've had enough of that for a while.

Update 7/24/10 6:20pm EDT

If anyone is curious, a #3 Philips Screwdriver and a hammer to tap on the right crankcase screws when its in there along with some significant elbow grease is enough to get the screws out. If you try something smaller, you're more than likely going start rounding out a screw or two.

(I found this out after driving more miles than I care to mention and then giving up trying to find 4 inch long #3 hand impact bits and decided to take a risk.) Of course the screws were all slightly rusted at the point where the cases actually meet but nothing horrible.

Once the screws were out, got the right cover off after rapping it a little with a rubber mallet. A few thin shards of what were probably once the edges of gears in the bottom of the case (hopefully benign, since there have never been transmission issues).

Now off for some more disassembly to replace the right crank seal and O-ring. I'm taking pictures, but can't figure out why they never show on the site even when think I followed the instructions in the FAQs, so I'll give up on trying for a while.

Hopefully some good news that I'm finished later.

I had problems removing the Stator plate screws on my DT175. I ended up drilling the center out and then jambing a flat screwdriver bit into the center hole to extract them. I got them out but they were pretty much toast. I happed to be at the Yamaha dealer and asked if they had any replacements. I was able to replace them with identical screws however they tighten with an allen wrench rather than a phillips bit. The previous owner of my bike had rounded out a couple of the coverplate screws. I was able to replace them with one of 3 options: either a phillips bit screw, an allen wrench head or an 8mm bolt head. They had all of the required lengths. JW896

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  • 2 weeks later...

First off, thanks for the notes on the stator screws. I'll be checking that out a little later on.

As to the suggestion of the exhaust blockage, it seems clear. I was easily able to blow and suck air through it with my compressor and shop vac.

At this point, I'm a bit baffled by what's been going on with the repair/restoration, though.

I was getting a lot of smoke as I said, and the clutch wouldn't disengage, so I tore it down again to see what I might have messed up.

Replaced both left and right seals again (boy was it easier after having the experience of doing it once).

Took apart the clutch basket and saw absolutely no obvious issues.

Scratched my head a lot, but after coming up with no answers I reassembled everything, checking myself wherever possible along the way for correct movement in the clutch, and general careful assembly.

Problem was, that when everything was finished, it wouldn't even start!

It sputtered (more like farted) once or twice through the exhaust, but nothing meaningful.

I checked spark with the plug (which looks good) lying out against the head and it seems OK; thought it had gas, but nothing.

Tried putting a bit of gas directly into the plug hole and kicked it, but nothing.

About the only thing different in assembly was that I had some help putting on the head gasket and thought it might have been put on incorrectly, so I got a compression gauge to see if there was anything strange there.

With wide open throttle, it went to 30PSI on the first and stabilized at about 65 by the fourth.

To me this seems very low and maybe not enough to run, but since my old gauge broke early on, I have no reference point. I know it should be above 100, but will it run this low?

I wonder if I scratched a ring or something in installation of the cylinder, or if one spun around in its groove while holding it for installation...

In any case, it's another trip to the dealer for a couple of head gaskets (one for spare) and I'll take everything apart again. If I had more time, I'd probably oversize the stock piston and bore it right now. However, it's less than two weeks before my daughter goes back to college and I really want this done first. I will, however, check the ring gap when I tear it down, which I didn't bother with before, because even though it was intermittent, it was running. At this point, I'm dealing with something that WAS running before the repair and now isn't, so it's most likely something I did, otherwise I'd be checking all kinds of other things. For completeness, though, I think I'll pick up a dial indicator and check the timing while the head is off though, because even though it has spark, it could be in the wrong place (I can't imaging it changing during the repair, but it was something I'd wanted to check, but hadn't.)

On a better note, to calm my nerves, I took the FZR600 out for a spin for an hour or so last evening now that it runs. I still need to find a miss in that one, but all in all it's OK. (I think there's a cylinder imbalance there because the exhaust pipes have a significant temp mismatch when I point the IR temp gun at them.) Riding is simply a magnificent non-chemical way to relax.

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Update for Aug 19th


My CT3 is finally running! Let the bells ring out and the townspeople rejoice!

Here's what happened late today:

After the prior compression tests showed a horrible 65PSI, I wanted to see why.

Took off the head and cylinder They looked OK. No significant scratches inside the bore to account for leaks.

Checked the ring gap and it was outside of spec - about 0.019 vs 0.014 max spec. That would account for some poor compression, but probably not all (but I'm guessing there). Unfortunately no new rings on hand. However, it ran before without new rings, so pressed on.

Didn't have good micrometer to measure piston clearance, but no evidence of scoring or cosmetic issues.

Reassembled piston and cylinder, leaving off the head in order to check timing.

Installed dial indicator and checked timing of original points at 0.071 Before TDC.

Didn't write down what it really was, but it didn't appear close to correct.

Removed the points and checked them. More pitting than I'd noticed before, but not horrible.

Ordering new ones and a new condenser, but for time being, filed existing one with a point file that I still had from the 1970s (!), then cleaned and reinstalled them.

Now decided to check out stator coils again and saw that a splice I'd made in a wire from the source coil probably in 1974 had a small bare metal area that just might occasionally touch the flywheel if things vibrated enough (as in max throttle when it always died in the past). Possibly a stretch, but plausible. I removed the splice and cleanly soldered and insulated the new splice, tucking it safely out of the way between the coils. This was very promising for my intermittent stall problem, but no guarantees.

Next replaced the flywheel and set timing.

Timing was a bit annoying, because every time I tried to tighten the set screw, the points moved slightly. Got frustrated at one point (puns are everywhere)and settled for just opening at about 0.068 - much better than original, but a bit advanced from the 0.071 spec.

Replaced the head with new gaskets top and bottom. Took a small risk and cheated on the torque by tightening the bolts to a fraction of a ft lb more than 14.5.

Checked compression. Now tops out at just under 70 lbs. Bad, but better.

Connected everything and kicked it a couple of times. Nothing.

Squirted a couple of CCs of gas from a syringe into the spark plus hole.

Kicked it and it fired up first time! Problem was that it was locked wide open from the compression tests (I had thought that the throttle felt too loose) so I immediately shut it down.

Cleared the stuck slide in the carb, cleared the cables that were not smooth under the tank ad tried again.

Started on first kick and seemed to run pretty well.

I put on the helmet and took a quick spin around the neighborhood although it was starting to get dark.

After a short return home, went on longer circles around the neighborhood. Finally went on a 3 mile one way trip to the gas station and it had no issues. It was completely dark now and didn't want to push things at that hour, so upon return home decided to quit for the night. However, I did wind it up a bit in the last mile home to around 7k RPM and all was still good!

The engine still isn't as smooth as I remember it being, but at this point it rides well enough as long as everything holds together.

Tomorrow the plan is to go for a ride with my daughter on the CT3 and me on the FZR600. I will check on that intermittently sticky carb first, though.

I plan to deal with oversizing the piston, and whatever else needed to deal with the compression in the off-season. I also might replace that carb that seems to refuse to act politely no matter what I do. The plan is also to continue to restore the bike rather than just make it safely rideable, which was the mission this time.

BTW, I never did find anything that was definitely the cause of the clutch not disengaging as I described previously. I took it apart and reassembled it the exact same way as far as I could tell. It could still use a slight adjustment, but it was fine.

Oh yes, when I first started it up, it smoked like an aircraft on fire, but it quickly got better. By the end of the ride it was only slightly more than I remembered. I'll check the autolube pump next time to make sure it's not burning too much.

For the time being, life is good.

It took longer and took more cash than I'd expected, but for now, I'm living the dream...

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Well I must say that this board is a life saver to me as I have recently begun a restoration of my 1973 Yamaha CT3 and I know that I will be in desperate need of advice and help! I am glad to hear that you have gotten yours up and running Davinci! Congratulations and enjoy the ride! I actually do have a question right off the bat and that is, how do you remove the gas tank? I have a Clymers manual and it says nothing about it but if this motorcycle ran off of rust I would be good to go for a long time but unfortunately those kinds of things never happen so alas I am in need of a good Kreem bath for it! Any help you have is greatly appreciated! Also what fuel filter did you finally find that worked? I am in need of one of those as well and havent found anything to my liking either!



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As far as the tank, it shouldn't be a big problem. First, of course, you'd need to shut off the fuel and disconnect the fuel line from the carb with either the spring clip at the carb end or the petcock end. (Plan on buying a new rubber piece for the inside of that petcock, BTW. Mine leaked like a sieve because it had dried out). In general, if there is a rubber seal someplace, you'll probably be replacing it before you're done. I'll leave it at that for now and not spoil some of the surprises. Luckily, with the exception of the gas tank cap gasket, they're mostly pretty easy to get.

Anyway, then lift the seat and you'll see a rubber band that holds the rear of the tank down to the frame (or, in a lot of cases there was once one there, but it broke and was forgotten years ago). Once the band is off, just sort of wiggle the tank diagonally up toward the rear. There are two hollow rubber discs that are in slots between the tank and the frame that keep pressure on the tank to hold it in place. There are no real bolts or screws of any kind normally. It's just held in by rubber. Of course, it could certainly have hardened over the years, making it hard to move, but that's all there is.

As far as the fuel filter, I'm using one now, but don't recall the number off the top of my head - mostly because I still hate it. The darn thing is still way too big, but it works fine (which was a big step from most). I'll see if I can find a receipt or a box somewhere with the number, but I'm really still searching for something better.

Good Luck!

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As far as being back sometime, you won't be done with me that easily. Everyone here has been great just to bounce ideas off of and get some needed wisdom from. I'll be tinkering with things for quite a while yet just because it's something I like to do.

Who knows, it's even possible that I could help someone else avoid the holes I've fallen into. :)


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Just wanted to drop into this thread and say that even though I'm a rank beginner in all this stuff, it's been great watching this thread as you progressed through all these seemingly-impossible problems. I grinned like crazy when I saw your "success" post-- it really is possible!

Anyway, good to hear you got that all tied up- great work on your part.

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