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CT3 175 Runs Runs but then Doesn't


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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.

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Its possible the filter(s) in the petcock are partially blocked, hence it will potter about ok but will fail with higher demand.

Not sure about the CT3 but some petcocks have a filter screen within the petcock, the giveaway is a round bowl with a hexagon on the bottom. Some petcocks have a screen within the fuel tank and would need completely removing from the tank to clean.

so to test just pull of the fuel pipe from the carb spigot and open the cock...good flow?....bad flow? :huh:

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Thanks for the reply.

When I started dusting the bike off, one of the first things I had to do was replace the gasket in the petcock valve because it leaked like the proverbial sieve. At that time I had to remove what was left of the screen because it had rusted as badly as the tank. After I cleaned the rust out of the tank I wasn't able to find a new screen and wanted to put in an inline fuel filter instead. However, I haven't been able to find a style and size to fit in the cramped space that didn't affect fuel flow so far, so I've been been running naked and dangerous while looking for the right one. I do note that the clear fuel tube doesn't fill all the way usually and thought it might be an issue, but when the bike is running fine (for the first half hour) the tube looks the same half full as it does when it only runs for a few seconds. If the fuel tube is removed from the carb, it gushes out forever, but I'm assuming the float valve is only taking when it needs and then when it shuts, it is what is keeping the air from leaving the tube. I thought the float valve might be sticking and rapped on the carb a bit, but no change. I think I just found a fuel filter that will work, however, so when I put it back together shortly I'll use it, but I'm still wondering what's going on.

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running without a screen is risky, now youve told me that and coupled with you tank cleaning escapades...it's a good bet there is crud and rust between the carb spogot and the carb float valve, however to sort this out you would have to remove the carb, remove the float bowl, remove the float, remove the float valve seat (the brass thing) and its gasket...and blow it back with compressed air.

I have witnessed this crud in this place myself ;)

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when the temps went up last year (spring in vega$ is 90+ f)

my bike did the sme sort of thing. eventually i discovered that i had a severely clogged main jet intake tube. turns out that the idiot before me or before him has replaced the banjo bolt and main jet assy with a nasty chunk of lead out of a small calibre firearm.(what their thinking was i will never, ever know (or want to)) during the winter it was a bit starved for fuel but seemed to do ok, but when it warmed up it was running just on the wrong side of too lean and since the air was thinner due to the temp, fuel was not able to be sucked around the chunk of lead as well as it had been before.

so im with OG on this one. drop your bowl, pull your main jet and then really clean out the whole tube assembly.

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Thanks again for the words of wisdom.

My big worry with all this was that by going totally unfiltered for a while I was asking for trouble, and I just may have gotten what I asked for...

I pulled the carb later today and the main jet was clean, the float valve was clean, but although the Main and Pilot jets themselves were clean, there was some granular stuff in the little well where the main jet makes a right angle connection to the main nozzle in the bottom of the bowl. I'll be cleaning this again and after fitting the filter in the line, I'll see if there is a difference. There wasn't a lot of junk in there, but then again, since idle was OK and there was nothing in that jet area, but the main is what works when the throttle is opened and there was a little junk there, it's a possibility. It seems like its only barely enough to cause trouble, and it puzzles me that everything clears when it sits, but crud shouldn't be there in any case, so cleaning it is a good thing.

I'm also thinking that after looking at the condition of the banjo bolt more closely and the hole where it screws into, that this junk may be old corrosion from the bolt and it's mounting area rather than the gas (but it doesn't matter where it comes from in the long run).

My biggest issue now is what to clean this with, since it's obviously corrosion residue, but very resistant to carb cleaning spray and I dont have any carb dip.

Right now, it's my only concrete info though, so I'll go with it and let you know.

I took a few pictures as well.



Hopefully these will clean up, but I don't know at this point. Wish me luck.

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One day, I had a similar symptom on my CT3 of running until it was warm, then stalling, and not being able to run beyond idle. After fooling around for awhile, I realized that the choke was still on (duh). Not that you would do this, but you might check the choke circuit to see if it is somehow leaking extra gas when not needed.

Another problem that developed was a small amount of rust on the flywheel cam where it rubs against the points. It didn't take long to wear the contact part of the points so that I had to adjust it. Over a matter of hours it would run worse and worse and finally die, and I'd have to adjust the points again. A new flywheel fixed that.

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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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An update -

With the clean carb and fuel filter, rode about 20 miles today. It wasn't as smooth as it should have been, but it wasn't horrible either.

The fastest I went sustained was only a little over 50 MPH, at which the engine sounded fair, but not as good as I'd have liked.

Oh, yes, near the end of the ride (near home...I learned a little) I wound it out really high (maybe barely redline, but maybe not) and sure enough, it failed the same way as before - idles great, but won't run above about 3000 RPM.

The temp was much cooler today, (about 80 and cloudy) so I think that had something to do with the long time before a problem.

I'm thinking about replacing the points and condenser just as a shotgun approach, but hate the idea as a matter of principle. (Of course if I pull them and see a crater in points, that will tell me something, but still won't tell me why it fails for so long after it's run hard and is then fine after a rest. I have crank seals on hand, and may do those as well (or first instead) because although there are a lot of things I'm planning on doing, just finding out what is causing this is making me a bit nuts. I'm wondering if engine oil splashing somewhere past a seal when it's stressed and then slowly easing it's way back, which would be an explanation- but not a great one. If the darn thing just failed completely after a hard run I'd understand, but it idles just fine! While writing this though, I think I've decided to check basic stuff and see where it leads me. Do a compression test, a closer visual of the magneto, etc. Of course, I could pull the head and check that for carbon and such, but I don't have a new gasket set for that area handy yet (I'll be ordering some anyway, of course). Maybe a slight head warp when it's hot? Right now, I'm doing a good imitation of fumbling in the dark trying to make this run right. There must be a light switch around here somewhere. More later...

I went to check the compression and unfortunately my gauge was damaged and I wasn't able to get an accurate measurement (for future reference, don't let the silly thing fall from your hand and smack up against the side of the engine - they just don't work so well after that).

In any case, I decided to remove the head and check things out. The piston had some carbon on it, but not horrible. There was a lot more oil than I expected to see there, though. I wonder if that's evidence of a right seal issue. Also, the head was surprising to me. Instead of an even carbon coating, the rear facing part was clean!. Is that evidence of a small leak?

***Update: Originally couldn't get pictures, but now they post just fine.***



Anyone that can give an opinion here would be most appreciated.

In any case, I'll be cleaning things, replacing gaskets and seals, and putting things back together ASAP.


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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.

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Minor update:

Hit a bump in my road this weekend.

Pressure plate looks fine, disc look fine, all looks good that I've seen so far.

I was hoping that I could get away with using a rubber strap wrench on the clutch to to take off the nut holding it, but no such luck.

Since I'm a regular coward about breaking things, I'll be taking a couple of clutch plates to a welding shop up the street this week to make a clutch holding tool. Which will, of course require a minor expenditure to replace them, but luckily they're inexpensive.

I hope there's a special place in the afterlife for engineers that design equipment that needs special tools for common repairs (like seals)... (I actually considered making a tool out of an oak board I had lying around, which would have been fun just to take pictures of had it worked, but abandoned the idea in favor of sanity.)

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The left seal didn't need a split and is done.

As long as you have the flywheel puller for the magneto and either an impact driver or a large Phillips and brute strength for the stator screws, that side wasn't bad at all.

The right one isn't done, but I expect it won't be an issue after I get the clutch basket off - need to get the clutch holder tool made first.

I'll post another update later in the week when I get back to work on the right side (business out of town for a few days).

I'm happy to post the updates. Nice to see that someone might get something out of them!

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The right one isn't done, but I expect it won't be an issue after I get the clutch basket off - need to get the clutch holder tool made first.

Welding a handle to a couple of plain plates is one way to do it but like you say it leaves you wanting more plates. :unsure:

Another 'Bling' way is to buy one of these if you can find one, this is mine for a DT175MX (DT175E in USA)


However the cheapest way is to make one of these from some 1/4" flat bar


This was a method as shown in my Haynes manual and the one I used to use before the 'Bling' one. Here is a clip from said Haynes manual



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That tears it. Now I have tool envy (yet again).

The Clymers manual that I have talked about wrapping an old fan belt around things, but I figured that the strap wrench would have been safer.

They didn't even hint about using a bit of angle iron.

I was a bit concerned about just using one tooth of the inner basket to hold things without chipping a tooth. (I almost tried some other methods.) However, you were obviously successful, so it can be done.

My personal concern was because I believe the few little metal slivers that I found in the bottom of the case when I removed the side cover came from the ends of the teeth on the outer basket (if you're looking at the installed basket, the edges on the furthest away from the bike) and was unsure how strong that metal actually was. It looks as it the pressure plate shaved a few tiny pieces off at one time or another.

I've already arranged for a couple of new plates to be sent to me, otherwise I'd make a go of it, but that's great info there.

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Update 7/30/2010

I'm an idiot and now I have proof...

I picked up my lovely newly made clutch basket removal tool at the welder today. I had given him 2 old clutch plates and a picture with instructions to use a 3/8" square steel bar to weld to edge of the plates in a slot he should cut in the end of the bar. A beautiful wrench was born.

I got it home along with the replacement plates as well as a few new seals, gaskets and screws; totally expecting life to soon be great. I stuffed an old towel between the primary gear and the basket, applied the new basket wrench to the inner teeth, and the center nut came off easily.

Next I tried to remove the primary drive gear, but the same towel I jammed in the gear tended to actually get worked into the gears rather than stop everything when I tried to remove the primary gear nut.

I got wondering on how to better stop the primary gear from moving and got the idiotic idea that the new clutch wrench would hold it just fine if wedged up again the frame when the basket tried to turn...

Those who didn't sleep through every physics class can guess what happened next. (I liked physics, but sometimes don't think.)

A small primary drive gear with torque applied and large gear holding it near it's circumference means much more torque in the wrong place.

I broke a tooth off of the clutch basket as the new tool handle bent very slightly.

It was all I could do not to break down weeping. (Having my 21 year old daughter watching me at work helped.)

I'm guessing it would be another mistake to reassemble a now imperfectly balanced basket with a broken tooth after going back to the initial idea of jamming a rag, a penny, a finger, my tongue, some of my gray matter (or anything else deemed useless) between the original gears to remove the nut and get at the crank seal and replace it...

Of course the basket isn't officially available any more, but I'm searching for another.

I took pictures of everything today, but have mostly given up on why I can't make them visible. I've also lost my initiative for the time being to find out why I can't make them visible.

*sigh* I'm not giving up, but for the time being, I'm a pretty disheartened. A separate project resurrecting an FZR600 that can't get out of idle will now take up Saturday morning, since I have no replacement basket handy for the CT3. For that project, I've at least got 2 of the 4 carbs cleaned and am very cautiously optimistic that the other two will quickly clean and my problems with be gone with the dirt. I'll cover that project elsewhere however if it proves interesting.

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PMSL but also gutted for you mate, your description of jamming inert useless material such as your grey matter was highly amusing.

On a more serious note




Dohhh!!! one of these NW Vintage jobbies is $99 on ebay but the url ling takes it to their $150 one??

Just paste this into ebay motors and you will see it for $99

NOS Yamaha AT1 AT1M CT1 CT2 Clutch Basket 248-16150-02

What I do when undoing the primary drive gear is to remove the barrel, head, piston and small end bearing. then place a 1/2" socket drive extension bar through the small end in the con-rod. Now turn the crank until the stroke of the rod is 1/2 way down. Now pack under each side of the soket bar so that it will jam against the packing when you undo or re-tighten the primary gear nut.

Hope you can make sense of that ;)


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Thanks Paul:

I was obviously pretty depressed last night writing that.

What a difference a good night's sleep makes, however.

I considered writing nothing until I had solved the problem, but then thought that for me at least, the journey is as important as the destination and my bit of failure might help someone else. The satisfaction (and sometimes pain) of figuring out a problem is what makes it better in the end. And while I wasn't necessarily looking for help, part of this group is that there was always the chance that those with more experience, such as yourself, could offer a totally new way - which you certainly did. The idea of using the piston rod was a clear description of an excellent method that I'd not considered. They cylinder and everything else is still in pieces, so doing it that way would be a simple matter. Given that I'm a bit gun-shy now, I may try that along with a rag in the primary to distribute the force, but Lord knows, I have time to figure this out before a new basket arrives (though may try later today if there's time after the FZR work).

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. It looks like the NW Vintage and Vintage may be different places because they have different store sites. However, you may have saved me a third of the money for the same thing, because I may end up there.

In any case, thanks again for your comraderie and wisdom. Onward and upward!

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I may try that along with a rag in the primary to distribute the force, but Lord knows, I have time to figure this out before a new basket arrives (though may try later today if there's time after the FZR work).

If you think about it the rag is not needed, there is no force because you have the crank locked while you undo the crank nut.

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