oldbikerehab

I've never done an official plug chop with a steady rpm, kill it and coast, but I've been checking the plug and it's consistently an even cocoa brown with a couple of dark threads. The bike's a 78 actually, so no points. I would be most suspicious of the after market carb jetting if it weren't for this bonehead gas move on my part. I think I will look into rebuilding my Mikuni though. I was afraid the votes would start coming in for splitting the case.

The weather today was about 74 and sunny so I decided that it was time to get my DT 175 out of town for the first time and take a cruise through the local state park. After about 30 min of making my way through some winding roads, up and down hills, and screaming through some straights. All on asphalt and all the while maintaining an even purr, buzzing along around 5000 revs. Thinking, "Man, this bike is fantastic!" as the revs held steady and smooth through all the gears. And then I found myself with a giant school bus right on my tail in a series of pretty steep hills where the speed limit was 55mph. I made it up one hill and was on my way down another steep one at 50 mph and 5000 revs when I started to hear a flapping sound from the cylinder. I eased off the gas and it stopped, so I downshifted and just wanted to make the hill and get off the road when the flapping started again. Just as I made the top of the hill . . . http://i1054.photobucket.com/albums/s481/interestedineverything/piston-burnout.jpg"]http:// 15 miles from home and no cell service I started pushing, glad that I didn't wind up over the handlebars and that my bike only weighs 250lbs, but super !@#$%^& pissed! Luckily, an old friend noticed my long hippy hair while driving by, happened to be in his pickup truck with his ramps, on his way to pick up his yard tractor to take to his farm so he got me and the bike home in short order. After opening a beer and breaking out the tools for a diagnosis, I sat down to figure this out. From what I can gather the most common reasons for this type of failure are, air leak at the magneto-side crankshaft seal (I doubt it), too lean carb jetting (possible), too far advanced ignition timing, or faulty CDI (I doubt it), too-hot spark plug range (NGK B8ES - so nope), too high compression ratio (I doubt it), or a too low octane fuel (my guess). Before my ride, I decided to top off the fuel and grabbed what remained in a 5gal can of gas that I filled last year and added Stabil fuel stabilizer to. There's 2 stroke oil in the line to the carb so I think I just basically filled my tank with ethanol without thinking and killed my piston. Any other votes? Will I need to split the cases now since there's probably junk that fell into the lower chamber? Any advice, jokes, or lessons welcome.

Nice turnaround! Now that I've got a better feel for working on these bikes myself, I'm keeping an eye out for a second DT for a MX/ offroad/parts /rat bike. Looks like yours is going to be pretty sweet though. It's funny, I work in digital media and most of my friends and colleagues who work with precision cameras, recorders, computers, jets, etc. are addicted to some sort of analog rattle trap machine in their free time.

Powersportsplus.com has the best prices I've found on the web for OEM. Sometimes shipping is fast, sometimes slow but customer service has always been awesome if I want to add or change something on an order. Here's a link to their parts list for cables. http://www.powersportsplus.com/parts/search/Yamaha/Motorcycle/1978/DT175E/HANDLE+-+WIRE/parts.html I tried an aftermarket throttle cable for my bike and it was unusable garbage. I ordered a new OEM throttle cable from the above that I'm going to install next week. Your bike is wired from the factory to run the headlight only when the engine is running. Signals and instrument lights are on the battery.

natedogg, Try some anti-seize lubricant on your spark plug and see if that helps the hard start when the bike is hot. I have the same bike as you and had the exact same problem. On a cool morning it would be a first or second kick starter. If I ran a few errands around town it would get progressively harder to start and once hot wouldn't start at all, but a new spark plug would make it start right up despite the old plug looking perfect. I used Permatex Anti-Seize for a $1.99 solution and my bike is almost always a first kick starter now at any temp. Just use a dab though on the middle threads. Hope that works.

!!!!!!!! FWIW this build was my final factor in deciding that the DT175 was gonna be my rebuild project last year. I figured if a bike that looked like yours ran and someone had faith in getting it back together it was good enough for me. I had mine in pieces right along side you and just got mine started. Been robbed before too so I feel your pain. Spread the word wide and keep the eyes and ears open for that very distinctive bike. Hope it shows up.

Honestly, I couldn't spot the air screw on your carb at first since it looks like yours has been stored in a bucket of grease and mud! LOL But it did get me to dig my Mikuni out to assess its condition and was yet another reminder of how much abuse these bikes and still be brought back from the dead. I'm sure under all that gunk is a much better carb than the knockoff. You might just be down to some elbow grease and a few (more) tiny parts to be ready for the races! I probably won't get back to much in depth wrenching or carb rebuilding for a few weeks when my new throttle cable comes in. I'll be following your lead to see how things work out though.

I sure hope that pilot jet works out for you. Otherwise that means I'll have to start looking into rebuilding my Mikuni asap since I won't be able to make the summer knowing there's a box of increased performance sitting idle in my shed.

I have the same generic carb unmodified on my DT and have the same sputter in first and second gear. Once I'm out in the powerband I don't really notice it. I have my idle set around 1,400-1,500 and noticed yesterday that it likes to climb to 2,000 at stop lights like yours as well. Mind doesn't die with the idle below 1,400 but it sounds like it's on the verge so I keep it a little high and tbh, I haven't really left it below 1,500 to find out. When one of the mechanics dialed in my carb at the bike shop, he was mumbling and counting, and at one point said that the adjustments on the generic weren't quite what he remembered for the Mikuni, but it sounds like you've worked the air and throttle screws. Btw, my throttle screw is in almost all the way, much tighter than the Mikuni when I bought the bike, and the air screw is out about 4 1/2 turns, waaay more than the 1 1/4 recommended. I did notice a slight improvement after refueling with pure gas and gapping my plug to max spec. The rain has settled in here for the next few days so I won't be doing any more experiments for a bit but I'll keep you posted and keep an eye on what you discover. Other than the fact that we are both using the same aftermarket carb, I wonder if the fact that we both have lowered our final drive gear ratio with sprocket modifications could be causing sputtering in lower gears? It is kind of like we are starting out in 2nd or 3rd gear. But that wouldn't explain your idle troubles .

LOL! No wheelies for this rider. But you bring up a good point that I forgot to mention. My setup is kind of a dog when I get into the hills if I don't drop down around 4th gear. My top speeds are on a straightaway flat and good headwind would probably slow me down.

Forgot the kickstarter link. http://www.ebay.com/itm/Yamaha-DT175-DT-175-Enduro-2148-Kick-Start-Kick-Starter-Shaft-/110842468451?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item19ceb9d863#ht_500wt_949

Here's a kickstarter assembly auction that ends in one day. It's from a 1980 but the kick was the same from 78-81 (E,F,G,H). The big catch with finding an engine in my experience is if they are ready for a rebuild, people tend to just take them apart and sell them in parts. If they are still running good they are on a bike and the quote I keep hearing from 2 strokers is "When you find an old 2 stroke that runs good, you buy it." Seems to be lots of crankcases as parts on the bay, but this is my favorite place for oem parts at the best prices I've found on my dt175e - http://www.powersportsplus.com/parts/search/Yamaha/Motorcycle/1978/DT175E/parts.html Good luck!

100 Mile update So I finally got out for a ride and here's how the break in went: 0-20 miles were pretty good, just stop and go around town but the engine would bog down around 3500 rpms. One of my mirrors was loose and I was near the bike shop so I figured it was as good a place as any to tighten up. I mentioned to one of the old MXers that I needed to dial in the carb and within seconds he had a screwdriver out of his pocket and tuned it for me. Huge huge difference and the only payment was to let him take it around the block. 20-40 miles I was still trying to keep it under 5000 rpms but getting out on some longer country roads. I'm guessing the rings seated themselves around 40 miles because acceleration and performance seemed noticeably smoother. 40-60 miles I decided to go for some winding country asphalt that would need a lot of shifting and tried to move through the gears while staying between 4000 and 6000 rpms whenever possible. That seems to be where this bike wants to live. This is where I really started having fun. 60-80 miles I found some longer stretches of road to get up to speed, maxing out at 60 mph and just under 6000 rpms on a smooth straightaway. I didn't push it any further than this. 80-100 miles was time to take a night ride and try out the halogen headlight. It was fine for driving around town but I don't think it was bright enough to be safe once I was out in the country in pitch dark. Maybe at around 20-30mph on a road I know but It pretty much just lights up they land a little bit. My high beam is out of whack and wasn't worth using, probably because I had to turn the Husqvarna lens off axis a bit to make it fit. Flyday mentioned earlier that he changed his rear sprocket to 45 teeth on the rear and kept 16 on the front for a final drive ratio of 2.8125. I currently have 49 teeth on the rear and 18 on the front for a final drive ratio of 2.7222. I've been pulling just under 4500 rpms at 45 mph, and just under 5500 rpms at 55mph with a new 66.75mm Yamaha piston and rings on this rebuild. Probably pretty close to being six of one, half dozen when comparing these drive setups on the same model bike but in theory, flyday should still have a little more power off the line and I should be able to hit top speed pulling slightly less rpms. Here's some pics: Exhaust side closeup Right side full Handlebars http://www.flickr.com/photos/76003800@N02/6852633856/ Engine closeup Left side full And what's a countdown to startup without a startup vid?

Wow, either way that pump bleeding took a lot longer than I would have thought, just like this whole build I guess. LOL If I hadn't had you guys here to help out I wouldn't have been able to get this thing going. So after having it in pieces since November, it's finally running and the sun is shining. Time to tool around the neighborhood at some low rpms to break it in but I'll be back with a report and happy to fill anyone in who may stumble into this thread about where I got my parts, etc. Thanks again!

If there's only one bleed screw on the side, with the red washer, then I did. Let me give it another shot . . .

Oil line at carb has slowly filled to mid way and it doesn't seem to want to go all the way to the carb. Does that sound about right? When I rev the engine it seems to pull a few little drops to the carb or does the tube need to be full all the way to the carb? I'll owe you a pint of something the next time I'm in the middle of middle England for all your help Cynic. For now I'll have to repay with pics of this bad bike once everything's dialed in.

Alright! Here's the latest- I flipped the slide, gave it a kick, started right up and idled away. But . . . I can see the oil pump moving in and out so I know it's working, but I don't really know how much flow should be going to the carb. It looks like there's just a light coating inside the oil tube to the carb. Shouldn't it be full? I've just been adding a few drops of two stroke to the cylinder when I start to make sure it's not dry and only running it for about 30 sec at a time. The oil line from the tank to the pump is full btw. Hopefully someone is still hanging around the forum.

Thanks Cynic, you've refreshed my memory and I think I remember that groove on the slide facing me on the magneto side. I'll flip it after lunch and hopefully that will be the last trick.

After a few kicks this morning and nothing, I gave a shot of starting fluid in the air cleaner, gave a kick and she started but went full throttle so I hit the kill switch. I turned the throttle, thinking the carb was stuck but could hear the slide moving so I tried to start it again and same thing. It looks like the oil pump has sputtered a little bit of oil towards the carb, but nothing reaching the carb yet. I've bled the pump but I don't think there's a need to prime it to get oil to the carb that I know of. I guess it's time for a lunch break to reassess and probably take the carb apart, again.

Thanks for the info flyday! I'm sure I'll fog the neighborhood as well if she starts up and all goes well. Everything is back together, torqued to spec and fluids filled. The only thing I'm thinking about changing out is the oil line coming out of the oil tank since it's a little bigger diameter than my old one and I'm not sure if it will have an effect on the pressure in the oil pump. It's dark now so I'm going to wait until morning to give it a once over safety check in the daylight before turning the key. Otherwise, I gave a few kicks without the ignition on and the compression sounds solid and I have a feeling it should be a quick start. I hope . Regarding your sprocket swap: Mine came with an 18 tooth sprocket on the front and the 49 on the rear. When I was riding before the rebuild I never went over 55mph because the bike was a little creaky and I didn't want to push it, but I don't remember my rpms climbing very high at all. I'll definitely post my results after the break in period.

Thanks! I couldn't agree more on the autolube pump. It blows my mind when I see commenters in forums say that they want to disconnect it. Seafoam is motor treatment that is supposed to be good for storing engines and bringing them back from storage/rebuild. Since the only thing that didn't get taken apart on this project is the bottom end, (flywheel was solid, if it ain't broke, don't fix it type thing), I've had a few people suggest it might be a good idea to help loosen up any junk in the crank case. Now that I think about it, I think I'm just going to probably go with gas and oil and let this machine do its thing. http://www.seafoamsales.com/gasoline-engine-faqs.html

Two unfortunately pricey parts. I'll have to make do with my repaired cable for a while longer. The bike is just about together. I guess I'm going to go with the ridge on the top end gasket facing up. It just seems to look right that way. I'm also going to tighten it down dry per Cynic and a few of the local wrenches I've talked to, though I'm curious why they Clymer manual says to smear it with grease. Are there any performance related issues? I can't find an answer. The gap between my front wheel and spoke seems pretty tight to me. It's just shy of 1mm. The front axle is torqued to spec, the boss is in the groove and the wheel turns fine. I'm not sure if I should take it off and try to re-mount. The electrics are all working right now with a better ground and I'm getting a really nice blue spark at the plug, though I'll have to wait for startup to check the headlamp which is a German 6V halogen in a Husqvarna lens. I guess all the electrics are aftermarket. I've got a decent coat of Pennzoil 2 stroke in the cylinder and wiped the reeds and inside of the carb with Seafoam. I've heard mixed opinions about gas after a rebuild. I've heard some say, to just add a tablespoon of 2 stroke oil to the tank, others to go straight gas and just put a teaspoon of 2 stroke oil in the cylinder, some say to add a bit of Seafoam to the tank and keep the cylinder coated just so it doesn't puddle at TDC. I'm leaning towards the latter Any thoughts? Getting closer . . .

Success! I had been using those exploded parts lists and my manual but couldn't make sense of alignment for the spring but your pic helped put it together. Kickstarter is working again, without removing the clutch! They were able to modify my old broken cable at the shop so I can use that until I order a new one. I guess the aftermarket that I bought is a bust. Countdown to startup is taking longer than planned, but I'm back on track . . .

Right now I think the only thing I need is a different throttle cable. I got the kickstarter in without removing the clutch and and it turns everything over just fine, but doesn't return to the up position. I think I remember someone else with the same problem on here so I'll have to look for their solution.

Great! I'll see what I can maneuver. I possibly have a throttle cable lined up at the salvage yard so I might not be as delayed as I thought. I'll get some pics and maybe a video up when everything comes together.