It's a 1973 yamaha CT3. -New spark plug -New contact breaker -Fresh 20:1 fuel -Rebuilt and cleaned carb -New K&N air filter -Engine has compression of 120 PSI I am at my wits end with this thing. The only thing left for me to check is the timing but I cannot find a good resource online telling me how to do that. The service manual is very vague about it and specifies using a dial indicator which I don't have. How do I check timing?
Ok I found a video on youtube and checked for TDC and measured 1.8mm before TDC. It look like the timing on this thing is WAYYY off. It's about 90 degrees off... After looking over the flywheel and stator I can't figure out why this timing is so off. Any ideas?
Sheared key on the crankshaft? The flywheel could have rotated with nobody knowing. It happens. If it hasn't run for you, it could have sheared that key for the previous owner, they never knew why it didn't run, then parked it. You might also check the crank seals. If they are leaking, you won't get proper fuel induction. Take the plug out, put your hand over the carb and crank the engine through a stroke. It should suck your hand firmly against the intake.
He said it had new points so he had the flywheel off and you'd think would have seen a sheared keyway, But that sounds like the problem to me also. Its possible he dislodged the keyway reinstalling the flywheel.
I suspect the key fell out and he did not notice while re-installing the flywheel. If you need a replacement key make sure to use the correct metric key.
Alright it turns out that it was a sheared keyway. I put a good keyway in when I re-assembled it but it must have sheared when I kicked it 1000x trying to start it last week. Well I just ordered a new key and I'll try again next weekend. If it doesn't start I'm done with it and just selling it.
Don't give up, these bikes are fairly easy to get going and still a lot of fun to ride. BTW, when I purchase flywheel keys, I always buy two, one to use, one to lose. Good luck!
Flywheel keys are only an alignment devise and have very little shear strength, if you are shearing keys you are not getting a good connection between the crankshaft and the flywheel. The tapered connection is what holds the flywheel to the crankshaft from turning.
That's probably what caused it. I don't have a torque wrench so I am only tightening the flywheel nut as much as I can before the engine starts to turn over with a regular socket wrench. When the new flywheel comes in I'll make sure it's not going anywhere.
Before putting the flywheel on ,take a little valve lapping compound and put it on the taper and spin the flywheel back and forth to remate the surfaces. Be sure to clean it off thoroughly afterwards.. Another trick I've done is made keyways fron valve shims. They're very hard and if you have an assortment you can find a real tight fit.
Alright I pulled the spark plug and put my hand over the carb to test for vacuum. There was vacuum but it was felt a bit weak. I can't objectively tell whether it was in fact weak or if it would be considered good. It did not pull my hand "firmly", but I could tell that there was in fact vacuum. I might as well just replace the seals. Can anyone tell me how to replace the seal on the right hand side? The one on the left looks like it just pries out and the new one gets tapped in. It looks like i'll have to pull the engine halves apart in order to get to the one on the right, but I can't really tell. The factory service manual for this bike really sucks. Oh and I have the cylinder head bolts tightened pretty tight. The service manual says 14-17 ft/lbs but I have them way tighter than that. Originally when I did a compression test the engine only had 20 psi. I checked the cylinder heads and they were pretty loose. I cranked them down a lot and got the compression up to 120psi. Could worn out oil seals cause low cylinder compression?
I'm only using the valve shim rig in cases where theres already damage from multiple key shearings and the slots are a little oversized from the rocking action that takes place before the key actually shears. It works to stave off replacing a crank end and flywheel and if you shear one of these off thats your only alternative anyway.
This may be a dumb question, or comment...but have you actually checked for a spark at the spark plug? lay an old plug with the gap widened out to 1/8" on the head and spin the engine over...should be able to see a nice spark. You should also be able to hear a light "pop" sound come from the spark plug hole, indicating crankcase compression if forcing air up into the cylinder. Leaking crankshaft seals and/or cylinder base gasket could affect cylinder compression, since the cylinder wouldn't fully fill with air. Tightening down the head bolts might have "cured" a leaking base gasket. You might try dropping a few drops of fuel down into the cylinder thru the spark plug hole, then try to start it. if it fires for a few seconds it'd mean you aren't getting fuel to the cylinder.
You should have a manual before you attempt to replace the seals if it's your first time and you don't have a knowledgable friend watching and directing you. The left side seal (as you sit on the bike) requires you to remove the flywheel and you need the correct puller. The right side seal requires the draining of the oil, removal of the right side clutch cover, removal of the clutch (make sure you have a clutch holding tool), then you can access the seal. There are ways to get around not having all the correct tools but for a newbie with no experiance, the right tools will make all the difference. Do you have a friend who has worked on these bikes before? If not, you need a manual before proceeding.
I already have the flywheel off. It looks like the rest should be straightforward. Do I really need a flywheel holder? What does it do exactly? How do I actually get the seals out? Do I just pry them out and tap the new ones in?
A clutch holding tool is nice but not required, just jam a penny in the gears. Yes, you just pry the seals out. Just make sure you don't break any of the clutch housing fingers. If you have a impact gun, the large nuts come off easy.
