82'yz100

Let me see if I can translate that....

You just did a top end rebuild on the bike, plus changed out the reeds and replaced the coil.

Why did you replace the reeds and the coil?


Now that you have it back together again it starts very easily and when it gets into the power band it runs very strong but it bog/hesitates/misses when you gas it to get to the power band.

Did it have this problem before?

Sounds to me like a jetting issue but I would like to know any prior history.

Rod

I Had a '81 yz100. ( back in 84 ) Sounds like a problem i had, i was a kid, didnt relize it till too late, but...My piston was too small for my bore. Bike fired up, ran ok till the powerband. I guess there was a preasure leak or something? Anyways...try a leakdown test.

keip82 said:

i replaced the reeds because i thought it was the reeds and i bought coil because i had no spark.but listen i got the bike for free everyone keeps telling its crank seal.do u think it could possible be that please help. o and i try a new jet today the guy i bought jet off said came stock wit a 210 main jet but i look it up and said sizes 180,190,200.i have a 190 in now.

Click to expand...

thats a little bit difficult to understand. If you want help you have to speak propper english.

Well the seals could be bad but the jetting is probably the problem.

i had a 75 yz 80 and i thought it ran good till i cleaned the stator contacts and magnets on the magneto, then it was a beast, just a thought

What about the pilot jet? Have you removed and cleaned that out? Blow out the passage behind it with some compressed air. The carb in general?

Although these bikes are naturally peaky and throttle hungry, (a little weak on the low end, but run like a raped ape when your on it), your bike sounds to me like it has a problem with the pilot system.

What if you pull the choke when its warm? does that dead spot go away? try it, but not for long!

That is a surge canister or something like that,it never caught on in the dirtbike world!I would try and find an intake manifold without that connection or see about sealing it off and ditching that canister.

Hold on a minute

That "energy induction system" hollow black plastic box does serve an important purpose. It is known as a "boost bottle" in most circles and I believe Yamaha actually pioneered it. The idea is to have a known volume of air in a container just behind the reed valve. The additional volume of air works like an inertial damper for the fuel/oil/air mix to smooth out the flow's natural "putters" and "pulses" at low RPM.

This may not have caught on in the motocross world because it was pretty pointless. In a typical moto on a small bore 2 stroke you were running it in the power band all the time so who cares about a little low end torque??? You are running it balls to the wall all the time.

However, the YZ100 was a superior trail bike as well precisely because of its boosted low end torque and smoother low end performance. And when you needed it---Lots of power and torque on top end. So you could putter around without overheating and enjoy some useable low end and sip the gas, and when you needed to break some balls the beast could be summoned.

The bike is tough as nails to boot. I've been running the crap out of mine since 1983, when I bought it new for about $1000.00. I still ride mine at least monthly. And not just on the easy stuff. She can still dish it out.

So, I wouldn't ditch the empty plastic box-- I'd seal up the leaks.