Originally Posted by Motor Slut
it's always nice when a motor runs right after a complete teardown
Originally Posted by Mike Hancho
I wouldn't say it was nice, I'd say it was done right...how it should be..
It was nice this time because of one thing: the carb situation.
The bike should have a 36mm Keihin PWK stock - mine came (bought used) with a 38mm PWM. The PWM has a horrible idle / off idle circuit - I could jet it to run clean at low throttle openings, but it would lean out when I went over 1/4 throttle. I had to compromise and let the jetting be rich enough for larger throttle openings and let the low RPM / throttle riding load up and foul the plug.
I switched to a 38mm PWK airstryker and the difference was night and day (better), but my deteriorating crank bearings made me pull trans oil into the crankcase. The result was trans-oil fouled plugs when the bike was jetted right. I just rebuilt the whole engine and replaced all the bearings and seals, rebuilt the crank and put it back together with a "stock" 36mm PWK.
Over the winter, I sent the head and cylinder out to Slavens and had the base decked and the head welded and re-machined to get better squish characteristics. With the 38mm PWK, when the powervalve opened, the front end would loft almost uncontrollably.
The 36mm should give me a bit more low end and keep the top end manageable in the trees.
I'm all geeked right now because this weekend we're meeting a coworker and his family up north and they are going to start trail riding for the very first time. He has a son that is 9 that he bought a TTR90 from here for. I'm looking forward to 4 solid days of zipping through the trees.