Vintage Dirt Bike Q & A

hi all, have a 2000 TTR 90 that runs however..
1.) with the air cleaner on the carb the motor runs terrible, excessive smoke, no power, uneven idle.
this is with the air box only, filter element in the bike and it dies.
2.) with air cleaner off, bike runs better but fuel will spray out the intake end of the carb when the throttle is applied.
a.) if I turn the fuel petcock off the bike continues on like this for a minute but then "cleans out" and runs great, nice throttle
response, good power etc.. This leads me to believe float bowl level is "Too full" so I reset it to barley open, no change in
performance. I can run the bike till it dies (ie.. carb is out of fuel).. when I open the float bowl drain screw a full bowl of fuel will
empty out.

Now, I have been wrenching for a few decades and this has me a bit confused..

I rebuilt the carb (yep, pilot was plugged.. welding tip cleaner fixed that) main jet is good, cleaned all components but the bike continues to run rich. this leads me to the needle/seat.. the rubber tip on the needle has a wear ring around it that can be seen with a magnifying glass, I looked into the seat (drilled into the carb body and not replaceable) and it appears to have pitting at the bottom of the seat (Damn ethanol).. needle/seat not doing their job, overfilling the float bowl is my diagnosis... or is there something I am missing?

also wanted to check valve adjustment before I return it to the young man, does anyone have tolerances?

Thanks in advance for your response.

You can set the valve clearance at .08-.10mm intake and .10-.15 exhaust and that should be real close.

As far as the running problem,it sounds like it has gas in the oil. I've seen an atv that was so bad it would run when the tank was empty. Be sure to check the carb vent hoses,make sure they are not stopped up.

Appreciate the reply, here is what I found and hope someone else may be able to use this.

1. Intake Valve adjustment was at zero clearance on a cold motor.
set adjustment to .003 (this was the recommendation of an individual I trust)

2. disassembled and soaked the carb in mineral spirits overnight, re-inspected the pilot jet and found the opening was LARGER than the main jet.
replaced the pilot with a 12.5 as recommended. (I should have picked up on this the first time I had it apart.)

reassembled the carb, installed it on the bike.. started on 2nd kick and it's 27 degree's outside. set air adjust screw to a hair past 1 full turn. great throttle response, runs great with new air filter element installed.

Thanks again.