Yep sound right to me!
Also, It is possible that the air cleaner filter may be clogged up with debris. Smaller CC engines are sensitive in this area.
Do not forget there are 2 air screws!
They also work in conjunction with each other to get an optimum intermediate cross over!
Idle adjustment which lifts and lowers the slide sometimes is mistaken for the Main jet adj.

The larger of the 2 tweeking air mix is for the main or hi speed jet and the idle jet or low end jet is usually located to the back side of the carb closer to the air cleaner.

 

Are you sure there are 2 air screws on the TRX90? Already cleaned air filter.

 

Carb Asm

Yep there is 2 mixture screws.
Sorry..I was incorrect on the location of the low end it is located in the front left of the idle screw.
And the main adj is on the right bottom of the bowl.
Make sure that the choke is solid I think there is a butterfly on a shaft make sure that is is not loose.
Just a double check leave nothing to chance.

Adjusting by ear!
Adj the low end jet being carefull not to sink it into the seat...
count the turns CW screw it in and a rule of thumb 1.5 turns out CCW. start the machine and adj for the best idle.
Go to the main adj Rt below bowl raise idle one hand on throttle adj it for the best and smoothest sound.

Back to the low speed jet let the engine come to an idle and readj for the better and smoothest idle.

Then give the throttle a crack and see if the running engine responds OK

 

I dont mean to sound like Im being negative because I appreciate all your help, but are you sure thats an air adjustment screw and not a drain for the bowl?

 

You are not sounding negative, just straightening me out!
I was looking at the parts layout and yep your correct it looks like a drain no spring on it!
Sorry...
Did the low end jet adj was I close on that?

You did mention something about the previous owner changing the exaust?
Is it not a stock machine?

You have the parts layout for the trx 90 online, compare that to what you have it also shows the jet sizes. I may have the wrong year but you can find the exact one it is there.

 

Well, I check the jets and they are the stock ones, 40 and 80. Check the gap on spark plug and it was good (.026). I also moved the clip on the needle all the way up to try to lean it up some. No better!!!! I swear its running rich when its at idle but I cant think of anything else to check. It seems to come back to idle good but loads up after running for a minute. Anyone have any ideas?

 

IS it a stock machine?

You mentioned
---------------------------------
I have tried adjusting the air screw all the way out and it doesnt help. The valves are good.
Im wondering if the folks who owned it before me maybe changed the pipe and rejeted and when they went to sell it put the old pipe back on and didnt change the jets back. Or if it was sold at a higher altitude and came with larger jets. The only thing I can think of that I havent checked are the correct jets.
==================
If it is stock the JC clip on the needle should remain in the optimum cut groove (middle groove)

Please humor me for a moment...

Please, Describe the reason why you think it is running rich...

Is there any heavy black residue in at the end of the exaust?
At an idle or any time riding, Is it puffing black smoke or blueish white?

At an idle can you make it stall, by turning the air mix screw in, not all the way to seat, just enough to see if it will start to break up, then return it to a proper point tfor a smooth idle!

Sitting there at idle usually the engine will load up and appear to be running rich only at idle.
Maybe all you need to do is to take it for a good hard ride and blow it out!
Then check the color of the spark plug should turn coco brown...

 

The machine is stock. The 2 main reasons I think its running rich are 1 the plug is always black when checked and 2 when cold it starts and runs perfect, maybe at a little higher idle than when warm but you can rev it and it wont cut out or off. Also when it idles it does start to smoke but the smokes looks blue to me which would indicate oil rather than rich. Maybe the smoke is another issue but I only see it when idling and not when riding.

 

Tommy,
Read my 3rd post in this thread. It list all the symptoms with the bike. Let me know what you think it could be.
Thanks,
Randall

 

OK read it and the others also.
You mentioned after the engine is warm, you thottle it to hi rpm and release the thottle the engine does not come to an idle quickly. Am I clear on this?

After the engine is warmed up it also smokes blue smoke at an idle. Do I have this straight?
Yes it sounds like oil smoke... possible rings maybe..

When you checked the plug you mentioned that the plug was black!
Looking at the small ceramic insulator around the electrode,
it must of looked sort of tar like not dry black.

When the engine comes to an idle, when you snap the thottle quickly the idle returns fine, but then it slowly arrives to cut off after a little bit of time? You cleaned the carb 3 times and you made sure the slide is not binding?

Do you have access to a compression tester guage?

Check the compression while the engine is cold and then warm see if there is a big difference.
Should be better than 100 lb/sq in ...120-125 is good... 130 is lucky.

One test alternative is to loosen both valves to 0.004 inch it will sound a little noisy, but what else can we think of.

This will not solve the smoke problem but it may show some sign of an idle difference.
You can readj them back to the spec suggested at any time.

I want to see this work for you, really. I am just going by what I know of hondas and that is like 1968-75.
Designs are the same tols change electronic ignitions came in to play but it is the same o same oh.