I have i problem that i can't figure out. I own a nice 87 TRX 250R, with FMF pipe and powercore silencer, uni air filter and prolite piston. When riding and getting to full throttle the quad doesn't rev high it "chokes up" i can't get high rpm. So i am not getting much power and it doesn't feel like i need to shift yet. I am at about sea level, have the stock carb set at fouth needle clip from top,with a 160 main jet and air screw 2 turns out. I'm stumped guys any ideas would be appreciated.

 

sounds to me like you are leaning out.

Go bigger on your main.

 

You're probably too "fat" on the main jet.
Do a plug check. If your plug is black and wet, it's too rich.
Is your air box stock? If so, try taking the lid off and see what happens. With the increase in flow of the pipe/silencer and the air filter, you gotta give it even more air. If this lets you get your high revs, then do a plug check.
If you take off the air box lid and it still won't get the high revs, try going down one step on the main jet. From a .160 to a .158.
Your R should rev up crisply and pull strong all the way to the top end.
One caveat,
Don't just keep going down on main jet sizes. If you go down too far you will have it running too lean. Running "fat" will not hurt your motor at all. Running lean will make it run great, but it will burn up quickly.

 

Thanks ill try that, It is the stock air box. i did i plug check previously and after i did the plug fouled. so it must be a little rich. the plug was not wet but there was a thin film of oil on it and it was black with carbon buildup.?? Is this ok?? I think it should be a brown paper bag color. i'll do a plug check with no lid a 158 main and a new plug. I hope this works. Is there apossibility the plug is not hot enough?? Bad stator?? i have know clue just guessing, i sure don't want it to be my stator!!

 

First thing, calm down!
There is nothing major wrong with your ride! It's just jetting and air box mods. Now relax and quit looking at everything else.
Anyway,
black plug, thin film of oil=too fat. Go ahead with the air box lid removal. Easiest to do. Try it out. Better, but not quite right? Go down one main jet size. That ought to do it. Also, try putting the needle in the middle slot.
For plugs, just get NGK's. BR8ES, or BR9ES. Either one, although the 8 is hotter and what you want in the winter.
Get a handful of jets, they're cheap enough. And get a jet tool. Then, along with a 17mm box wrench, the jet tool, some jets, a plug wrench and some plugs all in your tool pouch, hit the trails and have some fun!!!

 

trapperb1 is right with taking the airbox lid off to check if you're running rich. Like trapperb1 said, if you take the airbox lid off and it runs better, then you're running too rich - drop down a main jet size and test again (with the airbox lid on).

A quick way to find out if you're running lean is to put the choke on while your riding (3/4 to full throttle for main jet testing), which will cause your machine to richen. If it runs better with the choke on, then your main is too small. Go up a size on your main jet and recheck.

These tests are to give a ballpark assessment. After you figure out which way you need to go on the main, use a proven technique to dial it in (i.e., reading color of your plug, increase the size of your main jet till your machine "blubbers," then drop down one size, etc.).

good luck,
ogre

 

i'm not questioning anyone..

but, when my 300ex was running like this, i was running way lean. That cured my problem...

 

Apples and oranges.
What makes a 4-stroke run bad is different than a 2 stroke.
When a 2-stroke won't hit high revs and has black plugs it's too rich.
When your 4-stroke wouldn't hit high revs it was too lean and not getting enough fuel.
It's like if you ported out your 4-stoke head, put in a massive cam, changed the timing etc., then left the carb completely stock, what would happen? It'd run crappy until you give the engine some fuel to burn.