It could really be either one, rich or lean. If it is rich, it will run worse as it warms up, but if it gets really hot and then runs bad it is too lean. Did you try flipping the choke on when it started bogging down?? If so and it gets worse, it is definatley too rich, if it improves, it is too lean. I would try that to see where you stand, but the throttle chops that Modquad described would also be needed.

 

Usually you can check your mixture by the color of the spark plug. Rusty brown is perfect, black is rich and white is too lean. Of course this can vary with throttle position as a previous lister mentioned.
The way I test is as follows.
Find a long straight-away preferably with a slight incline.
Starting with a clean plug run your quad at approx 1/3 throttle for the whole distance then check the color of the plug.
Clean the plug and do the same at approx 1/3 to 2/3 throttle and check the color of the plug again.
Repeat the procedure at full throttle. If all tests give you a rusty brown plug then your mixture is OK fine. If not some adjustment is required. For upto the first 1/3 throttle adjust the pilot jet, 1/3 to 2/3 throttle adjust needle and for full throttle change the main jet.
Hope this is of some help.

 

Modquad, you mentioned that you need to keep on the throttle when you hit the kill switch, I heard that you need to let go of the throttle at the same time as you hit the kill switch. Now im confused. Which is the right way? Traildog didnt mention which way either.

 

Leave the throttle alone, any change with the throttle would upset the reading.

 

NCscrambler, this is what I got from this forum under search(carb tuning) as a matter of fact you replyed to this post.

Checking the Main Jet– Warm up the engine and go for a short ride letting the engine comes up to its normal operating temperature. Install a brand new plug that's been properly gapped. With the new plug installed aggressively accelerate through the gears until you reach 4th or 5th gear. For best results you should accelerate up a slight up hill section to place additional load on the engine. Continue to run the engine at WOT for 20 to 30 seconds longer if there is not fear the engine is running lean. If you suspect the engine is running lean 15 to 20 seconds to give you an indication. At the end of your full throttle run simultaneously push the kill button, chop the throttle and pull in the clutch. This procedure is often refereed to as a " plug chop". It is important to perform a plug chop exactly as described. If you allow the engine to run or leave the throttle open for even a few seconds after the plug chop the plug reading will be invalid. Now remove the spark plug and carefully look at its color.

Now my ? again is, do you let off the throttle or keep it wot while killing the motor? Chop to me means to cut . Am I right in saying so? You say leave the throttle alone if I leave it alone then it is still at wot.

 

Well, you got me there. Everyone has different ways of doing it, some say it will upset the reading while other's say it won't, so I guess you just have to do what works best for you. I have personally tried it both ways and haven't noticed a difference, but just to make sure you don't mess up the reading, it may be best to leave the throttle at the postion you intend to check.

 

Just reread the main post.Do a leak down test you could have a air leak some where.

 

I did a leak down test,compression test hot and cold,plug check everything I could think of. Everything checks out good. Just the other day I whent on a whim and put my stock carb on and it ran perfect. Hot and cold it did not change much. So now I know it is a carb problem. I cant seem to get the jetting right on the 34mm carb. I am running a 230 main jet but it does not bogg down. It just loses power when hot. Maybe I am using to big of a main.No one really had the correct jetting for the 34mm carb on the 250.

 

I can't say for sure but 230 sounds to be a bit on the large size and that would explain loosing power when hot. You didn't say what colour your plug was, or did I miss it?
Also on the issue of whether to leave the throttle open or closed after you hit the kill switch in my opinion it doesn't matter cos once you kill the spark the burn stops.

 

I am kind of in the same boat, 230 is the factory size for the 400, sounds kind of big.. Try the choke trick or just drop down the main one. Unless you are already lean, the drop shouldn't hurt anything. What size pilot and needle position are you using?? The needle is easy to get dialed in because when it is too rich, it will run like crap. You can drop the clip postion until it starts running awful (too rich) then back down one and you are good with it. The pilot can affect the main quite a bit also. Everything has to balanced to work together. Alos, check and make sure your choke is adjusted right because it can cause problems like that. I have went through the same stuff several times with the 38TMX and it is always something like, the choke or something just way out of balance. Be patient and hang in there.