I have an '86 TRX250R that keeps fouling plugs after about 15-30 minutes of use and I'd like to run my combination by you guys to see if anything stands out as a possible culprit for the problem.

I just got the machine a couple months ago and have only run about two tanks of gas through it, and it's gone through 4 spark plugs so far. I only use the choke to start it and then turn it off as soon as it fires up. I'm mixing it at 40:1 using Yamalube semi-synthetic premix oil, and using NGK "8" heat range plugs because that's what the NGK website recommends. It has a ProCircuit exhaust, VForce reed valve and a UNI filter with no airbox lid.

I figured it was jetted too rich, but the guy I got it from said he never had a problem with it even with the airbox lid and the factory inlet snorkel installed. Could ambient air temp. affect the mixture this much? I'm going to try one range hotter plug, and would appreciate any suggestions you guys could give me.

 

Stick with the stock plug, you risk holing a piston with to hot of a plug. Ambient temp will definitely affect the jetting, as temps rise you'll need to lean out the jetting. Do plug chops and adjust your carb from there, if the plug is black it's rich, white is lean. Your looking for paper bag brown color down inside the plug....

 

trx's are screamers...they like haulin *** and thats it...check the jetting, but most of all, don't bog it in high gears !!!!

 

Check your cylinder compression. My 250r would only foul a plug when it was time for a rebuild.

 

"you risk holing a piston with to hot of a plug."

You think one heat range may do that?

"Do plug chops"

Uhhh, what's that?

"Check your cylinder compression."

What's normal for one of these?

 

Check your main jet. It should be around 152-158.

 

You need to check your gear oil level. Had main seals go bad kept fouling plugs with gear oil. Never figured it out until I got home from a dune trip to service my R. It's rare but it happens. Good luck. Joe Aka " Jellyroll".

 

plug chop..... Is when you go (usually in a taller gear) for a while in the RPM range your trying to get jetter in (in your case, higher RPM, 3/4 and more throttle.) Then you shut it off and look at the color of the plug.

The stock compression for a R is 170-180 pounds.

 

Sweet, thanks again for the help! I got a lot of things to check now.

 

Has the frame been repainted? If so run a ground wire from the motor to the frame ground by the radiator on the left side tie it in with the main ground. I can run a B6ES or B7ES and have no problem. Get the Yamalube out of the quad. You only use Yamalube to seat the rings fast on a rebuild. Use Klotz or 927 16oz to 5 gal. As far as an " R" not been able to go slow, mine can go so slow up a hill it will make a 4x4 mad or I can just blast the hill. It can do both.

Her is one problem your pipe is for low to mid with some top. Your reeds are mid to high with little bottom. Your air filter is good.

Where do you want your quad to run? Low to mid with some top or mid to top with no low end?

If you want good over all power keep the pipe go to a stock reed cage with duel stage reeds or a Ram Valve. Use a reed spacer and put the lid back on. You need air velocity not volume for this.

If you want mid and top change your pipe keep the Vforce and leave the lid off.