I recently bought a used KLX from a gearhead that I believe knew what he was doing and regularly maintained the bike. It's got Bill Blue's 351, Mikuni TM33/34, full muzzy exhaust. Everything is tuned as it came from Bill -- 140/40 main/pilot jet, needle clip in the middle position. Running premium gas at 100-3000ft altitude.

I'm fouling plugs like crazy. Like within 50mi.

Some time within the first 150mi of my ownership I noticed the lever on the carb that actuates the pump was broken, and maybe the pump was stuck open (actuated). I replaced the lever, reset the idle air screw (two turns out from fully turned in) and idle throttle. Went on a ride and 50mi later had a fouled plug.

Have gone through 2 other plugs in ~250mi. The fouling is dry, completely black on the tip and threads. There is soot in the tailpipe. Throttle response is jerky and seems air-starved at low-mid throttle. I'm a new rider and spend most of my time in the bottom half of the throttle. It definitely seems like its running rich, but I've talked to Bill and looked over a bunch of stuff, we couldn't come up with anything definitive. I'm thinking maybe it's something else?? After all, i dont know much about bike engines so could be wrong about it being rich and thats a wild goose chase

I've cleaned the carb, everything looks good as far as I can tell, air filter is clean (no snorkel installed, this is how it was tuned). I haven't spent a lot of time on motorcycles but the engine sounds normal. Starts fine warm or cold, no black smoke in the exhaust. The previous owner said he never fouled a plug in 10 years, and I didn't change anything when I got the bike. I don't when the broken lever on the carb happened -- i could have bought it like that, or could have been damaged in transit or on a ride after I got it...

One theory is that the broken pump lever caused the accelerator pump on the carb to be stuck open, so that for a while there was constantly extra fuel being drawn thru that jet and I was running real rich. After I fixed everything up, there is still a bunch of carbon deposit in the top end and exhaust and it's ****ing things up? Say that pump is what was causing plugs to be fouled -- should I get a cleaner run right away with a fresh plug, or is it possible i put a fresh plug in and it looks like it gets fouled because i havent burnt off enough of the residual carbon?

 

U are running way to rich. I'm a little higher and running stock muffler, 130m, 32.5 pilot. Did you tune the idle air screw or just set it?

 

Forgot to mention its got a fully muzzy exhaust system. To set the idle air, i screwed it all the way in, backed it out 2.5 turns, started the bike let it warm up, turned in the screw til it started running rough, backed it out half a turn, set the throttle idle to where it died and then a turn in, did the same thing again.

 

Sounds good, I would try a new plug, sometimes they go bad.

 

Spark plug? ive gone through 3 in like 200miles. I just put a new plug on 50mi ago and its already really fouled

 

When you had the carb off and the accelerator pump fixed, did you try running a fuel line/supply into the carb to see if the accel pump nozzle is spraying in the right direction and for the proper amount of rod stroke? This observation would tell you if the pump is operating correctly and your fix was complete. Do you have some good Mikuni instructions for setting the accel pump on that carb? I have the 36mm pumper, but there are some minor differences.

Are you sure your choke rod/shaft is completely closing? There is a rubber o-ring on the choke piston that seals that circuit when the choke is off/in. Sometimes that seal gets worn or defective. You sound sure that this is a fuel richness problem instead of oil, and it sounds like your assessment is correct. On that Muzzy exhaust, that shouldn't be an issue. I have one on mine, and it's a good, solid, functioning aftermarket exhaust.

 

Could an incorrect carb float height be the cause for richness?

 

I once did a DS ride and ran out of gas, I couldn't figure out why my bike was running so crappy, but I didn't have time to check it out, I just twisted the throttle idle up. When I ran out of gas I figured out I had been running with the choke on for 55 miles.

 

I wondered about that too, but I think at the rate of richness he's describing, he'd be also be getting noticeable overflow from the drain tube when stopping/parking the bike.