why does a trx200 foul plugs

joshfancy · #1 12-21-2011, 11:11 PM

Ive been over this thing with a fine tooth comb. replaced all the top end gaskets because they were weeping, cleaned the carb, made sure and double checked timing, both cam and ignition, used the shop manual and tested each component of the ignition (except the cdi box) and yet this keeps happening. put a new plug in, start it right up, warm it up, take it out for a drive. as soon as you rev it up a little, it kills the plug and you might be able to keep it running for a few minutes, but probably not. this is getting expensive! taking a plug out and cleaning it doesnt fix the problem, yes its a little sooty, but i have to have the thing warmed up before i can tune it, and so far, i just have to go by factory specs until i can get the carb dialed in.
is there any help out there for me?

Here 2 help · #2 12-22-2011, 01:54 AM

Sounds as though the main jet is either way too big or it fell out. Take the float bowl off the carb and see if that may be the case.

joshfancy · #3 12-22-2011, 10:33 PM

everything is stock, motor, jetting, nothing is different than the showroom floor. i had the carb apart and cleaned the other day, main jet screwed in properly and tightened down just right. im going to tackle this some more this evening or tomorrow, so keep the suggestions coming. i'll have a look at the carb and see if anything is amiss.

joshfancy · #4 12-23-2011, 01:31 AM

ok, so a little more investigation. i took the plug out from yesterday, sooty as expected, cleaned it, gapped it, and the other plugs i had that werent old at all, all with less than half an hour on them. cleaned, gapped, and all checked and fired fine. good strong spark. any one of them put it, the thing starts right up, runs good at idle, as soon as you rev it up and let off the throttle a few times, it starts fouling the plug, backfiring, and eventually the more you rev, the less and less it will rev up, youd expect it to clean itself out but it doesnt. on a recap, fresh head and base gaskets, valve seals, lapped valves after decarboning them, triple checked timing and ignition system. oil and compression rings were in great shape and there was a good crosshatch still on the cylinder, albeit a small amount of glazing, not enough to get worried about. am i ripping the carb off again? i tried to change the jet needle groove settings and really, second groove gives the best performance i can get out of this thing so far. airscrew (is it an air or fuel screw? does turning it out make it richer or leaner, its opposite for an air or fuel screw) set around 2 1/4 but turning either way doesnt do much except how easily it falls on its face when you give it some gas. even then, not too much change

Here 2 help · #5 12-23-2011, 03:30 AM

You've done a lot of work, but let's start over. You bought this new in 84 and didn't have a problem till when?

joshfancy · #6 12-23-2011, 03:52 AM

I didn't, my grandfather did. I hadn't seen or heard about it in years, when he died it became mine. So, since last spring its been doing this, and probably longer.

Here 2 help · #7 12-23-2011, 08:41 PM

So when was the last time it ran right and then when did it start blowing plugs? What happened between the last time it ran right and now?

joshfancy · #8 12-23-2011, 10:58 PM

i have no idea when it ran right, or when the problem started, but last spring when i got it (after he died) it was already in this little mess. i got it this way.

Here 2 help · #9 12-25-2011, 07:33 PM

OK - that helps - the carb should be completely disassembled and all the parts professionally cleaned. It's likely it has an obstructed air passage causing it to get all fuel and no air at certain speeds.

joshfancy · #10 12-25-2011, 07:52 PM

I have taken it apart 3 times now, and after cleaning and then using the heavy duty dunk (I had to sign a paper saying I read the msds before I bought it) and blowing air through everything, I'm positive the carb is clean and the float is adjusted properly, along with fuel screw to factory settings, needle on 2nd groove. I am not positive the needle jet and jet needle aren't worn, thus dumping too much fuel all the time. If I turn on the gas, start the bike, then shut the gas off, as the bowl drains it ruins leaner, and that's when it runs better, until its too lean and dies.