Home. Back. ...... The Gas Gas Guru. Technical Information.
I have a 200 TXT 280, which I bought new. I run 50/50 supreme + 110 race gas, with Yamalube at 90:1. I ran 80:1 for some time, but went to 90 because of smoke, and oil accumulation at the silencer. 90:1 seems to work well, it runs quite crisply. Recently, the bike started to stall when the clutch was slipped at low RPM. The clutch is well adjusted, and functions beautifully most of the time, the motor just sporadically dies for no apparent reason. I thought maybe it needed to be cleaned out, since my riding for a month has been confined to a very small area. I took it out on the road, and went through the gears about like I would on the loop. It ran great until I hit fourth. It began to sputter and knock badly. When I slowed down, it ran great, until about the same place on the throttle, where it did the same thing. It also was smoking quite a bit. The bike ALWAYS starts on the first kick, and low speeds the bike runs great and does not smoke. Some riders said the main jet may just be cleaned out, but the knock sounds so bad I am afraid to keep running it when it happens. Do I just need to try to let it clean itself out, or is there a chance of damage keeping the gas on when this knocking occurs? Thanks, Mike.

Mike,

I've got a couple of ideas. Check the float level and make sure the carb vents are open. If the level is low and/or the vents are clogged or there is an obstruction in the float needle assembly not allowing fuel to flow into the carb, when you hit fourth gear the carb may have run out of fuel, going lean on the mixture just before sputtering, spiking the combustion chamber temperature, thereby causing the knocking symptoms. Jim Snell of Rising Sun Imports did a great article of checking the carb float level, and this is on the Gas-Gas webpage. Add a small inline fuel filter and take the petcock off the tank and clean the strainer assembly. Whenever a bike is knocking, it's trying to tell you it needs help because something is wrong. Don't ride it further until the problem is fixed.

I'd also take off the carb and give it a through cleaning and checkout. You'd be surprised how much gunk accumulates in the bottom of fuel cans and is transferred to the bike fuel tanks. The main jet could have an obstruction or a piece of dirt bouncing around in the bottom of the floatbowl depression by the jet. Your bike will start and run WITHOUT a main jet installed, for a piece of "funny information", as the starting and low speed circuits are separate from the needle/main jet circuits, the bike would however drown out when the throttle was turned.

If you want to be through, jot down your jetting spec.'s and ask your Gas-Gas dealer if he/she thinks they are in the ballpark. You may also have a slightly lean jetting problem which would make the symptoms you describe come on faster with a low fuel level condition.

Let me know if this helps.

Jon

Professional tuner and 'Trials Competition' writer Jon Stoodley has very kindly stepped up to the plate to answer your questions. If you're having problems, or need some advice just send an email to Jon. If it's something that could be useful to others, we'll post it on the site.
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