Hi, I have a Gas Gas txt 250 1999 and am having problems with the engine. The engine started knocking slightly when i rode it about 3 weeks ago. Since then i havent rode it but started it up this moring and with in half an hour of riding it around the farm it really started knocking to the extent the bike vibrates. The noise is coming from the top of the engine by the spark plug. Also, the revs are all over the place, when you open the throttle up and then shut it off it keeps reving. I couldnt even switch it off with the normal stop switch and had to stall it. when it does stop reving itself it cuts out. Its now not running for more than 20 secs before it cuts out. Also, all of the nuts around the head of the bike are smoking and it really smells like a burning smell!!! Ive cleaned the carb out thinking it could be a lack of fuel getting through, but it hasent done anything to help. Now starting to think gasket or piston but as im not at all mechanicaqlly minded need some advice. Help!

I had this happen on a sherco once. You could even shut off the fuel and the damn bike would still run! We found that the crank bearing on the clutch side had gone and it was sucking oil from the case and running on that. It was easy to see once we pulled the case cover on the clutch side. When that bearing goes the crank and its mating gear will bang into the clutch gear. If this is your problem then it will require that the cases be split and bearings along with seals replaced.

--Biff

Hi Mal,

Only just checked your post sorry..hopefully you'll get more replies later, as I cant think of anymore than what we said on the phone. Dont forget if you want a ride tommorow though you're very welcome to use the Beta.

Interesting post from bifgasgas although for your sake I hope it might be something else, coz splitting the engine etc would be a bit pricey I suspect, unless you have a go yourself.

this might be different from yours but my lads gasser did a simaler thing a few weeks ago the revs all over the place and a knocking noise from the top end but only after a while tryed alsorts then someone said at a trial have i checked the water strange i thought but when i did check sure enough it was low so i toped it up and the difference was unberleavable it was back to normal as i say this may not be like yours but worth a look good luck

this might be different from yours but my lads gasser did a simaler thing a few weeks ago the revs all over the place and a knocking noise from the top end but only after a while tryed alsorts then someone said at a trial have i checked the water strange i thought but when i did check sure enough it was low so i toped it up and the difference was unberleavable it was back to normal as i say this may not be like yours but worth a look good luck

Ok...spot the idiot . Just checked the water as sutty just said...and there was none there . I checked it two rides ago and it was fine, and on closer inspection have found a split on one of the hoses. Changed the hose, put coolant in, tryed to kick it over and the coolant started to come out of the nuts on the head by the spark plug Can anyone tell me what i need to change, and how much damage ive probably caused and whether it can be sorted easily...or expensivly!!

Sounds like youve cooked the cilinder head gasket running with no water. Simple job if the head is not warped.

God luck

Sweet! glad you found your problem. Sorry to have mislead. I will keep this one in the back of the brain.

--Biff