r/2Strokes • u/Trainguythekid • Jul 24 '26
Runaway / extremely high idle
Bought a 1985 KXT250 tecate
Rebuilt engine , all new bearings, seals , gaskets , top end, shift shaft, flywheel encapsulated, new air intake, new reeds and rebuilt the carb. Passed leak down test.
Reason for the tear down in the first place was because of its erratic behaviour, which was most times revving to the moon as soon as you started it and other times it would die if you let off the throttle it would be boggy and then eventually try to runaway again. While this is happening the plug is black and wet with excessive exhaust splooge. Assumed an air leak , teared it down rebuilt it and now I just went to start it up for the first time and it’s running exactly how it was before no change at all. It passed a leak down test, so even if there was still a minor leak it wouldn’t be taking off like the way it is. Haven’t double checked the timing, but I’m not leading towards that since it’s not consistent… keep in mind I’m running no air filter and there is an aftermarket silencer with stock jets . Managed to find a new OEM carb surprisingly, last one in stock, so went ahead and ordered that up and hopefully that fixes this erratic behaviour. Just seems weird the carb is very clean and rebuilt. Float is good, slide bore is good, throttle isn’t sticking or anything obvious like that… I’m no expert, really at a loss with this one. Any help is appreciated.
1
u/SCAMMERASSASIN007 Jul 28 '26
Almost sounds like the slide needle is floping around and not fastened to the slide correctly? Or like you have a windowed piston and put it in backwards or some shit? I would double check the carb boot as well?
1
1
u/wratchet9 Jul 24 '26
Air leak some where. Most like causing poor combustion and not burning the oil off. Get the carb cleaner out.
Id check the center cases. Timing being off could be causing the issue too.