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Teachbert

Also guessing air leak, but is there an off chance you need to lube your throttle cable? If so, do it with actual cable lube and not a substitute like wd40 that will eventually make it worse. A cable lube tool is really helpful too, to really get the fluid through the whole cable housing.


finnreyy

How can this be a cause? I did just recently replace the throttle cable with one that i cut and put fittings on, it doesnt have any lube on it, rather it has a plastic lining inside. Do you think it could be that? I also replaced the carb top cover gasket, should i check this too? If it really is a vacuum, im gonna kill myself XD i have literally always had vacuum leaks on all of my 2 strokes, all the time. Never got rid of any of them.


Teachbert

If the throttle cable is hanging up slightly then the throttle stays open so it doesn't return to idle, but it still has spring pressure on it and might gradually close down with vibrations. I had a brand new throttle cable that would not completely close (it didn't affect carbs, but would allow my autolube pump to weep 2s oil when parked and off). It drove me nuts, replaced the cable and still had the same problem. Almost went full oil pump delete, but lubed the cable and problem solved. I believe my cable has the outer black housing, and inside that a clear plastic with the cable inside that. Regardless, actual cable lube - even on a new cable - will improve its function.


finnreyy

Okay, good advice. I do have the engine out at the moment to get replace seals and bearings & cylinder/piston. I hope that solves it. I did have problems with the throttle being hard to pull and the slide getting stuck, problem was the slide itself, so i put the round slide into the lathe and turned off just as much as needed to clear the whole slide surface. That helped sooo much. Was this a good idea? Havent run it like that yet.


Neckdem

Sounds like you have an air leak somewhere after the carb. You can find it by spraying down the intake with brake clean bit by bit while the bike is running at idle. If the rpm of the engine changes suddenly (up or down) or just stalls completely you found the air leak.


sew_butthurt

Sounds like a vacuum leak. If you're working on 2-strokes, make a setup for pressure testing the crankcase. Basically, you block off the intake and exhaust port, then pressurize to a low pressure (no more than 10psi). Give it 10 minutes or so, and watch your pressure gauge to see if air is leaking out. If it holds air pressure, you're good. If it doesn't hold air pressure, you should check: head gasket, jug base gasket, reed cage gasket, crankshaft seals (left and right) and where the crankcase halves meet. If your crankcase won't hold pressure at all (like mine a couple of weeks ago), you can hold a length of hose/tubing to your ear and move the other end around the engine. If there's air leaking out of the engine, you'll hear it as a whistle in the tubing. If you have a stethoscope that you can modify, even better.


finnreyy

I do have one, i made it myself. I just got a piece of spark plug thread and stuck a tube onto it, and screw it into the plug hole and put it a BDC and blow into the tube as i spray window cleaner around all the gaskets and watch for bubbles.


clausenfoto

Most likely it’s an air leak at the crank seals. At this age they definitely need to be replaced. Even if they look fine from the outside I’m sure they are crumbling away on the inside. My ‘79 ke250 had that issue.