irishjohn Posted November 17, 2008 Report Share Posted November 17, 2008 (edited) I finally have the restoration done on my '76 KT 250. Got it started and finally found the right combination of carb settings so it will idel smoothly. However, without any warning the engine starts running wide open. The only way I can make it stop is pull the spark plug and cut off the gas. It does it at irregular intervals, when it is restarted it runs fine for a while then goes wild. Needless to say, this makes it difficult to ride sections. I have checked the following, throttle cable- no kinks, no burrs, it does not drag or bind; throttle assem.- it works fine does not stick, opens and closes easily; slide moves freely in the carb body and when it runs wild the throttle open and closes as normal. I have a suspicion that I may have a bad crank seal on the clutch side as the oil level in the case seems to drop mysteriouly, there are no oil leaks from the cases. Would or could this also cause the wild running of the engine? Edited November 17, 2008 by irishjohn Quote Link to comment Share on other sites More sharing options...
davyb Posted November 17, 2008 Report Share Posted November 17, 2008 Could be fuel starvation or a leak in the carb manifold. Quote Link to comment Share on other sites More sharing options...
irishjohn Posted November 17, 2008 Author Report Share Posted November 17, 2008 Seems to be getting gas so I don't think it is fuel starvation. I will check the manifold for cracks and the gasket. If it is the manifold, would this cause the problem to be itermitent? Quote Link to comment Share on other sites More sharing options...
totalshell Posted November 17, 2008 Report Share Posted November 17, 2008 my suspcion would be a crank seal however.. start with the cheap and easy stuff. it sounds like the problem only happens when the bike is 'hot' suggesting that something is expanding and 'opening'. get the bike running and have to hand a small bowl of engine /gearbox oil. when the bike starts to run away with itself 'paint' the oil on the manifold joints/ rubbers any cracks will be temporary blocked and the bike will stop revving and you will know where your problem is and how to cure it. if it carries on runnning away whip the covers off and check the seals , one may have just been squezed out and a bit of a push may get it back in ( twas the case with my greeves which used to scare the be-jesus out of me all for a crank seal that was not in properly and only req. a bit of pressure from a screw driver to sort out...). Quote Link to comment Share on other sites More sharing options...
irishjohn Posted November 17, 2008 Author Report Share Posted November 17, 2008 (edited) Totalshell, golden info. I'll give this a try tonight. Edited November 17, 2008 by irishjohn Quote Link to comment Share on other sites More sharing options...
lineaway Posted November 18, 2008 Report Share Posted November 18, 2008 Remember the simple things like the fuel tank not venting properly, and or the floats sticking. Both common problems on old iron. Quote Link to comment Share on other sites More sharing options...
davieboy Posted November 18, 2008 Report Share Posted November 18, 2008 Some good advice there. Mine would be to fit a cut-out switch. I always have one on all my bikes.Very important and take away the need to take the plug cap off and risk a shock. Quote Link to comment Share on other sites More sharing options...
swooshdave Posted November 19, 2008 Report Share Posted November 19, 2008 Some good advice there.Mine would be to fit a cut-out switch. I always have one on all my bikes.Very important and take away the need to take the plug cap off and risk a shock. Too easy for a run away engine to self-ignite and a kill switch becomes useless. You should have a kill switch but don't expect it to always work on a screaming engine. I had that happen on my Pursang (12k rpm in a garage is a wee bit deafening) and the kill switch did nothing. I couldn't get under the tank to pull the plug wire so I pulled the gas lines. Not ideal but it worked. Quote Link to comment Share on other sites More sharing options...
big john Posted November 19, 2008 Report Share Posted November 19, 2008 Best tip for stopping a 'runaway' motor is block the exhaust outlet with a rag or glove, this is the only way to 'snuff' a motor. Kill buttons stop working when a motor hits peak revs and pulling the plug cap off doesn't work when the carbon on the cylinder head gets red hot, it effectively 'diesels' Big John Quote Link to comment Share on other sites More sharing options...
fsb Posted November 25, 2008 Report Share Posted November 25, 2008 Hi. It's nice to know that I am not the only one who had this problem. This summer my Bulto also didn't react after I pulled off the plug cap, it just screamed on till I stopped it by using the rear brake. Fortunately the engine didn't seize. Bye, Felix. Quote Link to comment Share on other sites More sharing options...
irishjohn Posted December 1, 2008 Author Report Share Posted December 1, 2008 Ok, I followed everyone's advice, replaced crank seals, new carb to engine boot. Now it just runs away when the engine rpms get high. For example, if I am decending a hill and this causes the engine rpms to increase, when I get the bottom of the hill the engine runs wild unless I slow the rpms with the rear brake on the decent. Or if I am riding between sections and get the rpms up in 4th or 5th gear, the engine starts to run away. This makes for pretty exciting sections... At lower rpms, it runs fine. When it runs wild, the throttle opens and closes fine, no hang ups there. As before the only way to stop the run away is turn off the gas, pull the plug wire and wait for it to run out of gas. Do I need to call a priest? Quote Link to comment Share on other sites More sharing options...
08colin Posted December 1, 2008 Report Share Posted December 1, 2008 Hi John as i work in the motor trade any engine needs three things air, fuel, and means of ignition ie spark if it's a petrol engine these three elements have got to be in the right order ie timing (suck,squeeze,bang) in your case for the engine to run away youv'e got to be getting fuel and air from somewhere as you say the slide in the carb is not sticking open so it can't be getting more fuel therefore youv'e got to have an air leak somewhere,the only thing iv'e had was an ossa that ticked over when cold but as the engine warmed up the tick over increased this was down when traced to a badly worn slide and carb body work on the engine methodicly to isolate the fault to a fuel and air problem you can rule out the ignition side. Hope this helps Colin Quote Link to comment Share on other sites More sharing options...
irishjohn Posted December 1, 2008 Author Report Share Posted December 1, 2008 Thanks Colin. I have not replaced the boot from the airbox to the carb but wouldn't imagine that is the issue since it is outside the intake. A worn slide, would that allow enough air to leak in to make it run away? Where else should I look? Quote Link to comment Share on other sites More sharing options...
08colin Posted December 1, 2008 Report Share Posted December 1, 2008 Hi John what state is the carb body and slide in are all the bolts there bolting the crank cases together don't know your engine casing layout, are the crank seals direct into the crank case halves, is there any damage or cracks in there versinity also what state are the crank cases in general is it a good sealed joint between barrel and crank case and good sealed joints from carb, manifold to barrel. try these, other thing i have heard of was pourus crank cases but was on the old style two strokes. Hope this helps Colin Quote Link to comment Share on other sites More sharing options...
fsb Posted December 2, 2008 Report Share Posted December 2, 2008 (edited) Have you already tried to mount the needle in a richer position or to richen the idle by turning the idle-screw clockwise? Bye, Felix Edited December 2, 2008 by FSB Quote Link to comment Share on other sites More sharing options...
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