notfallenyet Posted January 11, 2009 Report Share Posted January 11, 2009 (edited) Hi Folks, Well the story goes like this, up at 7am have some porridge (need the strength) load the 2 bikes. Drive 15 minutes and meet my pal. Take the 2 bikes out, 1999 TXT270 and 2002 TXT280. Jump on my old 270 starts first kick!! Turn around and look at my pal who normally takes 3-4 kicks to start the 280 and he's bent over the bike. What's wrong now?? Seems that when he started the bike which happened to start first kick, it over revved uncontrollably. We started it again twice and the same thing happened. The engine kill switch did not seem to perform it's function as efficiently as I would have liked during this over revving. It took quite a while for the engine to stop. Load the bikes up again and home to the dungeon. Cleaned the carb which was not dirty. Air filter is clean. Petrol is fresh. Carb / throttle function is correct. Spark plug was slightly creamy in colour but dry and clean with a good spark. The bike is in very good condition overall and has not been abused. We're not talking about a bag of bolts here!! The last time the bike was used was a week ago and then it did not want to idle, it settled down after about 20 minutes so we passed no heed of that. So anyway people, what do ye think is the reason for this over revving. Thank you in advance. Edited January 11, 2009 by Notfallenyet Quote Link to comment Share on other sites More sharing options...
feetupfun Posted January 11, 2009 Report Share Posted January 11, 2009 Sounds like a crankcase air leak has developed - possible locations: rubber connector between carby and reed cage cylinder base gasket crankshaft seal Quote Link to comment Share on other sites More sharing options...
notfallenyet Posted January 11, 2009 Author Report Share Posted January 11, 2009 (edited) Sounds like a crankcase air leak has developed - possible locations:rubber connector between carby and reed cage cylinder base gasket crankshaft seal Thanks for your input. Rubber connector was checked when we removed the carb to clean and was found to be perfect. Can you please explain how the engine had the ability to rev so high without any extra fuel been supplied by the carburettor. Am I correct is saying that the only fuel entering the crank case was through the idle jet which was not altered at that specific time and does not allow a variable amount of fuel through. Why did the engine cutout switch not do it's job, yet still when checked it does remove power to the ignition circuit. Does ATF which is been used in the gearbox ignite on compression? Edited January 11, 2009 by Notfallenyet Quote Link to comment Share on other sites More sharing options...
micm Posted January 11, 2009 Report Share Posted January 11, 2009 I sold my gasser when that happened to me - all rather painful I recall with a lot of limping about. I couldn't find an explanation. The ignition cut out also failed to work at the high revs. So I sold it, though I did tell the buyer of my experience, before he bought it! Quote Link to comment Share on other sites More sharing options...
dan williams Posted January 11, 2009 Report Share Posted January 11, 2009 Can you please explain how the engine had the ability to rev so high without any extra fuel been supplied by the carburettor. Doesn't take much. If the engine is unloaded then it's free to really wind up with just a little more air in the mix. If you had the choke on that would also help supply fuel. An engine can run quite happily on a very lean mixture once its going. Since you were not at operating temperature and it was going at high revs you probably wouldn't have noticed if it was in pre-ignition or detonation anyway. As for the kill switch they are not as hardy as you would hope. At full rev there is quite a lot of current coming out of those ignition coils and any resistance in the kill switch circuit, which works perfectly at lower revs, might be enough to impair the function of the kill switch circuit at full blat. That's why clean connections and nice fat wires to hard ground points is essential for a kill circuit. Quote Link to comment Share on other sites More sharing options...
paul w Posted January 11, 2009 Report Share Posted January 11, 2009 long shot.............remove the flywheel ,check the woodruff key and make sure the timing has'nt slipped. Quote Link to comment Share on other sites More sharing options...
hop blip and a jump Posted January 11, 2009 Report Share Posted January 11, 2009 I had this happen on an 03' sherco 290!! Real scary! It turned out to be the throttle cable had been pulled while being transported. Quote Link to comment Share on other sites More sharing options...
hamster Posted January 11, 2009 Report Share Posted January 11, 2009 my gasgas has done this when the carb ice's up in very cold weather Quote Link to comment Share on other sites More sharing options...
notfallenyet Posted January 12, 2009 Author Report Share Posted January 12, 2009 Doesn't take much. If the engine is unloaded then it's free to really wind up with just a little more air in the mix. If you had the choke on that would also help supply fuel. An engine can run quite happily on a very lean mixture once its going. Since you were not at operating temperature and it was going at high revs you probably wouldn't have noticed if it was in pre-ignition or detonation anyway. Thanks for your reply. The choke was on the first time it happened but not on the 2 subsequent occasions. Quote Link to comment Share on other sites More sharing options...
redneck Posted January 12, 2009 Report Share Posted January 12, 2009 my dad's old aprilia would do that with the choke on and would not idle at all with it off and my dad's monty will do that with the choke on. id say to check the low speed/idle jet to make sure its clean. thats what happened to the aprilia. Quote Link to comment Share on other sites More sharing options...
tsr22b Posted January 12, 2009 Report Share Posted January 12, 2009 It wont be the idle jet, that only controls fuel at tickover anyway. If the flywheel key had sheered it wouldn't start at all, or if it did it would just run very badly. You cant get enough air in through a leaky rubber to cause the engine to scream, dont forget when you close the throttle you close the air off with the slide and shut the fuel off with the needle at the bottom of the slide. Do you still have the problem in the workshop? Can you remove the airbox and look in to the carb and make absolutely sure the slide is going down when the throttle is shut off? Carb freezing is a plausible reason, i have known moisture in an airbox be sucked in to the carb and causing the slide to freeze. Air entering the carb is sucked in, so it is colder. The colder the weather, the worse the problem can become. hope this helps. Quote Link to comment Share on other sites More sharing options...
gasgasboi14 Posted January 17, 2009 Report Share Posted January 17, 2009 same thing happend to my dads scorpa ,, kill switch wouldnt work soo we had to put it on its side and flood the carb to **** it off lol it was just the throttle cable. hope this helps somehow Quote Link to comment Share on other sites More sharing options...
b40rt Posted January 17, 2009 Report Share Posted January 17, 2009 First thing I would rule out is the slide seating fully. Glove our the exhaust will also slow the engine down, if not kill it. Would resist the temptation to stick it in gear and kill it that way. Quote Link to comment Share on other sites More sharing options...
notfallenyet Posted January 18, 2009 Author Report Share Posted January 18, 2009 Well folks, after a LOT of searching and examination I have come to the conclusion that it could only have been the throttle cable not allowing the slide to sit down fully. Possibly caused by the outer covering of the cable sitting on the collar at either the carb or throttle end. Thanks for all your suggestions. Hopefully this experience will help others in the future. Quote Link to comment Share on other sites More sharing options...
stueyb Posted January 20, 2009 Report Share Posted January 20, 2009 ive seen this happen loads of times, i also have a 2001 280 gasser, i know it sounds stupid but the rubber dust cap that goes into the throttle twist grip on your bars could be causing this, peel the rubber back and see if the cable has been pulled out slightly and is sitting on the end of the cables seat instead of being in the seat itself... it only takes a slight pull and it falls out of position and revs through the roof like you said.... Quote Link to comment Share on other sites More sharing options...
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