June 19, 201115 yr Oops! First proper outing on my 2002 TXT Pro. (Just got back into trialsing after a few years absence) Had been fettling controls and settings. Started it up and throttle cable was not seated correctly in the adjuster where it enters the carb. Result - one screaming engine!! I went for the kill switch wich did nothing but give me a elec shock. So I turned the fuel off - Which obviously has no imediate affect. Hindsight is a wonderful thing and there's a few other things I could of done - Plug cap off, in gear and stall engine or cable out of throttle on handlebar. After what seemed an eternety, it boiled and started to spit coolant out. Another few seconds of panic elapsed and I decided to tip the bike on its (right hand) side, hoping the carb wouldn't supply fuel properly. It died alost immediatly. Waited about half an hour to let things cool down. Replenished the cooling fluid and seated cable correctly - but it wouldn't start. So...Damage - Possibly? probably? or no way of knowing without stripping the engine down? There's still compression when kicking the engine over. Any advice would be appreciated.
June 19, 201115 yr eliminating the simple things first, is it getting fuel? ie is the plug wet? have you switched the fuel back on? are you getting a spark/have you changed the plug? (might have cooked it) have you tried disconnecting the kill switch? (may have damaged it with the higher current/voltage going through when you tried to kill it) if you have compression and its not locked solid it cant be too bad. Trials engines are pretty robust, so it might be something simple. (fingers crossed)
June 19, 201115 yr Author eliminating the simple things first, is it getting fuel? ie is the plug wet? have you switched the fuel back on? are you getting a spark/have you changed the plug? (might have cooked it) have you tried disconnecting the kill switch? (may have damaged it with the higher current/voltage going through when you tried to kill it) if you have compression and its not locked solid it cant be too bad. Trials engines are pretty robust, so it might be something simple. (fingers crossed) Yeah, fuel on, and there is compression still. Never really thought to start checking the basics like spark etc. - just had that feeling of doom. Have the bike half stripped now. clutch side off and no sign of damage. Any further than this and I'm getting out of my depth. Eeek! Thanks for the advice. I'll put it back together this week and check the basics.
June 20, 201115 yr Usually the piston slightly siezes & smears alloy over piston rings, trapping them in place. To check remove exhaust pipe & shine torch up ex port. If lucky a stip & clean up will cure. If unlucky it's ripped the barrel coating and a replate & piston is needed.
June 20, 201115 yr For the future...make sure your exhaust is well sealed and you can kill the engine by blocking it. I've never put a runaway in gear, held the brakes and let out the clutch, but it sounds incredibly scary. Good idea laying it on its side. Edited June 20, 201115 yr by charliechitlins
June 20, 201115 yr Author Update. Looking through the exhaust port all seems ok. took the flywheel cover off, just to see if there was any bits or evidence of damage and found that the flywheel was loose and sheered wudruff key!! Strange coincidence but would seem to be the main reason for not starting. Been to GG this afternoon for gaskets and bits (also new clutch plate to bring into spec) and will build it all back up. Fingers crossed! Oh..and i bought a new kill switch
June 20, 201115 yr Maybe you dodged a bullet! A new kill switch can't hurt, but even the best kill switch usually won't stop a runaway engine. Not sure why. I think they start to "diesel". The high heat generated from the engine spinning so fast ignites the fuel...or something like that...
June 21, 201115 yr Maybe you dodged a bullet! A new kill switch can't hurt, but even the best kill switch usually won't stop a runaway engine. Not sure why. I think they start to "diesel". The high heat generated from the engine spinning so fast ignites the fuel...or something like that... Trials bikes are configured to run cleanly at certain RPM/load conditions and, as such, they tend to go lean at WFO throttle settings. Combustion temps quickly spike and "autoignition" ensues. To stop a runaway engine I take off one glove, wad it in the other hand and cover the exhaust exit. When the RPMs drop down, the killswitch will often work then. To keep from getting zapped by the killswitch, use a two-wire type like a KX or YZ that grounds at the CDI ground and not a one-wire that grounds on the handlebar (makes me think of my old Bultaco days and riding a wet Trial, never had to worry about going to sleep during the event.....). Jon
June 23, 201115 yr I've just stripped my 07 sherco 290 engine, i bought it from a guy last week that had a similar thing happen and it killed the big end bearing because none of his mates tried to kill the motor from revving flat out!! he had fell down a banking when he came off! Edited June 23, 201115 yr by hop blip and a jump
July 3, 201115 yr Best way of stopping over run is to put the choke on and lie the bike down. Never put it into gear as it will most likely burn the clutch out
July 3, 201115 yr Author So....conclusion seems to be... Do's: Bung exhaust. Choke on Tip bike on side Dont's: Rip plug cap off Put into gear and stall
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