August 5, 201214 yr Just picked up my little mont mh123. The guy I bought it off said that the revs build up without you touching the throttle to the point it's about to go bang. He thought it was an air leak so he had bought a new inlet rubber from carb to cylinder head but still the same problem. He had also bought a new needle as he thought the original was a bit scarred. I've literally just brought the bike home so I haven't even had time to look at it. Any ideas ? It does sound like an air leak to me. He also said that the motoplat ignition system won't cut out with a kill switch when the revs build beyond a point and you have to pull the plug cap off. Is this the case or do i just need a better kill switch ? The current one looks like an old bicycle bell. I want to be able to kill the engine as I don't want to be over revving a cold engine.
August 5, 201214 yr most kill switches wont work on a singing engine , make sure there is slack in throttle cable make sure slide is in correct and is capable of sitting right down so you cant see any air through it if it still does it its poss the main crank seals prob best to give carb a good clean out and check air filter before attempting to start
August 5, 201214 yr Author most kill switches wont work on a singing engine , make sure there is slack in throttle cable make sure slide is in correct and is capable of sitting right down so you cant see any air through it if it still does it its poss the main crank seals prob best to give carb a good clean out and check air filter before attempting to start Thanks for that. I will give it a good inspection this week. I'm hoping it's not the crank seals but it maybe as the bike has been stood many years. Is it possible to replace the ignition side crank seal without splitting the cases ?
August 6, 201214 yr You should b able to replace both crank seals without splitting case however i would not think crank seals would cause engine to run flat out think problem is more likely to be carburetor. good luck.
August 6, 201214 yr NO NO NO NO. Do not pull off the plug cap. It will hurt like f**k and it could kill you. Take off your glove and hold it against the exhaust / tail pipe exit. Do not let go and push hard.
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