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Scooters - 50cc => zx50 => Topic started by: MarcusB on July 27, 2018, 08:51:17 PM
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Ok, New thread...
I had an issue with my scooter not starting. Found an Fawlty piston and rings. Every rhing else seende fine. Changed piston and rings and gaskets. Started up right away.
Had it running on idle for an hour or two, then started to run it but slow. Now its dying when it gets hot, it seems like its pinching. A soon as it cools down it starts right up like before.
It is original cylinder, and i got an original piston with rings. What am i doing wrong?
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First, bad idea to let anything idle for an hour or two, especially a two-stroke. Second, ring end gap should be checked before final engine assembly. Just because the rings are for that engine and piston does not mean the end gap is right for the cylinder size.
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Well that Did not help me at all... someone with something more constructive
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First, bad idea to let anything idle for an hour or two, especially a two-stroke. Second, ring end gap should be checked before final engine assembly. Just because the rings are for that engine and piston does not mean the end gap is right for the cylinder size.
Tell me why is it a bad Idea running a fan cooled 2 stroke on idle?
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Glad you asked that question! Idle speed on any engine is tough on spark plugs and rings because of partially burned fuel making carbon deposits. Not as bad on 4-strokes these days with EFI and electronic ignition but still tough on 2-strokes even with CDI. The plug is "heat ranged" for normal operating temps and idle does not come near those temps that will burn deposits off. The rings in a 2-stroke are pinned so the won't rotate and they tend to carbon up anyway but really collect the stuff at idle speeds. Now granted, the best thing to ever happen to a 2x was CDI as it reduces the tendency to "load up" the plug compared to old battery, coil and breaker point systems of yesteryear. I guess some of this is from "old school" experience, too.
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So How am i supposed to ride in the New piston do you think?
Over to the problem, What could be the issue with geting to hot. It starts really fine, a can ride 5-10 minutes and then it shuts down. Sounds like its pinching but i am not sure. It Will not start again until its cooler
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After the engine "shuts down", when you try to re-start it, will the motor turn over at all or does it feel like the piston is stuck place?
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Those are the classic symptoms of too small of piston ring end gap. There is no "riding in" to fix this. Riding much more will score the cylinder so badly that rebore or replace will be required. What to do now is remove the cylinder and piston. Remove the rings from the piston and stick them in the cylinder one at a time and measure the gap between the ends of the ring with a feeler gage. The ends will have to be ground off carefully if (and it will be!) too small. There is a specification for this and it usually is posted by the service manual or by the ring manufacturer. .003" will generally work. Check Youtube, there has to be one that covers this procedure.
I had to learn this the hard way on a 59 SAAB GT750 three-cylinder 2-stroke!