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Post by blackdogadv on Aug 14, 2023 19:12:56 GMT -5
I was just gifted this scooter. It has a recent 70cc big bore kit installed. Will not fire so I checked air, ignition and fuel. Pulled the plug and found no compression at all. Reed valve looks good. What now?
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Post by oldgeek on Aug 14, 2023 21:09:11 GMT -5
Pull the head off and see if they holed the piston?
Which Derbi do you have?
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Post by blackdogadv on Aug 14, 2023 23:50:33 GMT -5
Pull the head off and see if they holed the piston? Which Derbi do you have? I pulled the head and cylinder and everything appeared new. The base gasket was bad but I might have torn it during disassembly. |
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Post by blackdogadv on Aug 14, 2023 23:54:12 GMT -5
It’s the Atlantis.   |
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Post by oldgeek on Aug 15, 2023 5:41:17 GMT -5
Well I am at a loss then, no compression at all and no holed piston.
I see you have an earlier one with the Derbi motor I believe. I have a later one after they switched over to the Piaggio motor. The motor you have is a bit of an orphan I think, not a lot of performance parts available for it.
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Post by Lucass2T on Aug 15, 2023 7:41:45 GMT -5
I was just gifted this scooter. It has a recent 70cc big bore kit installed. Will not fire so I checked air, ignition and fuel. Pulled the plug and found no compression at all. Reed valve looks good. What now? No compression means probably secondairy compression (compression in the combustion chamber). That would be a holed piston, damaged piston rings or damaged piston. If it doesn't have one of those, then probably something went wrong during assembly. Forgot head gasket, or a base gasket got frumbled up underneath the cylinders base and combustion chamber volume is too big now. No primary compression (compression in the crank case) are most likely worn crank seals or a base gasket failure. You have the engine with the watercooled head and aircooled cylinder. |
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