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1979 lb80 losing compression


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Hello everyone! Newb here, I own a 79 yamaha chappy lb80. This bike has over 12000 miles and i think the engine is worn. recently i noticed a lack of power and compression usually after a long ride. Everything is clean, sparkplug is new, carb rebuilt, clean airfilter and exhaust. In low gear at full throttle i was able to keep the bike from moving by keeping my feet planted. Ive talked to several people saying i probobly need to bore out the engine. But have been told no bore kit exists for this bike. And would probobly need to find someone to do a custom job which could run up to 1000$ or more. Any advice on getting more power or if any bore kits exist or which cylinders and rings i should look for? thanks!

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Well if you have the manual for the bike piston and rings should be in there along with the info you need as to what to buy. But best really to get the engine out (looks simple enough) and strip the head and barrel off to see what's going on inside the motor, but before you do any of that just check that the chain and sprockets are ok as it might be something simple rather than expensive. a stiff un-lubed chain can really drag your speed down as can underinflated tyres or quite simply bad fuel, wheel bearings can bind as well so don't forget those either, binding brakes can also cause this sort of thing. Just suggestions really as it could just be a fucked piston and your gunna have to bite the bullet and bore it. :shrug:

Found these at CMSL good price to. Where are you in the world? it pays to fill in your profile as no point in saying the parts you want are in Birmingham if your in Timbuctoo..! https://www.cmsnl.com/search.php?model_id=8620&partblk_block=A-06

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Don't need more power on wheels that size.

Like slice said, parts to rebuild the top end will be readily available, probably the same engine as the YB series. Cant get much simpler or easier to work on. Handfull of nuts and the barrel/head is off.

Piston and bore swap would take an hour tops, with a fag and tidying up.

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Just had another thought about your problem have you looked at the clutch at all or the drive/auto clutch? Cos if you can keep it still by just having your feet planted to the floor then it might just be the clutch needs sorting and nothing at all to do with the piston or barrel..! Just sayin..!

Image result for Clutch schematic Yamaha Lb80

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