Yamaha moto 4 80 rebuild Model # help

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Nov 2, 2010 | 10:08 AM

#11

mektech

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Help, 1988 Yamaha 80 moto4 compression low

Well now that all the new parts are on this 1988 Yamaha 80 moto4 and I crank it to start it has everthing but compression. This rig sat for two years, does the ring pack seize and valves seats corrode over time? I did shoot penetrating oil in the cyl and crank it to spread it around. one other question does the unit have a decompression valve? Any help to get me to the next step. do I have to pull the cyl head off?

Jul 8, 2011 | 10:34 AM

#12

moto480

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Quote:

Originally Posted by mektech

Hi, I have a project, this Yamaha moto 4 80 in shop for my friend and can't find the Model # I have the VIN reg # but it wont get me parts. Can anyone help me out. First need is a starter kit or new starter. Then a repair manual. This is a 1988.
Thanks ,
Mike

yes i have a moto-4 80 and i just use JY455Y00XF0021220

Jul 10, 2011 | 11:13 PM

#13

beyondupnorth

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They need really good compression or they won't start unless you tow them. Manual says min 140 ish lbs. 175 is normal compression.
Link to manual here
6789438-Yamaha_Badger_80_Service_Manual_Repair_1985-1988_Yfm80.pdf

Whatever you do don't try to run it with the left side cover off over the flywheel or you will be pulling the tranny apart with me

Nov 6, 2012 | 10:16 AM

#14

MPDano

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Quote:

Originally Posted by beyondupnorth

Oh man, that's a lot of compression. I'm sure the free one I just picked doesn't have that high of compression. It must be tired and in need of a rebuild.