$20 Yamaha CV80

[cwazywazy]

Just got this thing home. It's a Yamaha CV80, guy said it was a "1986ish" but that's just the registration stickers expiry date, and there's clearly an older sticker underneath. I washed it off and got the seat off. The lock mechanism was broken as hell. No keys btw. It has at least some oil in the tank and some nasty old gas. I can feel compression when kicking it over, gonna do a compression test later, but I can't really check for spark because I can't find the spark plug boot or the coil or anything sparky related..


imgur.com/a/g2h10

[cwazywazy]

90 whopping PSIs. Now, how do I get spark? I've got an old GY6 coil..

[cwazywazy]

Got a GY6 coil on there and after I figured out the screwdriver ignition (I'm like 99% sure it was stolen at some point) it makes spark. Pretty sure I got it to fire once.

I've basically decided to part it out at this point, but I'd still like to make it run.

[gsx600racer]

Well you saved the guy a trip to the scrap yard. Hopefully you make a few bucks parting it out.

[cwazywazy]

I'm having daydreams of duct taping it together then getting a big carb, expansion chamber, CVT stuff, etc..

This is one of the older (1983) and slower models with a top speed of about 36MPH.. From a 2 stroke 80cc..

[cwazywazy]

It's got good spark, I think 90PSI is probably enough to run, and I'm spraying starter fluid down the carb. Still nothing. Is there some magic two stroke voodoo I can do to it?

[gsx600racer]

Trying to start a 2 stroke engine on starter fluid is like draining the oil on a 4 stroke and replacing it with lacquer thinner. Any oil coating the inside of that engine is being washed away by the starter fluid and pushed out the exhaust. Better to use gas and splash some 2 stroke oil in it and use that to prime/start the engine. Starter fluid will make things worse than they already are.

[cwazywazy]

Drained and filled the gas tank, added some fresh 2takt oil. No change.

[gsx600racer]

90 psi is on the weak side for compression on a 2 stroke.

[cwazywazy]

These do have low compression ratios, but it should run right? How come I can't get it to fire at all?

[gsx600racer]

Without tearing into the engine to see the condition of the piston and cylinder and checking the reeds, I would be guessing what was wrong and why its not firing off.

I shoot for 140-160 PSI on my builds, Iv built one that had 190-200 and it overheated and soft seized. 

2T's are finicky sometimes when it comes to low compression.


If its a vertical engine(piston moves up and down) you could try putting some oil in the cylinder and roll the over a couple times without the plug and let it set for a bit. Then try to start it. The oil might help bump up the compression and you might get lucky an it will fire off

[cwazywazy]

Horizontal engine, no idea what it is beyond Yamaha 80cc 2 stroke.

[cwazywazy]

Got the airbox out, looked like a mouse was living in it, and the carb off. Still can't see why it won't run.

['O'Verse]

With the old petcock make sure it's getting fuel. Replace the old fuel line with clear fuel rated hose. If it's got spark, the carbs working, and you think it's got enough compression to start usually it's fuel delivery or quality. Throw a cap or two of oil in the tank incase the pumps dried up. And then not recommended but spray a shot of the carb cleaner in the spark plug hole. Throw the spark plug back in and kick it over. See if that changes anything. If not than tear the top end down check the rings and piston.
EDIT: gxr600 is correct you don't want to wash the piston and cylinder with the carb cleaner. But it Can indicate if your gas isn't cutting it.

[cwazywazy]

It's getting fuel fine, I tested the petcock and sucked on it to fill the bowl. Carb is fairly clean inside, gets strong spark, and I still can't get it to fire at all with or without starting fluid.