I posted this previously in the wrong forum, and didn't receive any responses, hopefully now that I'm in the correct someone with some knowhow can assist.

In a nutshell, I can't get my 1985 YFM80N to turn over. I'm the original owner and the 4wheeler had been garaged at my grandparents up in Dallas for 20 years, and the gas in the tank and carburetor had turned to varnish and the air filter was rotten to the point of falling apart.

Here's what I've done so far:
-Replaced the battery. Full Charge. Have good strong neutral light when I turn the key.
-Took off the carb, disassembled it and ran it through an ultrasonic cleaner. (Here's where I think I may have messed up as the simple green/water solution pitted the aluminum...learned a lesson there) Float was fine. Jets seemed clear but the main nozzle was very difficult to remove and get back in and the main jet doesn't thread flush with the alum body of the carb (not sure if it is supposed to, but there is definitely a gap there.) I also noticed that the choke was a little slow in closing but figured that could be due to it being dry. When wet it seemed to open and close okay so I figured with gas in the carb it would probably be ok. I was careful to back out the jet 2.5 turns per the manual. Re-assembled carb and re-installed with new O-rings and new gaskets.
-Replaced the air filter with a new one (oiled it per instructions)
-Cleaned out the gas tank and confirmed that gas flows through the gas line
-Replaced the spark plug (checked the gap)
-Cleaned the muffler element
-Checked the gas tank breather hose, its not plugged
-checked the carb breather, not plugged
-fuel empties from the carb when you unscrew the drain valve

When I tried starting it wouldn't turn over and flooded the engine. The pistons are making the thud thud thud like they are moving up and down. The break is engaged, run switch is on, fuel is on (obviously). I performed a spark plug test and I'm getting a spark, but I did notice a very small amount of black almost like grease on the spark plug electrode. I also did the thumb over the spark plug hole compression test and seem to be getting plenty of compression.

The main nozzle and jets can't be purchased for this model anymore, and other than replacing the carb I'm out of ideas. Before I cough up another $80(for an aftermarket) or $250(for OEM) carb I'd appreciate if anyone else with experience on this model could weigh in on potential problems based on the above diagnostics.

Thanks in advance!

 

I'm currently in the same position. While it may seem like good compression, it's not. Mine had 90 psi and it wouldn't even try to run. It needs 170 psi. 140 is the min. I pulled the engine apart and the valves are bad. I'm in the process of getting it back together now. Good luck.

 

You could eliminate the fuel problem by pouring a small amount of fuel into the sparkplug hole, reinstalling the sparkplug and then try to start it. If it starts then fuel is your only problem. If it doesn't start then of course you have other issues. A true compression tester will take the guesswork out of the compression as stated, and it will not hurt to check the timing. You would think the timing could not get off if it's been sitting for 20 years but stranger things have happened.