I would do the leak down test to see where the compression is escaping. If it is a head gasket than that is a easy fix. if ring leakage do as Jon said and take it out and work it hard for some time and see if it gets better with use. Depending on how long it has sat the rings might be sticking. Put some Marvel Mystery oil in the Gas and crank case and just run it. Good luck.
Tom

Never try that Mystery oil before but they have that at the local Canadian tire store so I give it a shot for fun :beerchug:

Today I change the gas filter, change the air filter and swap the carburetor for the one I have on the M18 but before I can start that engine again a leak need to be repair, the oil filter cover gasket (KH-52-41-16) need to be replaced. I call all local source but few are open because of the Canada Birthday and those who are open have none, one of them tell me they are B/O at the distribution center....Gosh! Got no choice, I need to make one! Using the old one to make a template over a single side adhesive gasket sheet, I then use my template to cut one out of a 1/16" thick oil resistant gasket sheet.
https://scontent-yyz1-1.xx.fbcdn.net...77&oe=5A429526

I just add Brad Penn 10-30W high zinc content oil in the engine and crank the puppy up, he run better and my home made gasket hold on apparently. I take care of most of the gremlin's .... Put a new battery (11LU1), a new solenoid, change the starter cable (M20 need longer one), put a new seat and...More later :biggrin2:

One thing at a time will get it fixed. :beerchug:


Now go run the dog sheet out of it and see if it runs better. :biggrin2:

Well I'm not sure anymore, he now back fire and smoke, G.... I need to take care of that carburetor, I try again tomorrow and if nothing change, I check the valves clearance, do a leak test and remove both head.

I'm already looking for spare parts just in case.... Finding pistons and rings for a M20 is pretty expensive, I found piston and rings 52 874 17-S (+.003 rings) for $126.63 each (I need 2) and 52 874 18-S (+.010) for $126.40 each, Can't find intake valves nowhere. If anyone have a better deal let me know, I'm not having fun working on this one at all but I have too, and I want to!

PS: breather is all ok..

try this guy for a gasket set, I am pleased with mine. Know your part # first!!
http://tewarehouse.com/7-02654

Got a fuel pump from here, appears a lot of folks selling them on Ebay
This is the guy I think Jmech gets a lot of parts from
419-337-1548 (9A.M-12N EASTER TIME M-F).
Ebay seller name is bakt4kids
He had pistons for my M18, but doesn't list them for a M20. He said he didn't have anything for the m18 engine, but I told them he had a listing for them. So far they are working great--word of warning--I learned the hard way about checking ring gap and filing it. I would ask him to check to see if he can get them for the m20

How bad are your valves? Maybe let the machine shop inspect them before you go any further. Mine were a little loose it seems, but engine is running fine. I think I miked the stems, but I don't remember for sure.

Have you tried IHCCW? He comes across a lot of stuff, it will be OEM and pricey, but if you really need it....

Thanks for the link John.:beerchug:

Just take this as a notice John:
Rule of thumb for ring gap is .004 per inch of piston.

Today I disassembled the carburetor, give him a good bath and try to adjust again this POS (2 screws model) Well I manage to adjust the idle to 1200 rpm and he purr like a kitten, compression is now 105psi on both cylinders but he puff black smoke during first startups, a bit less on all next one so is it valves seal or piston rings? Leak test need to be done but I think I run the $hit out of it next winter with the 45" 364 snow blower and we will see!
In the mid time I can focus on finding spare parts for the M18 and M20 for a partial rebuild.

Please post if you find a supplier for valves, not just some guy clearing out old dealer stock. I don't need any but did notice I wasn't having luck finding them or pistons for the M20. Sometimes it seems a good automotive machine shop can do wonders coming up with components that can be modified to work. It might be worth a call to your local shop to see if they can supply them. If it is just stem wear, maybe new guides honed to fit wold be the answer.