M18 vs. M20 question
 

I have an 1812 with 900+ hrs. I also have a 2072 with 600 hrs. I just got last fall. The m20 in super runs so smooth compared to the m18 in the 1812. Its ran like that for the last 7 yrs. Is that typical of the 18's and 20's? Would the 18 be in need of a rebuild? or would it be better to repower it? and with what? I've always liked the 1812 but I'm REALLY liking the 2072! Advice and opinions welcome....

I've rebuilt carb (walbro fixed main jet) fuel pump is good,good consistent spark. I haven't pulled the heads to decarbon. I've started running sea-foam in the gas seems to help but still sounds like one cylinder cuts out intermittently sorta. I just thought it was normal for the magnums! Until I got the 2072....

They should both run about the same. The 18 may need a little TLC.

Both engines are identical except for the carbs. Should run exactly the same. Tune the 18 up, clean the fuel system, and while your at it do a compression check. Figure out what's wrong with it and fix it. It's never "normal" for an engine to run rough.

Compression is down 88lbs. Both cylinders....

That's lower than I like to see..... but it's not horrible. Pull the heads. Clean it up, check the valves. May even just have a leaking head gasket.

Agreed! Don't forget to clean and lube the starter while it's apart :beerchug:

I didn't know that! So a guy could get an M20 carb and put it on an M18 and be good to go then?

Didn't mean to thread jack BTW :biggrin2:

Edit: According to the Magnum manual, the strokes and compression are different between the two. Oh well haha

Yes, my bad, I know the stroke is different. Same bore, same jugs, same pistons. Compression is different because of the stroke.

Longer stroke should not have different compression. Unless someone has been "fixing" it. Factory compensates for it in the design.