Mcculloch 797, Super 797 thread

[Lee H]

So this last Super 797 i got pictured above has given me a fit. It had a couple issues although it ran great.
But you know how it goe's before you know it it is in pieces. I had the cylinder bored .004 over since i had
a piston on hand from Terry Ives, All new gaskets, seals, point's cond, carb kit, etc. Got it all together and
it ran great. I started it a few days later for a friend to hear and it ran great. I started it again that evening
and it ran great then went lean. HMMM, What the hell happened, Can't really pressure test these with the
style decomp they have. I went through the carb again, Still lean, Replace crank seals again, Still lean. I had
the saw on it's side with the lower handle brace off and while pulling it over i could see 2 of the welch plugs
in the cylinder moving. Yes i found the problem. Replaced them and sealed them, Nope still lean, I then tried
to pressure test and while i had a shop air hose blowing very little air in the fitting i have on the carb block
off plate i could feel air blowing right in my face. I kept looking and found a crack in the carb mounting flange
which is part of the lower fuel tank. Found another in my stash and put it on with all new gaskets again. it
is still lean. Removed the points side cover and resealed, Still lean, Replaced the oil pump thinking it might
causing it since it's a pressure pulse pump, Nope still lean. While it's running in normal position it is lean
but when i put it on either side it drastically changes and idles down. Crank is tight in the case and does not
move side to side or up and down on either side. I'm at a loss.

You guys that have been in these have any suggestions as to where i can look. TIA

 

[jacob j.]

Usually if a saw richens back up when placed on its' side, I think crank seals. Which seals are you using on
the flywheel side? And are you sealing the flywheel side plate (crankcase cover behind the flywheel) with an
anaerobic sealer?

 

[Lee H]

Jacob, I'm using original Mac seals and three bond for the side case, It is what i have always used.
I also used the brown aviation sealer on the OD of the seals

 

[jacob j.]

It should be plenty sealed up then. Maybe the carb has an internal issue? Have you been able to
try another carb on it?

 

[Lee H]

Tried 2 carbs and both the same issue. One carb is the one that was on the saw which is a HL63
and i tried a HL 103 and no change. Been through both carbs a few times.

 

[Lee H]

The thing that puzzles me is i found loose plugs in the cylinder and a crack in the carb mounting flange
on the tank and i still have issues but it ran perfect when i put it together then all of a sudden it went
lean. I have fixed all the issues i have found and still lean. I know it's getting air somewhere, but where.
I think my next step is to start over and completely disassemble the saw and start over but i'm just to
frustrated to do so right now. Need to take a break from it for a bit.

 

[jacob j.]

I was working on a 795/797 chassis for a member here and I had a lot of problems getting that one
to seal up as well - it turned out the stuffer had some corrosion and was sucking the tiniest bit of air
but only at medium to high speeds. It would idle perfectly. That's when I started sealing the stuffers
with Loctite 518 on both sides.

 

[Maintenance Chief]

Bob J. Told me when he had saws that no one could find a leak in he'd light up a good stogie and blow it full of smoke! He said he's found defects in castings that way.

 

[Bigmac]

How quick dose it go lean? Bad tank vent?

 

[Lee H]

How quick dose it go lean? Bad tank vent?

As soon as it is started, Ran it with the gas cap off and no difference

 

[Bigmac]

Impulse hole lined up or plugged? Have had some bad gaskets cause issues

 

[Lee H]

All lined up. One of the first things i checked

 

[Bigmac]

And as an fyi I was able to do a leak down test on my cp by putting grease in the dsp, worked good enough to find the air leak

 

[Lee H]

I will have to try that, Thanks

 

[sawfun]

Hows that, Love the sound of a 797 over a 125. And this one is fourty ova.

So did RandyMac like the sound of a 797. I believe he referred to it once as "barely contained violence".

 

[Stihlalltheway]

Got a question about my 797, not meaning to hijack the thread but this seems to be the best place for it. Bought it running, 2 pumps of the primer and it would start and run. About a month later, wouldn’t prime or pick up fuel. Stored dry. Rebuilt and cleaned carb, cleaned the little primer module thing, checked all lines and filter, still nothing. Am I dumb? (Yes, I am) or just missing something? Any help is appreciated

 

[Bigmac]

Got a question about my 797, not meaning to hijack the thread but this seems to be the best place for it. Bought it running, 2 pumps of the primer and it would start and run. About a month later, wouldn’t prime or pick up fuel. Stored dry. Rebuilt and cleaned carb, cleaned the little primer module thing, checked all lines and filter, still nothing. Am I dumb? (Yes, I am) or just missing something? Any help is appreciated

I would check the carb to manifold gasket, make sure the impulse hole is lined up. It can take a while to prime the carb on these. I also use a primer bottle to start mine

 

[Stihlalltheway]

I would check the carb to manifold gasket, make sure the impulse hole is lined up. It can take a while to prime the carb on these. I also use a primer bottle to start mine

I’ll look at this tomorrow, thanks

 

[Lee H]

As @Bigmac stated, use a primer bottle of mix fuel down the carb to get it going after they sit for so time.
Those primers can go bad and are very hard to find.

 

[Stihlalltheway]

Well I got it goin yesterday, and it ran like it had a massive air leak. Probably the primer that’s no longer functional if I had to guess. Looks like it’s coming apart again to get plugged