McCulloch PM 700 fuel problem

[Evil XL 12]

Hi. I recently traded a Stihl 029 for a McCulloch PM 700. The guy told me that the McCulloch needed a coil checked out okay. I found that the fuel line had totally decayed. The saw started and ran for a few seconds with fuel mix poured into the carb. I rebuilt the carburetor which is a Walbro SDC, replaced the fuel filter, the line and replaced the tank gasket as it was leaking. The fuel line doesn't leak fuel when disconnected from the carburetor and it doesn't seem to be pulling fuel either. I replaced the fuel line with a molded one made for those series of saws. I tried swapping the fuel cap out with one from one of my 10-10 saws as well. Do any of you have ideas?

 

[Jethro 2t sniffer]

Try a runner 10-10 carb

 

[Evil XL 12]

Try a runner 10-10 carb

That's a great idea. I'll do it. Thank you.

 

[stihltech]

Common issue with 10-10 and 700. Also on 610, 605 series. Fixed this on all.
There is a spacer between the cylinder and the carburetor/ air filter housing. Over time they leak. Sucks air and also lessens the pulse signal. The fix is disassemble, check spacer for cracks, new gaskets and reassemble.
My first saw was a 10-10. Solved a bad idle and lean run. My uncle had a 700, same issues.
Fixed up a few 610s. actually ran pretty well after repair.
It is possible a carb issue also with the hose deterioration.
Just something I have seen over the years.
Yes, I am a Stihl tech, but I always liked the way the Mac 700 ran!

 

[Evil XL 12]

Common issue with 10-10 and 700. Also on 610, 605 series. Fixed this on all.
There is a spacer between the cylinder and the carburetor/ air filter housing. Over time they leak. Sucks air and also lessens the pulse signal. The fix is disassemble, check spacer for cracks, new gaskets and reassemble.
My first saw was a 10-10. Solved a bad idle and lean run. My uncle had a 700, same issues.
Fixed up a few 610s. actually ran pretty well after repair.
It is possible a carb issue also with the hose deterioration.
Just something I have seen over the years.
Yes, I am a Stihl tech, but I always liked the way the Mac 700 ran!

Thanks for the advice. I took a sp

 

[Evil XL 12]

Thanks for the advice. I was curious about that. I couldn't see any type of crack or damage on it. I took a spacer from a running 10-10 to try to rule that out. It still acts the same way. I haven't swapped to a different carburetor from one of my 10-10 saws yet. I'm going to try that next. I've never used one of these yet but I think it's going to be a strong runner.

 

[MAC 7-10]

Stihlteck I think hit it on the head. I had same exact senerio with a mac 7-10. Replaced all new componets just like you did but noticed it was not pulling fuel. took carb apart it looked like it was just rebuilt, all parts were like new and never seen fuel,. I cleaned and rebuilt any way using the old parts which were new any way. Same problem would not pull fuel, had tygon fuel line so could see no fuel was being pulled. Evidently when carb was carb last rebuilt they also changed the carb insulator gaskets. Sometimes people put the gaskets between the carb insulators in wrong and it blocks the impulse and thus blocks the impulse signal. I think the gasket on bottom of insulator is slightly different from top gasket also check for gasket sealant blocking impulse hole. I only use a very thin layer to hold gaskets in place during assembly

 

[Syncop8r]

I replaced the fuel line with a molded one made for those series of saws.

I think I have heard that the aftermarket fuel lines don't work so well - perhaps someone else can confirm?

 

[stihltech]

Almost every one of the 10 series (and 700) I have repaired had this same issue. Things shrink from age and loose sealing. Amazing how much better the saw runs with new intake gaskets.
When you are not controlling the air, the saw runs lousy.

 

[Evil XL 12]

I wanted to give an update on this. The saw runs strong now. It didn't work well with the factory type fuel lines. It came with a metal bushing that fit through the hole in the tank. I installed it and used a little motoseal on it. I rebuilt the carburetor and installed a tygon fuel line. I also had to change the inlet nozzle on the carburetor for the smaller line. The saw runs great. Thank you all for your advice.