Cheap saw needs TLC.....

[Jumper]

I have a 55cc McCullough Power Mac saw-all you pros do not laugh too loudly-it was bought for $200 US with one task in mind, clearing a friend's house lot of pines and it did its job, and I ended up with it at the end of the day.

Just got the ?%$#@! thing back from the repair guy and it ran about three hours, until now. Starts, idles and low speed OK, and initially revs up to high speed, then dies off-catches again if you ease up on the gas and I assume the low speed jet engages again.

I have cleaned filters, put new super gas into it, and fiddled with the high speed jet adjustment, all to no avail. Dirty carb?

Next step?

 

[oakman]

$200 US? wow, i hope it was in really nice shape! it could just need a carb kit, could be a restricted fuel line, tank filter, leaking carb-manifold gasket. also could be leaking crank seals and or worn crank bearings. i'm presuming it has good spark and plug. two strokes are like air pumps. if the crankcase is leaking air past the seals, or crankcase halves if it happens to be that style, or cylinder base gasket they will run poorly or not at all. if your lucky, it will be a carb kit. should be able to get one at manufacturers supply(mfgsupply.com) if its not that, then the crankcase will have to be pressure tested to find any leaks. basically you block off the intake and exhaust ports with a steel plate and gasket, i use 10 gauge(1/8") to make mine, drill a 1/4"hole in the exhaust plate, before you mount it, of course, put the piston at bdc, and use a rubber tip blow gun to apply 7- 10 psi of air to the crankcase. hold the blow gun tightly to prevent it from leaking. you can also pop in a rubber tire valve if you wanna get real fancy. spray soapy water around the crank seals and cylinder base gasket or anywhere else you think there may be a leak. i also use a mighty vac pump to apply vacuum to the crankcase, as seals can leak that way too. this should find any air leaks. sounds complex, but its really not. test plates can be made in a few minutes out of steel, aluminum, 1/4 inch plexiglass, even wood, although that would surely be my last resort! good luck with it.

 

[Jumper]

Thanks for the info....it was new when I bought it from Crappy aka Canadian Tire. I think this is carb related as it was running fine last Friday when I used it at my sister's place for a couple of hours cutting up five cords of wood I had given her. Carb is a Walbro with high and low speed adjustment and I see from their site that there are a lot of parts available to fix.

 

[oakman]

well it shouldn't need a kit if it is that new, although it's possible. i would carefully and completely disassemble the carb, including the hi and low screws,and needle valve. look at the diaphragm against a bright light, for tiny holes or tears, and all other gaskets, and blow it all out good with compressed air. also check to see if fuel flows good through the fuel line, and that it has no holes. also if it has an impulse line, that is a small line from the crankcase to the carb, make sure it is connected and not leaking. it could be that a small piece of dirt got into the carb somewhere.
when you reinstall the hi n low screws, screw them in lightly till they seat, then back the low out 1 1/2 turns, and the hi 2 turns, to start, then adjust from there. you want the saw to 4 cycle rich slightly when wide open- no load. and it should transition from idle to wide open smoothly, if it hesitates or stalls, the low speed is too lean, if it sputters and smokes, too rich. then adjust throttle stop(idle speed) screw till the chain stops moving completely. you want as high an idle as you can get without the clutch shoes engaging. i've found most 2 strokes don't wanna idle down to low.

 

[treeclimber165]

sounds like a blocked high speed jet

And I have found a way to clear this about half the time. I'm assuming it is starving out at high throttle, so this is what I do.

Screw the high speed jet all the way in, counting the turns. Then back it out about 6-7 turns.
Turn off the ignition, pull the trigger to full throttle and pull the saw over about 15-20 times. Flood it as badly as you can, hopefully flushing out whatever is blocking the jet.
Turn the high speed jet back to the origional position, turn on the switch and start the saw. This may take a few pulls since the saw is flooded.

This is my 'in-the-field' first attempt at clearing a blocked jet. Works about half the time. If it doesn't work, try it again but this time remove the high speed jet and gently blow some air or aerosol carb cleaner in the hole first. Then put the jet back in and try to flood the trash out.

 

[DDM]

I like that Idea Brian

 

[Jumper]

Filter

The problem was not in the carb, but the in the tank fuel filter, which was starving the saw for fuel at high speed. Finally noticed this when I was running it with the air filter off and could see the fuel line was getting full of bubbles when I gave her the gas. New filter and all is well, and my wood pile complete for the winter!