OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Chainsaws and Concrete Cutters McCulloch Chainsaws McCulloch Mac Cat Issue!

I have been trying to fault a problem with a mcculloch mac cat chainsaw. The saw starts up and runs fine, but after about 5-10 mins work it stops. After a few mins it will start and run fine again. I have checked all the fuel lines and primer bulb for leaks/blockages, stripped down and cleaned the carby, the diaphram and gaskets still seems in good nick. Any ideas on what may be causing the problem? the carby is a Zama.

Cheers
Paul

Paul,

Check the fuel filter in the tank.

Already checked that as a possible cause, I'm thinking it is carby related, Might just have to replace the diaphrams and see if that solves the problem.

Cheers

My problem continues. I have installed a new carby kit into the carby, checked all the passages for blockages, installed new fuel lines, she still is a no go, infact it is worse. It will start some of the time when cold but will eventualy die once it has heated up. Got any more ideas on this one Bruce?

Cheers
Paul

paulthepilot5,

Once again I will say replace the fuel filter in the tank. Once you have done that then we will go further.

I had tried to eliminate the fuel filter as a cause by removing it and sticking a non filtered pickup weight on the end of the fuel line, but that did not solve the problem so I stuck the old filtered pickup back on.

Paul

Paul, A clogged spark arrestor screen inside the muffler can cause a chainsaw to stop after a few minutes.
Or a blocked fuel tank vent could be the problem, you can check by running the chainsaw with the fuel cap on loose.

cheers gmax

Paul as gmax said that could be an issue and one other thing that I would look at is the exhaust port does not have any blockage.

Ok cheers, I'll check the muffler and see if that fixes it. This model dose not have a breather in the cap, just the fuel line to the carby and one to the primer.

Paul

Well I checked the muffler and there are no obstructions in it. but just ran into another problem when I put the muffler back on. One of the oil pump bolts has managed to work its way loose and foul the flywheel, so I have had to take apart the flywheel to re install the bolt this thing just wants to be a pain in the butt.

Maybe the coil is breaking down when it gets warm, next time it stops remove the plug & check for spark, I'm just about out of ideas.

Well I got it running well after i pulled out the mixture needles again and re set them. But after it runs for a while it stops again as before I can actualy see the problem now, the fuel tank seems to be pressurising and flooding the carby via the primer line. Fuel flowing into the carby throat and flooding it once it has stopped running. The tank has a breather on it but it is a rubber one way valve only designed to let air in not out. could this be a problem with the metering needle adjustment? I did replace the needle and diaphram and set the lever correctly.

Paul

I think I have solved my problem now. The original primer bulb in the machine was not in the correct way nor was the check valve in working order. When I replaced the bulb I stuck it in with the same orientation as the original one (without double checking the direction of flow ). This was alowing fuel to flow directly into the carby and was not priming the rest of the system properly.

Thanks for the quick replys.

Cheers
Paul

Paul, Good to see you have it running properly, I was running out of ideas

I am a bit annoyed at myself I missed the fact the original primer was in the wrong way, would have saved two days of stuffing around. It would have been about 30 seconds to fix the original problem.