OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Chainsaws and Concrete Cutters McCulloch Chainsaws McCullough chain saw won't start

Have had this MAC140 chain saw for a while. It's been sitting around for at least a couple of years. I checked the compression and it's very good. I get a reasonable spark, so I put a little petrol in the spark plug hole and it does not fire up. Is there anything else I should do? Only other thing I can add to this is that the spark plug is hard to screw in by hand so I used a socket and wrench but I'm pretty sure the spark plug is on properly.

Have got it to start once. I need to get to the carby but this thing has an unusual design and I can't see how to take this apart, any ideas?

Well I've never seen one tiger, but as they say "Fortune favours the brave" Take the bar and the handle off and see what you can see. Give it a good degrease and clean... Ya gotta start somewhere!

It probably could do with a carby kit and a general de-coke etc. You might want to give it the full rebuild rings and seals and the like. It could be a bit of fun, I hope you have not stripped or cross threaded the plug hole.... might have to take it in to a repair shop and get a "helli coil" / tread repair kit put in.

Thanks Fast Grass, Compression is excellent, around the 100 psi mark. I think the plug hole is ok, definitely a carb/fuel line issue, the carb is pressed into the chainsaw housing I just can't see how it can come out?

Care to Upload some pictures Of this Carby?

Because Without them, We are really At a loss.

Thanks

Kori

Here are some instructions for taking it apart:
http://www.arboristsite.com/chainsaw/23064.htm

If you still want to bother after you read that (I wouldn't), here is the illustrated parts list (go down to 21527):
http://www.mymowerparts.com/pdf/McCulloch-Parts-Service-Repair-Manuals/Gas_Powered_Chain_Saws/

Thanks Grumpy, found your first site ie the arboristsite and it wasn't much help, only saw your second site after I had already pulled this apart, carby is at the very end so you need to move everything else first. I took the carby to a mower place and he told me he had no rebuild kit for this carby, said it's too old. So I took the carby apart and washed it with carb cleaner, diaphragms were in pretty good condition BUT I have really struggled getting this back together, main problem is the throttle switch. A wire much like a paper clip joins the throttle plate of the carb to the plastic switch in the handle but I cannot get the wire to stay on both, as soon as it is moved even a little the wire falls off. I have included some photos but I think this is going to be difficult. I have spent a number of hours on this and would still like to see if I at least cleaned the carby right, can I still run the chainsaw without the bar and chain and also without the throttle switch?
Also included is a photo of the carb.

That carburetor is a Walbro MDC. The MAC140 can be fitted with either that carburetor or a Zama - I suspect you have the better of the two.

If by the throttle switch you mean the engine stop switch (kill switch), its only function is to stop the engine when you push it. Hence you will not hurt the engine by running it without it connected, but you have to give thought to how you will stop the engine, either because you want to or because you suddenly need to. In old chainsaws like that one there is nearly always a choke control, and you can stop the engine by operating it. If it is a "primer-only" carburetor, with no choke, that won't work and you need another way to stop the engine. In my opinion is it much better to run the saw with no bar or chain, for your purposes, and it won't hurt the saw to do this for a brief test.

If you find that your engine runs and you want to put the saw back into operation, the original kill switch can be replaced by an ordinary on/off toggle switch, placed in a convenient location, with one side of it grounded and the other side connected to the kill wire that should run to the original red switch. Because many cheap chainsaws have kill switches almost as bad as yours, this is a common modification.

Hi again Grumpy, the kill switch is fine, it's the switch that operates the throttle plate of the carby that has been difficult. I've found it just about impossible to connect the wire to both the throttle plate attachment and the the plastic switch that is suppose to control how much throttle you apply. Does this makes sense?

I read that as the trigger-control that operates the throttle. The arboristsite people have characterised your chainsaw as a particularly nasty one to work on, so it isn't surprising that you are having trouble with the throttle mechanism.

The essential things to have when starting an engine, are a preplanned way to stop it, and a basis for being confident that it won't hurt you or itself. In this case, the key question is whether the throttle return spring is on the carburetor, or on the trigger mechanism you are proposing to run the engine without. When the remote throttle control is disconnected, the way you want to run it, does the throttle on the carburetor still spring closed? If not, do not start the engine in that condition: it is likely to over-rev and it may self-destruct. It would also be dangerous and unpleasant handling an over-revving engine to get at its kill switch. If there is an adequate throttle return spring on the carburetor, and it still works when the remote control is disconnected, it is safe to run the engine that way but it may be pointless: chainsaw engines usually will only start with the throttle propped part-way open, and the little latch that holds them in that start position is part of the remote control. Your engine will not start with the throttle in the closed position.

Ok good advice. Was thinking of somehow rigging this up so that I can control the throttle plate with some string or other wire. It would necessitate cutting away part of the housing so that I can better control the throttle. I've almost given up being able to get this back to ever running properly but I'd at least like to know whether what I've done has helped. If anyone knows how to hook up this wire from the carby to the throttle switch, please chime in, I have searched for a while but can't find any instructions on how to do this.

One thing that was also hard to re-assemble was the coil in the sense that I could get one magnet to be 4 to 5 thous away from the coil but the other one was about twice as far. I could not get the coil to sit the same distance from both magnets, will this affect the ability to get a spark?

The two sides of the magnetic yoke (the laminated steel part of the ignition module) should be the same distance from the magnet on the flywheel, and the distance should be about 0.012". Having said that, Honda specifies 0.016" plus or minus 0.008", so obviously they aren't all that fussy. Nevertheless the ends of the yoke need to be parallel to the surface of the flywheel. It sounds as if you may need to file the screw holes in the yoke just slightly with a needle file, to create some clearance. Warning: do not try to put a drill bit through those holes, or you will de-laminate the yoke, which will ruin the module.

Thanks for that Grumpy, so what you're saying is that it may be more important that the magnets are equidistant rather than the actual distance apart. I think it's going to be a challenge to get them the same distance apart as I have tried and got it as close as I could. In regard to filing the hole, won't that affect the ability of the hole to hold the thread in ie won't it be loose?

I haven't seen your engine and ignition module tiger, but the modules I am used to are retained by two screws that screw into threads in the cylinder casting. There is a bit of slack in the clearance holes in the laminated magnetic yoke, and you adjust the clearance between the yoke and the flywheel by moving the yoke when the screws are loose, then tightening the screws when the clearance is correct. Sometimes the holes in the yoke are actually oval to allow for this movement.

Incidentally the magnet is embedded in the flywheel, the laminated yoke does not contain a magnet. It is made of a stack of thin stampings of dead soft mild steel.

On my one, the flywheel is held down by a single bolt. The coil sits on top of the carby and is held down by 3 long screws that also hold down the carby, there is a little bit of give but not much. I'm wondering, should you get a spark by spinning the flywheel or do you need to use the starter cord at greater velocity to generate a spark, is there a way to test that the coil is set right without having to assemble the whole thing first as it's such a pain to have to re-assemble?

A marvellous chainsaw, to be sure. On a par with the VW Beetle, on which the screws that held the dashboard also held the fuel tank, IIRC. And that was because the fuel tank was right in front of the occupants' knees, to ensure that the fuel was first on the scene of any accident that occurred. Obviously the advantage was, that made it highly likely it would ignite, so the firemen wouldn't have to waste their time hosing it away.

I don't think you can get a reliable indication of whether the module will spark, unless it is in the right position and clamped down.

I have partially assembled the chainsaw but I'm now not getting a spark. Any further advice on how to set the coil would be appreciated. I thought I had it the correct distance away, obviously not.

The distance between flywheel and yoke is not the only critical parameter when you install it. The module also had to be grounded to the engine casting (usually through its mounting surfaces), and the kill wire has to not be grounded.

Thanks Grumpy for clarifying that, I did notice that the Earth wire had become slightly detached from the module ie the wire was fraying at the module. By the way, the module is not grounded on the engine casting, it is also connected by a screw which holds down the carby as well.

So the Earth wire must be grounded to get a spark, I wasn't sure whether that was essential or not. It's possible that the wire has completely come off the module because you have to squeeze everything in tight during re-assembly. If the wire has come away, can it be reconnected?