McCulloch PM610 hard start

[jdburton]

This saw is agonizingly hard to start.Carb issues have been worked out,new Walbro kit and defective check valve replaced along with new fuel line and filter.Saw has 150 psi compression cold.Spark seems weak and you need to really rip the cord to get any spark at all...and this is with a new NOS coil and flywheel with .012 gap,new kill wire and switch.When and if you finally get it started,it idles, runs and cuts great. let it cool down,same no start situation. Any ideas? Thanks!

 

[Wood Doctor]

Possibly a defective plug or the wrong one. I once had a customer give me a new plug to use with his saw while I made other repairs. Turns out that the plug he gave me to use was the only one I tried that refused to allow that saw to run. It's rare but possible. I must admire your other servicing. That saw should be purring like a kitten. My circa 1977 Mac 610 still does.

 

[Old2stroke]

Are you sure the fast idle feature is working properly? A cold saw will be extremely hard to start if the throttle is not partially open for start up. If set right, the saw should run very fast until you blip the throttle after start up.

 

[EastCoastSawGuy]

first of all, if the plug is good, I would check the magnets on the flywheel, on some of the older saws they can lose their magnetism over time, (though I am not sure with the mccullochs) Also, make sure the magnets on the flywheel are clean, I have come across saws that have dirty or rusty magnets, and once they are cleaned up they will start up easier. If none of that fixes it, I would play around with the gap a little bit, I had a pioneer 620 super with no spark, all the problem was that the coil was not close enough to the flywheel. Maybe try a .011 or .010 gap, it never hurts to try, least before you put anymore money into it.

 

[Wood Doctor]

Are you sure the fast idle feature is working properly? A cold saw will be extremely hard to start if the throttle is not partially open for start up. If set right, the saw should run very fast until you blip the throttle after start up.

Very good point. Somehow I missed that possibility. Tha fast idle setting is a must on these saw engines. You can crank forever on low idle and the engine will act like it's asleep.

 

[KASH]

I have over 40 saws and I start them all on the idle circuit the only time I use the throttle lock is to clear a saw if it is flooded;
Each to their own.
Kash

 

[jdburton]

Thanks guys! The fast idle does work and I have tried to start both with it set and off.The flywheel was replaced due to several fins broken.The top flywheel housing screw was broken and apparently got mixed up with the flywheel sometime in the past. I will try .011 or .010 coil gap and see what happens.Spark plug used was Champion DJ8J which was at the recommended gap.I did notice that the only time it does start,it's with a new plug although the plug that was in it had a short run time.Maybe I should try an NGK or other brand of plug.Who knows? This thing has me stumped!

 

[Old2stroke]

Is it hard to start because it's difficult to spin it over fast enough to get a good spark or because you have to pull it over a zillion times before it fires? Does it start easily when hot? Every coil has a minimum rpm that must be met before the FW magnets will induce enough current in the coil to produce a spark, when you test spark with the plug out, you are probably spinning the engine over faster than with the plug in. A good test to see if you are getting consistent spark at cranking speed with the plug in, is to hook up a timing light and see if it flashes every revolution of the crank.
Is the choke butterfly closing completely? If not, there won't be enough vacuum generated at the carb to pull fuel up the line and into the carb. Need lots of pulling.

 

[Old2stroke]

I have over 40 saws and I start them all on the idle circuit the only time I use the throttle lock is to clear a saw if it is flooded;
Each to their own.
Kash

Not disputing your experience but there is a reason why all saws (except some small ones) have a fast idle feature, in fact many have carbs that automatically latch the throttle open with linkage from the choke, when starting with full choke, and the throttle won't return to idle until the trigger is blipped.

 

[heimannm]

The choke shutter on the 600 Series saws can get bent or otherwise warped so it does not properly close off the inlet to the carburetor when you are attempting to start it cold. Have a close look to make sure 1) the choke is actually moving all the way to the closed position and 2) that the choke shutter (plate, etc.) fits tightly to the top of the carburetor. You may find it necessary to remove the AF bracket and choke to manipulate things to get it to work properly.

Mark

 

[KASH]

The Jonsereds 630s and 670s have the auto throttle advance and I detest it.Some of the Stihls I own have the all in one choke throttle shutoff piece of s---t I hate that even worse than the Jonsereds setup dont even mention flippy caps or plastic saws.
Each to their own.If it was a perfect world Elvis would be alive and the impersonators would be dead.
Kash

 

[jdburton]

Update...The choke is working correctly with full travel and laying flat on the carb.The flywheel magnets are clean and appear to have good strength.I rigged up a 12v induction timing light and got an occasional flash with a good rip on the starter but probably not enough to start.I then used a drill on the flywheel to spin it over to check spark at the plug which was removed from the saw, I checked the 3 used plugs that had maybe 1 hour run time between them.All 3 would spark but IMO,took way more rpm to fire then could be done with the pull start.I then checked a new plug which fired at half the rpm of the used plugs.Plugs were Champion DJ8J,gapped .025.The saw started after a couple pulls with new plug.I'm thinking either the new coil is weak or I got into a bad batch of plugs which all came out of the same box at the same place.I did the plug test with the coil gap at .012 and .010,no difference.I haven't had a chance to do any cutting but I'm betting that after some use,the saw won't start again.

 

[Old2stroke]

A good test for sufficient high voltage is to gap a plug to 0.100", if it will fire that in open air, it will probably fire it in the engine under compression. If it won't fire the plug at slow cranking speeds, the coil would be a suspect even though it is new. Are you SURE it's the right one for that model of saw? If there is enough high voltage, the sparking should not be dependent on the plug being used as long as they are clean and dry.
Just for info, those timing lights are usually meant to be powered from the vehicle battery where there is a ground return from cylinder to battery and when you jury rig them from a bench power supply you often have to connect the negative of the supply to the cylinder of the saw to get a consistent flash with every spark.

 

[Wood Doctor]

JDBurton said, "I then checked a new plug which fired at half the rpm of the used plugs. Plugs were Champion DJ8J, gapped .025 in. The saw started after a couple pulls with new plug. I'm thinking either the new coil is weak or I got into a bad batch of plugs which all came out of the same box at the same place. I did the plug test with the coil gap at .012 and .010, no difference. I haven't had a chance to do any cutting but I'm betting that after some use, the saw won't start again."
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That's the correct gap. The owner's manual suggests these plugs: AC CS 45T or Champion RDJ6. If the coil is good, you should be running fine for quite some time.