McCulloch Chain Saws

[promac850]

The difference in the spark plug won't really affect the way it starts and runs, most in fact were intended the be able to operate with either type. The gasket design will form a complete seal, just make sure the reach is correct so you are firing in the cylinder and the plug will not punch a hole in the piston.

Ron - I have three different "bodies" but no cover. One has the spark arrestor screen so I will probably use that until I can get one whole muffler. $50 for a new one is high, but not unreasonable.

By the way, the 850 is now a runner. My compression gauge must be on the Fritz as this thing has very good compression but the guage only reads 120 PSI now. I can't wait to try this one along side my SP81 and PM800.

I will try to get photo's up tomorrow.

Mark

So maybe the plug isn't quite reaching into the chamber and that's why it pops/sputters every now and then, but won't run?

I must be stupid for pulling the starter cord over and over in attempt to get it to run. It's so close to running that it doesn't make any sense why it won't. I'll try a new plug tomorrow... hopefully that will solve the problem. If not, I think I'll look for where that little bit of fuel came from.

 

[promac850]

I'm betting the timing is off, the symptoms indicate too much advance.

I'll check that again tomorrow as well. It popped plenty of times, but took the starter handle out of my hand more so. Is there a good tip to ensure the timing is set just right?

 

[Steve NW WI]

So maybe the plug isn't quite reaching into the chamber and that's why it pops/sputters every now and then, but won't run?

Doubtful, but possible. As much time, effort, and money as you have into this project, take the time, run to town, and spend a few bucks on a new (correct) plug, and that will be one more variable you can rule out. - see you're already taking this advice, but keep it in mind for future projects as well. Always start with the easy, cheap possibilities and work into a problem from there.

I must be stupid for pulling the starter cord over and over in attempt to get it to run. It's so close to running that it doesn't make any sense why it won't. I'll try a new plug tomorrow... hopefully that will solve the problem. If not, I think I'll look for where that little bit of fuel came from.

Don't beat yourself up. I've been there myself and done the same. Sometimes it's best to just admit that the battle is lost for the day, walk out of the shop, have a cold (root in your case) beer and forget about it. Come back later with a fresh mind and a better attitude and something simple may well jump out at you. This is supposed to be a fun hobby, not a pain in the butt that causes your blood to boil, it can be hard to realize that when you're "this close"!

One other possibility that should be easy to check. If the 790 has a single wire kill switch, disconnect it, and make sure the wire isn't grounding anywhere. An old switch could be partially grounding from corrosion and not letting it get full fire, yet still showing some spark. It about drove me nuts on an old trimmer I had till I left the wire off out of rushing it back together for the 39th time, and it ran. Put it together right, no run. Replaced the switch and all was well again. See - little things strike again.

 

[Eccentric]

Some days you get the bear...........................and some days the bear gets you....

 

[little possum]

What you need is a Mac 3 man saw....

Dont lose the temper either, I promise it will get you nowhere.

 

[RandyMac]

Oh waiter!

I have experienced advanced timing with three McCullochs, all had the +5 flywheels, they would suddenly turn evil, they would pop and flood. The fix was checking the points gap, it worked well, but there was a very narrow variance, too little the motor lost the edge, too much, well we know what happens there, you can't pull it over fast enough. Try closing the gap a touch.

 

[Eccentric]

Oh waiter!

I have experienced advanced timing with three McCullochs, all had the +5 flywheels, they would suddenly turn evil, they would pop and flood. The fix was checking the points gap, it worked well, but there was a very narrow variance, too little the motor lost the edge, too much, well we know what happens there, you can't pull it over fast enough. Try closing the gap a touch.

Yep. If he has it set at .020" he should try .017".

 

[heimannm]

Fellow member 54 Stude was looking for a fuel tank for a PM800/850 type saw and I knew I had this one still in a box in the attic.

I started dismantling it to remove the tank for him, and thought I might as well take it all the way down and clean up the remaining parts in case there was some good left in some of it. I picked it up a long while back and knew it had real compression issues so i was expecting toast. Instead, I noticed some strange movement though the intake port and upon further investigation discovered this.

Surprisingly, the bore did not look that bad. I am currently lacking the 1-2" snap gauge from my set so I couldn't measure it, but I did have a NOS "B" piston on hand and discovered this cylinder was also stamped with a "B" so why not?

Mark

 

[heimannm]

I didn't bother with any intemediate photo's, but here it is all done. I was able to find all the parts I needed to get it whole again in the shop except for a decent muffler. As I noted earlier, my compression gauge must have a problem since this only registers 120-130 PSI but I can tell you it is a lot better than than. Tillotson HS carburetor, 24" B&C for now, maybe I can try it out Saturday just to see how it really works.

Mark

 

[promac850]

Thanks everyone. I'm going to go pick up a new spark plug and reset the points.

I'll be back with news later today as to whether that fixed it or not.

Also gonna grab a better recoil handle, the one I have is missing the top cover thing and someone tied a steel rod onto the rope... Needless to say, that took a little chunk out of the recoil cover on one of those snap backs. Can't find that little chunk, so it really went flying somewhere into the yard.

 

[promac850]

Well, I got the new plug and installed it. It's noticeably different from the other one. (DJ8/DJ8J compared to the J6J)

However, that and resetting the timing did not fix the problem. I popped a couple times, but still didn't run. Broke out the multimeter and found out the kill switch is indeed shorting itself out... little *******. I cleaned it, put it back together properly, and it still tortured me...

So, I'll be looking for a kill switch. I don't dare run this thing without a properly working kill switch for obvious reasons. (want to be able to shut the engine down if it is running improperly such as an incorrectable lean condition, etc.)

 

[Steve NW WI]

Kyle, what does the new plug look like now? With all the time you spent trying to start it, the crankcase could be flooded. If the plug's wet, dry it off, pull it over a few times with the plug out, and start over. Remember, simple things first.

After ruling that out, I think I'd be looking toward the coil for answers, but others here know a heck of a lot more than me.

Keep after it, but don't let it get ya down buddy! We will wait patiently for the victory video, whenever it comes.

 

[dieselsmoke]

First start up

Hey Kyle, as others have said you've probably flooded the thing. You should have a consistant nice blue spark. Vent the crankcase by pulling it through a few times, no plug, switch off, very important, dont ask.
Use a NEW plug to start with throttle WO. And crank a few times. If no start then read your plug. Wet and no start is no spark. Bone dry means no fuel. so then prime and try again.
Randy's spot on about too much advance, I did that same thing to my 740 (1-86) a while back. Your symptom of handle rippage is a clue.
Good luck, we know your right on the edge of making that thing bark.

 

[paccity]

sorting and stacking , allmost done with the mac,s.

 

[Eccentric]

Wow.........

 

[Ambull]

Well, I got the new plug and installed it. It's noticeably different from the other one. (DJ8/DJ8J compared to the J6J)

However, that and resetting the timing did not fix the problem. I popped a couple times, but still didn't run. Broke out the multimeter and found out the kill switch is indeed shorting itself out... little *******. I cleaned it, put it back together properly, and it still tortured me...

So, I'll be looking for a kill switch. I don't dare run this thing without a properly working kill switch for obvious reasons. (want to be able to shut the engine down if it is running improperly such as an incorrectable lean condition, etc.)

If the kill switch was shorted out, it would not have fired at all. You should probably check it again. You have to disconnect the wire in order to check it. Just check resistance from the terminal to any ground point on the saw.

 

[paccity]

Wow.........

then the fun starts in cleaning and making them run.:biggrin:

 

[joeymt33]

[video=youtube;xC0roQng-as]http://www.youtube.com/watch?v=xC0roQng-as[/video]

i've got David's saw just about complete. here is a couple vids of it

 

[joeymt33]

[video=youtube;gJHUHpGs4TY]http://www.youtube.com/watch?v=gJHUHpGs4TY[/video]

this saw is pretty nice to run. its got a 8 tooth sprocket since david will be running a 24" bar. it pulls this 28" bar fine though

 

[joeymt33]

While cutting and breaking in the new rings with 32:1 mix. I heard something that scared the crap out of me. I thought I just smoked the motor. I immediately shut it down ad found the clutch to be broke.

The tip of the spider broke and the other piece that goes inside the spring flung out. What causes this?