McCulloch Chain Saws

[promac850]

Kyle the trigger spring does NOT go on the throttle shaft (or anywhere else on the carb). It's on the trigger itself, inside the rear handle assembly.

It's #9 in the Figure-7 Handle and Control Assembly page of the 790 IPL.

When I first fired up my 790 a year or two ago, the throttle spring wasn't installed right (or was broken). Felt 'OK' before I started the saw, but something must've come loose when I fired it up. Damn thing went right to WFO as soon as it fired. Luckily the saw had an HL swapped on in place of the primer carb, as I was able to push the choke down (faster than I could have shifted my thumb over to the the kill switch). That saw had quite a few 'shadetree modifications'.

Okay. You were talking about the trigger spring. Yes, that is on there. I'll check that spring again. It's not broken but it could be installed wrong.

 

[Eccentric]

Interesting. That carb has a throttle arm that I haven't seen on these saws before. Very different than the 'hook' arm that was on the primer-flatback that I took off of RandyMac's 790. Looks like you have things installed correctly. I do see an idle governor spring on your carb (again, unlike Randy's carb). That isn't causing your WFO problem however. My money's on the trigger return spring being the issue here. It's a very strong 'mousetrap' spring that pulls the throttle link back with authority when you let off the trigger. It hooks onto the throttle link next to where the link passes through the hole in the trigger. The tail of the spring bears against the top of the inside of the rear handle casting. Best way to get to that is to unbolt the rear handle casting from the tank/carb box. It's easy to take off once you remove the oiler and primer/choke (depending on which carb ya got) buttons by sliding out their retainer pin. this pin is held in place by the tiny slotted head set screw that threads into the top of the rear handle.

 

[ozflea]

It is nice to have great friends.

What friends thread hacker ????????????????

Especially after calling my chainsaw a toaster hur

 

[RandyMac]

:hmm3grin2orange::hmm3grin2orange:

 

[Eccentric]

What friends thread hacker ????????????????

Especially after calling my chainsaw a toaster hur

I like the look of your Svedish McToaster Bob.

 

[ozflea]

:hmm3grin2orange::hmm3grin2orange:

Go on laugh you hacker i dug up old Bob and made sure your excluded from his will
And and Electric Eccentric your out as well

 

[Eccentric]

Go on laugh you hacker i dug up old Bob and made sure your excluded from his will
And and Electric Eccentric your out as well

Dangit. And I was hoping for the Homelites in the McBob collection.......

While we're drifting off-topic.................did I tell you that the yahoo with the Mall-6 that we tried to get to you from here (the deal that was killed by the outrageous shipping quote) later listed the same saw for about $100 MORE than what he had it listed for before? Must've got it in his head that the saw was worth more since some guy 1/2 way around the world with a funny accent was interested in it...:bang:

 

[cpr]

Haven't been paying close attention, Kyle. I'm glad you have that box of parts looking good and on the verge of running. The rest of it isn't as pretty and currently doesn't run at all pending some carb work that is still weeks away.

 

[cpr]

It is nice to have great friends.

That's funny, I don't care who you are...

 

[promac850]

Interesting. That carb has a throttle arm that I haven't seen on these saws before. Very different than the 'hook' arm that was on the primer-flatback that I took off of RandyMac's 790. Looks like you have things installed correctly. I do see an idle governor spring on your carb (again, unlike Randy's carb). That isn't causing your WFO problem however. My money's on the trigger return spring being the issue here. It's a very strong 'mousetrap' spring that pulls the throttle link back with authority when you let off the trigger. It hooks onto the throttle link next to where the link passes through the hole in the trigger. The tail of the spring bears against the top of the inside of the rear handle casting. Best way to get to that is to unbolt the rear handle casting from the tank/carb box. It's easy to take off once you remove the oiler and primer/choke (depending on which carb ya got) buttons by sliding out their retainer pin. this pin is held in place by the tiny slotted head set screw that threads into the top of the rear handle.

I checked things closely, and that throttle butterfly arm was the problem, as well as the linkage not quite bent the right way. I swapped out the throttle butterfly rod and arm from the original flat back that came off of this tank (it was a 1-76) and installed that into the good flat back that is on the saw. Then tweaked the linkage a little bit to ensure it allowed the trigger spring to pull the arm all the way back. It was getting caught up on the boot and not letting the rod end pull the arm back far enough.

Once that was done, it worked properly and shut the butterfly (checked with the inspection mirror) I took it outside and tried to start it. No dice.

We're back to no spark/weak spark. Got some work to do tomorrow. Or I might go out there and work on it later tonight if I am restless enough. Yeah, the neighbors might get a little angry at me if I end up starting it at 1-2 am... but I don't care. :biggrinbounce2:

 

[promac850]

Go on laugh you hacker i dug up old Bob and made sure your excluded from his will
And and Electric Eccentric your out as well

Out of all due respect Sir Bob, where am I? :cool2:

 

[a. palmer jr.]

I checked things closely, and that throttle butterfly arm was the problem, as well as the linkage not quite bent the right way. I swapped out the throttle butterfly rod and arm from the original flat back that came off of this tank (it was a 1-76) and installed that into the good flat back that is on the saw. Then tweaked the linkage a little bit to ensure it allowed the trigger spring to pull the arm all the way back. It was getting caught up on the boot and not letting the rod end pull the arm back far enough.

Once that was done, it worked properly and shut the butterfly (checked with the inspection mirror) I took it outside and tried to start it. No dice.

We're back to no spark/weak spark. Got some work to do tomorrow. Or I might go out there and work on it later tonight if I am restless enough. Yeah, the neighbors might get a little angry at me if I end up starting it at 1-2 am... but I don't care. :biggrinbounce2:

I thought you said it started and ran wide open, wouldn't that mean the spark is okay? Even if it does have spark you still might want to change the spark plug. My echo JD 80VL was running real well and all of a sudden it died, it still had spark but wouldn't start...I installed a new plug and it took right off. It just wouldn't fire under compression.

 

[Eccentric]

Out of all due respect Sir Bob, where am I? :cool2:

Sweeping up in the shop of course....

 

[ozflea]

Sweeping up in the shop of course....

Next to Randy attached to a rather large anchor and preferrably about mid pacific

 

[promac850]

I thought you said it started and ran wide open, wouldn't that mean the spark is okay? Even if it does have spark you still might want to change the spark plug. My echo JD 80VL was running real well and all of a sudden it died, it still had spark but wouldn't start...I installed a new plug and it took right off. It just wouldn't fire under compression.

It did. Fixed the throttle problem and now no spark. It had weak/no spark even when it was grounded to the cylinder, outside where there is no compression.

 

[promac850]

Sweeping up in the shop of course....

Did that already.

Next to Randy attached to a rather large anchor and preferrably about mid pacific

I have no problem stabbing sharks to death with the Case bowie.

 

[rwoods]

Where is Mark H. when you need him?

You guys are cracking me up. Since Mark is not around for crowd control, I guess I'll have to step in with a MAC picture. PM805 is 2nd from the left. I am going to need more space when I get the other MACs done. Carry on. Ron

View attachment 246473

 

[a. palmer jr.]

It did. Fixed the throttle problem and now no spark. It had weak/no spark even when it was grounded to the cylinder, outside where there is no compression.

It's possible you might need to look at those points again, they might have bent themselves a little when you ran it. Did you put a small amount of lube on the rubbing block? If you didn't it's a high wear spot and will affect the point gap. As the rubbing block wears down it will set the points closer together and retard the timing.

 

[promac850]

It's possible you might need to look at those points again, they might have bent themselves a little when you ran it. Did you put a small amount of lube on the rubbing block? If you didn't it's a high wear spot and will affect the point gap. As the rubbing block wears down it will set the points closer together and retard the timing.

The felt wiper leaves a good coat of oil on the cam. Should I put a thin layer of grease on the rubbing block as well?

 

[a. palmer jr.]

The felt wiper leaves a good coat of oil on the cam. Should I put a thin layer of grease on the rubbing block as well?

On new points the most wear on the block occurs during break in, yes I would put a little grease (not too much) behind the rubbing block on the cam side where it forms an "L". A slight bit on the cam itself wouldn't hurt.
By small amount I mean about the size of 3 BBs in all.