McCulloch Chain Saws

[heimannm]

McCulloch 10 Series Fuel Cap Repair

I took a couple minutes this morning to snap a few photo's of several different 10 Series fuel caps and try to demonstrate the duck bill valve repair.

First up is one with the plastic insert

Just grab it with a pair of pliers then twist and pull, hopefully it will come out and look something like this. Notice the little black duck bill valve stuck to the brass. The valve looks O.K. but...

The valve had seriously degraded into something between crumbs and goo

Fortunately the red Homelite duck bill valve is a drop in replacement on the brass fitting.

Unfortunately the OD it too big to fit in the plastic body so it is necessary to drill it out to 5/32" to fit.

Mark

 

[heimannm]

Here is the duck bill valve in the body, brass fitting in place. The 5/32" hole just clears the body so the flange of the duck bill valve still seals nicely against the black plastic body.

Spring in place

And it is back together - notice this is not the original photo, see the remains of the old duck bill valve laying there.

Maybe I could have shown these first but here are a couple of photo's showing the original McCulloch duck bill valve, and the Homelite replacement that I have used in both fuel caps and in the 10 Series flat back / bullfrog carburetors. To use the Homelite in the carburetor also requires drilling out one hole a bit for clearance for the body.

Mark

 

[heimannm]

And now one of the later style caps with the brass inserts. These are my favorite to work of as they are just so simple to repair. Grab with the pliers, twist and pull (notice that these brass inserts have already been in and out a time or two), replace the old duck bill valve with the new one, and you're finished. If the spring is damaged or destroyed in the process, I have been successful stacking 3 pieces of #0 o-ring over the nipple to take the place of the spring. I can't say if they are calibrated the same as the spring to "pop off" if the tank pressure is excessive, but for my purposes it works.

Notice two o-rings in the hole and one stuck to the duck bill valve

And finally my least favorite, I have a hard time getting the plastic insert out of the cap without damaging it, as you can see.

However, just drop in the Homelite duck bill valve, install the spring, and press it back together and you are finished.

There are several other styles of fuel caps found on 10 Series saws, but I have not figured out yet how to get them apart to make repairs.

Mark

 

[OldDeadWood]

Gas Caps

I'd like to ad a little to my cap experiance tails.

A while ago when I was just starting with McCullochs I had a fuel starvation problem.

I had put a none vented cap on a front tank saw that did not have the vent tube that comes
out down by the guide bar.

So I had no vent at all, and at some point no fuel would flow.

Sometimes I'm a slow learner but I get there eventualy.:msp_rolleyes:

Note: Thanks for the great info Mark.

ODW

 

[heimannm]

If you can get them to run long enough to warm up and start to create some pressure in the tank you are O.K., if it won't run long enough to get warm and pressurize the tank, not so much...

Mark

 

[promac850]

Check the timing again?

I'll try the fuel cap... if that doesn't work, then I'll try resetting the timing, again.

I'll have to see if any of the cd manuals have a how to in them... hopefully one of them does. I did find one write up done on a kart engine, he said he set the points at 25 degrees BTDC... is that a good place for a saw engine as well?

... I think I may have found the problem. Apparently, points need to smash against each other dead center. The new points that I have do not line up well.

The 790's points are lined up like example #2. Way off to the side.

Guess I got more work to do. Hopefully it'll run today.

BTW, I forgot to mention. I would have needed a new coil at some point, the original had cracks all over it. One big one near the spot where the spark plug wire comes out. It may have been part of the problem, or at least would've become a problem.

 

[a. palmer jr.]

If you can get them to run long enough to warm up and start to create some pressure in the tank you are O.K., if it won't run long enough to get warm and pressurize the tank, not so much...

Mark

I can see where a metal tank saw might not need as much venting as a plastic tank. I guess you could always loosen the gas cap before starting then tighten it up after it gets going.

 

[a. palmer jr.]

Check the timing again?

I'll try the fuel cap... if that doesn't work, then I'll try resetting the timing, again.

I'll have to see if any of the cd manuals have a how to in them... hopefully one of them does. I did find one write up done on a kart engine, he said he set the points at 25 degrees BTDC... is that a good place for a saw engine as well?

... I think I may have found the problem. Apparently, points need to smash against each other dead center. The new points that I have do not line up well.

The 790's points are lined up like example #2. Way off to the side.

Guess I got more work to do. Hopefully it'll run today.

BTW, I forgot to mention. I would have needed a new coil at some point, the original had cracks all over it. One big one near the spot where the spark plug wire comes out. It may have been part of the problem, or at least would've become a problem.

You may have to check other things beside the timing. Just do a basic check of ignition and fuel systems just like you had just got the saw. There's probably something you overlooked, easy to do, I do it all the time. I haven't read the full thread, I assume the saw has plenty of compression, no leaks, etc. Good Luck.
Finally got my nemesis running yesterday, John Deere 80VL. Had it apart for a couple of weeks. It happens.

 

[rwoods]

Thanks, Mark. Ron

 

[heimannm]

Kyle - Set the point gap so they are loose on 0.018" and 0.020" won't go though, timing will be correct at that point. Once they are set, put a clean piece of paper in the gap and rotate the crank shaft a bit so they close on the paper, carefully pull the paper through to make sure they are wiped clean. At long as the point make contact to allow current to flow, then open to interrupt the flow they should work. I like to clean mine with some fine emery paper to make sure are clean and conduct electricity efficiently.

After that, no more than a teaspoon of mix right down the throat of the carburetor, hold the throttle wide open and give it a few pulls. You should get a pop or two then run for a bit. If the carburetor is working properly is shouldn't take more than a few rounds of prime like that to get it pulling fuel and running on its own.

Mark

 

[promac850]

You may have to check other things beside the timing. Just do a basic check of ignition and fuel systems just like you had just got the saw. There's probably something you overlooked, easy to do, I do it all the time. I haven't read the full thread, I assume the saw has plenty of compression, no leaks, etc. Good Luck.
Finally got my nemesis running yesterday, John Deere 80VL. Had it apart for a couple of weeks. It happens.

Tons of compression, and doesn't appear to have any leaks, other than the bar oil tank. (may be the gasket between the tank and the stuffer plate) There is a little oil on the bottom handle brace/lower shroud/louver part, but I think it's just a little oil that dripped there after I got the engine all assembled and let it sit on its side. Everything regarding the engine, I tell you, was lightly coated with oil for corrosion protection and proper assembly. Even the outside of the cylinder has a light coat of oil.

I'm going back out, and am going to take the points out of the saw and ensure they have flat contact surfaces, and meet up properly. I lined them up better than they were before, but they still may be a little off.

I'll be back in a little while...

 

[promac850]

Holy ####... :msp_blink:

This thing is LOUD and MEAN...

Yep, she barked to life. One problem. WFO only. Obviously, I killed it to keep it from blowing up.

Now I need the how to for setting the carb idle governor...

My deaf ass left ear is still ringing...

Oh, part of my ignition problem was that I forgot to set the coil air gap after I put the new coil on. D'oh. Cleaning and lining up the points had to have helped a lot as well.

 

[Eccentric]

Holy ####... :msp_blink:

This thing is LOUD and MEAN...

Yep, she barked to life. One problem. WFO only. Obviously, I killed it to keep it from blowing up.

Now I need the how to for setting the carb idle governor...

My deaf ass left ear is still ringing...

Oh, part of my ignition problem was that I forgot to set the coil air gap after I put the new coil on. D'oh. Cleaning and lining up the points had to have helped a lot as well.

WFO only? The idle governor wouldn't make it rev to the moon like that no matter how grossly out of adjustment it was. Does your 790 have the air vane governor? Show a pic of the carb box and throttle linkage. Something ain't right. Glad you shut it off before it tossed a rod....

 

[promac850]

Here's a couple pics of the carb box. If I need to remove that air filter brace and take another pic ot show everything better, I'll do that in a little while. Going out to grab supper.

I also checked the bolts holding the oil tank on (remember I said it was leaking oil?) and they felt a little loose, so I tightened them all down. That may have been part of the problem.

It could be the carb. Both low and high speed screws are set at 1 turn out...

Throttle rod is not putting any pressure on the butterfly when I let go of it. IIRC, somewhere, someone said that it needs to shut the butterfly. It only pushes the lever forward.

Yes, that ugly fuel line has fuel in it. It doesn't seem to be drawing any air through it.

 

[heimannm]

From my 795 I believe, you can see that the throttle rod pushes the throttle fully open, but when you release the throttle it only pulls it part way back, the idea is the spring coiled on the throttle shaft pulls it open, and the air flow over the butterfly pushes it closed. When the idle speed is too low, the spring pull it open, too fast and the air flow over the butterfly pushes it closed. Sort of a self blipping throttle and rather cool to listen and watch when they work properly.

According to the IPL that I have, the 790 does have an air vane governer that should also be pushing the throttle closed, you may have to fiddle with that a bit to get is set up just right. It is a good idea to have it in place and operating, at least until you get the other bugs worked out and understand how to manage the saw.

Mark

 

[Eccentric]

It would help if you shot a pic without the AF nut crossbar in place. I can see the air vane governor fork on the left side in one pic. It does look like the throttle arm roller is where it's supposed to be in the fork. Can't see the throttle linkage side at all with the crossbar in the way however. A 740 or 790 will have the air vane governor, while a 795 (like Mark's saw) will not.

The air vane governor saws do not have the idle governor spring setup (at least the saws I've seen haven't had it). The air vane governor saws in this series (740/790/840/890) instead have a throttle arm on the carb that's a 'hook' which only is pulled back (or held in place) by the throttle link, and never pushed forward by the link. Pulling the trigger (which moves the link forward) only 'allows' the throttle arm to move forward more (doesn't push it). There's a spring on the air vane governor that rotates the governor fork, pulling the roller on the left side throttle shaft arm on the carb to open the throttle. Airflow from the flywheel pushes against the vane, counteracting the force of the spring and closing the throttle when engine speed is high enough.

The spring on the trigger is stronger than the spring on the air vane, so the throttle is pulled closed when the trigger is released. Maybe the spring on your trigger is missing, broken, or not installed right. If that was the case, then the air vane spring would open the throttle up until the airflow was sufficient to overcome the air vane spring. Basically, your saw wouldn't blow up, but it'd go to the highest governed speed, totally ignoring whatever you do with the trigger. If the governor vane has been cut off (some people do that to disable the governor) then the engine would indeed race up to max ungoverned RPM's. If the trigger spring is in place and functional, then you'd be able to control the engine speed with the trigger (with no governor affect on the saw). That's how my 740 and 790 and RandyMac's 790 are all set up. Without a functioning trigger spring however, there's absolutely nothing closing the throttle, and the engine will wind up until she blows.

All the above rambling boils down to this. Take another pic of the carb box, but with the crossbar removed.............................and make damn sure your trigger spring is in place and functional.

 

[promac850]

I can tell you it does not have a trigger spring on the throttle butterfly shaft. There's my problem.

I don't recall one being on there in the first place. Must've been left behind on the bench. I'll check that all over again, and I'll also post pics of how the lever is set up. I want everything to be where it should be before I bolt the carb back in...

I'll get another pic of the carb box up soon.

Maybe I did forget to put it on.

Just checked, it does have all of the springs, the one on the trigger, throttle shaft near the air vane governor fork, and throttle shaft near the throttle rod.

Maybe the tension is wrong? Pics in next post...

 

[Eccentric]

There's your problem young man.

I can tell you it does not have a trigger spring. There's my problem.

I don't recall one being on there in the first place. Must've been left behind on the bench. I'll check that all over again, and I'll also post pics of how the lever is set up. I want everything to be where it should be before I bolt the carb back in...

I'll get another pic of the carb box up soon.

Maybe I did forget to put it on.

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'.

 

[promac850]

 

[RandyMac]

It is nice to have great friends.