MCCULLOCH The official McCulloch thread

[Al Smith]

I may have a good carb on the 700 carcass. I dont see a high speed adjustment on this Tilly carb.

The IPL of both 1972 and 1977 only show adjustable jet carbs but the 1974 IPL shows both a Tilley HS and a Walbro sdc with fixed jets as well as two with adjustable jets .One of McCulloch brain storms that was not needed evidently

 

[Dream]

Poge, thanks so much for the IPL! The 700 carb is different. 700 had the idle adjust screw that goes thru the air box wall. 7-10 had the idle screw on the carb. The 1010A carb has the idle screw made into the carb if it will work. I know theres a lot of difference in fuel needs for a 54 cc saw versus a 70 cc. Just hoping the venturis are the same and maybe I can open the jets enough to give jer tje fuel she needs. Dont want to run her lean.

 

[Dream]

On a PM6A in working on, removed the Welsh plugs to clean the orifices and screen. I cant remember what sealer to use on these. Looks like they had the yellow stuff on them.

 

[Al Smith]

That 10-10 carb should work on a 7-10 or at least better than a fixed jet .I have a 105 that had a carb with a fixed jet ,would not run right ,I replaced it with one from a 125 adjustable jets .That cured it .As I understand it McCulloch with it's infinite wisdom thought fixed jets would curb a warranty issues .Turns out it was just a bad idea .

 

[fossil]

On a PM6A in working on, removed the Welsh plugs to clean the orifices and screen. I cant remember what sealer to use on these. Looks like they had the yellow stuff on them.

I don't feel there's any need for sealer for welch plugs. Once they're set they shouldn't leak at all.

Some guys used nail polish but I think ethanol eats that.

 

[sawfun]

That 10-10 carb should work on a 7-10 or at least better than a fixed jet .I have a 105 that had a carb with a fixed jet ,would not run right ,I replaced it with one from a 125 adjustable jets .That cured it .As I understand it McCulloch with it's infinite wisdom thought fixed jets would curb a warranty issues .Turns out it was just a bad idea .

My 125c's seemed to work just fine with fixed jet carbs.

 

[Al Smith]

I suppose if you had the right jet it would make a difference.On the SP 105 it shows 4 different size jets and the SP 125 C 6 jets If I read it correctly from 26 to 31 thou.

 

[Al Smith]

If I get some time I think one of my micro fiche slides talks about the jet size as related to altitude .

 

[PogoInTheWoods]

I don't feel there's any need for sealer for welch plugs. Once they're set they shouldn't leak at all.

Some guys used nail polish but I think ethanol eats that.

I've found plenty of welch plugs floating around the metering chamber from deteriorated original sealant or just from being poorly punched down in the first place. I wouldn't count on any such plugs to re-seal by simply punching them back into place with a drift or punch without also using some type of sealant..., if I had to reuse them as the only viable alternative, of course. Nail polish has worked for me in the past and I've actually seen it recommended in a service manual somewhere (as I recall). Some suggest Seal-All or Indian Head shellac but I've found clear acrylic nail polish to be quite effective and much easier to apply. New plugs should indeed stay in place by a friction fit if designed to to so and installed carefully. Otherwise, and if in doubt about the fit, I'll seal em.

 

[Dream]

Good to know. Whatever I decide to use has to be gasoline resistant.
Also as an unrelated but interesting thing, when I tore down the Walbro SDC carb from the 1010A I found someone had used two fuel pump diaphragms. There was the black rubber and the white Teflon diaphragm. I dont think that was supposed to be that way. Anyone know which one it was supposed to have?
If this carb would work on the 7-10, would I want to use the Teflon, as it pumps a bit more fuel?

 

[Al Smith]

I assume you are talking about what I call the check valves often referred to as fuel pump diaphragm .If so depending on the kits it could have what might be considered as double .These kit could have black buna n impregnated paper,some kind of yellow stuff ,this double deal or what looks like mylar .They all work so it's just depends on ones preference IMO .

 

[PogoInTheWoods]

While compatibility with different fuel quality is the main reason for the different types of materials, pumping efficiency relative to the pulse strength is also another important consideration and the reason for certain diaphragm material over another in most carbs.

Many SDC's used both a check valve and a pump diaphragm back to back, so that may be what was on the 10-10A. Here's an SDC3. Needless to say, the 10 series Macs have plenty of pulse power.

​

And while hardly all encompassing, here's a general rundown of the basic qualities/differences between rubberized, acetate, and teflon from a Walbro source. Notice the differences in pump capability among the three.

​

 

[Al Smith]

Okay now still another story .I tinker ,I putz ,I try a lot of things .Once on a 6-10( 70 CC ) I was more familiar with it's insides than I was an ex wife I had the bright idea of building up a carb from parts from about three which called for the removal of the throttle shaft and butter fly ,larger hole ,larger butter fly .
The brass screws are peened so they don't back out .in just testing I sucked a damned little screw into the crank case and it blew out the transfer,clunk . I was nearly sick,all that work .Talk about lucky it only stuck it no damage ,dodged a bullet .Put it back together and peened that rascal .

 

[fossil]

Good to know. Whatever I decide to use has to be gasoline resistant.
Also as an unrelated but interesting thing, when I tore down the Walbro SDC carb from the 1010A I found someone had used two fuel pump diaphragms. There was the black rubber and the white Teflon diaphragm. I dont think that was supposed to be that way. Anyone know which one it was supposed to have?
If this carb would work on the 7-10, would I want to use the Teflon, as it pumps a bit more fuel?

Most SDC's have a pump diaphragm and a check valve diaphragm. Some do not use the check valve diaphragm. If you let me know the carb model number I can let you know or you can check the IPL on Walbro's site.

Pump diaphragm does against the carb body, then the check valve diaphragm and then the gasket.

 

[Dream]

Well ok then. This is good to know. I see it now. The Teflon and the rubber diaphragms are different. Glad I asked.

 

[Dream]

Am, I see you have a nice looking 6-10 on Acres site as Well. That one is nicer looking than the 7-10 IMHO.

 

[Al Smith]

That 6-10 is a story in it's self .I am on the third crankshaft ,a screwed up flywheel killed the other two .I've had that thing apart more times than I can remember but I got it right .Over the blocks it will out run an 81 CC Mac and run about straight up with a stock 372 Husky .That's not bragging just a statement of fact and many have seen that little rascal in action .With the gutted muffler and slightly larger carb I don't run it as a work saw .That pot licker will make dogs howl .It's a keeper but I have hours in it getting it that way .If it wasn't fun I wouldn't have done it .It came from the Puget Sound area of Washington state -flea bay cheapie .

 

[Al Smith]

On the above I've got more saws than I can keep exercised .I usually use three ,an 024 Stihl,038 Mag,souped and a souped 200T .I've got a huge pile of oak that needs cut down to size which might provide at least a little bit of run time for some .It's not the best practice to have them be shelf queens .

 

[Steve]

That 6-10 is a story in it's self .I am on the third crankshaft ,a screwed up flywheel killed the other two .I've had that thing apart more times than I can remember but I got it right .Over the blocks it will out run an 81 CC Mac and run about straight up with a stock 372 Husky .That's not bragging just a statement of fact and many have seen that little rascal in action .With the gutted muffler and slightly larger carb I don't run it as a work saw .That pot licker will make dogs howl .It's a keeper but I have hours in it getting it that way .If it wasn't fun I wouldn't have done it .It came from the Puget Sound area of Washington state -flea bay cheapie .

I have rebuilt a standard 250 that ended up like that. Mark H. and Joe Taylor both couldn't believe how well it ran when i took it to the WKY GTG back in 2014.

 

[Al Smith]

Well there you go .Mac reeders had second cousins that were kart engines .Nothings to say they can't be pepped up .Almost nobody does it except a few of us .It's part of the great challenge to see if you can do it .Some can't, some can ,some don't give two shakes of a lambs tail one way or another .