McCulloch Carburetors

[cpr]

Anyone? Anyone? Bueller? Bueller?

 

[heimannm]

Are you sure the pulse port is open in the carb, gaskets are not blocking the ports, the internal port in the air box is open to the crankcase?

I usually tap the carburetor down a bit before final tightening of the screws to make sure the holes in the gasket and ports are all aligned.

Mark

 

[cpr]

Yep, open in the crank and through the carb. Pretty sure I had the carb "down" all the way.

One thing I did notice is the new gaskets between the carb and the tank body are thinner and the needle boot doesn't line up good anymore. Not a big deal, just an observation.

I found a new carb fuel filter. I may buy it and try switching them out.

Thanks Mark, at least I'm on the right track.

 

[heimannm]

I've never had one that would not pull fuel after a prime, no matter how I had fuel pump diapragm and gaskets arranged, that's why I think it must be something else.

Check all of the metering circuit as well, height of the metering lever, proper orientation of the gasket and diaphragm, make sure the passages are clear, you get the picture. If fuel can enter the metering section it won't run on it's own.

Even if the high speed passage is blocked, it should still idle though it would run out of fuel when the engine speeds up if fuel is pumping into the carburetor.

Mark

 

[cpr]

After a several month's hiatus, I returned to the Super 250. Fixing that clutch drum last night left me no excuse to assemble it and try. I checked over the carb once, just to make sure, but changed nothing. Lo and behold it runs! Idles great and accelerates like mad, but the high jet isn't working. Guess I get to pull it once more, but I'm farther than I was.

First time the Super 250's done more than pop on a prime. I love my big bores, but goodness this thing is MEAN. Ferocious acceleration and the bark out of it is otherworldly, even for a Mac... No wonder you guys love them.

 

[slipknot]

Wasnt this thread 2010 thread of the year? I know I learned so much from this thread alone it crazy...in fact once I understood things a little better I went from buying a mac 790 to get running and sell to get a mac 790 and then get mac 1-70 and many more macs...lol....i became a collector once I got my 790 running....once I cut wood I was hooked....watch out now...it could happen to anyone. Muscle saws are very addictive. Thanks Mark.

 

[promac850]

Subscribing... good info here.

 

[cpr]

Finally, it's alive and behaving! Up to 3 saws to test and tune this weekend. Tomorrow, I'll attack a fourth languishing project before the 101s start arriving.

 

[RandyMac]

So cpr, you are a convert to the mighty Supers. Too bad our muscle saws won't get to saw the wood they were intended to.
I'm switching out the choked Flatback on my Super, to a primer equipped one, with a larger venturi.

 

[cpr]

May have to try that in there next. I have one in the rescued 790 that I won't be using in that saw.

 

[Brian13]

While we are on the subject of swapping out carbs for a bigger one, what about a BDC14 on a 797?

 

[cpr]

Not sure there's sufficient room for the double pumper to fit. Plus the fuel intake would be straight down in the center. I've thought about it, but Lee says they don't fit.

 

[leeha]

While we are on the subject of swapping out carbs for a bigger one, what about a BDC14 on a 797?

Thats a no go. The BDC is much larger than the standard flatback or the 48890.
Plus the venturi is way to big for the intake system on the 797 or any saw.



Lee

 

[Brian13]

That is what I was wondering. I thought I saw one on a 797/101b once, but it was pretty heavily modified. It had a manifold between the block and tank. There is one on ebay right now for pretty cheap, so I figured I would investigate.

 

[stinkbait]

I need some more info on the whole check valve assembly in these carbs. Apparently all the flatbacks don't have the check valve assembly. What's the deal with that? And, is there anything behind the small welch plug? I have a check valve kit with the new ball and seat and the new large welch plug. The instructions that came with the check valve kits shows the installation of the kit in a flatback carb that didn't initially have the check valve system. But the instructions doesn't give any info as to why it's needed or how it operates.

 

[cpr]

I need some more info on the whole check valve assembly in these carbs. Apparently all the flatbacks don't have the check valve assembly. What's the deal with that? And, is there anything behind the small welch plug? I have a check valve kit with the new ball and seat and the new large welch plug. The instructions that came with the check valve kits shows the installation of the kit in a flatback carb that didn't initially have the check valve system. But the instructions doesn't give any info as to why it's needed or how it operates.

I have one I need to install this week... I'll report my findings.

 

[heimannm]

Before they were equipped with the check valve, the flat back carburetors had another simple "capillary seal", like the sintered metal fuel filter but smaller.

Mark

 

[stinkbait]

Before they were equipped with the check valve, the flat back carburetors had another simple "capillary seal", like the sintered metal fuel filter but smaller.

Mark

Yeah, I took that out and installed the check valve assembly. I made the mistake of putting too much grease in the assembly to secure the ball. Had to remove the carb and flush it out with carb cleaner before I got the saw to run right. Now it runs like a brand new one.

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[Eccentric]

Before they were equipped with the check valve, the flat back carburetors had another simple "capillary seal", like the sintered metal fuel filter but smaller.

Mark

The 1965 Supplement to the McCulloch 1-40/1-50/1-60 series service manual describes both valve systems in detail, and instructs technitians to replace the older capilary screen type setup with the ball type check valve when servicing older carbs.

 

[wendell]

Took out the carb out on my Super Pro 70 and cleaned it up and still can't get the saw to fire (but it will sometimes act like it wants to). What are the base carb settings that i should start with? I'm used to 1 turn out on the H and L but not sure if that is correct for this saw. Also, is there any adjustment that needs to be made to the butterfly?