McCulloch Carburetors

[heimannm]

Look carefully at the discusson regarding the metering diaphragm and the extra holes. If you have the parts that are meant for the kart carburetors there will be some holes uncovered that will let gas run out the atmospheric vent on the "dry" side of the metering diaphragm.

Mark

 

[kev1n]

i did look carefully at that. i got mine from bob. it didn't have those holes yours did. i also picked up an oem 55067c off ebay. i was hopeing to save it but i might have to throw it in, it's not raised up with that nipple

 

[cbfarmall]

Mark,

Thank goodness for this thread. I just picked up a nice 550 from a member here and you supplied an IPL and this great tutorial. Followed it to the letter, including your little tip about the extra holes in the metering diaphragm. Only had to remove the carb 1 time and that was to lower the lever height a touch as it was running very rich and flooding. I don't think the primer is working, but what else is new? Now, I may go pull out my 890 with SP125 power and fix that carb, again.

Chris B.

 

[stinkbait]

I would like to add to the thread

If the rubber seat for the primer pump check valve happens to bad you can replace it with the rubber seat from a Tillotson HL inlet needle seat. Check it out.

 

[leeha]

Nice Stinky.
Great tip.
I will remember that.

Thanks

Lee

 

[stinkbait]

Yeah, I figured that out last night while rebuilding the mac flatback off of my 440. Now, with the new rubber seat, the primer works like a charm.

 

[blsnelling]

Does anyone know if welch plugs are available for these carbs? I just cleaned up a super corroded one and had to pull them.

 

[stinkbait]

Does anyone know if welch plugs are available for these carbs? I just cleaned up a super corroded one and had to pull them.

The kits that I bought didn't come with any. You may have to get them made.

 

[blsnelling]

It seems like I've seen a source for different size welch plugs. I can't seem to find it though. I think it was FATGUY that showed me, and he's not available right now.

 

[Urbicide]

Does anyone know if welch plugs are available for these carbs? I just cleaned up a super corroded one and had to pull them.

Mac part # 110179 Plug, expansion 1/2"

Mac part # 104407 Plug, expansion 1"


Don't know if the numbers are current or not. Mac loved changing part numbers. Probably could find some generic plugs at a good OPE dealer or auto parts store. I would use some sealer around the edges of the replacements since the corrosion & cleaning operation might have slightly enlarged the actual openings a bit in the carb body.




(Nice job, Brad, on cleaning that carburetor. Looks good. You should get into the used car refinishing business. )

 

[Urbicide]

It seems like I've seen a source for different size welch plugs. I can't seem to find it though. I think it was FATGUY that showed me, and he's not available right now.

He must be in the can. :greenchainsaw:

 

[blsnelling]

He must be in the can. :greenchainsaw:

I think he's home sick in bed

 

[blsnelling]

Here it is, thanks to Nik. Expansion Plugs

 

[Urbicide]

I think he's home sick in bed

Nik, hope you get to feeling better soon!

 

[heimannm]

More to add...

I was making sure my 550 would be ready in case I get to go the the GTG in Illinois next Saturday. The saw would start and idle just fine but when I ran it up to full speed it would simply run out of fuel. No adjusting of the High Speed jet would help.

I started out by replacing the diaphragms assuming one or the other was a bit stiff but no improvement there.

I then replaced the fuel filter (felt plug in the bell at the end of the fuel line) but no improvement there either.

I then replaced the pick up line altogether but still no improvement.

O.K., time to get more serious. I took the carburetor completely apart and popped out the large expansion plug and tried a shot of carburetor cleaner in the hole and could actually hear the check valve pop free. To make sure, I popped out the smaller expansion plug and shot come carburetor cleaner through those hole as well.

Put it back together and once again it runs like a top. Not sure why the check valve got stuck, but I had run the saw enough that it should have come loose if it ever was going to on its own.

The check valve is closed under low speed conditions, but opens up at high speed to provide the extra fuel needed. I could not figure out out to remove the seat so I simply shot the carburetor cleaner through several times and gave it a blast of air as well to make sure everything was clear.

Now I need to check out the source for expansion (welch) plugs as I need a small supply of 1/2" and 1" plugs to allow me to work on several remaining McCulloch carburetors.

I didn't take time to photograph this one with the expansion plug out, but I will do that next time assuming I can find some more plugs.

Mark

 

[Brian13]

Bob Johnson had the ones for me. I replaced both plugs.

 

[heimannm]

I guess I will be calling Bob on Monday, I am sure I can think of a few more things to pick up at the same time.

There I was thinking I got all the plugs he had some while ago...

Mark

 

[Brian13]

I believe he even had the check valves, he was at least asking me if mine were still good.

 

[cpr]

Fighting with one of these for a Super 250. No primer, it's the model specific choke carb.

I'm a little stumped. I have a Sugar Creek kit for it, but I can't get it to pass fuel. I am tempted to play around with gasket stacking like Mark did, but of the 6 times I've tried, only once have I managed to get fuel to the pump chamber and beyond and I am unable to identify why it worked that one time. At no time, however, have I been able to make the saw run on anything other than a shot down the bore. Runs like a champ for 4 seconds when I do that! Just enough to tease me. In addition to the gasket stack, I have concern with the fuel filter pressed into the bottom. For now, that part is resting in a carb cleaner dip tank overnight to see what happens. I'll eliminate that problem source if all goes well tomorrow. I can make air go through evey passage on the carb, no blockages I can identify. I have not pulled the welch plugs only because I don't have any... yet?

Getting good with this thing. I can go from spread on the bench to installed test and back out to spread on the bench in under 5 minutes...

A few pictures. One thing different (besides the choke in place of the primer) is the metering seat is pressed in, not threaded.

Sugar Creek Kit like the OEM.

Casting on the front. I assume it was made in October 1973.

 

[stinkbait]

Fighting with one of these for a Super 250. No primer, it's the model specific choke carb.

I'm a little stumped. I have a Sugar Creek kit for it, but I can't get it to pass fuel. I am tempted to play around with gasket stacking like Mark did, but of the 6 times I've tried, only once have I managed to get fuel to the pump chamber and beyond and I am unable to identify why it worked that one time. At no time, however, have I been able to make the saw run on anything other than a shot down the bore. Runs like a champ for 4 seconds when I do that! Just enough to tease me. In addition to the gasket stack, I have concern with the fuel filter pressed into the bottom. For now, that part is resting in a carb cleaner dip tank overnight to see what happens. I'll eliminate that problem source if all goes well tomorrow. I can make air go through evey passage on the carb, no blockages I can identify. I have not pulled the welch plugs only because I don't have any... yet?

Getting good with this thing. I can go from spread on the bench to installed test and back out to spread on the bench in under 5 minutes...

A few pictures. One thing different (besides the choke in place of the primer) is the metering seat is pressed in, not threaded.

Been fighting witn the same crap on my mcculloch 440. i just gave up for a while I'm sure that I will get back to it one day. I bought the sugar creek kit and the kit from discount marine, and no luck.