McCulloch 1-93 Project

[stinkbait]

I am fixing this 1-93 for Igpoe in trade for a nice Super Wizz 66. I started by just putting a new kit in the flatback carb and installing new fuel lines. That was a no go. After digging into it some more I noticed that the block was replaced at one time because ther was no yellow paint on it anywhere. Piston and cylinder look awesome, and a thin ring piston too. I ended up making a new stuffer gasket and all new intake gaskets. After reassembling everything with all new gaskets the carb still will not pump fuel from the tank. My thinking behind making all new gaskets was to eliminate the possibility of an impulse tract leak. I'm thinking that the problem still lies in the carb, but I'm going to pressure test the engine now. The only locations left that could possibly be sucking air is the crank seals and where the flywheel side of the crankcase bolts to the engine block. Well here are some pics. I'm giving up for the night.

My new gaskets that I made.

 

[ford832]

Sweet saw,good luck.

 

[little possum]

opcorn:

 

[cpr]

Cool project.

Turns out I've got one that refuses to pump fuel right now, too. New gaskets, lines are good, new filter, tank vent good, etc. Still no pump. :msp_confused:

 

[stinkbait]

Cool project.

Turns out I've got one that refuses to pump fuel right now, too. New gaskets, lines are good, new filter, tank vent good, etc. Still no pump. :msp_confused:

I'm pretty sure that it's the carb on mine as well. I have not had good results with these new flatback kits. The metering diaphragm seems way too tight (no deflection). The last flatback that I done was on my 440. I did everything to that carb. Removed welch plugs, new check ball kit, new o-rings on adjustment screws, new o-rings on primer pump. I finally got it to work after heating and stretching the metering diaphragm to give it more deflection. Even now though I have to baby the saw with the primer pump for a few seconds after it starts before the carb will start pumping on its own. The only problem is that the 1-93 doesn't have the primer pump, just a choke. I have just come to the conclusion that these carbs suck. I will make it work, but I won't like it.

 

[Bill G]

Have you tried switching to a HL carb?

Bill

 

[stinkbait]

Have you tried switching to a HL carb?

Bill

No not yet. That will be last resort. I'm gonna beat the flatbacks one day. The only ones that I have had real luck with are the ones with the primer. There is no way that people had as many problems with flatbacks back in the day or McCulloch would have went out of business earlier.

 

[leeha]

Sweet project and great job on the gaskets.
As for the carb with no pump problem. Make
sure you have the correct gasket between the
carb and intake. I had this same problem on a
797 i did a couple years ago. Mac has two types
of gaskets both with the pulse hole in different
locations. Just a thought.


Lee

 

[stinkbait]

Sweet project and great job on the gaskets.
As for the carb with no pump problem. Make
sure you have the correct gasket between the
carb and intake. I had this same problem on a
797 i did a couple years ago. Mac has two types
of gaskets both with the pulse hole in different
locations. Just a thought.


Lee

Thanks Lee! I have to pull it back down again anyway so I'll check the impulse alignment then. It should be right though because I traced the originals. One thing that I don't like about this saw is that the 4 bolts that hold the carb and intake on has to go through several gaskets, the reed valve plate, and the plastic spacer. I think that I might try to make some studs to replace those bolts. It will make for easy alignment of the gaskets and will hold everything in place while the carb is off.

 

[leeha]

As far as i know, All of that series engine
have the same intake set up.
You have the block, read plate, spacer plate,
Then in your case the intake. When i assemble
my saws i use two alignment studs. Makes it go
together much easier.
It's the gasket between the carb and intake that
i was refering to.



Lee

 

[cpr]

I'm with you, flatties will bend to my will. Mine's on the 91 kartsaw. It ran fine before, now it refuses to pump fuel. I had this on the s250, too. Finally, it worked though I have no clue as to why. As for the gasket, it ran with a multihole kart kit one, but now it won't with that or one I cut. Humph, the fight resumes tomorrow.

 

[cpr]

I genuinely believe the source of the problem is the sandwich fuel pump gasket/diaphram. None of my flatty-equipped saws will run. They all used to when the parts were new.

Spare me the "put in an HL" story. Super 250s were choker flatties and mine will be. As for my 91 kartsaw, an HL is an airflow RETREAT. The 101, it's not an option, period. There is no other explanation. Everything is as it should be. Vents work, passages clear, impulse signal strong. It just won't pump any fuel...

3 hours in the shop tonight and nothin' but mad. May not make the OH GTG if none of my junk will run...

I'm washin' up and headin' for bed before I pop any more capillaries...

 

[Bill G]

........... There is no way that people had as many problems with flatbacks back in the day or McCulloch would have went out of business earlier.

Well that may be because back in the day the carbs were not 40 years old and new parts were readily available.

 

[Eccentric]

Charles some Super 250's had HL's. My 1970 S-250 IPL shows both HL and flatback carbs. Also, many 123cc 797's had HL's. 650/660 gear drives had HL's, primer flatbacks, and choke flatbacks.....depending on what was in stock. There are also HL variants which would NOT be an airflow retreat. They weren't stock saw carbs however.

I do hope you get those flatbacks sorted. Have you checked the carb bodies and pump plates for straightness? A warped/defective pump plate could cause a loss of impulse signal. Check for cracks/voids too...

 

[stinkbait]

I feel your pain CPR. I haven't had a chance to work on mine anymore since I posted up the latest pics. I plan to work on the saw a lot this weekend though.

 

[stinkbait]

Update

I finally got around to getting this saw running. Ended up ditching the flatback and going with a HL that has a huge venturi. Looks like the carb throat has the same diameter from one end to the other. Also fixed up an on/off switch because there wasn't one. I will try to get some pics of the carb up tonight. Going to make a video real soon.

New on/off switch

 

[sledrat]

You one lucky guy very cool SAW~!

wish i had one like that!!!

cant wait to see the vid!

 

[stinkbait]

You one lucky guy very cool SAW~!

wish i had one like that!!!

cant wait to see the vid!

It's not my saw. Just working on it for a guy. I wish it was mine. Maybe one day. Wait till you see the bar for it.

 

[heimannm]

That switch is a little over the top for a 1-93...

I have had pretty good success with the flat back carburetors, primers are often faulty but the carburetors seem to work O.k., just a bit more sensitive to small adjustments.

Make sure the metering lever is adjusted correctly, won't move any fuel if the needle isn't opening.

As I noted my the McCulloch carburetor thread, I assembled the fuel pump "sandwich" several different ways and found that all would run if I primed the saw manually to get it started. I have no explanation beyone that.

You just reminded me that I have a choke equipped FB soaking in the USC that I started on Saturday, hope it's all still there.

Mark

 

[stinkbait]

Here is the carb. Only issue is choke linkage. Runs great though.