Ford 94 lean at light throttle?

ajmac

ajmac

Member
I’ve just had my flatty running following a rebuild of everything. It idles great and revs very well but if I touch the throttle gently it will stall, must be over lean. If I hit the throttle to make the accel pump operate it revs up fine, probably too rich actually. It’s got an electric pump set to 3psi. Not that it matters but it’s a 1942 3.6 24 stud, lend lease from Detroit to England!

Does that sound like the float isn’t set correctly?

Video of it running and a light throttle stumble.
https://youtu.be/shsXxIbZP5Q
 
Put a vacuum gauge on the warm engine to make sure there are no vacuum leaks at idle. Adjust idle mixture screws for the highest and smoothest idle RPM, and the steady and highest vacuum reading. If you put the choke closed slightly does the flat spot go away? Screwing the idle mixture screws out makes the mixture richer.
 
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ajmac said:
Does that sound like the float isn’t set correctly?
Click to expand...

Assuming the carb is squeaky clean, that is what my experience has been. (float level too low). One band-aid would be to run on the "fat side" of the idle mixture screws. Jet sizing for your altitude could be a factor. Last but not least would be sloppy throttle shaft bores (unmetered air).

Good luck and please keep the board informed.
 
I don't know what kind of carburetor this vehicle has, but if it's a Holley 94. it could also be a non-functional or wrong power valve.The power valve functions like a "mini accelerator pump". When the throttle opens, the vacuum drops, and the power valve opens, enriching the mixture. With a bad power valve, no opening, no mixture enrichment, and a "stumble".
 
ajmac said:
I’ve just had my flatty running following a rebuild of everything. It idles great and revs very well but if I touch the throttle gently it will stall, must be over lean. If I hit the throttle to make the accel pump operate it revs up fine, probably too rich actually. It’s got an electric pump set to 3psi. Not that it matters but it’s a 1942 3.6 24 stud, lend lease from Detroit to England!

Does that sound like the float isn’t set correctly?

Video of it running and a light throttle stumble.
https://youtu.be/shsXxIbZP5Q
Click to expand...

The accelerator pump should work when the throttle is gently touched too.
It sounds like you had slop in the linkage that puls the pump rod down. The rod should move with the slighest movement of the throttle lever.

Sal
 
tubman said:
I don't know what kind of carburetor this vehicle has, but if it's a Holley 94. it could also be a non-functional or wrong power valve.The power valve functions like a "mini accelerator pump". When the throttle opens, the vacuum drops, and the power valve opens, enriching the mixture. With a bad power valve, no opening, no mixture enrichment, and a "stumble".
Click to expand...

I don't agree with your assessment. The power valve will indeed increase fuel flow at low vacuum, but is controlled by flow through the venturi. There will be a good lag in it's operation as opposed to the accelerator pump.
 
It has a Ford 94 carb, I rebuilt it with a macs kit but fitted a power valve from the guys in Florida who machine then to have the washer seat as it required in these early 94s. The idle screws make quite a difference to idle, I can get it quite low but have it up at about 700RPM. I haven’t adjusted the float yet but have tried very slowly opening the throttle and the engine doesn’t survive it.
 
You want to adjust the two brass idle MIXTURE adjustment screws before increasing the idle with the steel idle RPM screw. The mixture adjustment screws have to be adjusted on a warm engine at low idle RPM and if while adjusting mixture the RPM becomes higher than wanted reduce the RPM setting with the steel screw. and continue adjusting the mixture brass screws. When finished test the throttle and if the idle seems too lean back the screws out slightly for a slightly richer idle.
 
If the engine dies when opening the throttle extremely slowly, the accelerator pump is probably not the issue. It's possible that the main fuel circuit isn't starting to flow as the throttle plates pass the transfer circuit. You may need to take the carb apart to see if there are air leaks at the booster assemblies...may be missing sealing washers. Of course this will be the time to check float level as well.



Terry
 
With the fuel we have now very dry less oil ,gets a coating of rust in the small throttle plate jets soak the cast base of the carb in Vinegar over night ,blow it out with air assemble and drive ,Ted
 
Charlie Schwendler mentioned to me that often times during a 94 rebuild it is necessary to make sure the needle under the pump discharge nozzle seats properly.
 
Hello Alastair.

Do you know anyone with a Ford V8 Flathead that runs well? Could you swap your carb on to see if it is the same on another engine?

Do you ever come over to the midlands?
If you turned up at my house we could bolt your carb on my truck and try and adjust it. We could also tear it down for some simple checks.
If we could get it running well on my truck it will run well when bolted back on your motor.

I am about 100 miles away. Shirley, Solihull.

Mart.
 
ajmac said:
Thanks for the advice guys.
Put the tracks on today and ran it in and out of the garage, Flatty running ok, I will follow terrys advice. Mart, my dad lives in Dudley so you are on the way as it were.

https://youtu.be/nM-XTCetz7c?si=PsAwMAAMQj7HI8f8
Click to expand...
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Very interesting application. I would like to see more of that vehicle. Do you know the purpose of the spare tire, are there three other ones onboard so that it can be fitted to drive on pavement? Thanks for posting.
 
It was used to tow an anti tank gun in Normandy after D-Day, they all carried a spare wheel for the gun they were towing as well as the ammunition and the gun crew. Mine was sold to the Belgian army after the war and served into the Cold War as an ammunition carrying vehicle for a modern anti tank gun designed to take on the Soviets. I’ve restored it to its 1944 configuration. All the automotive parts were taken from the 1930s ford truck parts lists, chassis, axle, torque tube, 4 speed gearbox etc….all ford parts.
 
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