Holly 94 issues

mrlaser

mrlaser

Senior Member
I have a 1951 Ford Victoria which I have completed a frame off 8 year restoration. The engine was rebuilt including boring, reground cam and crank, a 3 angle valve job with adjustable lifters and rotator type valve spring retainers and correct valve springs, proper installed height, and adjusted spring pressure of 50 pounds. The carburetor is an "all new" 94 from Mac's. The engine runs well but has two issues: 1. difficult starting after sitting for a few days, and 2. When driving and coming to a stop with the transmission in OD, and the engine free wheeling, the engine frequently stalls unless the choke is partly engaged. The timing appears to be correct and the dwell is 33. I have tried to adjust the the idle needles from their initial setting of 1-1/2 turns to 2-3 turns with no apparent change in the engine idle/rpm. When the choke is pulled out slightly, the engine idles smoothly. At 600 rpm with this choke setting, the manifold vacuum reading Is fairly steady at 18-20. Any advice, or suggested solutions, would be greatly appreciated.
 
Difficulty starting after a few days is symptomatic of no fuel in the float bowl, requiring extended cranking to get enough gas to the carb. The 94 is notorious for power valves not seating properly and leaking down. Absent that problem, the float bowl should not evaporate down for weeks.

Stalling at idle can be several things. You noted that opening the idle mixture screws does not affect the rpm. If you slowly close one, does the rpm drop at some point? It should do that for both jets. If not the engine is idling on fuel from another source, like the main jets, or leakage from the power valve.

Another thing to think about is a newly rebuild engine can be a little tight. You may need to crank up the idle rpm to 600+ until it is broken in, - like over 1000 miles.
 
If the car is in OD when you are on the road and you slow down to a round 27 mph the OD should drop out of OD and it will then free wheel. If the OD does not drop out and it stays in OD the car will not go into reverse!
 
I when the idle screws are turned to nearly closed the engine begins to stumble. As I mentioned, turning the screws to open seems to have little effect on engine rpm. The OD is functioning normally. (See my previous posts on its problems) I mentioned the fact that I have the car in OD because the freewheeling features prevents "" popping the clutch to restart the engine.
I have wondered about the power valve but wasn't sure whether a replacement would work with this "all new" Mac's carburetor.
 

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You can check for a leaking power valve by removing the top of the carburetor and making sure the float bowl is full. Then cover it temporarily (I use aluminum foil formed around the carburetor) and check it every day or two. If the bowl empties in a week, you have a problem.

This precludes you from using the car for this period, which can be a major drawback where you are, but it works for me in Minnesota in the fall and winter.

The new power valves are so "iffy", that I do this test on every one I rebuild.
 
mrlaser said:
I when the idle screws are turned to nearly closed the engine begins to stumble. As I mentioned, turning the screws to open seems to have little effect on engine rpm. The OD is functioning normally. (See my previous posts on its problems) I mentioned the fact that I have the car in OD because the freewheeling features prevents "" popping the clutch to restart the engine.
I have wondered about the power valve but wasn't sure whether a replacement would work with this "all new" Mac's carburetor.
Click to expand...

Good that closing the idle mixture screws will cause the idle to slow. When you hit that point, back off until the stumble stops, then open the mixture screws no more than half a turn. Opening them further will may produce a stumble from being too rich, or it may not. But having them open too far could cause an idle stall from too rich a mixture at the moment you let off the gas and spike the vacuum.
 
A leaking power valve doesn't make sense to be the problem, if closing the choke slightly cures the problem. The leaking power valve would do about the same thing as closing the choke a little bit.

Sal
 
scicala said:
A leaking power valve doesn't make sense to be the problem, if closing the choke slightly cures the problem. The leaking power valve would do about the same thing as closing the choke a little bit.

Sal
Click to expand...

i thought the same thing, but then figured that the "open slightly" was probably just the idle increase, not choke, that keeps it running.
 
I found this while searching the internet. Is this likely the cause of the stalling when coming to a stop from cursing speed? Incidentally, I have checked for vacuum leaks but found none.

"One or Both Idle Mixtures Screws Doesn't Change Anything

Most likely there is a plugged passage. Check the venturi's closely. The holes are small and easily plugged.
If the engine has been sitting for a period of time, then the gas may have turned and varnished the inside of the carburetor"
 
mrlaser said:
I found this while searching the internet. Is this likely the cause of the stalling when coming to a stop from cursing speed? Incidentally, I have checked for vacuum leaks but found none.

"One or Both Idle Mixtures Screws Doesn't Change Anything

Most likely there is a plugged passage. Check the venturi's closely. The holes are small and easily plugged.
If the engine has been sitting for a period of time, then the gas may have turned and varnished the inside of the carburetor"
Click to expand...

This answer from the internet is not applicable if closing each the idle mixture screws actually causes the idle rpm to slow. That test proves that the idle circuits are actually providing the idle fuel mixture, and are not plugged. Try setting the idle screws as suggested in my previous post, and see if your stalling problem is improved.
 
Come out to California and see how long fuel stays in a float bowl....

Depends upon where the OP lives. If they have real gasoline, and fuel
doesn't hang in the float bowl for a week, then you definitely have
a float bowl leaking down.
 
I am actually sending the Holly 94 ( an original 94) to Charlie today. I am in Savannah Ga and we have easy availability to non ethanol fuel because of marine use. That is all that I have used in the car since its restoration. Thanks for the advice and information. Incidentally, I am a former L.A. resident.
 
First a correction then a follow up to my original post. The carburetor that I was having issues with was in fact, an original Holly 94. I had another '51 Ford convertible which I have since sold on which the "all new" carburetor was fitted. (senior moment) The current carburetor was rebuilt by a major parts house a number of years ago. While it looked fantastic, no amount of fiddling with it resulted in a smooth idle or corrected the stalling when coming to a stop. Very frustrating.

I recently sent this carburetor to CharlieNY for his evaluation. The following is an email I sent to Charlie after he returned the repaired carburetor.

Charlie,

You probably don't need any more positive feedback, but I must tell you that my engine ran perfectly (right out of the box) with the carburetor that you recently rebuilt for me. The idle is spot on and there is no more stalling when coming to a stop. As I mentioned previously, I had sent my original carburetor to .... for a rebuild. While it looked amazing when it was returned, no amount of "adjusting" resulted in a smooth idle or correction of the stalling issues. If it isn't too much trouble, would you let me know what was required to restore the proper function? Thank you for your excellent service.
 
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