1939 Ford Flathead idle problem

Dan39Deluxe

Dan39Deluxe

Member
Hey guys,
The car will fire right up off a cold start, switch off the choke, it will idle down and run great for a min, then it starts to starve for fuel or get flooded.

We've rebuilt the carburetor, made sure everything was clean, and the float has fuel in it every time we check (not positive the float is set perfectly but the fuel line rests just below the accelerator pump rod hole when you take the float out
 
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What's going on with all the air bubbles in the fuel pump glass bowl at
different times in the video.
 
what happens if you slowly add more choke? does it continue to run bad or does it get better? have you checked fuel flow/pressure? vented gas cap in place?
 
alanwoodieman said:
what happens if you slowly add more choke? does it continue to run bad or does it get better? have you checked fuel flow/pressure? vented gas cap in place?
Click to expand...
If you add more choke it stops it from puttering out for the most part but it runs at very high idle doing that.
I've tried running it with no gas cap on to see if it was a gas cap vent issue and it didn't change anything.
How do you check the fuel pressure?
 
Dan39Deluxe said:
If you add more choke it stops it from puttering out for the most part but it runs at very high idle doing that.
I've tried running it with no gas cap on to see if it was a gas cap vent issue and it didn't change anything.
How do you check the fuel pressure?
Click to expand...
You can buy a in-line fuel pressure gauge and install it. I would first start and make sure all the fuel lines you took loose are GOOD and tight!!! How is the gasket on the glass fuel pump bowl??? I would try and eliminate ANY of the locations it could be sucking air.......AS adding more choke introduces more fuel/Less air!!!!


Who rebuild the carburetor and how knowledgeable are they with the ins and outs of all the wear parts within the carburetor???
 
I chased a problem for months that finally turned out to be a leaking fuel pump bowl gasket. For some reason, the cork gaskets seem to seal better that the neoprene ones. The bubbles are suspicious.
 
rockfla said:
You can buy a in-line fuel pressure gauge and install it. I would first start and make sure all the fuel lines you took loose are GOOD and tight!!! How is the gasket on the glass fuel pump bowl??? I would try and eliminate ANY of the locations it could be sucking air.......AS adding more choke introduces more fuel/Less air!!!!


Who rebuild the carburetor and how knowledgeable are they with the ins and outs of all the wear parts within the carburetor???
Click to expand...


my dad rebuilt it, and it's his first. We get all our knowledge from you guys and youtube. We've had it off and re checked everything several times.



What's confusing me right now the most is if I put the choke on and it's getting more fuel/less air it will stay running, I can also keep it running off choke by hitting the accelerator. So it seems to me like its running out of fuel, not flooding.

I'll check all the fuel line connections to see if anything is loose.
 
I would "think" that given the way it runs AND "IF" all the fuel line fittings are tight AND the fuel pump bowl gasket is "tight" (which as Tubman indicates above as suspicious bubbles...which should not be) THEN I would think the float level would be where I focus my attention!!!!! IMO....logic says "as the fuel level in the carb drops, adding choke refills the bowl (temporarily) thus it runs right "again" UNTIL the level in the carb drops THEN adding more choke (OR more accelerator) adds more fuel flow to the bowl of the carb again!!! SO logic says IF all else is air tight THEN something is off within the carburetor!!
 
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A tiny leak in the fuel bowl gasket may nearly stop fuel flow at a slow idle, but not at fast idle or higher rpm.

Let the engine die, or shut it off while stumbling at idle. Disconnect the fuel line from the carburetor; leave the ignition off, crank the engine with a cup under the disconnected fuel line. The pump should put out a significant spurt of fuel with each stroke; about a tablespoon. If less, or sputtering, the fuel pump needs to be taken apart to be sure there is no debris under the little valves, and the bowl gasket gives a perfect seal.

With the fuel pump off, crank the engine and be sure you have proper stroke of the fuel pump push rod. About 0.2"
 
rockfla said:
I would "think" that given the way it runs AND "IF" all the fuel line fittings are tight AND the fuel pump bowl gasket is "tight" (which as Tubman indicates above as suspicious bubbles...which should not be) THEN I would think the float level would be where I focus my attention!!!!! IMO....logic says "as the fuel level in the carb drops, adding choke refills the bowl (temporarily) thus it runs right "again" UNTIL the level in the carb drops THEN adding more choke (OR more accelerator) adds more fuel flow to the bowl of the carb again!!! SO logic says IF all else is air tight THEN something is off within the carburetor!!
Click to expand...


Thanks,

I ordered a new fuel pump rebuild kit. I'll let you guys know if that fixes it.


The thing with the float level though is every time I take off the top of the carb to check it, the fuel level seems fine. Even after it has just stalled out.
 
drolston said:
A tiny leak in the fuel bowl gasket may nearly stop fuel flow at a slow idle, but not at fast idle or higher rpm.

Let the engine die, or shut it off while stumbling at idle. Disconnect the fuel line from the carburetor; leave the ignition off, crank the engine with a cup under the disconnected fuel line. The pump should put out a significant spurt of fuel with each stroke; about a tablespoon. If less, or sputtering, the fuel pump needs to be taken apart to be sure there is no debris under the little valves, and the bowl gasket gives a perfect seal.

With the fuel pump off, crank the engine and be sure you have proper stroke of the fuel pump push rod. About 0.2"
Click to expand...


Thanks, I'm gonna check all this and I'll let you know.
 
Dan39Deluxe said:
If you add more choke it stops it from puttering out for the most part but it runs at very high idle doing that.
I've tried running it with no gas cap on to see if it was a gas cap vent issue and it didn't change anything.
How do you check the fuel pressure?
Click to expand...

I checked the pressure on my 39 by cutting a tee in the line. Aftermarket pump putting out 5psi. Installed a rebuilt ac pump and got 3psi. Not sayin this is your problem but it's good to know for piece of mind. Ps. Pump pressure should be 2.5-3 psi.
 
I bought an intake manifold from a reputable source.
Turned out to have a hole between the carburetor heat-
under the carb, and the intake right under the carb.
Would have been a huge vacuum leak.
some degree of this would give your symptoms.

Karl
 
marko39 said:
I checked the pressure on my 39 by cutting a tee in the line. Aftermarket pump putting out 5psi. Installed a rebuilt ac pump and got 3psi. Not sayin this is your problem but it's good to know for piece of mind. Ps. Pump pressure should be 2.5-3 psi.
Click to expand...


thanks, I'm going to rebuild the pump and if it doesn't solve it I'll buy a gauge to check the pressure.


Karl Wolf said:
I bought an intake manifold from a reputable source.
Turned out to have a hole between the carburetor heat-
under the carb, and the intake right under the carb.
Would have been a huge vacuum leak.
some degree of this would give your symptoms.

Karl
Click to expand...


what did you do to check that? Spray some soapy water around the base of carb/top of manifold to check for bubbles?
 
What carb are you running? What jets are fitted? The idle circuit jets are normally carefully turned in, till closed then 1.5 turns out Fine tuning can be carried out from here. Whats the state of carb air cleaner? any difference in idle speed with air cleaner removed?
The air in your fuel would appear to be the major issue.
Phil NZ
 
Phil Gillespie said:
What carb are you running? What jets are fitted? The idle circuit jets are normally carefully turned in, till closed then 1.5 turns out Fine tuning can be carried out from here. Whats the state of carb air cleaner? any difference in idle speed with air cleaner removed?
The air in your fuel would appear to be the major issue.
Phil NZ
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It's a Holly 94 Carb, original jets I think. I've gone from 1.5 turns to higher/lower on both with the same idle stall out issue. The air cleaner is clean and has a new filter. It was roughly the same idle stall out with or without the air cleaner on.
 
Dan, you get A+ for posting the video!! It makes trying to help you a lot easier!!

As noted above, I'm with the crowd that thinks the issue is with your fuel pump....should never be air bubbles in the bowl if everything is tight....air's getting in there somewhere and starving your carb. JMO!! Good idea to rebuild your fuel pump with a kit....and you'll learn how it works in the process!!

Best of luck and congratulations on working your this '39 with you Dad....was the highlight of my '39 Deluxe experience as well!!
 
RKS.PA said:
Dan, you get A+ for posting the video!! It makes trying to help you a lot easier!!

As noted above, I'm with the crowd that thinks the issue is with your fuel pump....should never be air bubbles in the bowl if everything is tight....air's getting in there somewhere and starving your carb. JMO!! Good idea to rebuild your fuel pump with a kit....and you'll learn how it works in the process!!

Best of luck and congratulations on working your this '39 with you Dad....was the highlight of my '39 Deluxe experience as well!!
Click to expand...


thanks for the kind words, you nailed it spot on. We rebuilt and replaced the original fuel pump (non sediment bowl type). The car idled! But ran poorly and the fuel pump was leaking around the diaphragm. The glass type one has bad cross threaded threads. And this one I think has been sanded down too many times in the past where the diaphragm rests.

But it did Idle!!


So we ordered a new pump and I have all the confidence in the world it will run beautifully with the new pump.
 
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