Running, idling, not driving

[Squadron]

So I've got my '47 ford (v8 flathead) starting and idling. It will warm up and then I push in the choke and it hums pretty well.

However when I put it into gear (forward or reverse) it craps the bed. Jerking, popping, barely creating enough power to move the car forward.

It doesn't matter how gently I give it gas (if I go a hair too hard it dies).

I got the carb completely tuned and rebuilt about a year ago and it's a 12v system with new plugs. I've made sure the fuel pump is pumping (it still has the mechanical pump).

What should I be checking? Some sort of vacuum somewhere?

Things that have changed since the last time I had the car running under load (it was running very rich but not dying):

* Had the carb tuned and rebuilt off engine
* Put the new carb on
* Hooked up and primed the carb with the fuel pump
* Replaced the ignition coil

tl;dr: Idles smooth, but as soon as it's asked to do work (in gear) it complains bitterly and tries to die.

[69a]

Check accelerator pump, there should be a steady stream visible from the top.
Vacuum leak.
What carb? I'm guessing 94

[Squadron]

Originally Posted by 69a

Check accelerator pump, there should be a steady stream visible from the top.
Vacuum leak.
What carb? I'm guessing 94

It's a horrible repro carb, but it's a 94. Not the good one, but one of the no-name brands that are out there. I sent it to the guy everyone here loves (whose name escapes me) and he rejetted it properly and got it running on his test engine. AFAIK he also checked out the accelerator pump.

Vacuum leak is my suspicion but I don't really know how to check for that either, can you give any tips there?

Also, if I rev the engine when it's not under load the engine revs up fine. No misfires or anything. It's only when I have it in gear.

[69a]

Get a vacuum gauge, it's a handy tool to have. It should come with instructions and how to diagnose problems.
It sounds like a major leak if it is vacuum.
Start by disconnecting wiper vacuum line, you can hook up the vacuum gauge there. If the problem persists, disconnect the vacuum advance line and plug it.
Try giving it some choke when you are trying to drive it. That will richen the mixture going to the engine and give support to the vacuum leak idea.
Check the gaskets on either side of the throttle casting and the intake to block gasket.
You can spray some easy start spray, penetrating spray, or propane near where you suspect the leak to be. If vacuum gauge reads higher then you are close to the leak.

[Squadron]

Originally Posted by 69a

Get a vacuum gauge, it's a handy tool to have. It should come with instructions and how to diagnose problems.
It sounds like a major leak if it is vacuum.
Start by disconnecting wiper vacuum line, you can hook up the vacuum gauge there. If the problem persists, disconnect the vacuum advance line and plug it.
Try giving it some choke when you are trying to drive it. That will richen the mixture going to the engine and give support to the vacuum leak idea.
Check the gaskets on either side of the throttle casting and the intake to block gasket.
You can spray some easy start spray, penetrating spray, or propane near where you suspect the leak to be. If vacuum gauge reads higher then you are close to the leak.

Great advice. I'll give that a shot.

[Terry,OH]

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Could the problem also be the clutch grabbing? Clutch chatter? are the engine steady rods in place and the motor mounts front and rear tight?

[47topless]

Do you have a spare condenser to swap out? If you had Charlie NY do your carb, it ain't the carb that's the problem.

[kevinshea]

What did you replace the coil with? and have you checked the spark to see if it is strong.. a nice blue spark that jumps a 1/4" gap to ground very easily? You may have enough spark to idle, but not strong enough to do anything else??

[JayChicago]

I would suggest you do the basic “fuel or spark problem” check first. When the problem occurs, do as per post 2 and post 8.

[Flathead Fever]

I was a mechanic for 30-years. Sometimes it's hard to tell if it's a fuel problem or ignition problem, especially without a scope to look at the firing pattern. One thing you can try is to take a can of carb spray and spray it into the engine while you open the throttle and if it runs on the spray then it is a fuel delivery problem, if it doesn't and still cuts out it's probably an ignition problem. A lot of timed the jets in the carb will be able flow enough fuel to idle but not enough to drive the car. Like others have said, also check the accelerator pump to make sure it squirts. Even if it was a bad accelerator pump the engine would hesitate when you first opened the throttle but then when the main jets took over it would straighten out. If your engine is falling on its face and staying there after you open the throttle then it's probably not the accelerator pump. Even if the carb was recently rebuilt there is so much junk in these old gas tanks that sometimes the carbs plug right back up again. Make sure there is a large metal, not plastic fuel filter located down on the frame to catch any crud in the tank. You can also easily remove the top from the carb with it still on the engine and look in there to see if there is rust and junk in the float bowl. You can also check the float height while you have the top off. There can be so many different things on an engine to make it run bad, but you have to start somewhere until you finally find the problem.

[35fordtn]

Sure sounds like a condensor

[Seth Swoboda]

Originally Posted by 35fordtn

Sure sounds like a condensor

Agree

[hueyhoolihan]

IME, an unloaded engine that is revved needs relatively little increase in fuel compared to a loaded one. IOW, i would be questioning the repro 94 and its accelerator pump.

one way to test that would be to wait until the engine is warmed up to a point where it will run (as the OP noted) well at idle and rev well in neutral, then get on the road and before stepping on it, pull the choke out all the way. that will enrichen the mixture and should make a failed or failing accelerator pump less of an issue. IOW i'd be looking for possibly less hesitation when the choke is pulled out on a warmed up engine that is experiencing difficulties when accelerated under load. as the enrichened mixture may compensate somewhat for a faulty accelerator pump. and if that's what i found, i would seriously consider getting an original rebuilt Ford carb.

it's a cheap and easy test...

and don't think i know a lot about Holley 94's because i don't, but i did purchase one of the cheap 94s and it didn't help with a problem i was having with my flathead.

so i eventually took it to an expert that got my motor running like a top. the first thing he did (he was old...very old) was ditch the cheap knockoff (he was nice about it, but i could almost hear him clucking his tongue) and install a freshly rebuilt original Ford carb. he also ditched the diver's helmet distributor that came with the car and installed a crab distributor and canister coil originally from a post 1945 Ford. he said the repro coils, which i had installed, for the diver's helmet distributors were garbage. seeing the results of his work i have little reason to question his opinion.

[91A-77B]

How fresh is your gas? Try feeding fresh. Old gas will show those symptoms. Cheap, fast and easy test.

[Squadron]

NEW NEWS HERE!!!

Video/sound of it going here. The squealing is a belt I need to tighten:

https://www.youtube.com/shorts/uyAKo_xW3eA

You can hear what it's doing, basically. I was wrong about it only happening in gear.

I took the car out today and tried reproducing the engine problem out of gear and do more work to it. Mostly just troubleshooting and trying to think through the problem.

So here's what happens, very specifically:

When I crank the car from cold and let it warm up, the engine hums at idle. It will idle smoothly for 10m if I let it.

When the engine is warm, I can press on the accelerator. If I press on the accelerator gently at first, it revs up smoothly until it hits a comfortable point (I assume the end of it's rev range).

If I hold it at that rev range for about 30s, the engine begins sputtering. Lightly at first, then hiccupping and sputtering. If I let off on the gas hard, there's a 1 in 2 chance the engine just dies. If I let off it gentle, the engine might die.

It's not consistent after that. Sometimes if I rev up, it's ok until a belt starts squealing. Sometimes it's chokes and sputters again.

Originally Posted by Terry,OH

Could the problem also be the clutch grabbing? Clutch chatter? are the engine steady rods in place and the motor mounts front and rear tight?

Maybe? The rods are in place and the motor mounts are tight. When I rev the engine it doesn't rattle or anything or shake - and I don't see the mounts cracking or anything.

Do you have a spare condenser to swap out? If you had Charlie NY do your carb, it ain't the carb that's the problem.

No, but I can definitely order one. Is this the right one?

What did you replace the coil with? and have you checked the spark to see if it is strong.. a nice blue spark that jumps a 1/4" gap to ground very easily? You may have enough spark to idle, but not strong enough to do anything else??

This is what I bought PerTronix Flame-Thrower.

The car is rewired for 12v so I didn't look too hard. I'll check the spark to be certain, but would the spark change based on how high the engine is revved or how hot it gets?

I would suggest you do the basic “fuel or spark problem” check first. When the problem occurs, do as per post 2 and post 8.

I honestly don't know how to check the accelerator. Is there a vid or something? I was trusting Charlie that he didn't overlook that.

I was a mechanic for 30-years. Sometimes it's hard to tell if it's a fuel problem or ignition problem, especially without a scope to look at the firing pattern. One thing you can try is to take a can of carb spray and spray it into the engine while you open the throttle and if it runs on the spray then it is a fuel delivery problem, if it doesn't and still cuts out it's probably an ignition problem. A lot of timed the jets in the carb will be able flow enough fuel to idle but not enough to drive the car. Like others have said, also check the accelerator pump to make sure it squirts. Even if it was a bad accelerator pump the engine would hesitate when you first opened the throttle but then when the main jets took over it would straighten out. If your engine is falling on its face and staying there after you open the throttle then it's probably not the accelerator pump. Even if the carb was recently rebuilt there is so much junk in these old gas tanks that sometimes the carbs plug right back up again. Make sure there is a large metal, not plastic fuel filter located down on the frame to catch any crud in the tank. You can also easily remove the top from the carb with it still on the engine and look in there to see if there is rust and junk in the float bowl. You can also check the float height while you have the top off. There can be so many different things on an engine to make it run bad, but you have to start somewhere until you finally find the problem.

This makes sense. I'll pull the carb apart and look at it to see if there's anything down in there. I've got an older fuel filter on there too, I'll swap that off anyway. It's brand new gas and a fairly new gas tank so I kind of doubt it's bad gas but honestly who knows at this point.

IME, an unloaded engine that is revved needs relatively little increase in fuel compared to a loaded one. IOW, i would be questioning the repro 94 and its accelerator pump.

one way to test that would be to wait until the engine is warmed up to a point where it will run (as the OP noted) well at idle and rev well in neutral, then get on the road and before stepping on it, pull the choke out all the way. that will enrichen the mixture and should make a failed or failing accelerator pump less of an issue. IOW i'd be looking for possibly less hesitation when the choke is pulled out on a warmed up engine that is experiencing difficulties when accelerated under load. as the enrichened mixture may compensate somewhat for a faulty accelerator pump. and if that's what i found, i would seriously consider getting an original rebuilt Ford carb.

it's a cheap and easy test...

and don't think i know a lot about Holley 94's because i don't, but i did purchase one of the cheap 94s and it didn't help with a problem i was having with my flathead.

so i eventually took it to an expert that got my motor running like a top. the first thing he did (he was old...very old) was ditch the cheap knockoff (he was nice about it, but i could almost hear him clucking his tongue) and install a freshly rebuilt original Ford carb. he also ditched the diver's helmet distributor that came with the car and installed a crab distributor and canister coil originally from a post 1945 Ford. he said the repro coils, which i had installed, for the diver's helmet distributors were garbage. seeing the results of his work i have little reason to question his opinion.

I'd love to find an old guy who can work on this thing but I've had trouble with that. Plus I do kind of want to learn myself.

As I mentioned at the top - one the main jets hit it eventually starts losing power.

Could it still be overheating and that causing problems? To combat the overheating I:

Installed a new aluminum radiator
New water pumps
Cooling system flush
New hoses, etc
Auxiliary fan

[Ggmac]

If your belt is squealing it could mean your generator isn’t putting out enough voltage and or your waterpumps are not turning fast enough to keep it cool .

[47topless]

You can buy new condensers at most Napa stores.

[Drbrown]

Charlie NY has specific recomendations for a NAPA Coil and Condensor.

[glennpm]

Originally Posted by 47topless

you can buy new condensers at most napa stores.

napa fa54

[glennpm]

Originally Posted by Flathead Fever

I was a mechanic for 30-years. Sometimes it's hard to tell if it's a fuel problem or ignition problem, especially without a scope to look at the firing pattern. One thing you can try is to take a can of carb spray and spray it into the engine while you open the throttle and if it runs on the spray then it is a fuel delivery problem, if it doesn't and still cuts out it's probably an ignition problem. A lot of timed the jets in the carb will be able flow enough fuel to idle but not enough to drive the car. Like others have said, also check the accelerator pump to make sure it squirts. Even if it was a bad accelerator pump the engine would hesitate when you first opened the throttle but then when the main jets took over it would straighten out. If your engine is falling on its face and staying there after you open the throttle then it's probably not the accelerator pump. Even if the carb was recently rebuilt there is so much junk in these old gas tanks that sometimes the carbs plug right back up again. Make sure there is a large metal, not plastic fuel filter located down on the frame to catch any crud in the tank. You can also easily remove the top from the carb with it still on the engine and look in there to see if there is rust and junk in the float bowl. You can also check the float height while you have the top off. There can be so many different things on an engine to make it run bad, but you have to start somewhere until you finally find the problem.

Good advice here. You mention that "If I hold it at that rev range for about 30s, the engine begins sputtering. Lightly at first, then hiccupping and sputtering. If I let off on the gas hard, there's a 1 in 2 chance the engine just dies. If I let off it gentle, the engine might die." Seems like you are running out of gas due to carb floats being too low and/or junk in fuel supply.