Random Poor Running/Stalling

G72Zed

Veteran Member
Sep 8, 2015
4,090
Canada
Yes, very good idea to get the fuel pressure gauge to the "line of sight" so as to monitor what it's doing when the issue presents itself.

Keep in mind, but im sure you know this, that pressure and volume are two separate entities directly connected. You can have pressure, but no volume, and the opposite as well, volume with no pressure.

Holley N&S can take some good upper pressure spikes of 7-8.5 psi, but as the orifice get's larger, it does not stand as much head pressure. Kind of an oxymoron, pressure goes up, volume goes down.

You may have in fact have a "volume" delivery issue, if you over pressure to comesate, and the system design lacks the volume capacity to feed the engines requirement, you can over aerate the fuel, and then you get a massive lean spike but the pressure does not look to bad, hence the need for the AFR gauge.....just tossing this out there.
 

Ratty_81

Veteran Member
Nov 13, 2020
402
@G72Zed
Fuel lines are all 3/8” with a return style regular. New Carter 4594 fuel pump. Stock replacement sending unit/pick up. Fuel pump is mounted high above the axle(not ideal).
I really don’t think it’s a fuel delivery problem since it will not run better until the engine restarts either by key or bump. Fuel pump only runs when engine is running and for 5 seconds after turning the key to “on”.
If I was running out of fuel, I theoretically should have to wait for the bowls to refill. This isn’t the case. It’s literally like an electronic re-boot fixes it. I can also do multiple back to back WOT runs without issue, but have issues during normal steady state low rpm cruising. Once running badly, it will not clear up until a restart, then immediately runs fine.
 

my24ktrat

Veteran Member
Jul 5, 2007
1,240
Roch., NY
...Every once in a while ,I get the same thing . I have a brass float in the primaries, holley 670. I sometimes get a small amount of crust from today's fuel , it breaks off , clogs the jet, car acts up. Ever since I have put an additive to combat the ethanal by lucas in, it's been better, hope this helps, DC.
 

cadillac_al

Veteran Member
Apr 22, 2015
1,101
Maine
These weird symptoms remind me of a moisture in the distributor cap situation that comes and goes. I wonder if you have some small crack in the distributor cap or something.
 

hd_cat

Veteran Member
Sep 6, 2013
156
Cincinnati, Ohio
Could be, but I've got fresh engine to body ground straps and brand new high strand battery cables. My subframe and body are welded together.
I've hammered on the car WOT through 3rd gear without issue. The "tip in" today was to lightly accelerate from 65 or 68 to 70 mph.

My first suspicion is the Chinese Summit ignition parts.

Speaking of chinese ignition parts, check the distributor, the ground screw on the breaker plate was loose, when the ground lifted it felt like the car was being hit by a huge hammer. I tightened the screw and have not had that issue since. This is a Pertronix Billet Distributor, was installed on the car when I bought it. Other than that, I'd check the fuel system, water and alcohol do funny things to engines! In 2001 at the Indy Street Machine Nationals, the '73 with bad gas, ran like crap, seemed to flood and stumble, I think it was chevron gas, I have also experienced this with bp gasoline. For this reason, I ran Shell, Marathon, Sonoco or similar and sometimes added Turbo Blue to help with Octane.
 

Ratty_81

Veteran Member
Nov 13, 2020
402
Thanks all. @hd_cat great tip on the distributor. I replaced the module, but didn’t really give everything else a once over. Could be the pick up acting flaky too, I suppose.
Distributor is dry and carb is spotless inside.
Hoping to rule out fuel supply issues when I get a remote FP gage rigged up.
Hoping to get this figured out. Dream Cruise in a couple weeks!
 

74TAride

New Member
Feb 20, 2018
7
You may also double check for vacuum leaks [carb gasket, vac hose at base of carb, etc]. Sometimes these can cause periodic screwy lean outs under acceleration.
 

G72Zed

Veteran Member
Sep 8, 2015
4,090
Canada
@G72Zed
Fuel lines are all 3/8” with a return style regular. New Carter 4594 fuel pump. Stock replacement sending unit/pick up. Fuel pump is mounted high above the axle(not ideal).
I really don’t think it’s a fuel delivery problem since it will not run better until the engine restarts either by key or bump. Fuel pump only runs when engine is running and for 5 seconds after turning the key to “on”.
If I was running out of fuel, I theoretically should have to wait for the bowls to refill. This isn’t the case. It’s literally like an electronic re-boot fixes it. I can also do multiple back to back WOT runs without issue, but have issues during normal steady state low rpm cruising. Once running badly, it will not clear up until a restart, then immediately runs fine.

Ah, ok...the old Carter electric pump, could be a voltage issue, or internal regulator issue. It should be mounted lower than the fuel level to have it naturally gravity fed. I used those as a "helper" back in the day, but not on it's own.

Is the stock sending/pickup unit 3/8 or is it smaller?

None of the race cars I work on use electric, they are all mechanical, including my own ride, so nothing electric except on the dyno.

A good AFR gauge would help, and keep it to get the WOT dialed in to what the combo likes.
 
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CorkyE

Veteran Member
Lifetime Gold Member
Nov 4, 2004
11,783
Ringgold, GA
Did I miss in a post about what kind of fuel pump controller you have? Is it PWM? Can you bypass the controller and wire the pump direct, through a relay? There's a lot of difference between the two scenarios - short blast and long drive. I've used Carter and Holley electric pumps also, and like G72ed, I used them as a booster to the mechanical pump. And like said, the elect pump is better at pushing fuel, so it needs to be low in the back.

If you were near Chattanooga, TN, I could load you up on parts; carbs, elec & mech pumps, regulators, etc. I switched to PF4 EFI system and parts are collecting dust. I've just about always found the issue you're describing to be fuel delivery. And I've been wrong before also. I know it has to be getting frustrating, but hang in there.
 




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