Carb fuel pressure issues

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SRT_DSTRHOLC

SRT_DSTRHOLC

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So I have a 410 stroker and a Holley 750 dp, automatic trans with 4200 stall. I am having two issues. The first issue is that I adjust the carb to the fuel pressure it's set at. This means the bowls, front and back. Then in gear I adjust the idle mixture screws (4 corner). Take it for a drive and it's great. Next time out, it's breaking up when I press the throttle. Pull back into garage and it's dumping gas into carb, so I lower bowls until it stops. I keep doing this until bowl level is set so that when I turn the car off and shake the car, fuel comes out, with a hip check. Take it for a spin and the car wants to die when I come to a stop, I am guessing this is the idle mixture screws needing adjusting again, but the biggest issue that was scaring me was the engine breaking up..



The second issue is my fuel pressure. I have a carter Super Strip pump that flows 140gph at 8psi. The Holley regulator splits into two lines, one for each bowl. At cold start up I have 6 psi and then it gets to 8 where I want it. After driving it for a bit, the fuel pressure will vary from 6 to 8 and sometimes lower. Can you help me out with this? Do you guys think the pump is not handling the engine? Maybe the regulator is crap? And maybe this is causing my erratic bowl adjustments because of inconsistent change of fuel pressure?

The gauge is a Mechanical Autometer Gauge NEW!


Any help is greatly appreciated and I will do all steps asked to do, Thank You!
 
8 is too high set it at 5 to 6 psi. If your gauge is liquid filled the presure it shows will change as it heats up under the hood, set the pressure when everything is cold.
 
EL5DEMON340 said:
8 is too hi set it at 5 to 6 psi. If your gauge is liquid filled the presure it shows will change as it heats up under the hood
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If I set at 6, good chance it will lower with heat. The pressure is not consistent. It's not liquid filled.
 
Could be a bad regulator or crud in the carb or fuel line. I would use a filter just before the regulator and clean out the carb, then set the fuel to 6psi set your floats and see what happens
 
EL5DEMON340 said:
Could be a bad regulator or crud in the carb or fuel line. I would use a filter just before the regulator and clean out the carb, then set the fuel to 6psi set your floats and see what happens
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Could be the regulator, the carb was just rebuilt. I have a 100 micron filter after pump, 1/2 in line into pump then into regulator. Fuel line is new too.

Going to buy new fuel regulator, Quick Fuel, it's pre set at 6.5 psi and then re adjust everything and see what happens!
 
More than a few guys have trouble with the hi psi mechanical pumps. If you can't find a obvious problem go to the local auto part store and get a standard replacement pump and try it out, if that doesn't work you could always bring it back.
 
I had this pump on an engine before, I am going to try the regulator first. If it's not that and is the pump, I will be switching to electric pump for when I go E85 anyways
 
Do you have a fuel return line? A fuel return does several good things, not the least of which is making the fuel pressure ROCK steady with no spikes or drops.
 
RustyRatRod said:
Do you have a fuel return line? A fuel return does several good things, not the least of which is making the fuel pressure ROCK steady with no spikes or drops.
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No I do not. I use the regulator to split into each bowl, instead of using one side to feed both and one as a return.
 
Fst73_410 said:
I will be switching to electric pump for when I go E85 anyways
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This is a mechanical pump? I think you are stretching the boundries of a mechanical pump. They can only be as good as the design......which ain't too good. They are a constant spike drop spike drop. That's how they work. I think a good electric pump and return will solve your issues.
 
RustyRatRod said:
This is a mechanical pump? I think you are stretching the boundries of a mechanical pump. They can only be as good as the design......which ain't too good. They are a constant spike drop spike drop. That's how they work. I think a good electric pump and return will solve your issues.
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Im surprised, because I just had it running great. It was going lean above 5k and when I upped fuel pressure, it fixed the issue. So I guess new pump would solve all issues!? I will try lowering psi to around 7 currently and see how that works for temp., fix
 
I don't know. It might. This is just the internet. Without the car in front of me, it's just a guess at best. 410 with a 4200 stall and I assume a matching gear......3.91? 4.10? No way in hell would I have a mechanical pump on that. I am sure there are some that could do it, but I wouldn't be using them. JMO
 
RustyRatRod said:
I don't know. It might. This is just the internet. Without the car in front of me, it's just a guess at best. 410 with a 4200 stall and I assume a matching gear......3.91? 4.10? No way in hell would I have a mechanical pump on that. I am sure there are some that could do it, but I wouldn't be using them. JMO
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Yes 4.10 gears. I had been planning to switch soon anways. Need a pump for e85 and for future plans, i will just switch soon, it also is internally regulated so that is cool. Flows 260 at 6-7 psi
 
I think that and the return line will solve it.
 
i will do it once I get my refund. Just had to spend 700 on new tools and chest for new job.
 
Messed with fuel pressure today. Dropped it to 7psi. Adjusted bowls and then adjusted mixture screws. Took her out, still a bit rich and it has a hesitation when I floor it, instead of vrooooooom, it's ruh vrooom... and when I shut it off, it heat soaks and boils a bit of fuel into carb. I need to lower the bowl a little more hot lap it and turn it off and then check how it starts, but I have a base point. The only thing is when I was driving back from the store, the fuel pressure was at like 5.5-6 before it slowly raised to 7 about 10 min later.


I will also check the gap between the pump levers and make it .016
 
100 micron filter before the pump... not after it.
 
Don't forget, if you go with a fuel return, you will need a return style regulator. The dead head style will not be correct.
 
Holley says the 750 fuel pressure should be set from 6.0 to 6.5.
 
Ditto on the return line regulator, Dead heads raises fuel temps too, there is no where to go. When it returns to the fuel tank (or back behind the pump) it recirculates and cools, tank is best.
 
RustyRatRod said:
Don't forget, if you go with a fuel return, you will need a return style regulator. The dead head style will not be correct.
Click to expand...
Want to see how to convert a Holley dead head regulator into a return bypass style? Want to see why a regulator that has less parts in it cost you more money..
 
Johnny Dart said:
Holley says the 750 fuel pressure should be set from 6.0 to 6.5.
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Thanks! Read this last night set it at that today and adjusted bowls. Worked like a champ and then fuel pressure started to vary again and at one point I believe I sucked the bowl dry. Had to pull over and adjust it to get home. The fuel pressure is playing tag with me and therefore, the bowls are not staying consistent. I am parking the car and getting a electric pump and possibly doing that return line. Thank You
 
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