[Oneball]

I’m struggling to solve an issue with my car. Small block Chevy, Holley 750DP. Newly rebuilt engine with a used carb I’ve also re gasketed etc. If I do an emergency stop from say 20 mph it stalls and is difficult to restart.

I’ve disconnected the brake servo and it doesn’t make a difference.

It does it in gear and out of gear, so not clutch.

I raised the float levels above normal and it didn’t make a difference.

If you look at the carb mouth after it’s stalled and without doing anything else it’s wet with petrol. I lowered the floats to below normal and it made no difference. I also put two 4” lengths of tube on the vents and it made no difference. The only place I can think the fuel is escaping from the air bleeds but not sure.

Anyone got any suggestions on what to look at/try next?

 

[Torment]

Try a normal 600 vac sec carb...750 dp is a bit big for a street sbc.....as for the stalling has it got jet extension tubes on it..?

 

[Oneball]

Try a normal 600 vac sec carb...750 dp is a bit big for a street sbc.....as for the stalling has it got jet extension tubes on it..?

Thanks for the reply.

It’s not a street motor, it’s in my race car. It’s not got jet extensions on, as I understand it they’re ok for acceleration issues on a drag car but not suitable for a circuit car as they can cause fuel starvation.

 

[wakesupremo]

What about the power valve. Is it possible that the diaphragm has split.

 

[Oneball]

What about the power valve. Is it possible that the diaphragm has split.

Thanks

I put a new power valve in when I rebuilt it, then changed it for a new differently sized one, so I hope not.

 

[heavychevy]

I would suggest a lean idle mixture or a too low idle speed or a combination of the two. Are you running an 02 meter?

 

[Oneball]

I would suggest a lean idle mixture or a too low idle speed or a combination of the two. Are you running an 02 meter?

No O2 meter. Idle speed is quite high at just under 1000. It’s rich if anything at idle, but it doesn’t burn well, typical big cam issue on a SBC apparently. It could do with more advance at idle but without fitting a vac advance dissy I can’t do that.

There is definitely a lot of fuel splashing around when it stalls.

 

[heavychevy]

If it is too lean it can appear to be too rich as the incomplete combustion smells rich. Without an 02 meter it becomes guess work, I use mine to set the idle and would strongly reccommend one as it pays for itself in time not wasted. I found a bad plug the other week that would not have shown up readily, that bank was runnng rich.

 

[Oneball]

If it is too lean it can appear to be too rich as the incomplete combustion smells rich. Without an 02 meter it becomes guess work, I use mine to set the idle and would strongly reccommend one as it pays for itself in time not wasted. I found a bad plug the other week that would not have shown up readily, that bank was runnng rich.

Do you run a permanent sensor or just have a standalone sniffer.

 

[Oneball]

I’ve had another look and the floats weren’t where I thought they were. So put the secondary 1/8” below the sight and the primary just above. I’ll give it another go in the week. Not sure it’ll make a difference as I’ve raised and lowered them before.

 

[heavychevy]

I have a permanent system, but it is a stand alone operation as it is on a carbed motor.

 

[Torment]

Oneball...I am loving you have a full air filter on that.i run a 4 inch deep filter and a k&n filter top like yours on my 57 chevy..hate the steel top jobs.

 

[Torment]

Fuel pressure..?

 

[Oneball]

Fuel pressure..?

Ive had it at both 4psi and 7psi at idle and didn’t make a difference

 

[Oneball]

I’ve had another look and the floats weren’t where I thought they were. So put the secondary 1/8” below the sight and the primary just above. I’ll give it another go in the week. Not sure it’ll make a difference as I’ve raised and lowered them before.

Given it a run and it seems much better. Going to try raising the secondary float a flat at a time and see what it does.