Thread: Acceleration backfire?

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Hi folks, it's been a while!

I just got done building and installing my 355 in my '70 Nova, and I'm having some carburetor problems here.

The motor idles great, makes awesome vacuum and oil pressure, but I have a problem. I think it's getting way too much gas. On anything other than a slight acceleration, I get a tremendous bog (sometimes resulting in a backfire, and if from a dead stop, killing the motor!). I am using a Edelbrock 1405 carburetor and a Holley HP Mechanical fuel pump.

I thought that it could have been one of the following:

1) Too high of fuel pressure. I'm using a high performance holley pump, and I know the carb wants 5.5 lbs at idle, haven't been able to aquire a guage to check this.

2) Bad accellerator pump diaphragm? I don't know much about carburetors, so I couldn't say.

Here are the specs of the motor:
350 + .030 one-piece rear main seal block
Dart 185cc intake runner 72cc chamber heads
Small street split pattern cam
Accell blueprint distributor
MSD Blaster SS Coil
Edelbrock RPM Air Gap intake
3000 Stall

Any ideas? It's sad not being able to romp on the motor now that it's broken in, and if this is excessive fuel, I don't want to wash my cylinder walls here.

Check your timing, V-advance hooked to the right port on your carb, that's where I'd start.

what model of fuel pump are you using, a regulator is a good idea but a few of the holley pumps do not require one, but some do!

Bog and backfire is more likely a lean condition, not rich.

It's one of the Holley High Performance mechanical pumps. I don't have the model number handy, but I'll try to find the box for it. I think it's the 90GPH version.

I'm also not very good with carburetor tuning, so I need to make sure I'm running the proper jetting to support this motor. I'll try to find out a little more about it.

Upon further inspection, here are some more symptoms:
Excessive fuel consumption (Even for this motor)
Miss while cold under even slight acceleration
Seems to bog the second the secondaries begin to open.

This sound rich or lean?