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fastnloud 03-15-2013 06:15 PM

Holley 750 DP, Flooding on startup
My truck has a built 350 SBC. It did have an Edelbrock 650 on it, but now it has a Holley 750 double pumper, it is manual choke with a pull out cable.

The truck runs great, and much better with the Holley.

The issue I'm having is on cold starts I keep flooding it. I assume when I pump the pedal I'm putting too much gas in it with this bigger carb.

Should I try not pushing the pedal all the way to the floor? Maybe just pull the choke out half way only, and pump just half way?

I'm just looking for some tips with this. As I said the truck runs great out on the street, so I don't think I have any carb problems, I just can't seem to figure out the best way to operate the choke on start up with this new carb.

Thanks guys.

tresi 03-15-2013 06:46 PM

In most cases a well tuned carb should start with little or no pumping. Set the choke, if its actually required, then smoothly give it about half a pump to set the fast idle cam. In not so cold weather give no choke, no pumping a try. If the choke blade is closing fully that's usually too much choke. I don't have the figures handy but even at full choke there should be 3/16ths to 5/16ths gap at full choke. If it's closing fully it needs adjusted.
I'm assumming that you're just talking about having an overly rich mixture. If by flooding you mean raw gas running down the venturis or out of the carb the you have a float setting or a stuck float problem.

fastnloud 03-15-2013 06:55 PM

Thanks for the help. By setting the choke, do you mean pull the cable all the way out?

tresi 03-15-2013 07:21 PM

yes, here again full choke may only be needed until the engine fires. Once it hits push it in a little. As it warms up push the choke in a little at a time.

fastnloud 03-15-2013 07:28 PM


Originally Posted by tresi (Post 1657146)
yes, here again full choke may only be needed until the engine fires. Once it hits push it in a little. As it warms up push the choke in a little at a time.

Thanks, I will try this. It sounds like I've been unnecessarily pumping the gas, therefore causing my issue.

tresi 03-15-2013 08:10 PM

Some engines may need a little more pumping but it's best to start with less and go to more later. It's always easier to add a little gas later than clear out a flooded motor.

RWENUTS 03-15-2013 08:35 PM

I ran a 750 vac secondary on a built 350. Started it up once a month in the winter. Usually when it was 5-10* F out. I'd pump the pedal once then push the pedal down half way and pull the choke out all the way. Crank it, soon as it fired I'd push the choke back in halfway. As it warmed up I'd push the choke in a bit more.
I modified the choke ramp that the high idle screw ran on though. Factory set up I had too much choke (blade closed) and not enough rpm. I ground the cam to a better shape so I could have the choke blade half open but with lots of rpm to keep it from running rich, loading up and quitting.
You don't want to pump that holley too much or it will be a bear to get going.

tresi 03-16-2013 12:27 AM

Keep in mind you'll be pumping about twice the fuel as ^this guy with each pump of the throttle.

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