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Old 01-28-2011, 06:34 PM
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Holley Primary Booster Leak

Hey guys I have a 850 Holley double pumper and at idle the left side primary booster leaks fuel while the right side is dry. Its pretty much impossible to get idling correctly. Any ideas? I bought the carb rebuilt, which I have already taken it apart, everything including the power valve looks new. I did mess with the float levels before noticing the leaking so Im not sure if it started due to that. Thanks!

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Old 01-28-2011, 07:06 PM
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The usual cause in this is: Fuel pressure too high. Float level too high.
Blocked off fuel tank vent causing excess pressure to build in the tank and push the fuel pressure up. Butterflies open too far due to low spark timing, or the possibility one is bent or loose causing it to be open far enough to pull from the booster. What`s the fuel pressure? what`s the timing set at? What engine? what mods?
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Old 01-28-2011, 07:20 PM
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Motor is a 454 just rebuilt, its on a stand not in the car yet running. The timing was set by the builder but I cant get a timing light on it since the idle wont go down past 1400rpms and it just floods out. Pulled all eight plugs, 4 are soaked (side thats leaking) 4 are dry. Using a RPM airgap dual plane. I have a MSD magnetic pickup distrib. with vac. advance. Im not sure about the fuel pressure, but Im using a Holley mechanical on it.

I will try lowering/checking the float level again tomorrow, but just want to get some ideas in case that doesnt work.
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Old 01-28-2011, 07:41 PM
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Quote:
Originally Posted by jjgrizz73
Motor is a 454 just rebuilt, its on a stand not in the car yet running. The timing was set by the builder but I cant get a timing light on it since the idle wont go down past 1400rpms and it just floods out. Pulled all eight plugs, 4 are soaked (side thats leaking) 4 are dry. Using a RPM airgap dual plane. I have a MSD magnetic pickup distrib. with vac. advance. Im not sure about the fuel pressure, but Im using a Holley mechanical on it.

I will try lowering/checking the float level again tomorrow, but just want to get some ideas in case that doesnt work.
You need to check the registration between the throttle blades, it's possible that a bent blade or throttle shaft exists on that the side which would leak more air than the opposite side, therefore, would start that main circuit to metering earlier. This would also give you fits trying to get control of the idle speed.

Check the main jets to be sure they are the same size and the leaking side jets are seated. A similar check of the power valve to be sure there aren't any leaks past it into the main-well on the dribbling side.

Check the air bleeds on that side, a plugged or damaged air bleed jet will cause the main to start to pass fuel with less venturi flow than if they are working properly, it would pass nothing but fuel rather than the normal emulsion which will make for a richer than expected mixture. Along with this is plugging, damage or miss height adjustment of the emulsion tube. It has holes if not open or aligned properly fuel will be pulled without the emulsion with air occurring which makes the mixture rich.

As has been stated don't forget the regular stuff of float level, fuel pressure. Plus inspect the meter block and it's gaskets for cracking or warpage in the block or any lack of gasket sealing. The Holley metering block sometimes warps, loosening the gasket seal and lets the bowl reservoir leak into the main well. The only good fix for this which is a high candidate is a new metering block, man that hurts.

Watch for the flatness of the bottom flange, the Holley is easy to bend when tighting it to the manifold, if this is problem I'd expect that the non leaking side would be drawing air from between the carb and manifold which would have the effect of shutting the fuel off from the not dripping side, this would also make getting idle control nearly impossible.

Bogie

Last edited by oldbogie; 01-28-2011 at 07:48 PM. Reason: Bad sentence structure, poor spelling and a new idea
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Old 01-29-2011, 12:25 PM
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Ok some more info. after working on it this morning. I picked up a trick kit for it, replaced the power valve and needle. Adjusted the floats down pretty close to where they should be, actually lower. Still leaking out the one side of the primary. Also, I noticed that AFTER the motor was shut down, the secondary on one side leaked gas and pooled up on the butterflies. It didnt leak out the boosters it leaked out of the circuit down the bottom for awhile. I was thinking too much fuel pressure out of the holley mech. pump? Its the 110GPH model which doesnt require a regulator but that doesn't mean much to me right now ahah. Anyone with ideas?
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Old 01-29-2011, 12:51 PM
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Quote:
Originally Posted by jjgrizz73
Ok some more info. after working on it this morning. I picked up a trick kit for it, replaced the power valve and needle. Adjusted the floats down pretty close to where they should be, actually lower. Still leaking out the one side of the primary. Also, I noticed that AFTER the motor was shut down, the secondary on one side leaked gas and pooled up on the butterflies. It didnt leak out the boosters it leaked out of the circuit down the bottom for awhile. I was thinking too much fuel pressure out of the holley mech. pump? Its the 110GPH model which doesnt require a regulator but that doesn't mean much to me right now ahah. Anyone with ideas?
If the circuit at the bottom means from the rectangular slot above the throttle blade, it means either the gasket on the metering block is leaking, or the either the metering block or main body is cracked in this area.

As I said in a previous response, it is fairly common for the metering block to leak, they often warp, it's only a few thousandths but that's enough to break the gasket seal. As typically happens you re-gasket the carb and it works fine for a while then the leak returns. The only real repair is replacing the metering block, milling it flat is also a temporary repair, when you get one of these that warp, they just keep on warping after every repair.


Bogie
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Old 01-29-2011, 06:42 PM
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Thanks bogie, Ive decided to just put this carb aside and ordered a new edelbrock. I always had good luck with them and they are decently priced. Thanks again for the help!
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