500HP Carb issues
 

Need some help here. 1997 hp500 with carb. All stock. Nothing has ever been touched on it judging by the paint showing no wrench marks. Have fuel pouring out of secondaries when trying to start. Pulled plugs so didnt hydro lock it. Pulled rear bowl off and put in new needle and seat and adjusted tab on float up. With float screw turned all the way down (clockwise) it still overflows thru sight screw and into carb. Checked fuel psi at mechanical pump and although I didnt have correct fitting I did have a rubber cone style to shove into port and it read 8.5psi. Question is A, will a fuel filter cause higher psi as I have not changed this year, and B, will a bad pump cause higher psi? Its been perfect all year until today. If I crank long enuff it will come out front holes as well. The spigot looking spouts at the very top of the venturies will spill fuel too. Not much of a carb guy so hoping to get some advice. No kinks anywhere as all hard lines except from tank to pump.

Thanks and Happy Labor Day!

You said “Pulled rear bowl off and put in new needle and seat and adjusted tab on float up”

what do you mean adjust tab on float up ?

adjustment on float/fuel is how far the needle and seat is adjusted up/down.
Proper fuel level is when fuel just dribble out of side-window plug. A little morevto this procedure but that’s most of it.

Yea I understand that all of that. The tab is where the needle sets on the float. Its a procedure to lower float level if need be. Thats 100% not the problem as with the needle all the way closed off almost its over filling the bowl. Thinking more of a fuel psi issue at this point. Just not familiar with these mechanical pumps.

Only doing it to secondary bowl, not the primary?

Knowing your feed pressure before tearing everything apart would go a long way to eliminating potential culprits.

8 1/2 lbs is probably pushing it on a Holley carburetor. That being said if nothing has been done to the carb since 1997 it is well overdue for at least a re-gasket job. Especially if you are running ethanol fuel. I just did one for a car that was about that old and all of the gaskets were starting to fall apart. The gaskets available in the Holley kits now days are made to withstand the ethanol fuels.

Also I am not sure if your carb has a power valve in the secondaries but they will deteriorate too and start to dump fuel.

Every time one of my Holleys do that, it's one of the power valves. I agree, 8.5psi is pushing it. I've been running 7.25 psi via a press regulator (15 psi mechanical fuel pumps) for 10+ years with no issues.

You want to set/check float levels with the boat in the water.

Wouldnt power valve only be in primary metering block? If so my issue is with the secondaries.

Possible. What part number is the carburetor ? Its on the front of the choke housing. I dont know what carb was on those engines.

Were the needle and seats that you purchased genuine Holley parts ? You really should never have to bend the float tang to get the correct adjustment on a Holley with the adjustment screws.

yes holley oem. I bent the Tang just to make sure I could get the float to zero to make sure that was not the culprit.

Depends on the carb.

Double Pumper carbs typically have a secondary power valve. It's a large factor in tuning the top end.

Otherwise you secondary jets need to be massive, and you lose fidelity of the fuel control.