Holley Carb Float Bowl Idle Vent

[Michael M.]

Re: Holley Carb Float Bowl Idle Vent

I had the same problem as Jerry about four years ago due to a needle and seat hang-up. Although not the fault of the bowl vent, the gas pouring out of it was pretty scary. https://www.forums.ncrs.org/showthre...571#post564571

Note to Jerry - after installing a new needle and seat (Holley 6-510 with Viton tip) I've haven't had a problem in over four years.

[Gerard F.]

Re: Holley Carb Float Bowl Idle Vent

Hi Jerry,

I am curious what you find when opening the bowl, have you ever replaced the filter in the gas tank. If these float N/S's are the black rubber tips are you using e-10 fuel.

Tim,

Well I think I have it fixed for now. I pulled the 3810, then pulled the front bowl. Actually I couldn't see anything wrong with the needle and seat. The float tested out in hot water. Then I tested the power valve with a Miti-vac and a suction cup. It would open and close but would not hold a constant vacuum. I assume that it was leaking, I have been having flooding problems after a long hot run. Also I noticed that the float bowl was set high to the original Service Manual spec 5/32", this was latter changed by Holley to 5/16"

The crossover hot slot caps I put on some years ago were still in place and seemed to be still working. But in cleaning the intake manifold I noticed a very slight oil leak at one of the intake manifold bolts. Maybe it needs a little tightening, but I think I'm about ready to take the intake manifold off and replace the original gasket. The intake manifold has never been off this 67 327/300

Getting back to leakage problem, since I couldn't figured out what was wrong, I changed the needle and seat, and float with new.
Then I changed power valve with a new (tested) one, the jets, and all new gaskets. Put it back on and it seems to work, although I haven't taken a long hot drive yet. Thanks, Mike Mayland for your post.

I'm going to save my restored 3810 763 ( the one in the Restorer story) for a future project with an almost new and very correct intake manifold which I have. I need to put pipe plugs in the hot slot and find a good gasket. That's a future long weekend project. What is the best intake manifold gasket?

[Joe L.]

Re: Holley Carb Float Bowl Idle Vent

Tim,

Well I think I have it fixed for now. I pulled the 3810, then pulled the front bowl. Actually I couldn't see anything wrong with the needle and seat. The float tested out in hot water. Then I tested the power valve with a Miti-vac and a suction cup. It would open and close but would not hold a constant vacuum. I assume that it was leaking, I have been having flooding problems after a long hot run. Also I noticed that the float bowl was set high to the original Service Manual spec 5/32", this was latter changed by Holley to 5/16"

The crossover hot slot caps I put on some years ago were still in place and seemed to be still working. But in cleaning the intake manifold I noticed a very slight oil leak at one of the intake manifold bolts. Maybe it needs a little tightening, but I think I'm about ready to take the intake manifold off and replace the original gasket. The intake manifold has never been off this 67 327/300

Getting back to leakage problem, since I couldn't figured out what was wrong, I changed the needle and seat, and float with new.
Then I changed power valve with a new (tested) one, the jets, and all new gaskets. Put it back on and it seems to work, although I haven't taken a long hot drive yet. Thanks, Mike Mayland for your post.

I'm going to save my restored 3810 763 ( the one in the Restorer story) for a future project with an almost new and very correct intake manifold which I have. I need to put pipe plugs in the hot slot and find a good gasket. That's a future long weekend project. What is the best intake manifold gasket?

Jerry------


I like the embossed, original type intake gaskets. These are hard-to-find in the aftermarket. However, the reproduction gaskets as available from Paragon are of this type AND they're of the correct configuration (except for tiny GM markings on the end seals).

[Timothy B.]

Re: Holley Carb Float Bowl Idle Vent

Hi Jerry,

I think you mentioned fuel from the primary idle vent so that may have been a leaking needle and seat. FWIW, these power valve gaskets can leak and create a rich condition but hard to detect because it's under the throttle blade so there is no trace of fuel leakage looking at the carburetor. I think there torque is something like 100 inlbs.

My 3810 just got new gaskets also, carb man say's it's because these things don't get driven enough. Anyway, some time back I installed brass 6-32 set screws in place of the primary idle air bleeds with .076 size IAB and the motor likes it. I did the same with the idle feed restriction and leaned it but made it stupid so I went back to .031 then up on the air bleed. Cleaned the idle up nice, emulsion screws out approx 5/8 and 3/4 turn and no surge while running on the transfer slot.

[Gerard F.]

Re: Holley Carb Float Bowl Idle Vent

Tim,

A couple of questions:

1. Do you use any gasket sealant between the intake manifold and the gasket, and between the gasket and the baffle. I have been using these heavy duty gaskets with the hot slot on the manifold, and then with the baffle on top with no sealant, no gasket or sealant between the carb and the baffle. It makes it easy to switch carbs, but sometimes I wonder about lack of sealant. My hot slot holes have been plugged.

2. I have a very slight leak coming from the fuel bowl cap near the fuel filter housing. Is there any easy fix for this.

[Timothy B.]

Re: Holley Carb Float Bowl Idle Vent

Jerry,

I don't use any gasket sealer, mine is exactly like yours in that I use that thicker hot slot gasket then the stainless shim then carburetor. I doubt you have any issues here, it would show up as a vacuum leak and a higher than normal idle.

I have seen carburetor rebuilders use epoxy on the plugs regardless if they leak or not. Try to find some good epoxy and try that or just replace the bowl, don't take chances with the fuel leak.

[Patrick B.]

Re: Holley Carb Float Bowl Idle Vent

I don't know about other 70 Chevies, but 1970 Corvette Holley Carbs without EEC did not have bowl vents. The only 70 Vette with a Holley was an LT-1. Niether the original carb for my July LT-1 (dated 035) nor an earlier 4555 carb I have dated 9B1 have bowl vents. A Holley 4556 carb I have has a strange bowl vent with a large tube connection on it, probably for EEC.

BTW, I removed the bowl of the 4556 with the strange bowl vent and replaced it with a regular unvented bowl. The carb ran fine and I used it for years. Maybe this answers the original question.