Holley carb problem

[george worley]

I have a 750 vac secondary on my 390, 6 months or so ago the back barrels started leaking after the engine was turned off. Rebilt the carb using a holley kit, truck runs fine but has same problem. needle-seat not leaking, put pressure regulator set at 4lbs no different still leaks. I looked in the back barrels and could see gas coming out of the idle transfer slots. Took carb apart and made sure the base plate and main body surfaces were perfectly clean and as near as i can tell not warped. I put 2 metering plate and 2 base plate gaskets on it is better but still leaks and cranks alot when warm. I then took off carb and filled float bowels with fuel sat over night on bench and never leaked, put carb back on and started engine and ran it a couple minutes turned it off and it started in leaking out of the idle slots Help Isure could some advice on this

[Fordlorn]

Blown power valve. Throw it away and put an Edelbrock on it. Or buy a box of power valves, your'e gonna need 'em. I won't run a Holley because of this. Remember, the carb you have is '50's tech..

[george worley]

thanks Fordlorn but it does'nt have a power valve in the secondary, just a metering plate

[mrtleavitt]

I had the same problem with my Holley and I did just as Fordlorn suggested. I rebuilt the dumb thing 3 times and went through about a dozen power valves. I tossed it and got an Edelbrock. I hate the power valve setups. This one was a 670 Truck Avenger with the vac secondaries with some sort of "un-blowable" power valve but I proved that wrong pretty fast. Good luck

[sideoilerfe]

Truck avenger/street avengers are crap. Holley's work fine. They're pretty good carbs. George, You might've got a defective one.

[Dragon]

Me and my 390 backfire all the time here in the cold and my Holley 80508S 750 4V VS Shiny has the antibackfire feature and I never have blown the valve.

[george worley]

I have had this carb for about 10 yrs. put about 1500 miles a year on it. rebilt it 3yrs. ago no problems till now, I wonder if I have a leak in the main body. Hate to give up on it, new ones are expensive and I don't really have extra money to spend

[Dragon]

The transfer slot gets it's fuel from the metering block. When the plates are open and at a certain vacuum level. Not engine vacuum but flow created vacuum.

http://www.holley.com/data/TechService/ ... 20Info.pdf

Are the fuel levels set to just below the fuel adjustment window. Putting fuel in and running it are two different items. The 4lb regulation is not the problem the needle and seat can hold almost 10 psi everyday in race cars. What is different is the float setting. If the fuel level got above the metering plate it would get in the air bleeds on the plate and cause this problem.

http://www.holley.com/data/TechService/ ... 20View.pdf

[My427stang]

As stated above, the only way to get fuel out of a transfer slot is to have airflow across it.

The transfer slot gets its air and fuel mix from the idle air bleed on the top of the throttle body, and the idle fuel restriction in the metering block.

This mixture feeds two passages, one is metered by the a/f adjusters and goes below the plate for idle fuel, and the other passes through a vertical passage , the transition slots

Theoretically, if you had plugged idle air bleeds, you could get solid fuel from the transition slots, but I have never seen it, and of course, you'd still need air rushing across to see it, and somehow be able to see down there.

Here are few questions though

1 - How do you see the transition slots when its running and under what situations do you see the fuel?

2 - How did you determine the metering surface was flat on the main body? (Loaded question in about 200 carbs I have never seen a straight one unless its just off the mill, the 4 float bowl screws pull the 4 corners high, even on new carbs)

3 - How do you have the secondary idle set in terms of how far open the slots are?

I dont want to offend, but I just want to make sure what you say you are seeing is really what you think it is. Carbs are pretty simple, but if we recommend something based on the wrong info, we wont get you anywhere

[Dragon]

So very true

[george worley]

I have the float set as low as it will go , when I rock truck no fuel spills out engine running or shut off. I checked for warp by using a small machinist straight edge and flat feeler guages using several different angles. I can see fuel coming out when I look down the back barrels with a light and the engine shut off. I will check the air bleeds and spray cleaner on them,I put my fingers over them and the idle speed drops. You have a good point about the secondary idle stop Dragon, it may be open to much or the vacum secundary chamber is not letting it close correctly, I guess it could also be sticking. what is the adjustment for the stop screw,I have never adjusted it from new but it could have changed over the years. Let me know what you think,also could unhook the vacum chamber link.

[Hawkrod]

If you have blown more than one power valve you need to learn to tune! LOL Most blown power valves are actually not blown. We used to get guys buying them all the time and I asked to see their old ones and they were almost never blown. It does take a lot to blow one these days but that was not the case 40 years ago because of design and material but now they just really don't blow very often. Most things blamed on blown power valves are tuning issues but because they used to blow people are happy to blame the power valve. In this case the leakage may actually be caused by plugged emulsification tubes acting as siphons. Unfortunately that is harder to fix as the tubes are sealed in the blocks on a Holley. Soak the block in good carb cleaner and make sure it is rotated and swished around so the block fills internally. Unfortunately if you just drop it in it the cleaner may have an air bubble that keeps the solution from cleaning some of the internal passages. Also as noted, the secondary does not normally have a power valve on a vacuum secondary carb so that isn't an issue. Hawkrod

[My427stang]

I have the float set as low as it will go , when I rock truck no fuel spills out engine running or shut off. I checked for warp by using a small machinist straight edge and flat feeler guages using several different angles. I can see fuel coming out when I look down the back barrels with a light and the engine shut off. I will check the air bleeds and spray cleaner on them,I put my fingers over them and the idle speed drops. You have a good point about the secondary idle stop Dragon, it may be open to much or the vacum secundary chamber is not letting it close correctly, I guess it could also be sticking. what is the adjustment for the stop screw,I have never adjusted it from new but it could have changed over the years. Let me know what you think,also could unhook the vacum chamber link.

Well first, having the float set lower than it should be really isnt helping anything. I'd put it back up where it should be.

A vac secondary chamber should have no resistance, just a very light amount of spring pressure, very light, but there is an adjustment there for secondary plate location, you can see it from the top, its either closed or it isnt, you can see at the base of the vacuum canister

Now is the fuel coming out of the boosters or way down low by the plate? or is there just fuel there in general?

Finally, does this carb have a rear metering block, or use a plate with clutch headed screws? If its the clutch headed screws, did it have a tin plate behind it with another gasket, or did it just use the big gasket to seal both?

[fitzwell]

[

Finally, does this carb have a rear metering block, or use a plate with clutch headed screws? If its the clutch headed screws, did it have a tin plate behind it with another gasket, or did it just use the big gasket to seal both?

Bingo! If the plate doesn't have the corect gasket, (or the body, for that matter) it will do exactly what you describe.

And if Holley's are '50s technology ,which admittedly they are, what of the edelbrock??

Based on the carter AFB, which was REAL rocket science

[george worley]

my carb has abig gasket against the main body also serves as bowel gasket and a gasket for the back of the metering plate. This is how it came new,no tin plate. I checked another geunine holley kit and those gaskets match mine on the carb exactly as did the ones I took off to rebuild carb. Gas is leaking out of the idle or the transion slot when the engine is not runing
I set the float low because the gas leaks out till it is empty, it makes it easier to start that way,i know that's not right but until i can figure this out thats the way i do it. I'm going to close the throtle plates more on secondaries and see if that helps any, they have'nt been changed from factory but might have moved anyway