Holley Leak Down
Thread Starter
Melting Slicks
Joined: Aug 2004
Posts: 3,078
Likes: 101
From: Riverhead New York
OK, I'm learning a lot by listening and looking. I'm thinking that if I start the car cold, run it for a minute, shut it down, and wait a half hour. Now, seeing as the engine is cold, there should not be any Percolation. If it's Flooded I'll know it's a deeper problem. Make sense? Al W.
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
OK, I'm learning a lot by listening and looking. I'm thinking that if I start the car cold, run it for a minute, shut it down, and wait a half hour. Now, seeing as the engine is cold, there should not be any Percolation. If it's Flooded I'll know it's a deeper problem. Make sense? Al W.
unless you discover something new, like "cold" perc. ......
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
OK, I'm learning a lot by listening and looking. I'm thinking that if I start the car cold, run it for a minute, shut it down, and wait a half hour. Now, seeing as the engine is cold, there should not be any Percolation. If it's Flooded I'll know it's a deeper problem. Make sense? Al W.
Drifting
Joined: Apr 2007
Posts: 1,442
Likes: 87
From: bluff dale tx
the power valve is tied directly to manifold vacuum. one good backfire or cough can rupture the rubber diaphragm . then today's fuel will make it worse over time . cold start is good . hot start is flooded condition . the fuel is not perking out the top but through the power valve . runs good at speed but when you come to an idle before shut down it goes full rich . this is the most common problem with a holley . the newer carbs have a check ball to stop this. works 90% of the time .
set of new blue gaskets and a new power valve is a quick check and fix most of the time.
hope this helps .
set of new blue gaskets and a new power valve is a quick check and fix most of the time.
hope this helps .
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
I ran 4150 Holleys continuously from 1965 through about 1990. Kinda' spotty after that. Never had a blown power valve. Never had one fail even using E 10 way back then. Yes, I had a few backfires and one engine fire!
I did use to swap carbs around and some would sit idle and dry out. That automatically meant new gaskets or it'd leak. Also add that none of mine have warped main bodies or metering bodies as I was the only person to work on them and never overtightened the bowl screws OR even the base plate. It was common to see an ear broken off a base plate due to overtorqueing to the manifold with a thick layer of gaskets.
Drifting
Joined: Apr 2007
Posts: 1,442
Likes: 87
From: bluff dale tx
i just did one last week. 37 ford truck i built 12 years ago for a customer. millage went away and after he would get to town it was hard to start . full rich and flooded . under throttle it ran great but would load up at a light or not want to start . no problem with a cold start . i've blown so many power valves back when racing i plugged them off and tuned around them . it is a neat circuit though, gives you that shot of fuel when you need it. very tune-able too . there are different vac set and also 2 stage valves.
Race Director
Joined: Oct 2000
Posts: 15,036
Likes: 79
From: central FL, near the beach.
i have not had a backfire since 2007. Prior to that, it would backfire below 50F, no choke. Never blew a PV.
Since 2007 i learned to fully divide the 2 planes. That cured all cold start backfires. I push in the clutch, put in R, start engine and back right out, no warmup, at 1000-1200 rpm, no choke, no backfires.
Since 2007 i learned to fully divide the 2 planes. That cured all cold start backfires. I push in the clutch, put in R, start engine and back right out, no warmup, at 1000-1200 rpm, no choke, no backfires.
Melting Slicks
Joined: May 2002
Posts: 2,225
Likes: 44
From: Penticton B.C. Canada
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Melting Slicks
Joined: May 2002
Posts: 2,225
Likes: 44
From: Penticton B.C. Canada
with the overtightened bowl screws.This sometimes happens when a leak started and the ham fist working on it tightened up the bowl screws instead of replacing the gasket(s).
The original Holley gaskets were okay if the engine was run everyday and the wet gas kept the gaskets swelled up. When the carbs sit empty, the old gaskets would shrink and cause them to leak gasoline and have vacuum leaks. At this point, tightening the bowl screws just warped the main body and the metering plates.
I understand the new, replacement gaskets don't have this problem but don't know as I haven't been inside a Holley in 10-12 years. Maybe longer.
It's been some years for me too ...
The replacement non shrinking Blue gaskets don't shrink but they are a dirty SOB to get off once they have been there for a while ... Maybe they've corrected that - they needed to ...
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
i have not had a backfire since 2007. Prior to that, it would backfire below 50F, no choke. Never blew a PV.
Since 2007 i learned to fully divide the 2 planes. That cured all cold start backfires. I push in the clutch, put in R, start engine and back right out, no warmup, at 1000-1200 rpm, no choke, no backfires.
Since 2007 i learned to fully divide the 2 planes. That cured all cold start backfires. I push in the clutch, put in R, start engine and back right out, no warmup, at 1000-1200 rpm, no choke, no backfires.
Still, no blown power valves.
Race Director
Joined: Oct 2000
Posts: 15,036
Likes: 79
From: central FL, near the beach.
Below 32F, i recommend a choke.
.
Mine don't even have the check valve.
So what is it that causes blown PV's?
All i can think of is WOT or near WOT, that would cause a bigger bang.
Or maybe the passage, about 3/16" on mine, is LARGER on some carbs?
I did buy a $45 holley that had a blown PV, so it can happen. It looked very old.
.
Mine don't even have the check valve.
So what is it that causes blown PV's?
All i can think of is WOT or near WOT, that would cause a bigger bang.
Or maybe the passage, about 3/16" on mine, is LARGER on some carbs?
I did buy a $45 holley that had a blown PV, so it can happen. It looked very old.
Thread Starter
Melting Slicks
Joined: Aug 2004
Posts: 3,078
Likes: 101
From: Riverhead New York
Update- Tried the cold start a couple of times and there was no problem. Cranked over a couple of times a fired up. Looking over the carb. I do see a lot of fuel residue Browning around the Vent on top of the front Bowl. Is this a sign of Percolating? maybe I should try lowering the Float level a little bit. Thoughts? Al W.
