Holley issue

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mopar head

mopar head

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4160 750cfm vac. sec.
Secondary plates always wet, primary dry.
I`m thinking this is why I get a backfire on cold starts.
Float setting seems good.
Anybody ever have this issue and figure it out?
I thought it was dripping from boosters, dabbed with paper towel pieces and dry?
Laced a strip across under both and checked after a few hours and dry...
How/Where, else could fuel keep the secondary plates wet looking all the time?
I cant find any sec. metering block cutaway views to help diagnose.
Thanks
 
History of the carb? New? Rebuilt? Used and just trying it out? Etc. Have you look the linkages over to be sure they are no bent or messed up in some way. Manual or electric Choke?
 
dano said:
History of the carb? New? Rebuilt? Used and just trying it out? Etc. Have you look the linkages over to be sure they are no bent or messed up in some way. Manual or electric Choke?
Click to expand...
New, well only a 1000 mi. on it but has backfired on cold startup from the git.
Electric choke, I`ll give the linkages a look see, but I never abused it.
 
Backfire could be timing....also Hollys have a habit of dumping fuel from the secondary bowls into the secondary venturies when you make a fast stop. I had to install overflow tubes on mine to keep fuel from spilling out of the vent tube on the secondaries.
 
Treblig said:
Backfire could be timing....also Hollys have a habit of dumping fuel from the secondary bowls into the secondary venturies when you make a fast stop. I had to install overflow tubes on mine to keep fuel from spilling out of the vent tube on the secondaries.
Click to expand...
Never heard of that either. I avoid making fast stops, and the car never backfires on warm restarts. I`ll check the vent tube.
 
This is fairly common to see on Vac Sec carbs. In my experience anyway....
On a vacsec carb, the secondary's slap closed by the diaphragm spring when you close the throttle, and the fuel flow doesn't stop right away and floods the tops of the throttle blades.
However, if you didn't get all of the way into the secondary's, you could have another problem.
To check this:
With the engine off, open the throttle 1/4 to 1/2 and hold it there. Now check to see if the secondary's stay closed on their own, or pull open a bit. (there's a link that forces the secondary's close at an idle)
If not, there's a couple of things that could be the cause. 1. wrong length Sec diaphragm rod. (too short)
2. Sec Dia spring is not returning the diaphragm to 'closed' (could also be stiff/old rubber dia)
3. and of coarse a binding shaft. In this case, the secondary's won't open correctly either.

My 2¢
 
'63GT said:
This is fairly common to see on Vac Sec carbs. In my experience anyway....
On a vacsec carb, the secondary's slap closed by the diaphragm spring when you close the throttle, and the fuel flow doesn't stop right away and floods the tops of the throttle blades.
However, if you didn't get all of the way into the secondary's, you could have another problem.
To check this:
With the engine off, open the throttle 1/4 to 1/2 and hold it there. Now check to see if the secondary's stay closed on their own, or pull open a bit. (there's a link that forces the secondary's close at an idle)
If not, there's a couple of things that could be the cause. 1. wrong length Sec diaphragm rod. (too short)
2. Sec Dia spring is not returning the diaphragm to 'closed' (could also be stiff/old rubber dia)
3. and of coarse a binding shaft. In this case, the secondary's won't open correctly either.

My 2¢
Click to expand...
Could your procedure be checked cold?
Carb was bought new, no modifying yet.
Car can set for a week and the sec. blades look wet. ?
 
Yes, it could be checked cold...
But if its doing that over night, the float is too high. (cold back-fires is chokes system is too lean)
 
'63GT said:
Yes, it could be checked cold...
But if its doing that over night, the float is too high. (cold back-fires is chokes system is too lean)
Click to expand...
I`ve checked the level hot and cold, running and not, seems to me fuel would run out of level port if float was too high? It does not.
Interesting that a cold backfire from being too lean, I`ll experiment with that.

Thanks for the tips fellas, I`ll update with results
 
Could you post some good clear close up pics of the secondaries/?? Maybe someone will see something that you're missing??
 
Treblig said:
Could you post some good clear close up pics of the secondaries/?? Maybe someone will see something that you're missing??
Click to expand...
I`ll do, cause it does look like a hole in the center of large hole venturi`s looks to have a tapered sleeve that maybe missing a cap? maybe not.
 
Last edited:
Don`t know if this is helpful.
IMG_20181202_201429.jpg

Wondering the purpose of the center boss with hole is for between the boosters?

IMG_20181202_201418.jpg
 
On my Holley that hole is where the center squirter is located:

DSC07926.JPG
DSC07927.JPG


If it's missing the center squirter fuel will pour out into the secondaries without any metering.
 
Mine only has the front pump...no rear pump. Going to bed so I'll have to continue this tomorrow. treblig
 
Looking on Holley's site, none of the pictures of a vacuum secondary 750 have a center squirter. They look like Mopar Head's carb.

Are you running a pressure regulator? I had an issue with a Demon carb over fueling at idle and it turned out the Holley mechanical pump I had put out way to much pressure and was over running the needle and seat. Stock pump fixed the issue.
 
dano said:
Looking on Holley's site, none of the pictures of a vacuum secondary 750 have a center squirter. They look like Mopar Head's carb.

Are you running a pressure regulator? I had an issue with a Demon carb over fueling at idle and it turned out the Holley mechanical pump I had put out way to much pressure and was over running the needle and seat. Stock pump fixed the issue.
Click to expand...
No regulator, bought new replacement pump, but it had a down pointing outlet compared to the original? pump. Dont know if their were different pressure applications for different 440s, I would think not. Motor was a non HP 72 car engine. I have a port for a gauge in the inlet manifold, probably should buy one and verify.
I`ve run the car many times, pull in shop, and check for dripping and never see anything.
 
If the pump has a spring that creates too much pressure, you'ld see it as overfilling bowls. That as you know would in turn result in in high level when you opened the sight plug and dripping from the boosters (or worse).

The throttles are below the seam with the main body. Off the top of my head I can't think of any passage on the secondary side that would let fuel come through there even with a bad or incorrect gasket. If I think of one I'll post. Its possible there's casting porosity.

The most likely explanation I can think of right now is fuel condensation. If you don't see it while running, but only when shutting down, give that some thought. The plate is cool, air is no longer flowing. Vapors condense out onto the surface.
Some posts about that at RFS. Here's one.
Capillary Action?

Here's another, in this case when engines are running.
Wet Palm
 
Last edited:
Agree on the passages Mattax, I remember one time after bringing home after shutdown, I noticed quite a bit of vapor/smoke? wafering out of the left tailpipe, same pipe that seems only to get the cold start backfire. Something to ponder...
 
Deleted as it was refering to backfire into the intake.
OK. Need to think about it different since its backfire in the exhaust.
Too rich and possibly combined with late timing.
 
'63GT said:
This is fairly common to see on Vac Sec carbs. In my experience anyway....
On a vacsec carb, the secondary's slap closed by the diaphragm spring when you close the throttle, and the fuel flow doesn't stop right away and floods the tops of the throttle blades.
However, if you didn't get all of the way into the secondary's, you could have another problem.
To check this:
With the engine off, open the throttle 1/4 to 1/2 and hold it there. Now check to see if the secondary's stay closed on their own, or pull open a bit. (there's a link that forces the secondary's close at an idle)
If not, there's a couple of things that could be the cause. 1. wrong length Sec diaphragm rod. (too short)
2. Sec Dia spring is not returning the diaphragm to 'closed' (could also be stiff/old rubber dia)
3. and of coarse a binding shaft. In this case, the secondary's won't open correctly either.

My 2¢
Click to expand...
No movement of secondaries
 
mopar head said:
Wondering the purpose of the center boss with hole is for between the boosters?
Click to expand...
That is simply the boss for secondary squirters. Not used on any vacuum secondaries I've seen except the one posted by Treblig.

Worst case, if its really leaking (should see that by fuel level dropping when the engine is shut off) might have to take it apart and look.
Sometimes even simple things like this can be hard to figure out. See last post, where he figured out where the leak was coming from.
4412 has me stumped
 
On holley`s blown view file they show a little cap/plug? listed #129 as secondary bowl vent valve, but hard to discern where it goes?
I`ve had this carb apart, just primary float bowl and put back to stock, messing with jets.
I`ve had it upside down draining gas out etc.
Later I found a small chrome?/shiny ball, little larger than a bb, under the car, and I could`nt figure where the heck it came from. I was wondering check ball? but holley tech says no way a check ball can fall out of this model carb... ?
https://documents.holley.com/techlibrary_4150_4160_exploded_view.pdf
 
There's a check ball, or needle under the shooter, and there's a check ball under the Vacuum Diaphragm cover and also in the bowl for the shooter diaphragm, but it is retained by a small flat wire (some use a red silicone rubber valve in place of it).
If you've had any of those apart, that's it.
 
'63GT said:
There's a check ball, or needle under the shooter, and there's a check ball under the Vacuum Diaphragm cover and also in the bowl for the shooter diaphragm, but it is retained by a small flat wire (some use a red silicone rubber valve in place of it).
If you've had any of those apart, that's it.
Click to expand...
I`ve had the acc. pump off to replace a leaking gasket with the blue upgrade gasket. Pretty sure the pump ball is crimped in and can`t fall out. Never messed with the vac. cover. Holley tech. says these are the only 2 check balls in the system. Parts list only state only 2 that I see. They note 70 and earlier used a ball under the nozzle.

That ball on the floor has been bugging me since.
Sure would be nice if someone has a modern 6140 and look if it looks the same as mine.
 
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