I have this Holley 750 double pumper carb that I bought from Summit. The floats are a little high and I want to adjust them down. Does anyone know how to do it? I can find any instructions.

 

There are two ways that I know of, one is with the carburetor installed and one with the carburetor removed and taken apart. I would pre-set them when the carburetor was apart or just adjust them when the fuel is flowing and the carburetor is on the engine. IF you do it on the engine I would be sure that the car is on it's four tires on a flat area as this is important.

Normally when I had to adjust my Float level on my C3 with a Holley Double Pumper I would first get a fire extinguisher and have it handy! Then you remove the sight glass plugs if you have them or if you have the plastic plugs that allow you to actually see the gas level then you can leave them alone unless they are cloudy. The newer carburetor models are coming with a built in glass plate to allow you to see the gas level. For these you don't have to do anything to them, just watch the fuel level inside the float bowl.

Then with a Flat blade screw driver in the large brass screw on the top of the float bowl to hold it in place while you gently loosen the nut that secures the screw in its place. At this point the large brass flat bladed screw on the top of the float bowls can be turned slightly while you are watching the float level. I don't remember which way you turn it to make the level go up but I think that you will be able to tell very quickly.

If you adjust the float higher then you might get gasoline leaking out the sight glass hole so keep some rags or a small container to catch the gasoline that comes out of the sight plug holes. I was taught to set the float level about 1mm below the site glass so it doesn't leak out of the site glass hole while the engine is running. Then when you get the fuel level where you want it simply hold the large brass fuel adjustment screw in place and gently tighten the nut that secures the brass adjustment screw. It doesn't need much just enough to secure it.

Then wipe everything down and double check to be sure the gas level is correct and that the hardware is secure as well.

I hope this helps, recently I removed my Holley Double Pumpers and went to a Holley EFI system so am done adjusting floats for a while. I would not do this when the engine is really hot, I did mine after start-up to reduce the chances of a fire.

 

Thats the exact write up I was looking for, thanks

 

As a side note:

With the fuel bowls on your work bench, turn it up-side-down. The float will hang towards the top of the bowl now. Using a #2 pencil, adjust the screw & nut until the float just rides on the pencil. Tightened everything up, do the other bowl.
That pencil is the perfect thickness to set the float level until the engine is running. Then you can tweak it a bit.

I was taught to set the fuel level just above the sight plug threads. Its ok if some dribbles out. This procedure of being on the "high-side" prevents your fuel system from leaning out under heavy acceleration, causing damage.

 

So I have the glass sight plugs on the side of the float bowls. With the engine running, what should the level be?

 

I just adjusted the fuel bowls and I think they were way high. The rear sight glass was about 3/4 full and the front was half. The car had always had a problem where it would diesel sometimes when I shut it off and I’ve had it into multiple shops to have it checked out they have always tried to adjust the timing but no one ever looked at the fuel bowls to see if they were maybe too full. Could that have been the issue?

 

If your carb has the non-removable sight glass instead of plugs, put the fuel level just under halfway up. You DO NOT want a lean condition. That's how you fry pistons.
In theory, if the bowls are always filled as much as allowed, the fuel pump can keep up under full throttle conditions. The bowls will have a slight "reserve" ready to go.
If the bowls are below half at full throttle, a dangerous condition will happen leaning out to the point of detonation.

And your secondary needs to be slightly lower to match.

Dieseling is sometimes caused by IGN timing issues and sometimes a finicky secondary throttle blade issue.
And also in some cases, a throttle stop solenoid, on certain models.

 

Old 4779 Holley double pumpers had brass sight plugs on the bowls. You adjust them so fuel just barely dribbles out then lock down the adjustment. If you have non removable sight glass like the newer versions you want to set the level in the middle of the glass.

If you have those floats set right, you want to set the transition slot with the idle speed screw. I suspect this is your issue.


This is where the transition slots need to be set.


You really need to set up your ignition curve first before messing with the carb. They work together to solve this problem you are experiencing.

 

Dieseling is not caused by the float levels you stated.
What is your idle rpm?
Do you have your distributor vacuum advance connected to manifold vacuum?
What is your initial advance set to?

 

On the float adjustment. YOu have to loosen the screw first. That is the lock, the nut adjusts it. Doing the nut first while it is locked will strip the bowl

 

heres the instructions fro holley
https://www.holley.com/blog/post/adj...ur_carburetor/

 

Only if you attempt to lower it with the lock nut tight.......if you raise it with the lock nut tight....the whole thing just spins out......

I like to use those stubby 5/8" wrenches and a thick flat blade that I like......
Put a rag under where the bowl is to catch dribbles......

Jebby

 

Actually, what you are supposed to do is loosen/remove the screw and give the adjustment nut a tap from below to free the surfaces from the gaskets. This then avoids tearing the gaskets, which you are prone to do if just turning the adjustment nut to loosen the assembly. When I put them back together, I put some lube on these two gaskets to avoid tearing in the future.

BTW, if you turn the nut clockwise, you lower the fuel level and vice versa.

It is very easy to have the levels too high and you can't get the car to idle to set them because it is flooding out. In this case you can turn the starter to fill the bowls, but don't start the engine, then check the level at the sight plugs with the engine off. If it spills out, it is too high. Lower the level and try this again until it no longer pours out with the engine off then set them, on level ground, with the engine running.

It is easy to tell if the secondary level is too high. Just do a "panic stop." If the level is too high, fuel will spill over and make the engine go over-rich and stall.

BTW, Holley says that the last adjustment should be made raising the floats.

 

To prevent braking slosh-over, Holley has fuel bowl Vent Whistles. Problem solved.

 

Every carb I build.....every carb I work on get neoprene adjustment seals. No tap required.
BTW....if you are using paper....have another handy....tap or not they will rip if they want to rip.....but if you have to replace it....just use neoprene.

Jebby

 

Everybody is talking about float levels but the problem the original poster has is dieseling when shutting off the engine which is not related to my knowledge to the float levels he currently has.

 

Post # 1. How do you set the float levels?

 

I see now where he has a diesel problem but it wasn’t for a few posts…..
He needs Lars papers to set timing, idle screws and idle speed…..

Jebby

 

But if you read his post #6, the real problem is dieseling and he's just wild guessing that it's float related.

 

I have the vent whistles and when the secondaries were set too high, they would still flood on a panic stop.