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Need some help trying to figure out this darn carb on my truck. It’s a 4 barrel Holley 600 with electric choke, vacuum secondaries, and single fuel inlet. The issue I’m having is that no matter what I do I can’t get the rear bowl to stop flooding. I have replaced the needle and seat, added a fuel pressure regulator, and replaced the float. The part that makes no sense is that the front bowl has never flooded like this but no matter what I do, the rear just blows past the needle and seat and shoots fuel out the vent tube. Any ideas? Thanks
Well,,, if that is a picture of the exact carb, that screw with the lock nut on top of the bowl is for flost adjustment.
USUALLY, Holleys have a screw on the side of the bowl, for fuel height in bowl.
As the screw is removed the fuel level should be even with the botton of the threads.
We used to adj the float so the gas would come over the threads when car, truck is rocked side to side al little.
I don’t think so, it uses the side hung floats. I added a picture of the exact carb I have for reference
it’s adjustable, the slotted “screw” on top of the bowl with jam nut is the float adjustement. Loosen nut, back out the screw to lower the bowl and tighten jam nut while holding the screw. Does it have a sight glass on the bowl?
it’s adjustable, the slotted “screw” on top of the bowl with jam nut is the float adjustement. Loosen nut, back out the screw to lower the bowl and tighten jam nut while holding the screw. Does it have a sight glass on the bowl?
ACTUALLY,,Been a while, BUT if I am not mistaken,, you have to tighten the sctew to lower the float.......on the Holley.
Any, once you work with it you'll figure it out, not a big deal...
Last edited by Old Guy F-250; Mar 30, 2025 at 12:03 PM.
Reason: added you'll figy=ure it out..
ACTUALLY,,Been a while, BUT if I am not mistaken,, you have to tighten the sctew to lower the float.......on the Holley.
Any, once you work with it you'll figure it out, not a big deal...
yep, I could be wrong…been a long time since I set the floats on a Holley.
ACTUALLY,,Been a while, BUT if I am not mistaken,, you have to tighten the sctew to lower the float.......on the Holley.
Any, once you work with it you'll figure it out, not a big deal...
IIRC (been a long time since I needed to adjust one) the screw is the jam part and the nut is the adjusting part.
Turn the screw CCW just a little then turn the nut CW to raise and CCW to lower the level again if I remember right.
Just make sure you tighten the jam screw once the level is set
You can also remove the needle & seat and swap them front to rear without removing the bowls.
Originally Posted by atitagain4
yep, I could be wrong…been a long time since I set the floats on a Holley.
From what I gather so far it sounds like the float has not been adjusted and why the rear bowl floods over.
If the front is not flooding then the PSI is not the cause.
Dave ----
it’s adjustable, the slotted “screw” on top of the bowl with jam nut is the float adjustement. Loosen nut, back out the screw to lower the bowl and tighten jam nut while holding the screw. Does it have a sight glass on the bowl?
yes it has the sight glass on the opposite side. Maybe I should have been more specific. When I installed the carb I was able to successfully adjust the front bowl no problem but no matter how much adjustment I do on the rear, it just comes out the vent tube. At this moment in time, the rear is adjusted all the way down to cut fuel off to the rear bowl so I can drive the truck as it is my only vehicle
yes it has the sight glass on the opposite side. Maybe I should have been more specific. When I installed the carb I was able to successfully adjust the front bowl no problem but no matter how much adjustment I do on the rear, it just comes out the vent tube. At this moment in time, the rear is adjusted all the way down to cut fuel off to the rear bowl so I can drive the truck as it is my only vehicle
Now you know the rear level will not drop unless the secondaries open.
Because of that I would drive and open them up a few times to drop or empty the bowl then pull the sight plug and adjust the level so it is just below the hole when you shake the truck and lock it down.
Go easy on the adjustment and sneak up on the level because if you go to high you dont have a way to lower it unless you drive it again.
OR
Racers trick:
If you have plastic washers on the bowl screws, on a cold motor, you can take a spray can cap and remove 1 of the lower screws and catch the gas in the cap as this will lower the level in the bowl.
Then do the adjustment sneaking up to the open hole.
Dave ----
Now you know the rear level will not drop unless the secondaries open.
Because of that I would drive and open them up a few times to drop or empty the bowl then pull the sight plug and adjust the level so it is just below the hole when you shake the truck and lock it down.
Go easy on the adjustment and sneak up on the level because if you go to high you dont have a way to lower it unless you drive it again.
OR
Racers trick:
If you have plastic washers on the bowl screws, on a cold motor, you can take a spray can cap and remove 1 of the lower screws and catch the gas in the cap as this will lower the level in the bowl.
Then do the adjustment sneaking up to the open hole.
Dave ----
yes sir I know the fuel won’t go down without the secondaries opening. The issue is that while the engine is running, the fuel comes out of the rear vent tube and completely floods out the engine. No amount of adjustment, hitting it with a hammer, or anything else I’ve tried has done anything to help this issue
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