Fuel Blowing Out Carb Vent Tubes Under Heavy Throttle: Expert Opinions Please

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The correct float setting for carbs with sight glasses is half way up the glass. Not the bottom of the glass.

I'd get a second gauge and check the pressure. It's possible at higher RPM the bypass in the pump is not working and running the fuel pressure up.
 
yellow rose said:
The correct float setting for carbs with sight glasses is half way up the glass. Not the bottom of the glass.

I'd get a second gauge and check the pressure. It's possible at higher RPM the bypass in the pump is not working and running the fuel pressure up.
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You must not be talking about Holleys.
 
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AED and David Vizard in his book on Holleys with the sight glass say to adjust to the middle of it. But I'm gonna try a little lower, the vent hose extensions, ordered a 5° wedge plate. I consider all that a work around, or trying to lessen the issue. Still, I think with two different carbs doing this, after a year with one not doing the spray deal until just recently before the swap, there is an unknown issue in my supply/delivery setup,
 
yellow rose said:
The correct float setting for carbs with sight glasses is half way up the glass. Not the bottom of the glass.
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Every Holley manual I've ever seen says to set the float so gas just dribbles out of the hole. Why would that change if you stick a clear piece of plastic in there?
 
From the Holley manual:

A “wet” level float adjustment can be performed on either the side or center hung floats, if the fuel bowls have provision for the externally adjustable needle and seats. This adjustment is made as follows. Start the vehicle up and move it out of the garage and into an open area where plenty of fresh ventilation is available. Allow the idle to stabilize. Turn the engine off and remove the sight plug from the primary fuel bowl to inspect the fuel level. If it’s been determined that adjustment is required use a large screw driver to crack loose the lock screw. With a 5/8" open-end wrench turn the adjusting nut clockwise to lower the float level.

Conversely, turn the adjusting nut counter-clockwise to raise the float level. Tighten the lock screw. Restart the vehicle and let the engine idle stabilize. Shut the engine off. Remove the sight plug to reinspect the fuel level. The fuel level should stabilize at just below the level of the fuel bowl sight plug hole. This same adjustment procedure is performed on the secondary bowl.
 
Tuning Tips. AED shows with the sight glass on their carbs to adjust differently, just for clarity here. I'll go out on a limb and speculate maybe its because their metering blocks are drilled or setup different than the Holley blocks?
 
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toolmanmike said:
You must not be talking about Holleys.
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toolmanmike said:
You must not be talking about Holleys.
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Any Holley or Holley clone with a sight WINDOW needs the fuel level half way up the widow. If it has a sight plug (why anyone would still use a float bowl with a junk plug in it I do not know) then it just dribbles out. If you have the plug, how could you have the fuel level be half way up the plug???? It always was a piss poor way to set the floats because the fire hazard is just ridiculous.

If you don't have bowls with a window it's time to upgrade.


Again, Holley or Holley clones with a window the correct setting is half way up the window.
 
Makes sense, climbing down from limb now.:rolleyes:
 
The thing is, you can adjust the float level to wherever you want. There are two many variations to say it has to be a certain way. Fuel makeup and therefore density, air cleaner restriction (on the vents), engine angle, fuel pump pressure and many other variables all affect the fuel level in the float bowl. If it doesn't normally flood out your needles and seats are obviously working, so there is another issue. I have always adjusted mine to the bottom of the sight glass or opening, so that you can just see it if you rock the vehicle. You can also fine tune mixture by adjusting the float level. You are way better off too low, than too high and coming out the vents.

Drop the float level and I would bet your issue goes away. And stay away from ethanol laced fuel..... use real gasoline if you can get it.
 
Yes, all good points. The thing I think maybe got lost (in long winded post) in my case is that I've done over a year of driving and strip time with a Street Demon that I've tuned on extensively (seat time, strip time, and with the aid of wide band) , with none of the spewing issues, ever. Then one day, last week this cropped up. Went ahead with planned carb change for future plans, and it too is doing the same. I really suspect I have issues besides float adjustments. Certainly will look into though.
 
12many said:
Vent tubes clear, no obstructions etc. Anyone have a clue as to why all of a sudden fuel now sprays out the vents of two different carbs. under primary or wot acceleration, when the pump psi and float levels seem to be good? Tank pressurized, vacuum in tank? Plugged fuel cap vent, issue with either fuel pump?
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There's only two possible scenarios here.
The pressure is going higher than the inlet valves because the pressure has gone over 7 psi or so.
or
The inlet valves can't hold 6 psi.

If its happened on all two carbs, both bowls, its almost certainly a pressure control situation.
The next question is what's the cause.
I'd be looking at the regulation.
 
Plan is to run just the electric pump (bypassing the mechanical) through the Holley billet regulator, then vice versa as I've ditched the fluctuating junk pot metal Holley regulator. Tinkering is on hold for a few days, but plan was to hit strip this coming weekend. Hope I can get it sorted, and do some carb tuning finally!​
 
I'll agree with Mattax on this, if its doing the same thing across 2 carbs, its a pressure/regulator issue...

I'd look for a pressure spike as you jump on the gas...
 
Not but a few things that can cause this. Float level too high, too much fuel pressure, or dirty or defective needle and seat. That's about it.
 
RustyRatRod said:
Not but a few things that can cause this. Float level too high, too much fuel pressure, or dirty or defective needle and seat. That's about it.
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One would think, just baffling it literally happened like flipping a switch, I didn't do anything or make any changes. After it cropped up I took apart the Street Demon, floats settings good, the needle and seats were fine, the seats have screens on the inlet side to help prevent any particles from getting through, no dirt or debris anywhere. Did all the other checks mentioned, and still doing it, and then with the AED. Put on the new regulator, doing iit still, swapped the gauge, and the same. Honestly thinking the mechanical or electrical pump is where the problem lies. I'll know hopefully by Friday morning!
 
RustyRatRod said:
Not but a few things that can cause this. Float level too high, too much fuel pressure, or dirty or defective needle and seat. That's about it.
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Don't forget you can get a bad float. Sometimes they have just enough bouyance to handle small needle and seat opening, but when the float drops under load it's too heavy and won't close the needle.

Other than that...that's about it.
 
12many said:
One would think, just baffling it literally happened like flipping a switch, I didn't do anything or make any changes. After it cropped up I took apart the Street Demon, floats settings good, the needle and seats were fine, the seats have screens on the inlet side to help prevent any particles from getting through, no dirt or debris anywhere. Did all the other checks mentioned, and still doing it, and then with the AED. Put on the new regulator, doing iit still, swapped the gauge, and the same. Honestly thinking the mechanical or electrical pump is where the problem lies. I'll know hopefully by Friday morning!
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As I said in post 41 (before I read all the recent posts) you can remove both floats and weigh them. It's possible you have a bad float. Also, you can check them in a small can of fuel. If one floats better than the other, you have a bad float.
 
yellow rose said:
Don't forget you can get a bad float. Sometimes they have just enough bouyance to handle small needle and seat opening, but when the float drops under load it's too heavy and won't close the needle.

Other than that...that's about it.
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Then that would fall under float level, wouldn't it? <sticking tongue out>
 
Quick update, not spewing anymore. Removed mechanical pump. Drilled a big hole in fuel cap (very suspect as to creating a vacuum and/or pressure in tank but its the same one I've been running from the beginning) drained fuel, dropped tank, inspected filler tube, tank, pickup, hoses, Fram cartridge filter etc. Only running the Carter 4594 electric pump, billet Holley regulater thats rock steady 5.5psi at any rpm. Float levels left as they were, slightly less than 1/2 in sight window. No vent extensions added. Put in 5 gallons of Sunoco 112 for good measure. ******* finally ready to fine tune the *****! Fuel cap not venting or mechanical pump issue I believe, don't care at this point. It ain't doing it anymore. Yeehaw:steering:
 
12many said:
Quick update, not spewing anymore. Removed mechanical pump. Drilled a big hole in fuel cap (very suspect as to creating a vacuum and/or pressure in tank but its the same one I've been running from the beginning) drained fuel, dropped tank, inspected filler tube, tank, pickup, hoses, Fram cartridge filter etc. Only running the Carter 4594 electric pump, billet Holley regulater thats rock steady 5.5psi at any rpm. Float levels left as they were, slightly less than 1/2 in sight window. No vent extensions added. Put in 5 gallons of Sunoco 112 for good measure. ******* finally ready to fine tune the *****! Fuel cap not venting or mechanical pump issue I believe, don't care at this point. It ain't doing it anymore. Yeehaw:steering:
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Do you actually need the regulator with that Carter pump? I thought that part number didn't need it?

Glad you have the fire hazard under control.
 
yellow rose said:
Do you actually need the regulator with that Carter pump? I thought that part number didn't need it?

Glad you have the fire hazard under control.
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I'm pretty sure it was mainly for running that Carter Strip 6270 mechanical. At the beginning of assembling the fuel system I think I over thought what I really needed for my setup, insurance maybe, but really no need for a mechanical AND an electrical, I've got a spare electric pump in case Murphys law strikes.....
 
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