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Old 01-16-2020, 10:08 AM
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Carb Barfing Gas at WOT

I have a 81 Firebird with :
468" Olds (455" .060 over)
Comp Cams XR276HR-10 cam (224/230 @ .050 )
w/ 1.6 Harland Roller rockers
Forged Pistons
Edlebrock Heads (Triple port Job?)
Air Gap Dual Plane Manifold
750 cfm Holley HP Double Pumper
3.73 Positraction
28" tires / Slicks
Balanced rotating assembly

When I accelerate at a medium rate everything is Good up to 4500 rpm (new engine). If I stuff it, it goes thru first and second OK but t the top of 2nd or 3rd it spits fuel back up through the carburetor where you can see it and I get fuel on the windshield ( engine seems to almost stop and has some times? ).
Fuel pressure is between 6 & 7 lbs. Before the rebuild I ran this engine with a 1050 Holley Dominator on a single plane Edlebrock Victor Jr. and went 116 mph @ 11.31 (consistently) no problems.

Why is this happening? Any suggestions?

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Old 01-16-2020, 10:47 AM
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valve float?
cam advanced too much?
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Old 01-16-2020, 12:38 PM
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I'd guess it going dead lean from a fuel pump not being able to keep up or perhaps a tank venting issue, leaky fuel line, ect...
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Old 01-16-2020, 04:37 PM
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By "spits out" do you mean from the airhorn or the vents?

Whose springs are on the Edlebrock heads?

Whose lifters?

Bogie
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Old 01-16-2020, 06:20 PM
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To answer the question ... out of the air horn... thanks for the reply.. I'm new but have read this forum for a yr.. Jerry
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Old 01-16-2020, 06:32 PM
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I have a Mister Gasket 105P . I also forgot I have a MSD mech adv dist #8566 (blue springs), MSD 6AL-2 Digital Box, Blaster-3 Coil, 3" Balanced Drive Shaft, .....
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Old 01-16-2020, 06:38 PM
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wild guess;


rev limiter set to low


lifter pump up with rockers too tight
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Old 01-16-2020, 06:43 PM
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Quote:
Originally Posted by lmsport View Post
valve float?
cam advanced too much?
valve float not likely, but considered. i ran these same heads/cam etc on this engine before i bent a rod to 5800 rpm with no noticeable float. Usually shift at 5000 - 5500 rpm to max torque/speed/ET.
Secondly: Cam advanced too much. The Cam is set per specifications from comp cams so ??
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Old 01-16-2020, 06:47 PM
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Quote:
Originally Posted by MGK View Post
wild guess;




lifter pump up with rockers too tight
X2

Or slighly restricted exhaust
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Old 01-16-2020, 06:51 PM
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Quote:
Originally Posted by MGK View Post
wild guess;


rev limiter set to low


lifter pump up with rockers too tight
!- I don't use the Rev Limiter (not legal in my class) although it's hooked to a button on my dash and set to 1500 rpm.
Lifter pump-up: we just adjusted the Valves again and havent run it yet .... tomorrow.
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Old 01-17-2020, 12:29 AM
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Blowing mixture out the airhorn sure speaks to reversion. That could be crappy flow dynamic between the manifold and cam timing, but as mentioned sure could be an inability to seat the intake valves, hence my earlier question about what lifters are used with that cam, push rods, and valve springs, Edlebrock's springs and studs or someone else's.

If the fuel source is splash in the float bowls coming from the vent tubes which on a Holley are right above the airhorn, it could be a venting issue where the fuel refill is splashing up the vent tube. Hence Holley whistles in the float chamber and using lengths of tube to stand the vent higher or tie them together, as done on marine carbs with a Tee in the center that may connect to a longer tube to simply catch the splash using length.

Bogie
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Old 01-17-2020, 06:48 AM
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Bogie, Thanks for reflecting on my problem. I do have a new/different intake manifold. i'm using an Edlebrock RPM Air Gap Dual Plane and was using a Victor JR. Single Plane Air Gap Manifold and a Holley-HP 750 cfm now. I was using a 1050 cfm Holley Dominator on the Victor Jr.? Could a 1" Spacer help?

I thing I'm using Edlebrock Studs and Comp Cams Push Rods from the Kit.
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Old 01-17-2020, 12:12 PM
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4500rpm and fuel on the windshield isn't reversion. That's a lean sneeze.
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Old 01-18-2020, 08:27 AM
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What can be done to stop reversion? Anybody have a guess?
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Old 01-18-2020, 09:01 AM
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750 cfm may not be enough carb. You might be pulling the max fuel the jets will allow. Try throwing 10% larger jets in carb.
My 70 boss 302 came with a 780 cfm vac secondary.
Or you could put in some heavier power valves, but these wouldnt like the sneeze, probably blow out the diaphrams.
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