Holley fuel problem

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MTXRACER
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Holley fuel problem

Post by MTXRACER »

Ok guy's. I don't post very often on here but I'm alway's lurking, this time maybe someone can help me?
Last year's combo was;
car weight-3000 lbs.
engine- 355cu.in.13.5 compression,Dart spotsman heads, 1.75 header's 750 carb, Team G intake, lunati cam, 259/266 @ .050 with.600 lift,42 degree's total.
Car ran 1.497/1.51-60 foot's, 11.17 @ 122.5 MPH.
Changed to Edelbrock aluminium heads and 1.825 header's everything else the same except timing backed down to 36 total.
Car won't launch now. loades up till 4500. boosters start dropping fuel @ 2400 rpm in neutral and 1700 in gear. It never did this before. Carb fuel level's are down 2 flats below window in the rear bowl, and 3 flats in the front. I just have too much signal at the boosters. Tried an 850 carb with modified boosters and throttle shafts, same thing, tried my friend's carb with a proform body that run's 10.80's and it's no different.
I'm at a loss, anyone got any idea's. fuel pressure set at 8 lbs.
Thank's Tim
MTXRACER
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holley fuel problem

Post by MTXRACER »

doesn't anyone have any ideas.
SchmidtMotorWorks
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Post by SchmidtMotorWorks »

By any chance do all the carbs you tried have power valves with similar numbers?
I have seen where retarding the timing on an engine reduced the vacuum and opened the power valve. Also made it have problems to idle in gear.
MTXRACER
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holley fuel problem

Post by MTXRACER »

2 of the carbs have plugs and the other a power valve. i tried retarding and advancing the timing also with no luck.
SchmidtMotorWorks
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Post by SchmidtMotorWorks »

Are you using a different spark plug than before? I've seen too hot of a plug make an engine run really bad. One time I put a Champion 13 heat plug where I usually ran a 9 just to see what would happen, the first symptom was after letting off the throttle the engine dies for a second then catches on again. After that it slowly ran worse and worse as the plugs fouled out.

What kind of distributor and coil? I have had shorts go through rotors, caps, and coils that felt like fuel load-up. Is your distributor cap on straight? Sometimes the notch doesn't engage but you can turn the latch screws.

Did you change the position of the fuel regulator?

Is your engine grounded OK?

What kind of air filter? Any change there?
MTXRACER
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holley fuel problem

Post by MTXRACER »

I am using NGK-8 plug's as per NGK rep.
Am running all MSD ignition, there has been no change in pressure regulator. The engine is grounded directly to the battery and frame. I don't run an air filter, and there has been no changes to the induction system at all.
Thank's Tim
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Post by SchmidtMotorWorks »

What do the plugs look like if you take them out just after the egine sounds loaded up? How about the inside of the headers and exhaust ports?
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Post by bill jones »

-You never said what the rpm was that your nozzles started to flow with the Dart heads and the Team G manifold.
-It sounds like you have dropped the float levels compared to when you had the Dart and the Team-G.
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-But the way I see the issue is why does the engine bog now and it didn't before?
-I personally feel fuel pressure is too high, regardless of what you think or what everybody else is telling you.
-If you'd take the float bowls off and measure the float levels with a dial caliper (bowls inverted) I like to know what the numbers are: primary and secondary.
-The O-rings on the OD of the needle/seat housing can leak and they need to be replaced when you can't feel the resiliency or the drag they create against the housing when you screw the housings in.
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-You are attempting to put blame on one of three things.
-1 is the heads.
-2 is the headers.
-3 is the booster nozzle pull over rpm.
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-Why did you retard the timing 6 degrees when you went from cast iron to aluminum?
-I don't see any logic to that at all.
-How can you blame the booster pull over point when you never told us of what you had before? we have no comparison as to what you had before.
----------------------------------------
-Retarding the timing would require more air thru the carburetor just to make the engine try to idle at the same rpm.
-The larger headers would basically do the same thing, hurt the bottom end and make the performance poor requiring the throttle to open even further at idle and at part throttle.
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-So if the throttle blades are open further up onto the transfer slots the you have fuel gushing from the slots plus you have the maybe 20 to 40% more actual air flowing thru the primary barrels which will start the booster pullover that much sooner.
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-I think that you need to look at:
a-the exposed slot length/s of the primary barrels and get the blades back down so that only .020" in length is showing, which means you need to get the idle air from somewhere else, particularly like use a PCV system or make an adjustable idle air bypass like BG is finally doing.
b-bump the timing back up and know exactly what the timing does in 500 rpm increments below 4500 rpm.
c-try the old headers to see what happens.
d-know what the dial calipers say about the float levels.
e-drop the fuel pressure to about 5.5 pounds at WOT at max rpm in high gear.
f-install new O-ring on the needle & seat housings.
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-High float levels, leaky O-rings, high fuel pressure, and too much idle air being brought in the thru the primary throttles (far any of another dozen reasons) , hot fuel and fuel evaporation rates of various fuel blends, and the orientation of the spray out from the needle and seat housing windows into the bowls all can change the booster pullover starting point rpm.
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Post by SchmidtMotorWorks »

Good point about the fuel pressure.

I made this test set-up with a floatbowl covered with a piece of glass on a and a valve to drain the fuel in a tank to try to figure out how much fuel pressure was needed to keep the bowl full at different fuel consumption rates. I was also interested in how much the fuel foamed due to high pressure.

I found that it was difficult to get the fuel to stop flowing about about 7.5 psi, it was worse if there was vibration involved. This is from memory of 15 years ago. I don't remember what the seat hole diameter was, it was from a Pro Stock from the late eighties making somwhere around 1000 hp (as I recall, sounds so small now)
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