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Old 02-13-2013, 08:08 PM
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421 SBC not making power

New to site need help please!!! I have built several motors for fun over my life but never anything like this. I built a 421 SBC with 18 degree Brodix heads and matching intake. Bottum end is strong with all good parts. Solid roller custom grind cam.

Problem is is falls on its face in 2nd gear. 1st gear will bust the 7000 chip but 2nd gear feels like its running out of gas. Ive changed pump twice and im running half inch line from fuel cell to regulator.

Im starting to think its in the distributor. Any ides?

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Old 02-13-2013, 08:13 PM
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Need more specs.
What carb?
What cam & specs?
What fuel pump?
What ignition system?
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Old 02-13-2013, 08:16 PM
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Welcome to the board

Maybe it is running out of fuel so to speak, check your float levels and fuel pressure. Could be first gear is strong with enough fuel to be happy, by 2nd gear the bowls are starving? Just a thought. Any chance acceleration is pulling fuel away from the jets?
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Old 02-13-2013, 08:19 PM
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Have you tried bowl extensions? the 421 needs fuel,,,lots.
I used 1/2 line and a nascar style fuel pump.
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Old 02-13-2013, 08:32 PM
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Haven't tried those yet but I am running 1/2 line.
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Old 02-13-2013, 08:44 PM
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Re: 1/2 inch line? did you drop the tank and make the pick up bigger too?
Have you tried just slowly accelerating in second and hammering it after 4k to see if it revs to redline?
your engine will use 50 gallons per hour at WOT (depending on HP) that has to be delivered through the small #10 AN fitting or holley fitting,,,w/e you use to fill carb bowls
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Old 02-13-2013, 08:55 PM
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I am running a fuel cell that came with an 8n outlet. From a dead stop it will bow the tires off and bust the 7000 chip. Go to 2nd and nothing. Yes I can run down the road in second roll into it and its flat.
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Old 02-13-2013, 09:28 PM
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Does it stay flat or does it start to take off once you have enough rev's on it?
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Old 02-13-2013, 09:32 PM
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Is the fuel cell properly vented?Im grasping at straws,,,,try driving it with the cap off?
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Old 02-13-2013, 09:38 PM
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Yea tried that too left vent off
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Old 02-13-2013, 10:50 PM
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i would start simple and check vacuum first, then check your timing and total timing. make sure your timing advance is working
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Old 02-13-2013, 11:02 PM
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What kind of tranny?
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Old 02-13-2013, 11:33 PM
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you didn't say. but a few things,
1) is the pump an electric near the fuel cell?
2)if the pump is an engine mounted mechanical. thats problem #1
3) what type regulator, deadhead or return style?

here is why..
1) an engine mounted pump has to pull the fuel and pump it to the carb.. 1/2 fuel line has a lot of fuel to try to suck forward..
if using a deadhead regulator with no return line, the fuel stops when the psi is reached, then when your engine wants more fuel the pump has to get all that fuel to start moving.. at 1/2" in size thats a tall order for a mechanical pump.. and even most electric untill you get to race style pumps.. psi means nothing, volume is where it's at with that big a line..
like said, jet ex. and do you have a fuel pressure gauge hooked up between the regulator and carb?

also if electric pump, is it getting full voltage, a pump that surply that much fuel will draw lottsa amps.. it needs a large power feed or when the amp draw goes up. the voltage will drop.. and the pump won't keep up..

need more info.. but I'd look squarely at the pump and if electric the wiring feeding it..

if a deadhead regulator take it off, and sell it to the next guy with more of a stocker type build.. as you need that volume in the line to be moving at all times, because when you need it, starting to move that much fuel from a standing stop is a tall order for even the best pumps.. and pumps that push that much fuel will burn up with fuel not moving through it..
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Old 02-14-2013, 12:05 AM
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Since we are on the subject of fuel pumps and "IF" it is electric, where is the pump mounted? If it's mounted in the engine compartment, that's the incorrect location. Electric pumps have very little suction, they are meant to push the fuel, not pull. It needs to be mounted as close to the fuel cell as possible.
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Old 02-14-2013, 05:16 AM
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Yes it is electric and I have a 10 gauge wire ran to it. I have it ran through a relay off the switch. It's approx. 4 feet from the fuel cell under the truck.

Now the return line issue is very interesting. I am running a deadhead style regulator to the carb. I have 3/8 lines from each side of the regulator to each bowl but no return. I do have a pressure gauge inline and I'm on 7-8 psi.

I wasn't aware that the electric pumps stop after reaching pressure so to speak.
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