Carb or something else.
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Junior User
Joined: Sep 2009
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Carb or something else.
Hello, I will fill you in on what I have first. I have a fresh 390FE bored .030 with the scat stroker kit pushing out 431 ci. It has c8ae heads, gone over, new seats. Factory intake 4 barrel S code intake. 268h camshaft. Stock electronic ignition. Stock replacement fuel pump to Edelbrcok 1405 600cfm carb. My problem right now is that it will start, idles fine, revs up to 4 grand no problem, take it down the road at 70 miles an hour it runs alright, go to climb a hill and it spits and sputters, doesn't backfire, but loses power. Is this carb to small for this set up or do I have problems elsewhere. Timing is dialed in as best as I can tell. 12 initial, 38 total at 3000 rpms. I know a 600 would work on a stock 390, but since this is a bigger stroke, slightly bigger cam I was kind of under the assumption that maybe it needs more fuel delivery. Thanks for any help.
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Junior User
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I thought about PMing you. But yea, I've monkeyed with the metering jets, the step up spring. The floats are also adjusted in accordance with the book. And my fuel filter is clear and looks brand new yet. I'm not sure what pressure the fuel pump is pumping. It's new, and a stock replacement, but I don't have a regulator on it. It pulls through the gears really well without even giving it any throttle, just didn't like that hill. I don't know what grade it was but it was probably a 1/4 mile in length.
Hotshot
Joined: May 2003
Posts: 11,141
Likes: 25
From: south louisiana
With that intake, heads and cam and carb, I would think it would be pretty much done pulling at 4 grand. That's a really small carb for a 430 cubic inch motor. The jetting would need to go up several steps to keep up with the airflow thru the venturis.
Hotshot
Joined: Jul 2005
Posts: 13,834
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From: Middle Tn.
A Holley street avenger 770 cfm with electric choke and vacum secondaries would be ideal on your motor. That's what I have on my 428 cj and she loves it and gets better mileage than the stock 735 got.
Post Fiend
Joined: Apr 2008
Posts: 8,261
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From: Big Sky Country
Are you convinced this is a fuel starvation issue and not timing related? (I recall you having timing issues).
A properly jetted 600cfm carb should be adequate for your motor, unless you're spinning 5,000 rpm plus.
Are you running 5/16" or 3/8" fuel line to the carb?
Just a thought, but the Performer carb can be drilled/tapped at the (blocked) driver side inlet for a dual feed fuel line (like the Thunder series).
A properly jetted 600cfm carb should be adequate for your motor, unless you're spinning 5,000 rpm plus.
Are you running 5/16" or 3/8" fuel line to the carb?
Just a thought, but the Performer carb can be drilled/tapped at the (blocked) driver side inlet for a dual feed fuel line (like the Thunder series).
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New User
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From: Denver
I hope this isn't a completely stupid suggestion but could it be a voltage leak? They can present themselves when accelerating up hills or the vehicle is under load.
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Thread Starter
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Junior User
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Voltage leak isn't a stupid suggestion, because I'm not sure what that is exactly. It could be the timing yet, although I do have it set I haven't ruled it out. I was just more inclined to think it was fuel. I can definitely feel it pulling better on take off. If I get into it just a little bit (not too much since the motor is fresh) on a flat straight it feels good, no sputters. It just didn't like that hill. I was cruising 70mph at 3000rpm at the bottom of the hill. Halfway up it started to sputter, I eased out of it but it was still coughing and then finally it smoothed out and I was going about 50mph. I thought this was maybe because the carb ran low on fuel or something.
I also thought maybe my vacuum advance was pulling too far but I couldn't distinguish any pinging, not rattling or anything.
3/8 fuel line to the carb.
I also thought maybe my vacuum advance was pulling too far but I couldn't distinguish any pinging, not rattling or anything.
3/8 fuel line to the carb.
Post Fiend
Joined: Apr 2008
Posts: 8,261
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From: Big Sky Country
You didn't hear any pinging, and your initial/mechanical is already maxed out at 38 total, so you may need more vacuum advance than the stock (fixed) canister offers.
Hotshot
Joined: May 2003
Posts: 11,141
Likes: 25
From: south louisiana
That's really too much compression with that cam. Unless you're running 93+ octane, you may have detonation issues here that may just be your problem. Pull the timing back about 6 degrees and see if that helps. If it does, then work on the timing til you get it to run the best. I would do a cam swap to something with more overlap to bleed off the compression.
