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Unread 02-25-2011, 01:23 PM   #1
kcaverly
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Chevy 350 Edelbrock Carb set-up

Hello,

I just swapped a 350 into my YJ and it nows runs and drives. I am having some issues though with getting it driving nicely.

I have an edelbrock performer 600 cfm (P/N #1405) on top of a mild/stock 350 out of an '86 caprice police edition.

Edit: installed WbO2 sensor, and I know it's running lean from idle all the way up. Now I just have to figure out why.

It idles nicely, then if you ease on the gas it picks up, then sputters, then picks up again, then sputters. It does this consistently any time I'm around 1/4 throttle, and it doesn't get through it. If I give it more throttle, it picks right up and goes great, but then if I back off to 1/4 throttle again she does the same sputtering.

I've played with the Idle Mixture Screws, and they can help to a degree. When I started it just fell on its face, now it at least stays running, and it idles better, but I can't get that sputter to go away.

I'm not that familiar with automotive carbs, I've put in my time on motorcycle carbs though so I know the principles, just not the systems this 4 barrel uses.

If anyone can help me out, that'd be great.

Kevin

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Unread 02-25-2011, 05:25 PM   #2
colojeepguy
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If you're lean all the way through the RPM range, you could try a bigger jet size. Also I think a heavier power piston spring might help your part throttle stumble.
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Unread 02-25-2011, 06:45 PM   #3
slowlowford
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If you go to the Edelbrock page, they have a good instruction manual that will tell you how to set them up. I have not messed with one for a while. I will do some reading. What kind of vacuum are you pulling at the ports and has any of the metering rods or springs been changed?
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Unread 02-27-2011, 07:03 PM   #4
kcaverly
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Well I pulled it apart and checked float level, it was pretty darn close, set it properly. Then checked the jets and found out the PO had gone down from a .100 main to a .089, and messed with the rods too.

I ordered the basic jet set-up, so we'll see how it goes when that gets here wednesday. It's a very easy carb to mess with, so if it's not spot on I'll probably get the calibration kit and dial it in.

Kevin
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Unread 02-28-2011, 11:13 AM   #5
slowlowford
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For your motor the stock setting should be good. You might just need to change the rods a few steps, but I highly doubt it.
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Unread 03-03-2011, 12:16 PM   #6
kcaverly
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You were right. Stock jets/rods and the beast runs like a champ. Now I have to get a set of springs though.

PO had the stiff silver springs in there, when it seems like they should be the medium orange. Changing the rods I dropped one of the springs, so now I have a clicky pen spring in one side.

Thanks for the tips.

Kevin
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Unread 03-03-2011, 03:59 PM   #7
slowlowford
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Cool, glad to hear it. Now if II could get mine figured out. I think my carb is bad though.
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Unread 03-04-2011, 07:59 AM   #8
kcaverly
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I thought I had it figured! Some tuning left to be done on mine. I love having the wideband though, it makes sure I'm not running off in the opposite direction.

Anyways, it idles great at around 15:1, and if you get on it hard it drops to low 13's:1 and really moves, but if you're just cruising, it runs fine, but it's really lean, 16+:1 and that makes me nervous. Mind you, most of my carb fine tuning experience recently has been on classic high strung two-stroke street bikes, where leaning fuel ratio also reduces the oil.

That to me sounds like I need to move to rods that are the same in power, but richer in cruise. Make sense to everyone?

Also, I got on the highway and really let 'er rip and after 5-6 seconds at 13:1 making good power the gauge swings all the way over to 16+ and power drops off. I'm thinking I'm draining the carb bowl, make sense?

Thanks,
Kevin
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Unread 03-04-2011, 02:44 PM   #9
TXvodoo
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My edelbrock has been doing the same thing so i'm thinking of changing to a holley. I'll be taking it to my engine builder for the new motor build and tune soon, maybe he can enlighten me why its acting like that.
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Unread 03-04-2011, 05:35 PM   #10
kcaverly
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"The same thing" being running out of fuel when you stay on the gas hard for a while?

I'm pretty sure that's the engine drinking fuel faster than the pump is re-filling the carb bowl. A holley won't change that unless it has bigger bowls, and that's just masking the problem. A larger bowl will let you go longer, but really the only answer I know of is a higher flow fuel pump.

As I've mentioned I'm not a real car carb guy, but that's the solution for snowmobiles that do that.
Kevin
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Unread 03-04-2011, 06:12 PM   #11
slowlowford
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I your pump should flow enough for a stock 350. I ran a built 302 shooting 75hp of NO2 with a stock ranger fuel efi system. I am going to pull out my notes and get back up to speed. You will probably need rods. I think whats happening is when you first hit the gas the accelerator pump provides enough fuel to run good then peters out. When you meter pegs does you motor start missing or popping? Are you still using the Jeep fuel system, and what fuel pressure regulator are you running?
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Unread 03-04-2011, 08:13 PM   #12
kcaverly
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Thanks a lot. The experience people have (and share) on this site is just awesome.

I have a mechanical pump on the block that feeds the carb. It draws and returns through the stock Jeep fuel lines, and the stock pump, which is still in-tank but not powered. This could be restricting it, I'm not sure.

When the meter pegs, the motor starts lunging. It loses power, then surges forward again, then drops. It does this until you let off the gas and give it a break, then it'll be happy to give'r again for a bit.

I can try rods, I have some that are 8% richer in power mode but the same in cruise. I think I might as well get the kit as I know I need to richen up in cruise as well. Maybe I should go up a jet size then if it has to be richer in both?

How long does the accelerator pump shot last. I know its done shooting as soon as the pedal stops going down, so I figured maybe 1-2 seconds of engine burn on that extra gas. I tried counting how long the motor ran well for, but then I had a vacuum line get stuck in the linkage and the throttle got stuck almost wide open and I was on a highway and ..... anyways, things got a little crazy and I forgot the count, but it ran well (and had good A/F) for at least 6 seconds before surging, which I thought was longer than the pump would provide.

Kevin
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Unread 03-04-2011, 09:11 PM   #13
slowlowford
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Is your block mounted pump the type that has the return built into it? Pulling through your electric could be causing a problem. I have seen it done before just never tried it myself.
What rods do you have? In order to get it 8% rich in both modes you need to change rods and jets. Sorry, if you already know this but here is some info: Power mode is when you floor it, but not WOT, your vacuum is low and rods are up. Cruise mode in normal driving. Vacuum is high, and rods are down. This is where the springs can change things. I have never seen much of a difference in changing springs, but people have.
But 8% is what I was thinking.
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Unread 03-04-2011, 11:38 PM   #14
kcaverly
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The block mounted pump does have a return line off it.
I am unsure about pulling through the electric, but I really don't want to drop the tank right now. It's a bit tough sometimes with it being a DD to do the work that maybe should be done.

The rods in there now are the "stock" 070x047 and I have rods that are 070 x 037. The edelbrock manual lists them as stock in cruise, 8% rich in power. I'll give them a shot and see if it helps the full throttle issues. If not, then I'll know that it's a fuel supply issue. If they do, then I should be able to figure something out from there.

Another thought I just had. How long do the vacuum secondaries take to open? Could I be lean on the secondaries and when they kick in is when it goes lean? That could explain the surge, as engine speed is climbing, they open, it goes lean, engine slows, they close, repeat? Make sense or am I making things up?

Kevin
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Unread 03-05-2011, 08:07 AM   #15
slowlowford
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Your carb was the 1405 correct? If so the The 070x030 will only richen up the power mode by 8% not the cruise mode. It will match up with #3 on the chart. 8% in both will put you at #15. Using these rods might determine if 8% will help though. But only when you get into it not riding around.

I think the secondaries time, vary depending on engine load. They work more like a quadrajet not like mechanical secondaries.

When you have a serge it can mean lean or rich. Since you have the WB that takes the guess out. It is always safer to err on the side of lean though.

As far as the fuel pump I would personally hook up the electric pump, but then you will need to get a regulator with a return. On a side note, per Edlebrock the performer carbs are not really for off road, you should make some modifications with the float level and something to do with the needle and seats.

Sorry I cant be more help right now, but not knowing the fuel pump situation its really hard to guess, but I would give those rods a try and see.
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