1987 318 Tuning with Summit Carb

Bewy said

I don't know why you removed a good carb: the Edel?????

So the E carb ran well for 10 min? That shows that it runs.
Maybe you got some dirt in the needle & seat when you re-fitted the E carb, now flooding.

But you also played with the timing. Check reluctor air gap.

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I know, I'm bouncing back and forth troubleshooting. I figured I'd give the Edelbrock a shot again since it was somewhat of a known quantity. I had it idling and running fine, then all the sudden it acted very lean at idle and with my foot on the gas. Wideband read like 14-15:1 when I limped it back home after the test drive. No clue why when I started driving it had enough fuel then all the sudden went lean. Maybe I've got a vacuum leak. Or maybe I'm an idiot and forgot to check to see if the choke was open...I threw the Eddy on and started adjusting it immediately, then started driving. If I adjusted it with the choke closed, then it opened as I was driving down the road, that would cause it to go lean. That's what I get for tuning when tired.

I'm pulling the dizzy. Takes 5 minutes to check. Plus I've been meaning to slow the curve a little more on it, so it needs to come out anyway. It's a Proform model that I put in when I pulled the stock Spark Control Computer. I have read that Proform basic dizzys aren't the best, so maybe I've worn mine out already and it's giving me inconsistent or weak spark.

RustyRatRod said

No, it's neither a Holley OR Carter style. He gave you the part number. Did you even bother to look it up? It's a Summit carburetor modeled after the old Ford Autolite four barrel. Do you know anything about those? If not, you're sending him down an unnecessary rabbit hole trying to show everybody how smart you are(n't). That's why I didn't respond. I don't know a thing about how those carburetors tune.


To the OP, I will say this. Holley (and everyone else) says the transition slots being square is a STARTING POINT, so keep that in mind. You may need "less" of a square, or you may need "more" of a square. I wouldn't box myself in trying to hold it to square. Also, IMO, you should play around more with the timing. You said it would idle up more when you pulled in 18 initial. So just for curiosity's sake, try pulling in timing until it stops idling up. You'll know when. It will start running "rough" when it gets too much. At that point, back off on the timing until that extra roughness clears up. This is really easy to feel for if you'll have your hand on the valve cover when you are pulling in more timing. You'll feel it, trust me.

Also, I see you said you closed the secondaries? HOW did you do that, exactly? I know. Seems like a dumb question, but here is how "I" 100% verify they are closed all the way. I adjust the screw until they close AND stick closed. Then, I carefully turn the screw a LITTLE at the time until the secondaries JUST BARELY don't stick closed anymore. From your description, it almost sounds like they might be a little open still. Might be worth checking into. That's a pretty mild cam and IMO should have more like 18 or maybe a little more hg vacuum at idle and it doesn't. That tells me maybe it needs a little more initial timing.

You might also play around with full manifold vacuum on the vacuum advance, but don't do that now. Work over what you have again and see. Just some ideas. Good luck and keep us posted.

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I understand that the speed screw and the transfer slots need to be adjusted. Before I made a post I spent a bunch of time adjusting the idle speed screw and the mixture screws. The thing that throws me off is that if I keep the speed screw open more than a turn, it will still run with the idle mixtures shut or barely open. I think it came out of the box open 1 to 1.5 turns. The way I understand the idle bleed screws is that they feed the circuit and the idle mixture screws fine tune the circuit. Still wondering if they idle bleeds need to be dropped another size or two.

Please see the attached pic. The red circle on the base of the carb shows where to adjust the secondary butterflies. They did stick too far closed, so I turned the screw enough where opening the secondaries felt smooth. But the slots are still covered 100%. It is a mild cam and when this thing ran well before I got water in the gas vacuum was up at 18-19 ad idled very smoothly. Now it's been idling with a slight RPM variation.

Timing is on the list to play around with still. But I feel like this thing should run somewhat well with initial timing anywhere between 8-16ish, based on tuning the Edelbrock 2 years ago when I put the 4 barrel on.

Dan the man said

You mentioned that the transfer slot being square, how can this be when the transfer slots are machined into the baseplate of the carburetor. I don't have the knowledge or experience with carburetors like the guy's on here do. Just exactly what is adjusted when you guys are talking about this, how's it adjusted?

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So for the primaries, by turning the idle speed screw, you are essentially showing more or less of the transfer slot. Only way to see how much is to pull the carb. On my Summit carb, there's a secondary adjustment screw on the bottom of the carb. Turn it in and it opens the secondary butterflies a bit and the transfer slot will start to appear.

Slantsix64 said

You probably have bad gas

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Yeah, I thought about that. Current gas is 89 octane (whatever the ethanol content is) with Stabil. Probably a month old mixed with older gas that was left in the tank. So it could be a gas issue. Maybe I'll pull a sample and see what it looks like.


Secondary adjustment screw.



Carb for reference.



The red circle above the butterfly, is a hole that starts to be shown with the idle speed screw one turn in. I have no idea if this hole should be exposed at idle or not.



The amount of transfer slot shown with the speed screw all the way out and the fast idle cam out of the way.