1987 318 Tuning with Summit Carb

[sarguy01]

Okay, I'm stumped. Need some help with troubleshooting / tuning. Engine is a 1987 318 (135-145ish PSI compression and 302 heads) sitting in a Ramcharger. Cam is a Summit 6900, Edel 2107 intake, Summit M2008 600 CFM carb. I cannot get this carb adjusted correctly. I replaced a worn out Edelbrock after I had a tank of bad gas. I bolted on the Summit carb, and it was idling really rich (like 10:1 on the wideband), the idle mixture screws were turned all the way in, and the idle screw was all the way out (idle was around 1,000). It had .046 idle feed restrictors in it, so I then threw in .043 idle feed restrictors in all four corners, and those leaned it out to 13:1. But, the idle mixture adjustment screws still are all the way in, with the idle at 1,000 rpm, vac at 16. The idle adjustment screw is still all the way out and not contacting the stop. The secondary butterflies are adjusted to where the transfer slot is barely showing (it looks like a tiny square). Timing is set at 14 degrees with the vac disconnected (there's a limiter plate in the dizzy and I'm running an orange box). Floats are adjusted. No fuel dribbling out in the primaries or secondaries and the power valve is new.

I've checked the top of the intake for vacuum leaks and sprayed the hoses with water, propane, and carb cleaner, just to be sure. Can't find anything. If this sounds like a vacuum leak maybe I need to pull the intake and start over. I just had it off, but cleaned it well and then used gasket shellac to on the gaskets. Wonder if it's leaking from the bottom of an intake runner? The heads haven't been milled and I don't think the intake has been either.

Timing? I think it will take more initial as the RPMs will climb if I go to 18. Haven't tried any more than that. I checked the balancer about a year ago and don't think it's slipped.

I can also pull the carb and try the secondary adjustment again. Maybe it's getting too much air through the secondary transfer slot?

Thoughts?

 

[AJ/FormS]

Assuming the PCV is working correctly, and, the booster is working correctly;
Do this:

1) Advance the timing until the rpm plateaus, and more timing slows it down. I don't care what the number is.
2) Shut the engine off, take the carb off, open the choke and make sure it stays open, flip it upside down.
3) using the speed screw, close the primaries up tight, then, examine the secondaries to make sure they are also closed up tight. That cam on your low-pressure engine, does not need 4-corner idle, so shut it down. With the speed screw, open the primaries until the Transfer slot is about dead square, to a little bit taller than wide, just enough so that you can see it ain't quite square.
4) Flip the carb back right-side up. and
Open the PRIMARY mixture screws to 2.5 turns out
5) restore the carb to stock.
6) put the carb back on, fill the bowl, and
7) from now on DO NOT RESET THE SPEED SCREW.
8) start it up and retard the timing until it idles at 750/800, then let it warm up. I still don't care what the number is.
9) AFTER IT HAS WARMED UP, Idle it down some more with timing, about 50 rpm atta time until it goes lean for lack of transfer fuel, or you hit 650.
If the idlespeed gets to 650, that's pretty good; bump it back to 700/750 with timing, and check your oil-pressure. If over 10 psi, go look for a tip in sag.
If you get a tip-in sag at 2.5 turns out, add 50 rpm using the speedscrew.
If it goes rich, take a little out of the mixture screws.
If the rpm is too high or too low, change with timing, DO NOT USE THE SPEEDSCREW.
10) after you get it ticking over real nice, NOW, check the timing. It should end up in a window of about 12 to 18 degrees. Somewhere in the middle with a stock convertor, going to the high side is permissible if you have a hi-stall, and
a manual trans car will run better at low mph, if set to the low-side.
11) go to the back of the car, and smell the exhaust. If it stinks real bad and burns your eyes, the engine wants some bypass air.

BTWs
1) that cam, at idle, will lie to you all day long, about AFR. Set your AFR at ~2400 rpm no load, then let it idle at whatever.
Specs for that 6900, are 278/288/112/59 overlap, 204/214 @050
2) That 59* overlap is gonna mess up your intake plenum until at least 2200, so 2400 should be safe.
3) At just 140psi cylinder pressure, You're gonna need; at least hi 3-series gears or a hi-stall, or some combination; or a clutch.
> on the hiway, that cam will suck gas big time, unless you get the rpm up, and run plenty of timing. But around town it will be really bad. That's just the way those long period cams are, running low rpms at low cylinder pressure.

 

[AJ/FormS]

To test for vacuum in the valley;
put a Vacuum gauge on the dipstick, flip the PCV out of the grommet and plug the hole, them plug the breather. Start the engine but do not rev it.
If the vacuum gauge reads a vacuum, then yes the intake is sucking air from the valley.
If you get pressure there, which would be correct, do not let it get over 3>4psi, as that could blow out a seal. Don't panic, at idle it will take a while.

 

[MomsDuster]

The secondary butterflies are adjusted to where the transfer slot is barely showing (it looks like a tiny square).

Close the secondaries!
Set the primary transfer slots square.

 

[MopaR&D]

Close the secondaries!
Set the primary transfer slots square.

This, no need for the secondaries being open at idle on a mild 318. That's why you can't get it to idle slower and leaner.

 

[sarguy01]

Assuming the PCV is working correctly, and, the booster is working correctly;
Do this:

1) Advance the timing until the rpm plateaus, and more timing slows it down. I don't care what the number is.
2) Shut the engine off, take the carb off, open the choke and make sure it stays open, flip it upside down.
3) using the speed screw, close the primaries up tight, then, examine the secondaries to make sure they are also closed up tight. That cam on your low-pressure engine, does not need 4-corner idle, so shut it down. With the speed screw, open the primaries until the Transfer slot is about dead square, to a little bit taller than wide, just enough so that you can see it ain't quite square.
4) Flip the carb back right-side up. and
Open the PRIMARY mixture screws to 2.5 turns out
5) restore the carb to stock.
6) put the carb back on, fill the bowl, and
7) from now on DO NOT RESET THE SPEED SCREW.
8) start it up and retard the timing until it idles at 750/800, then let it warm up. I still don't care what the number is.
9) AFTER IT HAS WARMED UP, Idle it down some more with timing, about 50 rpm atta time until it goes lean for lack of transfer fuel, or you hit 650.
If the idlespeed gets to 650, that's pretty good; bump it back to 700/750 with timing, and check your oil-pressure. If over 10 psi, go look for a tip in sag.
If you get a tip-in sag at 2.5 turns out, add 50 rpm using the speedscrew.
If it goes rich, take a little out of the mixture screws.
If the rpm is too high or too low, change with timing, DO NOT USE THE SPEEDSCREW.
10) after you get it ticking over real nice, NOW, check the timing. It should end up in a window of about 12 to 18 degrees. Somewhere in the middle with a stock convertor, going to the high side is permissible if you have a hi-stall, and
a manual trans car will run better at low mph, if set to the low-side.
11) go to the back of the car, and smell the exhaust. If it stinks real bad and burns your eyes, the engine wants some bypass air.

BTWs
1) that cam, at idle, will lie to you all day long, about AFR. Set your AFR at ~2400 rpm no load, then let it idle at whatever.
Specs for that 6900, are 278/288/112/59 overlap, 204/214 @050
2) That 59* overlap is gonna mess up your intake plenum until at least 2200, so 2400 should be safe.
3) At just 140psi cylinder pressure, You're gonna need; at least hi 3-series gears or a hi-stall, or some combination; or a clutch.
> on the hiway, that cam will suck gas big time, unless you get the rpm up, and run plenty of timing. But around town it will be really bad. That's just the way those long period cams are, running low rpms at low cylinder pressure.

PCV works.

To note, the M2008 is based on a 4010 I think, but I suspect that should make too much of a difference from a 4160.

1. Done.
2/3/4/5. Done. Shut the secondaries. In order to get an "almost square" in the primaries, the speed screw is all the way out, like the screw isn't touching the stop. With it in one turn, it's a solid rectangle. I started at half a screw in to get a smaller rectangle.
6/7/8. Done, noted and done. Started and it ran at 1,000 RPM, timing was (I'm guessing here, I don't have timing tape, 22 degrees)
9. Done, timed it down to 650 rpm. Timing at roughly 6 degrees. It did not like revving up here, there was a big hesitation and it backfired through the carb. Got the RPMs up to 750 with the dizzy and timing was at 14.
10. Wideband (I get that a wideband on a carb is more for a guideline) said 10:1 at 750. At 2,600 RPM it said 12.8. Could smell the gas and see slight clouds coming from the exhaust when I revved it. So I started half a turn at a time with the idle screws and let it settle, then revved it up. Could not get rid of the stumble. Idle wandered slightly. Got another fireball through the carb.

I added 50 rpm using the speed screw with the idle mixtures at 1.5 turns, then adjusted idle with the dizzy. Still stumbling, still rich. I went backwards and took out 100 rpm using the speed screw, mixtures at 1.5 turns, still rich, still stumbles. Tried speed screw at the initial 1/2 turn for the small rectangle, idle mixtures down to 1 turn out, then adjusted idle with the dizzy to 750. Still stumbling, still rich. Then added 1/2 a turn on the speed screw and removed timing to bring the idle back down, stumbles, fireball.

For giggles, I turned in the idle screws now that the secondaries are fully closed. It died with one all the way in and the second only .25 turns out. I'm suspecting this carb is still too rich. Wondering if I need to drop the idle feed restrictions down again, but I'd need to order them.

Couldn't get the vacuum gauge to read steady at idle. Has a 1 inch wander up and down.

With the 600 Eddy, the vacuum was steady at 18. I replaced the Eddy after I got a tank of water / gas. I went to rebuild the Eddy but it had so much play in the throttle shaft I decided to try my luck with the Holley style. With the Eddy, it ran pretty good, but I felt there was a little more to be gained with the Holley.

 

[Hysteric]

It had .046 idle feed restrictors in it, so I then threw in .043

Are you sure they are that size?

 

[sarguy01]

Close the secondaries!
Set the primary transfer slots square.

Yep, done. I opened them up a little after a full round of failed tuning. The primaries can't be set square. Yes, it's not on the high idle. The screw has to be loose and not touching for them to be square.

 

[sarguy01]

Are you sure they are that size?

fanstastic question. I don't have a pin gauge, but I've got some .035 wire to use as a guide. Going to check soon, but I'm pretty sure the ones I pulled from the case were the smallest.

 

[sarguy01]

This, no need for the secondaries being open at idle on a mild 318. That's why you can't get it to idle slower and leaner.

So, in an attempt to try something out of sheer frustration, I opened them slightly after a round of adjustments with them closed. They are closed again.

 

[sarguy01]

To test for vacuum in the valley;
put a Vacuum gauge on the dipstick, flip the PCV out of the grommet and plug the hole, them plug the breather. Start the engine but do not rev it.
If the vacuum gauge reads a vacuum, then yes the intake is sucking air from the valley.
If you get pressure there, which would be correct, do not let it get over 3>4psi, as that could blow out a seal. Don't panic, at idle it will take a while.

Done. I plugged the PCV on the carb and pulled the vent on the other valve cover, and water vapor was coming out. I covered the hole anyway and used the vacuum gauge, but there was no vacuum.

 

[AJ/FormS]

Ok hang on, I musthave got my wires crossed. In though you had installed a Carter type carb.
With a Holley type carb, and the 6900 cam, the Mixture screw adjustment should be ~3/4 turn out.
But I'll say it again; MAKE SURE the choke is OFF and is NOT interfering with the curb-idle screw.

The Transfer slot is your main low-throttle-opening fuel circuit. At idle, with the secondaries closed tight You have to have a slot exposure AT BLEAST square, as said before, AND you have to add a lil from the mixture screws just enough to smooth the idle.
Theoretically, you can idle the engine on one or the other circuit. But, the carb will not function correctly either way; it must have enough transfer fuel to not have a tip-in hesitation, as you have found out.

Otherwise all that I said is the same.

 

[sarguy01]

Ok hang on, I musthave got my wires crossed. In though you had installed a Carter type carb.
With a Holley type carb, and the 6900 cam, the Mixture screw adjustment should be ~3/4 turn out.
But I'll say it again; MAKE SURE the choke is OFF and is NOT interfering with the curb-idle screw.

The Transfer slot is your main low-throttle-opening fuel circuit. At idle, with the secondaries closed tight You have to have a slot exposure AT BLEAST square, as said before, AND you have to add a lil from the mixture screws just enough to smooth the idle.
Theoretically, you can idle the engine on one or the other circuit. But, the carb will not function correctly either way; it must have enough transfer fuel to not have a tip-in hesitation, as you have found out.

Otherwise all that I said is the same.

No worries. I'll try that.

But now I've got bigger problems. I just put the Edelbrock back on after I cleaned it. Just wanted to see if it would run okay. Ran well for about 10 minutes. Revved well, took right off, no hesitation. After 5 minutes of driving at 45 mph, it started backfiring out of the tailpipes and is barely running. Almost didn't make it home. Any ideas? I'm going to check the timing and ignition system. Wondering if I need to do a compression check again.

 

[sarguy01]

Compression is good enough. 1 - 143, 2 - 147, 3 - 130, 4 - 137, 5 - 140, 6 - 135, 7 - 150, 8 - 142. I daily drove this thing in FL just up to a year ago and never had an issue. Plugs are caked in carbon, go figure. Wires, cap, rotor all seem fine and are less then 2 years old. Dizzy shaft feels fine.

I don't know why I took off fine and after 5 minutes it started backfiring as I was driving down the road.

 

[Bewy]

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.

 

[RustyRatRod]

Ok hang on, I musthave got my wires crossed. In though you had installed a Carter type carb.
With a Holley type carb, and the 6900 cam, the Mixture screw adjustment should be ~3/4 turn out.
But I'll say it again; MAKE SURE the choke is OFF and is NOT interfering with the curb-idle screw.

The Transfer slot is your main low-throttle-opening fuel circuit. At idle, with the secondaries closed tight You have to have a slot exposure AT BLEAST square, as said before, AND you have to add a lil from the mixture screws just enough to smooth the idle.
Theoretically, you can idle the engine on one or the other circuit. But, the carb will not function correctly either way; it must have enough transfer fuel to not have a tip-in hesitation, as you have found out.

Otherwise all that I said is the same.

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.

 

[Dan the man]

Assuming the PCV is working correctly, and, the booster is working correctly;
Do this:

1) Advance the timing until the rpm plateaus, and more timing slows it down. I don't care what the number is.
2) Shut the engine off, take the carb off, open the choke and make sure it stays open, flip it upside down.
3) using the speed screw, close the primaries up tight, then, examine the secondaries to make sure they are also closed up tight. That cam on your low-pressure engine, does not need 4-corner idle, so shut it down. With the speed screw, open the primaries until the Transfer slot is about dead square, to a little bit taller than wide, just enough so that you can see it ain't quite square.
4) Flip the carb back right-side up. and
Open the PRIMARY mixture screws to 2.5 turns out
5) restore the carb to stock.
6) put the carb back on, fill the bowl, and
7) from now on DO NOT RESET THE SPEED SCREW.
8) start it up and retard the timing until it idles at 750/800, then let it warm up. I still don't care what the number is.
9) AFTER IT HAS WARMED UP, Idle it down some more with timing, about 50 rpm atta time until it goes lean for lack of transfer fuel, or you hit 650.
If the idlespeed gets to 650, that's pretty good; bump it back to 700/750 with timing, and check your oil-pressure. If over 10 psi, go look for a tip in sag.
If you get a tip-in sag at 2.5 turns out, add 50 rpm using the speedscrew.
If it goes rich, take a little out of the mixture screws.
If the rpm is too high or too low, change with timing, DO NOT USE THE SPEEDSCREW.
10) after you get it ticking over real nice, NOW, check the timing. It should end up in a window of about 12 to 18 degrees. Somewhere in the middle with a stock convertor, going to the high side is permissible if you have a hi-stall, and
a manual trans car will run better at low mph, if set to the low-side.
11) go to the back of the car, and smell the exhaust. If it stinks real bad and burns your eyes, the engine wants some bypass air.

BTWs
1) that cam, at idle, will lie to you all day long, about AFR. Set your AFR at ~2400 rpm no load, then let it idle at whatever.
Specs for that 6900, are 278/288/112/59 overlap, 204/214 @050
2) That 59* overlap is gonna mess up your intake plenum until at least 2200, so 2400 should be safe.
3) At just 140psi cylinder pressure, You're gonna need; at least hi 3-series gears or a hi-stall, or some combination; or a clutch.
> on the hiway, that cam will suck gas big time, unless you get the rpm up, and run plenty of timing. But around town it will be really bad. That's just the way those long period cams are, running low rpms at low cylinder pressure.

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?

 

[junkyardhero]

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?

in the lexicon of carb tuning "to square the transfer" refers to bringing the throttle blade perpendicular (or there abouts) to the rectangular transfer slot thus making the effective area "square".

 

[Slantsix64]

You probably have bad gas

 

[sarguy01]

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.

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.

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.

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.

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?

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.

You probably have bad gas

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.

 

[RustyRatRod]

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.

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.


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.

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.

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.


Pics. First is secondary adjustment screw. Second is the carb for reference. Third, with the red circle above the butterfly, is a hole that starts to be shown with the idle speed screw one turn out. I have no idea if this hole should be exposed at idle or not. Fourth is the amount of transfer slot shown with the speed screw all the way out and the fast idle cam out of the way.

View attachment 1716274964

View attachment 1716274968

View attachment 1716274969

View attachment 1716274970

How new is this carburetor? If it's new enough to return, you shouldn't rule out the possibility that it could be defective. It happens more than it used to and Summit has an excellent return policy.

 

[sarguy01]

How new is this carburetor? If it's new enough to return, you shouldn't rule out the possibility that it could be defective. It happens more than it used to and Summit has an excellent return policy.

Hmmm....good point. They won't take it back since it's been installed, but I might be able to send it back under warranty. It came with a one year warranty.

 

[RustyRatRod]

Hmmm....good point. They won't take it back since it's been installed, but I might be able to send it back under warranty. It came with a one year warranty.

The hell they won't. I had a defective Quick Fuel carburetor that had an internal vacuum leak and I couldn't get it to idle come hell or high water. Sent it right on back. The next one worked fine.

 

[Newbomb Turk]

Okay, I'm stumped. Need some help with troubleshooting / tuning. Engine is a 1987 318 (135-145ish PSI compression and 302 heads) sitting in a Ramcharger. Cam is a Summit 6900, Edel 2107 intake, Summit M2008 600 CFM carb. I cannot get this carb adjusted correctly. I replaced a worn out Edelbrock after I had a tank of bad gas. I bolted on the Summit carb, and it was idling really rich (like 10:1 on the wideband), the idle mixture screws were turned all the way in, and the idle screw was all the way out (idle was around 1,000). It had .046 idle feed restrictors in it, so I then threw in .043 idle feed restrictors in all four corners, and those leaned it out to 13:1. But, the idle mixture adjustment screws still are all the way in, with the idle at 1,000 rpm, vac at 16. The idle adjustment screw is still all the way out and not contacting the stop. The secondary butterflies are adjusted to where the transfer slot is barely showing (it looks like a tiny square). Timing is set at 14 degrees with the vac disconnected (there's a limiter plate in the dizzy and I'm running an orange box). Floats are adjusted. No fuel dribbling out in the primaries or secondaries and the power valve is new.

I've checked the top of the intake for vacuum leaks and sprayed the hoses with water, propane, and carb cleaner, just to be sure. Can't find anything. If this sounds like a vacuum leak maybe I need to pull the intake and start over. I just had it off, but cleaned it well and then used gasket shellac to on the gaskets. Wonder if it's leaking from the bottom of an intake runner? The heads haven't been milled and I don't think the intake has been either.

Timing? I think it will take more initial as the RPMs will climb if I go to 18. Haven't tried any more than that. I checked the balancer about a year ago and don't think it's slipped.

I can also pull the carb and try the secondary adjustment again. Maybe it's getting too much air through the secondary transfer slot?

Thoughts?

Hang on a second…are you sure a 600 CFM carb has a .046 idle feed restriction?? What size is the idle air bleed?

I’m saying that’s a huge jet for that size of carb. Crazy huge.

I start at .029 ifr and a .070 air bleed.

If that’s the size it is, imho you’re going to need to drop the ifr way more than you did.

 

[sarguy01]

Hang on a second…are you sure a 600 CFM carb has a .046 idle feed restriction?? What size is the idle air bleed?

I’m saying that’s a huge jet for that size of carb. Crazy huge.

I start at .029 ifr and a .070 air bleed.

If that’s the size it is, imho you’re going to need to drop the ifr way more than you did.

Stock the Summit came with four .046 idle feed restrictors on primaries and secondaries. I don't know that this model carb has screw in idle feeds. But I think I am confusing myself here. Question - A bleed is what allows air into the idle circuit and a restrictor allows fuel into it, correct? Then maybe I've got my terms messed up. I went smaller on the bleed, from .046 to .043 and it went from rich to rich, lol. I thought that smaller on the bleed meant leaner, but as I'm sitting here googling stuff, bigger hole (more air) on the bleed will lean it out. I went backwards. The reason I was calling it a restrictor was because the Summit spec sheet states "Idle Feed Restriction" as .046. I'm thinking terms are messed up, so I took pics. So maybe I'll throw in a .049 and see if that leans it out.

In the pic, circled in red, are what the Summit spec sheet calls idle air restrictors. They came as .046 and I went to .043. I believe these allow air into the system, so going smaller will richen and bigger will lean.

As far as the rest of the carb, I'm not even sure where the idle circuit pulls fuel from.