Spark plugs black
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It wants a lot of timing at idle. I think because it’s so rich. I tried that method where you increase your idle timing for highest rpm and Hughes vacuum then back off 2 inches of vacuum and 200 rpm. I was at almost 48 degrees at idle. It was smooth. I figured locked would be fine. I confirmed the timing with 2 regular timing lights. No light. My balancer has marks to 50 degrees. I confirmed TDC like 10 times.
What accelerator pump cam should I be using? Off white cams on the #1 hole right now.
sorry for the back to back posts.
What accelerator pump cam should I be using? Off white cams on the #1 hole right now.
sorry for the back to back posts.
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9,814 Posts
White cam in the number 1 hole is a generic middle road and probably fine as is.
Another idea, take off the carb spacer. It's hurting the carb signal.
Another idea, take off the carb spacer. It's hurting the carb signal.
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236 Posts
I didn’t think to remove the spacer. I only added it due to the PCV and brake booster ports hitting each other. I figured it would be ok because this Edelbrock air back having that cutaway allowing the left and right sides to be open to eachother.
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236 Posts
What are your thoughts on high initial timing theory and big cams? I read a few articles where they say, “Give it what it wants at idle”. That no load conditions won’t cause problems as long as the timing drops back down off idle. My car idle the best at 48 degrees. And yes, TDC has been confirmed and timing has been confirmed. A lot. I was too scared to run it like that so I dropped it to 36.
my timing is electronically set to function like this. Imagine the distributor locked out at 36 degrees with vacuum advance hooked to ported.
my timing is electronically set to function like this. Imagine the distributor locked out at 36 degrees with vacuum advance hooked to ported.
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9,814 Posts
Simple.
ignotion lead is added to start the burn process early enough that maximum pressure is produced when the piston/rod/crank is position to make best use of it.
Give it what it wants.
With mechanical devices, we have to compromises to make. We sacrifice slow speed timing for proper timing at high speeds and a curve is the best way to adjust it with the weights and springs. When electronics take over we don't have the same compromises so you can make it whatever it
Needs to be for the throttle angle, rpm, and loads.
On our competition engines we always lock timing to whatever makes best power. Nothing else is a concern.
Street rides can't get away with that because high timing and high loads break things.
Imma say use the electronics to the best you can to get the timing that makes the most power at all loads and rpm's you need.
Thinking modern computer operated cars. There's enough information being fed to the timing gods that can give the timing curves at 100rom increments, at all throttle positions and engine loads from 750-redline. You can't do that with a dist only looking at rpm and vacuum, but you can realize you have more control than the weights and springs of yesterday and it's one direction progressive style graphing curve.
ignotion lead is added to start the burn process early enough that maximum pressure is produced when the piston/rod/crank is position to make best use of it.
Give it what it wants.
With mechanical devices, we have to compromises to make. We sacrifice slow speed timing for proper timing at high speeds and a curve is the best way to adjust it with the weights and springs. When electronics take over we don't have the same compromises so you can make it whatever it
Needs to be for the throttle angle, rpm, and loads.
On our competition engines we always lock timing to whatever makes best power. Nothing else is a concern.
Street rides can't get away with that because high timing and high loads break things.
Imma say use the electronics to the best you can to get the timing that makes the most power at all loads and rpm's you need.
Thinking modern computer operated cars. There's enough information being fed to the timing gods that can give the timing curves at 100rom increments, at all throttle positions and engine loads from 750-redline. You can't do that with a dist only looking at rpm and vacuum, but you can realize you have more control than the weights and springs of yesterday and it's one direction progressive style graphing curve.
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236 Posts
That makes sense because I just read on a fuel injection tuning forum where this tuner set up a big cam small block with coil on plug ignition to idle at 48 degrees. Then above idle, the timing was traditional. 36 all in at 3000 and simulated vacuum advance 12 degrees.
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236 Posts
Update:
This is an update to my fouling plugs, misfire, primary throttle stumble, and rich idle.
One of you guys recommended trying with the secondary idle mixture screws closed all the way. I set them to 1/2 like a few of the guys did on the Chevelle site. I set the carb via highest vacuum with the primary mixture screws only. I ended up at 1.5 turns. That cleaned it up a lot. I mean a lot. Stumble remained. I learned that opening the secondaries anymore that 1/4 turn caused the stumble. I left them at 1/4 turn. In order to maintain my 900 rpm idle, I needed the primaries open 3/4 turn at .030 transition. It likes .020 better because it will stall if I close any of the 4 mixture screws, but idle would be too low. At .030 transition it will only stall if I close the front mixture screws. I can close both secondaries all the way and it will still run. It runs rough but runs. The secondaries still respond, just no stall. I left them at 1/2 turn anyway. This carb really likes this set up. AED said just because it doesn’t stall when closing mixture screws is not the whole picture. It runs cleaner now with no stumble.
i do have a small RPM dependable misfire. It started the second I installed these Autolite 3924’s. I’m switching to FR5’s soon pmug an oil change. Draining the 5w-30 Lucas break in oil for SAE 30 lucas breakin oil. I’m still.burning a little blue smoke at full temp under load.
have to wait though. I blew the radiator, so more delays.
also, call me crazy. I know this goes against the carburator gospel, but I swear that switching the primaries from 77 jets to 75 helped clean up my idle.
what do you guys think? Any issues with the above settings?
This is an update to my fouling plugs, misfire, primary throttle stumble, and rich idle.
One of you guys recommended trying with the secondary idle mixture screws closed all the way. I set them to 1/2 like a few of the guys did on the Chevelle site. I set the carb via highest vacuum with the primary mixture screws only. I ended up at 1.5 turns. That cleaned it up a lot. I mean a lot. Stumble remained. I learned that opening the secondaries anymore that 1/4 turn caused the stumble. I left them at 1/4 turn. In order to maintain my 900 rpm idle, I needed the primaries open 3/4 turn at .030 transition. It likes .020 better because it will stall if I close any of the 4 mixture screws, but idle would be too low. At .030 transition it will only stall if I close the front mixture screws. I can close both secondaries all the way and it will still run. It runs rough but runs. The secondaries still respond, just no stall. I left them at 1/2 turn anyway. This carb really likes this set up. AED said just because it doesn’t stall when closing mixture screws is not the whole picture. It runs cleaner now with no stumble.
i do have a small RPM dependable misfire. It started the second I installed these Autolite 3924’s. I’m switching to FR5’s soon pmug an oil change. Draining the 5w-30 Lucas break in oil for SAE 30 lucas breakin oil. I’m still.burning a little blue smoke at full temp under load.
have to wait though. I blew the radiator, so more delays.
also, call me crazy. I know this goes against the carburator gospel, but I swear that switching the primaries from 77 jets to 75 helped clean up my idle.
what do you guys think? Any issues with the above settings?
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22,051 Posts
If you study the fluid route through the metering block, you can see how jet changes will have no effect on idle.
What is more likely is the removal and retightening of the float bowl and bowl screws created a better seal at the metering block-to-main body gasket and sealed up a cross leak.
I've got no issues with the different primary and secondary mixture settings. If you've got the idle cleaned up leaner to where you are happy with it, now tune the stumble away with pump cam and pump squirter changes.
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236 Posts
I agree with you. I get it. I’m thinking it’s psychosomatic. More wishful thinking.
What cam do you recommend and what position? I have the white cams now in hole 1 with 31 squirters on both sides. Idle is at 900 ROM’s so I’m guessing hole 1? I was going to try the ORANGE cam still in position 1 and if that doesn’t work, a 35 squirter in the front. I don’t get a stumble from idle to WOT. I only get a stumble when I quickly go from idle to max primary opening without going into the secondaries at all.
What cam do you recommend and what position? I have the white cams now in hole 1 with 31 squirters on both sides. Idle is at 900 ROM’s so I’m guessing hole 1? I was going to try the ORANGE cam still in position 1 and if that doesn’t work, a 35 squirter in the front. I don’t get a stumble from idle to WOT. I only get a stumble when I quickly go from idle to max primary opening without going into the secondaries at all.
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i'd do the pump cam first, just in case it may manage to be enough, but would also expect to need a squirter change too.
Orange then 35 sounds good....I've taken a lifetime's of left-over 25's and re-drilled them to in-between sizes Holley doesn't offer.....made several 33's.Pin vise and #61-80 drill set.
Holley offers a 32 but you don't typically see them around.
Trial and error is about the only way to find the sweet spot.
Orange then 35 sounds good....I've taken a lifetime's of left-over 25's and re-drilled them to in-between sizes Holley doesn't offer.....made several 33's.Pin vise and #61-80 drill set.
Holley offers a 32 but you don't typically see them around.
Trial and error is about the only way to find the sweet spot.
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236 Posts
Wealth of knowledge. So orange cam first then 35 squirter on the front.
Should I do both cams orange?
Both squirters to 35?
What hole being that I’m at 900 rpm idle.
Should I change my spark plugs first? Incase this is a misfire issue causing the stumble? If that’s even a possibility. I developed a small misfire as soon as I installed these Autolites 3924’s.
Should I do both cams orange?
Both squirters to 35?
What hole being that I’m at 900 rpm idle.
Should I change my spark plugs first? Incase this is a misfire issue causing the stumble? If that’s even a possibility. I developed a small misfire as soon as I installed these Autolites 3924’s.
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Its been stated 100 times before you MUST SORT OUT THE IGNITION before you do anything with the carburetor.
Many "carburator problems" are related to a poor ignition. I've said it up there....others have said it.....believe it....
When you get your plugs in, you'll need to go back and do the carb over again.
Many "carburator problems" are related to a poor ignition. I've said it up there....others have said it.....believe it....
When you get your plugs in, you'll need to go back and do the carb over again.
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22,051 Posts
Yeah, fresh plugs first and foremost.
If needed...
Pump cam and squirter changes on the just the primary first, since you said no stumble if the throttle is opened enough to bring the secondary's in.
If needed...
Pump cam and squirter changes on the just the primary first, since you said no stumble if the throttle is opened enough to bring the secondary's in.
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