383 SBC Holley 750 eye burning stinky idle

[PRNDL]

i would get NGK #5671A-7 spark plugs. Also listed as part number 4091

Brian

Ok will do Brian. Due to my plugs turning black with door, I was told to run a hotter plug than my Autolite 3924. The NGK FR5 were a step up. The ones you recommended are pretty cold. I’m still learning here. Just curious why you recommended those. Thanks man

[rp930]

i would get NGK #5671A-7 spark plugs. Also listed as part number 4091

Brian

Ok will do Brian. Due to my plugs turning black with door, I was told to run a hotter plug than my Autolite 3924. The NGK FR5 were a step up. The ones you recommended are pretty cold. I’m still learning here. Just curious why you recommended those. Thanks man

Colder plugs will not fix this problem. The FR5’s are fine.

I’m sure you’ve looked at this. https://www.aedperformance.com/tuning-tips.html

[skinny z]

4 corner idle mixture screws should be around 3/4 turn out not 1.5 turns ( 1.5 turns is for a 2 corner idle carb )

My approach as well.
And successfully too.

[PRNDL]

4 corner idle mixture screws should be around 3/4 turn out not 1.5 turns ( 1.5 turns is for a 2 corner idle carb )

My approach as well.
And successfully too.

Yeah, I read through that so many times. Problem is they don’t have a baseline amount to start with on the idle mixture screws.

[PRNDL]

I had no freakin idea. All this time? I was doing all 4 at 1.5 and going down to 1-3/4 and even 1 turn then stopping because it was still so rich. Thinking it was out of range and something was wrong. I will restart. My radiator is blown now and I’m waiting for the one I ordered to show up. I’ll report back. Thanks guys.

Question. I found a sweet spot with the primary idle curb screw at 3/4 turn and .030 transition. Primary idle mixture screws sensitive and stall the engine if I close even 1. I found a good spot on the secondaries open only 1/2 out. Secondary mixture screws nice and sensitive. However, won’t stall the engine if I close them both all the way. I read somewhere that on a 4 corner idle, closing two won’t stall the engine due to having two idle circuits. So which is it? Rear mixture screws not sensitive enough or normal. If I close the secondaries and more, my idle will be too low. I may do that anyway and open the primaries to .040. Hopefully my primaries don’t go dead. I’m running a PCV and primary blades already drilled 1/8.

[prairiehotrodder]

i would get NGK #5671A-7 spark plugs. Also listed as part number 4091

Brian

Ok will do Brian. Due to my plugs turning black with door, I was told to run a hotter plug than my Autolite 3924. The NGK FR5 were a step up. The ones you recommended are pretty cold. I’m still learning here. Just curious why you recommended those. Thanks man

I didn't think the spark plugs were the problem. Just wanted to make sure you got ones that fit the heads properly.

[skinny z]

Someone can correct me if I'm wrong however I always operated on the notion that with the secondaries cracked open a little it helps offset the need for opening the primaries too far. Or thinking further, the need for the primary blades to be drilled.
So, that said, perhaps there's not as much importance attached to the secondary sensitivity as there might be otherwise.
That your carb people drilled the blades in the first place makes me wonder why. As was mentioned earlier, it didn't seem that the cam would present any particular tuning difficulties.
But, this is what you've got and it sounds like you're dialing it in.

I like to have the screws set such that there's a drop in manifold vacuum from whichever direction I go from ideal.

[1980RS]

Here's 2 things that fixed my stumble hesitations on a lot of carbs. First, I had an 830hp that had the holes drilled in the throttle blades and on my one 406 would only idle with the blades closed. I later found out that with the blades in that position having the t-slots not exposed caused my hesitations. Fix? was a new set of non-drilled blades from Allstate carburetor, put them in re-set the the throttle blades to about .025 or so and the hesitation was gone on that engine. The other one I had is my BG Might Demon 1000 with down leg boosters, no matter what I did inc. bigger and smaller squirters the dang thing would hesitate off idle. The fix? 2 Thompson power plates, as I already had them from a carb I bought bought from another guy and really wanted to test them and they worked. That 1000 is great carb at the track now. As for a stinky idle, you may need to add some t-slot restrictors in the main body like people do with Dominators that idle too fat. It does work as when I ran my 2 circuit 1050 I made that 1050 had a super clean idle after adding the restrictors. I know that may suck with a new AED but hey sometimes you just have to fix what the manufactures can't seem to get right out of the box.

[PRNDL]

Great info. Ok, small update. just for giggles, I turned all 4 corners to 1 turn. Never had them that low. Could not let the engine heat up because I have a radiator leak. Started right up. Warmed up for 30 seconds and gave it some gas. Stumble is gone. So weird. Was I that rich? Exhaust still smells, but it smells more like…. Regular exhaust? If that makes sense. I definitely have a misfire. It’s rpm dependent. It started when I put in those Autolite 3924’s. Plus they are fouled bad. Could not run it long.


Front curb idle 3/4 turn open. .030 transition.
Rear curb idle 1/8 turn open. No transition.
All 4 mixture screws at 1 turn.
Didn’t tune them to vacuum or rpm due to leaking radiator and can’t run it long. Ran far better though.

Any thoughts on why it doesn’t stall when I close the secondary mixture screws? I can close both all the way. Runs very rough but still runs.

[PRNDL]

Here's 2 things that fixed my stumble hesitations on a lot of carbs. First, I had an 830hp that had the holes drilled in the throttle blades and on my one 406 would only idle with the blades closed. I later found out that with the blades in that position having the t-slots not exposed caused my hesitations. Fix? was a new set of non-drilled blades from Allstate carburetor, put them in re-set the the throttle blades to about .025 or so and the hesitation was gone on that engine. The other one I had is my BG Might Demon 1000 with down leg boosters, no matter what I did inc. bigger and smaller squirters the dang thing would hesitate off idle. The fix? 2 Thompson power plates, as I already had them from a carb I bought bought from another guy and really wanted to test them and they worked. That 1000 is great carb at the track now. As for a stinky idle, you may need to add some t-slot restrictors in the main body like people do with Dominators that idle too fat. It does work as when I ran my 2 circuit 1050 I made that 1050 had a super clean idle after adding the restrictors. I know that may suck with a new AED but hey sometimes you just have to fix what the manufactures can't seem to get right out of the box.

Good to know brother. Thank you

[skinny z]

.

Any thoughts on why it doesn’t stall when I close the secondary mixture screws? I can close both all the way. Runs very rough but still runs.

I'll venture a guess and say that the primaries, most notably due to the holes, are providing what's needed to keep the engine alive.
But, that's a guess as I said.

[rebelrouser]

just to give you a different point of view. When messing with a carb many times more than one modification can fix the same issue. If I was to mess with it, first make the transfer slot is covered. If it needs more air to idle open the secondaries slightly, I personally don't drill throttle plate unless a last resort. Second I would play with the idle air bleeds. Go a little smaller first. If you are opening the throttle blades enough that fuel is dribbling out of the venturi, then a richer idle circuit may fix the issue. If that does not work try going bigger to lean the idle circuit. And always make sure the ignition timing is right before messing with the carb. If it has vacuum advance swap the hose from manifold vacuum to ported vacuum see what it likes better.

[PRNDL]

just to give you a different point of view. When messing with a carb many times more than one modification can fix the same issue. If I was to mess with it, first make the transfer slot is covered. If it needs more air to idle open the secondaries slightly, I personally don't drill throttle plate unless a last resort. Second I would play with the idle air bleeds. Go a little smaller first. If you are opening the throttle blades enough that fuel is dribbling out of the venturi, then a richer idle circuit may fix the issue. If that does not work try going bigger to lean the idle circuit. And always make sure the ignition timing is right before messing with the carb. If it has vacuum advance swap the hose from manifold vacuum to ported vacuum see what it likes better.

I agree with your method. I will keep the new plates in mind if all this don’t work. This carburator hates to have the secondaries open at all. I’ll get a stumble. Worse of a stumble than running on too much primary T-slot. I found a happy place here fronts at 3/4 turn. Rears at 1/4 turn. A 3rd ratio. Front mixture screws sensitive as heck. Rear mixture screws as sensitive as I can get them but do not stall engine if I close them. It’s the best I can do. No more gray smoke, no eyes burning, still a little smelly but I think it’s normal.

Need to fix radiator
Change the oil
Change the plugs
And tune based on all the advice given above.
So far leaning the mixture to 1 turn on all 4 helped. Slowly tried 3/4, but as I went around the engine wanted to die.

[HQM383]

just to give you a different point of view. When messing with a carb many times more than one modification can fix the same issue. If I was to mess with it, first make the transfer slot is covered. If it needs more air to idle open the secondaries slightly, I personally don't drill throttle plate unless a last resort. Second I would play with the idle air bleeds. Go a little smaller first. If you are opening the throttle blades enough that fuel is dribbling out of the venturi, then a richer idle circuit may fix the issue. If that does not work try going bigger to lean the idle circuit. And always make sure the ignition timing is right before messing with the carb. If it has vacuum advance swap the hose from manifold vacuum to ported vacuum see what it likes better.

I agree with your method. I will keep the new plates in mind if all this don’t work. This carburator hates to have the secondaries open at all. I’ll get a stumble. Worse of a stumble than running on too much primary T-slot. I found a happy place here fronts A 3rd ratio. Front mixture screws sensitive as heck. Rear mixture screws as sensitive as I can get them but do not stall engine if I close them. It’s the best I can do. No more gray smoke, no eyes burning, still a little smelly but I think it’s normal.

Need to fix radiator
Change the oil
Change the plugs
And tune based on all the advice given above.
So far leaning the mixture to 1 turn on all 4 helped. Slowly tried 3/4, but as I went around the engine wanted to die.

Have you tried 1/2 turn each end with same amount of throttle blade open each end?

After ‘change the plugs’ on your list should be ‘fit an AFR gauge’. You may have the idle improved but that doesn’t mean the IFR and IAB are putting out a good AFR for cruise. An IFR of .035” is big for what you have. IFR is #1 to get right.

https://www.summitracing.com/parts/avm-30-4110

[skinny z]

...on your list should be ‘fit an AFR gauge’.

I live and die tuning with my AFR gauge. I couldn't imagine a workaround otherwise (despite having had to do just that before they were available to the common man). I also have a vacuum gauge mounted in the dash.
It's not the tool for idle tuning necessarily although once the idle is confirmed best with a vacuum gauge and tach, I've found the air/fuel value can at least be referenced but it was very unlikely to be stoichiometric. With my cam (71°overlap), compression (10.2:1) and timing (30°at idle), AFR's were in or around 13-13.5:1.
Dialing in the cruise or WOT miuxture, while still tedious, at least gives a solid footing to work on.