Ok guys, I have a pump gas big block with an MP 557 solid cam, a 950HP ProSystems carb, and a 9.5" Dynamic converter. Car runs awesome and I've had a blast all summer, but the idle RPM has kinda stumped me.
The carb has .067 idle air bleeds, I've tried going up and down with those in the primary with no luck, a stock 950 Holley has .072 idle air bleeds at all 4 corners so I may try that this week. The 4 butterflies came from ProSystems with a small hole drilled in each one. My air/fuel mixture screws are 2 full turns out at all 4 corners.
I have a Pertronix IgnitorIII distributor with super light springs so timing is almost locked out.
It has to idle at 1200 to get it to idle at 900 in gear. I'm running 3.55 gears and might switch to 3.23's so I need the converter to be fairly tight but I'm thinking the converter is tight enough at idle to make the idle fight against it, maybe??

I have adjusted both butterflies, I've played with the air/fuel mixture screws, I've messed with the level of fuel in the bowls and I've tried different distributor springs.
I thought about drilling bigger holes in the primary butterflies but I'm not so sure that's what it needs since they are not open very far at all to get it to idle at 1200 in park.

I will have someone put the car in gear while I check to see what the timing is doing when we have time to do so. Also need to pull the carb off and double check the transition slots. Any other suggestions? This is not a huge problem, just a slight annoyance to me, I'd just like to see if I can get it to idle at 900 in gear and 950-1000 in park.

How much initial timing?

It's about 28-30 initial and 32 total. I have the Mr.Gasket light weight springs in the Pertronix distributor.

I had idle issues with the 950 I had on my little motor. When I bought the 750( that didn't do anything but slow it down) I sent my convertor out and had it loosened up. Flogged the 750 but couldn't match the 950's performance.
Put the 950 back on after the convertor loosen up and the car idles lke a Lexus.........

Don that's what I'm thinking. I re-sealed my transmission pan last weekend, I noticed it was idling pretty good in gear, then I checked the fluid level and it was a quart low. Once I got the trans fluid to the full mark on the dipstick the car started struggling to idle in gear.

I would try running a stiffer distributor spring setup. Based on what you've said and how its acting, it sounds like the timing could be getting into the advance curve right at that Neutral idle RPM, and dropping some timing when you put it in gear. (??)

Edit: by the way, I'd be shocked if 1 qt. of tranny fluid is effecting your idle quality. That's just me, though.

Yea I was shocked too but it sure seemed like that's how it went, I should drain a quart out and see how it acts lol.

I really need to have a friend put the car in gear so I can watch the timing gun. I tried heavier springs one time and it was really bad, it would just shut off when I put it in gear but I'm not sure if the springs effected the timing, maybe the distributor needed to be advanced after installing the heavier springs??

I drive this car almost every day so I haven't had alot of time to mess with it. Fortunately(and unfortunately), there's a different car show/cruise 7 days a week in my area.

I have a fairly loose 8" 5200+ and when tuned right I get about a 150-200 rpm drop which I feel is pretty good and you are asking a lot imo to get that or less w/a tight vert. Like you said, take the carb off and check t-slot location and for me on 4150`s I don`t always start off square ft. to rear and usually set the primary w/a small square and none on the secondary. I`d also try to lean it out w/.070`s-.072` like you said and go from there.......

After you confirm that the timing is solid from N to D, and you know the transfer slots are square, then adjust the idle mixture with the tranny in D after the engine is up to normal driving temps.
After a drive, put the tranny in D with the Ebrake applied or someone in the car applying the brakes. Adjust your rpm's in D where you want them and adjust your metering screws for best vacuum (you may have to readjust your rpm's again) Then move the tranny back to N and note the rpm change. If you still have too much rpm change, then open up the mixture screws (richer) app 1/12 of a turn each in D and then test your N Rpm's. You may need to richen it up a little at a time (1/12 turn or so) until you get the lowest rpm drop that you can achieve with your setup.

Note: I added a Holley idle solenoid to my carb so that I can adjust the 1/2/D rpms with the solenoid extended, and then when it is in N or P (solenoid retracts), I can adjust the rpms with the carb linkage like normal. This allows me to run about 50-100rpms more (900-950) in the Drive gears for charging purposes at a stop light and then it idles down (850-900) in N/P for shut down.

Although good ideas, he`s already 2 turns out on the idle mixture screws.......

Holley idle solenoid, interesting. Might have to look into that.

I made a rod for my 69 dart that I could control idle RPM with by a knob on the dash that turned the idle screw on the carb. If all my tuning fails and the problem just lies in my cam and converter combo I'll just make another rod and adjust idle from the drivers seat if I so desire.

Like I said earlier, this is not a big deal, I'm just curious and trying to learn more. The carb works great and will blow the tires off in any gear at any RPM.

But I'll admit the rear tires are not soft. I just looked into the idle solenoid, they are pretty pricey but would probably hide nicely under my air cleaner base.

You don`t need a solenoid if it`s tuned right. If I`m not mistaken, those things are "compensators" for ac to cover load drop. That`s crazy. Check the idle circuit first by blocking one air bleed while running and if the idle drops it`s rich if it raises, lean and adjust bleeds/air mixture screws accordingly.......

Will do.

Thumper if it's lean do I go up or down in idle bleed number?

Down........less air

Ok I just blocked one primary idle bleed and idle went down slightly, blocked the other primary side and it dropped a couple hundred rpm.

All 4 idle air bleeds are .067, should I try some .072's?

my secret timing curve and I don't know if you can do this with the dist your running but it works with the newer mopar ones was

just 1 light spring. not 2

set the timing when its cranking over at 22* then have the advance you want +12* and your timing is rock solid at idle. also ran a collar on my shaft

Do you have idle jets in your metering blocks? If they are billet metering blocks then you should have idle jets. I'd change the idle jets before changing the air bleeds. It seems to me that you might need to lean out the idle a little bit but I'm not too sure since you have the idle screws out 2 turns. They should really be out about 1.5 turns.

Idle/off-idle adjustments are tricky with a big cam and a cold intake manifold. Lots of variables in play. Gas quality, ignition timing and curve, fuel mixture, etc.

If you know anyone who has an Edelbrock 800 carb that they'll loan you it would be worth the try. You'll be amazed at how much better the Edelbrock will idle on that engine. You'll give up some hp on the top end and it might have other problems such as running out of fuel at WOT, but it will idle really nice.

I keep an Edelbrock 800 around just for tuning reasons. Whenever we bolt on an engine like yours the idle gets so much better the owner can't believe it.