I installed the HP950 today on my 406 and it runs better but I noticed when I disconnect the rubber cap from one of my vacuum ports on my spacer the idle picked up by 150RPM. It wasn't like that with the 700DP. Does that tell me my idle circuit is too rich? Water temp was also about 5 degrees colder at 175 and cold sart was much better so I think I'm way too rich.

Also it seems like my idle still drops 100-200 RPM after sitting at a light. I'm gonna go drive it some more and tweak the 4 corner.

It tells you that you have a vacuum leak. Main jets do not affect idle quality.

Sounds like your idle mixture is on the rich side. It is better to be just a tad lean to keep the plugs clean then dial in your main jets and powervalve.

I have Read that bigger main jets can introduce more fuel into the idle well and create a richer idle system, but who knows for sure...? I believe I read in in the HOT ROD where they did a whole article on how to tune a Holley HP. Its was Vbranic Bros Racing who did the article (A.K.A. the Carb Shop,Ontairo, Ca) If nothiing else call them
Later
Rassan

P.S.

It's Late and I forgot this info (sorry) Check you power valve vacuum rating, It should be at least two steps lower than your most consistant reading, in gear in auto. Also since it's an HP you have adjustable Idle-air bleeds(two OUTTER jets on main body,and many other aspects of the metering blocks. These usually shouldn't be messed with w/o a dyno, but you can play areound with them in two step increments ie. .075>.077 Might try there,also Idle screws usually work best 1-1.5 turns out from lightly seated for no hesitation of stumble. I hope that helps in some way and that it's not knowledge already known
Later (for real this time)

Rassan

Yeah guys I might be chasing my arse because I'm going by my factory tach that seams to be hanging up. When I do hook up my external tach for tuning it seems I have a hard time adjusting the air bleeds at under 1000 RPM because it picks up and settles down. Maybe like 50-100 RPM. When I bring the idle up to 1000 RPM it stays steady and I'm able to adjust the air bleeds easier. I don't have crap for vacuum lines so I'll check my intake.

Also my air bleeds are very sensitive. 3/4 out the car would barely run so went 1 turn out and it seemed about optimum.

What does uncapping one of my vacuum ports tell me when the RPM increase by 150???

Sounds rich but make sure you have some sort of a heat insulator under the carb. Remember a 4 sided idle circuit usually needs only about 1/2 turn out on all 4 screws.

Do Holley HP's have a secondary PV? If so that could be causing my rich condition because I only changed the primary side, I guess that explains why they come jetted square.

Yes they have a secondary powervalve. Mine has 6.5 pv's and 78 yets from Holley. Mike,with 4 corner idle mine wont idle at 1/2 turn out,to get the best idle on mine the fronts are 1.25 and the rear is 3/4 out,slightly rich,but it helps cold starts.

hilljack,

I have a Proform 950 on my big block with no vacuum. My carb is exactly like yours except my pv enrichment holes aren't changeable like yours. I drilled all four butterflies with a 9/32 bit, then opened up the secondaries,this allowed to close the primaries and cover more ofthe transfer slot, plugged the secondary pv, and then chnged my primary pump setting to the second notch. If your car idles best around 900-1000rpms then your pump cam should USUALLY be on the second or third notch not for every application I know. This allowed me to regain control over my idle mixture screws and tune it corretly. not all of this has to do with the idle system, but it helps with overall tuning of carb. I don't know what type of cam you are running but if it is a performance grind with lots of overlap, then these suggestions should help, also you can advance your INITIAL timing and this could help you lower the primary butterflies and performance. I run 18* initial on my cam. 255/265 @ .050 612/630 lift. I hope this helps in your quest for a cleaner idle.
Later
Rassan

Car idles like a stocker now smile.gif smooth and crisp! At first I didn't know they had secondary PV and to be on the safe side I put them both at 3.5 since she makes between 6-8" vacuum. Went from 79-77 in the back and 79-76 in the front. I backed all air bleed screws 1 full turn and squared up front and rear transfer slots. Bolted that baby on and she runs GOOOOOODDD graemlins/thumbsup.gif She ran so good I didn't even mess with the air bleed screws yet. The only thing is the primaries are just barely off there seat so I'm going to close up the secondary a bit. I also upped the stat to a 195.

Thanks for the input guys......much appreciated!

you mean the idle mixture screws. The air bleeds are the 8 holes on the top of the carb main body next to the boosters.

The air bleeds are what let in air to emulsify the fuel, the idle mixture screw, however, is what meters the amount of fuel at idle, to some degree, although alot plays into what effects the idle circuits mixture.

Idle screws are tricky as well, they effect much more then just idle mixture.

Yeah idle mixture screws, thanks for clarifying.