Holley Support is no Help!

[AM.MSCL]

I have a Holley 750 Double Pumper with Vac 2ndaries on my 400 Pontiac in my 69 Firebird. I have a 4 speed manual trans.
The car starts and idles at 900 rpms just fine when cold.
I get on the highway and drive a few miles at 70 mph which is 3200 rpms for the engine; now the car idles at 1200 rpms. I can park the car with it running and push the throttle lever in the direction that will reduce the rpms back to 900. Prior to pushing the throttle lever I make sure that there is no throttle cable hanging to cause the issue. Goose the throttle and it goes right back to 1200 rpms.
Next part of this craziness if I do not get on the high and just drive around the local streets and never get above 50 mph which is about 2500 rpms the idle will go back to 900.
Holley keeps telling me I have a vacuum leak which I have verified that I do not. I have taken Berryman's Chemtool and sprayed lightly around the intake and carb and no rpm change what so ever.
I honestly think something in the Carb is sticking after it has been around 3000 rpms for a while but can not get any help from Holley to check what.
Does anyone have any clues what is going on?
thanks
Ray

[Restomod Z28]

I didn't quite follow you there on pushing the throttle back and the idle drops. It almost makes it sound like the return spring isn't working as it should or that the cable is sticking... I think I'm missing your point though.

Regardless, the RPM range makes me think timing advance (which can improve idle quality) & mechanical advance weights that stick. Take off your distributor cap/rotor and check your mechanical advance weights. Make sure they return to their resting position when you snap them out all the way. Make sure they are not gummed up.

[Pro Stock]

I have a Holley 750 Double Pumper with Vac 2ndaries on my 400 Pontiac in my 69 Firebird. I have a 4 speed manual trans.
The car starts and idles at 900 rpms just fine when cold.
I get on the highway and drive a few miles at 70 mph which is 3200 rpms for the engine; now the car idles at 1200 rpms. I can park the car with it running and push the throttle lever in the direction that will reduce the rpms back to 900. Prior to pushing the throttle lever I make sure that there is no throttle cable hanging to cause the issue. Goose the throttle and it goes right back to 1200 rpms.
Next part of this craziness if I do not get on the high and just drive around the local streets and never get above 50 mph which is about 2500 rpms the idle will go back to 900.
Holley keeps telling me I have a vacuum leak which I have verified that I do not. I have taken Berryman's Chemtool and sprayed lightly around the intake and carb and no rpm change what so ever.
I honestly think something in the Carb is sticking after it has been around 3000 rpms for a while but can not get any help from Holley to check what.
Does anyone have any clues what is going on?
thanks
Ray

I know exactly what you are talking about, I have seen this problem before. Your problem is carb related, probably a combination of not enough return spring and sticky shafts and linkage. The spring probably was border line but worked fine when everything was fresh, as the carb linkage and butterfly shafts wear and with the accumulation of dirt the carb becomes sticky and the butterfies won't completly close causing your high idle, that's why when you manualy close the throttle by hand the idle drops. Use a spray lubricant and thourally spray the linkage and shafts and add a stiffer return spring and that should fix your problem. I have seen this happen on dyno carbs that have never even left the shop.

Dale

[AM.MSCL]

I know exactly what you are talking about, I have seen this problem before. Your problem is carb related, probably a combination of not enough return spring and sticky shafts and linkage. The spring probably was border line but worked fine when everything was fresh, as the carb linkage and butterfly shafts wear and with the accumulation of dirt the carb becomes sticky and the butterfies won't completly close causing your high idle, that's why when you manualy close the throttle by hand the idle drops. Use a spray lubricant and thourally spray the linkage and shafts and add a stiffer return spring and that should fix your problem. I have seen this happen on dyno carbs that have never even left the shop.

Dale

Dale
Thanks for the information. When you say return spring are you referring to the throttle cable springs?
thanks
Ray

[John Wright]

are you running a 4 hole spacer under the carb?.....how about a 4 hole gasket? Make certain that the butterflies are not hanging on the inside bore of the carb, or the gasket, or the spacer.....something is sticking that linkage. BTW, I've had throttle bodies do the same thing....

[AM.MSCL]

No spacer between the carb and intake; I do not have room for one under the hood. The gasket is a holley one hole gasket.

[John Wright]

Take the carb off and work the linkage by hand....you should be able to feel if the linkage is smooth or if it drags ever so slightly inside the bores....you might even be able to see some scratches or shiny spots where the blades are hanging up inside the bores.

[Taman]

I had the same problem. I had burrs on the throttle blades. Cleaned them up and problem Solved.

[Pro Stock]

Dale
Thanks for the information. When you say return spring are you referring to the throttle cable springs?
thanks
Ray
I'm talking about a return spring that most hot rodders add to thier carb, you can buy a small throttle return spring bracket from Jegs, Summit, ect, it will come with the spring also. bolt the bracket to one of the forward intake manifold bolts and connect the other end of the spring to the upper end of the throttle arm, you can shorten the spring some if you think that you need more return pressure.

Here are some from jegs


Moroso 64925
Throttle Return Spring Kit SBC Holley 2 or 4-bbl Carb Manifold Mount 1-13/16" Tall
Item# 710-64925
Ships Today
Only $19.99




Moroso 64927
Throttle Return Spring Kit
Holley 2300/2305 & 4150/4160 Carbs
Carb Mount

Item# 710-64927
Ships 10/30/10
Only $21.99




Moroso 64919
Throttle Return Spring Kit
4150 Holley Carbs Including HP Series
Carb Mount


Item# 710-64919
Ships Today
Only $32.99

[H2Ogbodies]

I've had one 750 carb that did the same thing on an S-10. The throttle shaft on the pass. side was hitting the baseplate ever so slightly so that anything just above idle or further kept it from coming back down to a 750 RPM idle. It would sit at 1500 @ idle unless I manually pulled it down. I too thought it was a butterfly hanging up inside the throttle bore but uon real close inspection, I found a slight gouge on the baseplate....then I traced it to the linkage hardware on the pass side. I got my dremel out, ground it down maybe 1/64". Hope this helps you out...something to check anyway. Is your carb an older model? It's been a long time since I've seen a vacuum sec. DP-unless it's custom made.

[John Wright]

Any word on the situation?....had time to investigate any further?...just wondering what you found.

[AM.MSCL]

On suggestions of a few different people on different boards I did some debugging last night.
I reset the Electric choke back to the manufacture default settings
Got the car out and reproduced the problem
With the car running:
I disconnected the throttle cable = no change
manually ran the rpms up to 3000 by hand with the throttle lever and let it re-establish idle = no change
Backed the Fast Idle screw until it no longer was touching to be causing it to hold the idle up = no change
manually ran the rpms up to 3000 by hand with the throttle lever and let it re-establish idle = no change
Took a long screw driver and tried to close the secondary butter-files; they would not close any more = no change
Added a 3rd return spring to the throttle lever but it is connected to another spot from the original 2 springs to make sure there was no interference with them = no change
Again took some B-12 Chemtool and spot shot different areas all around the carb base and intake = no increase or decrease surge
one spot shot into the primary of the carb and a did get a rpm increase for a split second
Looked around the choke area of the carb to try and determine if something was hanging or sticking but did not see anything obvious.
That was all the time I had last night; hopefully this weekend I will get to check the choke area more.

[H2Ogbodies]

You might want to double check your throttle cable too-sometimes the steel cable part can hang up on the inside of the plastic jacketing. I wonder if possibly the throttle shaft is still bent even though you don't have a vacuum leak.