holley carb problem
Thread Starter
6th Gear
Joined: Mar 2008
Posts: 6
Likes: 0
From: lake jackson texas
holley carb problem
I have an 82 that I just put a holley 600cfm carb and elelbrock intake on. Checked the numbers and it is an original 350 engine. The car had a holley 650 double pumper that had been re-jetted higher and different intake. Car hesitated at low rpm but a high rpm performed well. Put new carb in today and hesitation gone but at about 2000rpm losses power then gains some power around 3000 and shifts thereafter. New carb is electric choke vacuum secodary. Four barrel single pump. Also has a clearview fuel filter now, none before. Did not seem to matter much when i changed regulator setting. Taking the air cleaner off helped slightly. Car idles fine and revs up fine in park but with a load does not. Anyone have an suggestions about the loss of power?
Thanks everyone
Thanks everyone
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
I have an 82 that I just put a holley 600cfm carb and elelbrock intake on. Checked the numbers and it is an original 350 engine. The car had a holley 650 double pumper that had been re-jetted higher and different intake. Car hesitated at low rpm but a high rpm performed well. Put new carb in today and hesitation gone but at about 2000rpm losses power then gains some power around 3000 and shifts thereafter. New carb is electric choke vacuum secodary. Four barrel single pump. Also has a clearview fuel filter now, none before. Did not seem to matter much when i changed regulator setting. Taking the air cleaner off helped slightly. Car idles fine and revs up fine in park but with a load does not. Anyone have an suggestions about the loss of power?
Thanks everyone
Thanks everyone
Thread Starter
6th Gear
Joined: Mar 2008
Posts: 6
Likes: 0
From: lake jackson texas
Thanks guys will do tomorrow. I think I might be losing vacuum somewhere. Headlights are often sluggish to rise. With some luck a vacuum leak and lighter spring could be an easy fix.
Last edited by J-Vett; Mar 3, 2009 at 12:55 AM.
Safety Car
Joined: Nov 2004
Posts: 4,359
Likes: 57
From: Mundelein Illinois
if it's a brand new carb as you say, then it is probably the way you have it set up......are you sure the choke is opening all the way??.....have you checked fuel pressure? .....accelerator pump working?.....dirt in the fuel line?.....might want to try a lighter spring on the secondary diaphram....good luck
Yellow spring = least resistance per Lars Carb tech tip
Thread Starter
6th Gear
Joined: Mar 2008
Posts: 6
Likes: 0
From: lake jackson texas
Took fresh air flap off the front of car to get more air, fixed some vacuum leaks and opened up regulator all the way. Car runs better than ever before. Now I just have to get the transmission kickdown cable in the right spot so that it will have the right amount of tension to shift at the right time. Thanks alot guys.
Race Director
Joined: Feb 1999
Posts: 16,978
Likes: 7
From: In Dreams There Is Truth Ohio
not the best spring to use when lots of vacuum is present...only time it's useful if your vacuum is low, else your secondaries will ope way too soon and you're sucking gas like water through a screen. Try a spring with little more resistance...
Intermediate
Joined: Dec 2006
Posts: 46
Likes: 0
I agree with GDaina. If your secondaries are opening too soon you feel the engine bog down with too much gas and not enough air. If it has the correct spring you shouldn't feel anything when the secondaries open up.
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Race Director
Joined: Apr 1999
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From: CORVETTE 77 385 C.I. TEXAS
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
The Holley vacuum secondary (regardless of model) is affected by engine load, throttle position, and spring tension. Engine manifold vacuum has no affect on the tuning of the secondary opening rate. It is just a consequence of load and throttle position outside of how the secondary behaves. Airflow volume causes a depression over the air bleed hole at the throat of the primary venturi on the passenger side. Get a flashlight a take a peek at the hole. It's there. Most models also have the same hole on the secondary side. Once the secondary begins to open, the secondary bleed hole sees airflow and helps pull over the secondary. The primary bleed is the main source for the secondary vacuum motor and once the throttle starts to close, the secondary bleed no longer has enough influence and the secondary closes.
Tuning is pretty simple. You should be able to feel the secondary kick. Easiest way to do this is to put in the lightest spring and tune up until you don't have the bog and the power comes on smoothly. The higher (lower numerically) gear, the heavier the car, the bigger the engine, the heavier the spring you need. Most engines under 400ci on a Corvette would probably end up with the yellow spring. But you won't know that until you try it.
Tuning is pretty simple. You should be able to feel the secondary kick. Easiest way to do this is to put in the lightest spring and tune up until you don't have the bog and the power comes on smoothly. The higher (lower numerically) gear, the heavier the car, the bigger the engine, the heavier the spring you need. Most engines under 400ci on a Corvette would probably end up with the yellow spring. But you won't know that until you try it.