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Discussion Starter · #1 ·
I am decreaseing the the size of the idle feed restrictors on my 4150 holley carb. I am going from .035" to .031" dia. I noticed that the secondary metering block has the same restrictors. Does the secondary block need to be modified as well?, I thought only the primary block with the idle screws was part of the idle circut.
 

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66 El Camino 57 Chevy pickup 2004 Tahoe
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4150 Holleys have a sort of minimal secondary idle circuit, it was originally put in to keep gas from going stale in the rear bowl if the driver never used the secondaries. Not likely to be a problem around here.


There's an idle feed restriction and an idle channel restriction, make sure you which one you're changing....

Tom
 

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Discussion Starter · #3 ·
I'm getting my info. from a chevy High performance mag. They show a step by step procedure. I drilled new holes in both the primary & secondary restrictors, then flushed them out. This carb was running way too rich, there was a hell of a lot of carbon in the carb. I also bought a 4.5" Hg powervalve to try. I'm getting about 7" Hg at idle. I don't know how soon I'll be able to try it out, the car is totally dissassembled, and probably won't be running for a year or so, but maybe I can try it out on someone else's LS-6.

[This message has been edited by ETD66SS (edited 04-18-99).]
 

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>>This carb was running way too rich, there was a hell of a lot of
carbon in the carb. <<

Where in the carb? Running rich doesn't cause carbon buildups in a carburetor, the only thing I know of that causes carbon in a carb is backfiring through the intake manifold. Carbon residues are a by-product of combustion, not supposed to be any combustion in the intake/carb area. Do you have a working choke for cold starts?

Tom
 

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Discussion Starter · #5 ·
The entire venturi system that draws in the air was coated in a nice dark layer of carbon, including the choke horn, and chocke plate. I have a manual choke. I ran the car all last summer and no backfires. I know it's running rich because of the plugs and exhaust, but the carb was like this when I bought the car. The car did however diesel a lot after it was hot, could this explain the carbon build up? Pretty much every time the car was shut off, it would deisel for about 5 seconds, and maybe at this time something was comming up through the carb? I thought that fixing the richness problem would also help to solve the deiseling problem.
 

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ETD66SS, running on after the key is turned off is a sign of being lean. I found this out the hard way and almost ruined my jet hot coated headers.
 

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ETD66SS

The dieseling problem probably caused the carbon, I recommend you solve that first. What is the idle speed? Common cause of dieseling is too fast idle speed. Sometimes the deals pans out like this: 1)timing retarded due to mismatch timing marks, pinging from too high compression or some other reason. 2) idle speed screw turned way in to boost idle speed back up. 3) throttle blades now too far open, engine diesels on hot shutoff. 4)retarded timing also causes high chamber temps at idle making the dieseling problem worse. 5)lean idle mixtures also cause this deal but if the idle is that lean with a 4150 something else is probably goofed up, like a vac leak or something. 4150's are famous for having pig-rich idle and transfer circuits.

How big is your engine, what size cam is in it? I notice you mention some very low manifold vac numbers, is this a race car or a street car?

One solution is to install an idle stop solenoid, on when ignition on. Use the solenoid to set the idle speed, turn the regular idle speed screw completely out. When you turn off the key the throttle blades slam shut, killing the engine. I've built setups like this for guys who thought they could run 11:1 on pump gas, they end up killing the timing to get rid of the ping so they can drive the car, have a major dieseling problem.

Tom
 

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Discussion Starter · #8 ·
The engine is a LS-6 crate motor, with about 2000 mi. on it. I was told the compression is 10.25:1. Stricly a street machine. I run 93 Octane, no pinging.
I don't know the cam spec's, prev. owner said it was "mild". Vaccuum at 900 RPM is about 7" Hg. 4 spd. muncie tranny.
Idle speed was about 900 RPM
I never checked the timing, don't have a new timing light yet. Never had a hot start problem.
The idle speed screw is set in such a way that the screw moves the linkage arm about .032".
Engine temp never really went any higher than 185 deg.
Thats about all I got.
When I took the 66 Chevelle SS for a ride before I bought it, the owner said it runs a little rich because the jets are to big. I really did'nt know much about Holley's until I asked questions on this site, and the Holley site.
Thanks!
Gene
 

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ETD66SS

I'm not an LS-6 expert but it seems to me like your manifold vacuum is very low. Are you sure there's not a vacuum leak? Try pinching off the hose to the brake booster while idling, see if it changes the idle. Check your PCV to see if the guts haven't fallen out or something. Is there an adapter between the carb and manifold? Look around real good on that thing, I think it should have more manifold vac than you've got.

Maybe somebody with a stock LS-6 will check theirs for a comparison. You might want to post a question with that in the title. "LS-6 manifold vacuum question" or something like that.

Tom
 

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Discussion Starter · #10 ·
Tom,
This car does'nt have power brakes.
There is only one vacccuum line, and that goes from the base plate to the PCV valve, which is new. All the rest of the ports on the intake and carb are pluged off. When the car was running (all in pieces now) I could'nt hear any vaccuum leaks. I don't know how stock this engine is. The previous owner bought the crate engine, and immediately turned it over to a race engine builder. I don't know exactly what he did to it, but it dynoed at 500 HP. and 500 FT.-LBS. And yes, I am using a Mr. Gasket heat dissipator under the carb. I found no evidence of vaccuum leaks. Thanks for your help Tom!
Gene
 

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ETD66SS

It probably has a big cam in it causing the low idle vac. When it goes back together make sure you have all the initial advance you can stand, this will pick up the idle and allow the carb to be closed and the idle speed brought down to some reasonable figure. You might be able to get rid of the dieseling like this.
 
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