79vetter

When Lars worked on my Carb it was able to idle at a nice 700 rpm in his shop. When I install it on my car I cannot get it to idle below 1100 rpm. He also set up a new electric choke too - so the Carb seems unlikely as the leak source.
I capped the "T" coming out of the manifold for vacuum - no change in rpm
I put a vacuum pump on the vacuum advance can at the distributor - it holds vacuum steady.
I capped the metal vacuum line coming out of the Carb - no change.
All of the unused ports on the carb are capped.
I replaced the Carb mounting gasket. Bolts are lightly snug.
I sprayed carb cleaner around the intake and base of the carb- no change
I took a hose and tried to listen for a hiss around the intake.

I'm at a loss - any other suggestions on what to check?

woolf708

There's a steel line running down to the vacuum modulator on my '79 automatic transmission. Maybe the diaphragm inside or one of the short rubber hoses failed.

Mountainoakie

I just solved a vacuum leak/fast idle problem on an '82 and it turned out to be a leaking rod seal on the right headlight actuator. Another possibility would be distributor flyweight springs that are too light and allowing some mechanical advance to come in when it's not needed.

MelWff

Have you tried the idle speed screw to lower the rpm?
Is the choke fully open?

79vetter

I didn't want to mess around with that idle screw because it idles lower when Lars has the carb - theoretically it should idle the same here..

Yes - the choke opens fully.

MelWff

Why would it idle the same, do you have the exact same engine that Lars did the set up on? In all probability no. Adjust the idle speed screw and mixture screws for your engine.

drwet

The carb is not going to perform the same on your engine. Timing alone would make the two engines idle completely different. You need to set up the carb for your application.

woolf708

Don't jack with the carb! I've read here and other places most idle and performance issues are ignition related.
Lars set that carb up on a mule engine which is what these carb guys do. You mess with one adjustment it can throw off other adjustments... Call the guy that worked on it!
Good luck

babbah

You need to adjust the carb on your engine.
Don't be afraid to adjust it and see if you can get the idle lower. Also you can tweak the mixture screws as well to dial it in. No 2 engines are alike.

Shark Racer

Have you verified your carb is coming off of fast idle? IE, is there a gap between the throttle screw and throttle blade when you're at 1100 RPM?

Iron_dog

you can record Lars setting on the carb and revert back the setup if playing around doesn't change the situation...

7T1vette

Do you have power brakes? Have you removed (and blocked off) the vacuum feed to the booster?

In general, you need to disconnect/block-off ALL vacuum sources from the carb and manifold (except for distributor vacuum advance, which you have already checked out). Then, see how it idles. If different, then you need to chase down where your vacuum leak is located.

P.S. Did you install the gasket/spacer under the carb as recommended by Lars? Sometimes these Q-Jets require specific pieces so that manifold vacuum isn't lost. Check back with Lars, if not sure.

Any possibility that the intake manifold gasket[s] is leaking (sucking in excess air)?

79vetter

Yes - I have power brakes. I blocked off the manifold vacuum @ the source and the Carb vacuum source (independently) - but the idle rpm didn't change. I put a vacuum pump on the brake booster and it held and I installed a new carb base gasket yesterday - no change.

I have sprayed carb cleaner on the intake gasket areas - I didn't notice a change.

there aren't many other things left to check

Brcmpbl

Don't waste your time on another thing until you adjust your idle speed screw.

It's a carb, not a spaceship. Don't be afraid to tune it a little. All you need to do is back out the idle screw a half a turn and see what happens. If you don't like what happens, turn it back in. If it lowers the speed, which it likely will, turn it another half turn, and so on.

If you email Lars, he'll likely tell you the same thing.

bmotojoe

You now have an electric choke. Did the metal line from the hot air choke housing get capped off? After car has reached normal operating temp unhook throttle linkage, manually give the linkage on carb a short pull, let linkage on carb snap back to its home position restart engine and see if idle RPM changes.

79vetter

Not trying to start a war, but I did email Lars.

His response was that there should not be more than a 50 rpm difference between my carb on his test engine and on my engine.

On his engine:
Cold-start fired right up at 1250 rpm. Choke opened far enough after 4 minutes to drop the fast idle off the fast idle screw, putting the carb on the hot idle screw control at 750 rpm initially. After 5 minutes, the choke was fully open. After 6 minutes, the secondary lockout lever was fully retracted and the carb was hot-stabilized at 840 rpm hot idle.

On my engine:
1600 rpm cold start
1100 rpm hot idle

Question: Would adjusting the idle screw be masking a vacuum leak problem ?

MelWff

If you have a vacuum leak you will experience other symptoms than just a high idle, hesitation etc. Note the position of the idle speed screw and than start turning it counter clockwise and your problem will go away. This is basic adjustment of a carburetor.

blue by you

this is how I found my vaccum leak while running I took a pair of pliers and crimped ea hose 1 by 1 until I found which hose was leaking.
Is your timing set

mikem350

Did you check throttle linkage to see if its holding the throttle blades open?
Disconnect it, see what happens.

Another thing is the PCV HOOKED UP? This is a big "leak" and will affect idle speed!

I agree with Lars, the idle speed should be close. But it is easy to reset it!

woolf708

Might be timing. At least check to see where it is.
Lars has a slick way to set it.