Technical Dual 94's on Offenhauser Intake high RPM on start-up

Hello all,

I installed an Offenhauser intake, my first time. I have the idel screws bottomed out and have looked for vacuum leaks with out finding anything. I pressurized the system and blocked off one carb port to find vacuum leaks. Nothing. It is running very high idle with the ****erflies closed tight. I did check this several times. There is fule coming out the top of the fuel pump which is new last year. Is it possible that the fuel pump that was running fine on the old intake is now over pressurizing the carbs?

 

If the idle screws are bottomed out, the idle circuit is closed. It has to pull gas from somewhere so it's pulling out of the power circuit. On a 94 the idle circuit is there at the "****erflies". Vacuum could slightly pull the plates coving the idle circuit. Linkage out of adjustment can pull the plates over the idle circuit.
Look at how the choke works on a 94.
When the choke is slightly pulled, the throttle plates open slightly and the plates cover the idle circuit. (Fast Idle/Power circuit)
When the choke is completely pulled, the choke plate closes on top.
This could be a linkage issue.
I'm not saying this is your main problem but with the idle screws closed it has to get gas from the fast idle circuit.

It's always a good idea to test run each carburetor on a single intake first.

 

I did remove one carb and I am spraying the area looking for a vacuum leak. I spaced up the fuel pump with a thicker cork gasket. It is still very high rpm on idle. I am going to keep going on it.

 

It's always a good idea to test run each carburetor on a single intake first.[/QUOTE]

If I completely close the choke it will stall.

 

That's not a high idle!
That's 1/2 Throttle or better.!!!!!!
Sounds like 2500 RPM.

You are pulling air from somewhere. It's not good to run that engine that way.

 

Thanks F-One. It is much better now. You were right. One of the throttle plates was not in the bore center and that carb was open quite a bit. I adjusted it and it is back down to a normal idle. I only ran it that way for a few seconds because it sounded scary.

 

'Back to basics'. Good find.
Most of our 'issues' are found by retracing steps, esp. ignition improvements and increases in volumetric efficiency!