Hey guys,

My '87 Formula has a unmodified 350 crate motor with 1406 Edelbrock Performer series carb. Under load, at 3/4 to full throttle, the car makes this very loud whistling scream around 3000-4000 RPM. If I rev the engine through that range, there is no noise. If I roll through that range under partial throttle (~1/2), there is no noise.

Initially, the car would also stumble and felt like there was no power in conjunction with the noise. I adjusted the mixture idle screws and timing and the stumble and power loss has gone away, but the noise persists.

The timing at idle is at 8 degrees. The vacuum is at 15 in Hg at 800 RPM (low?)

Any suggestions on how to diagnose or fix this issue?

My limited experience and knowledge makes me think it's an issue with the carb, could it be elsewhere such as in the Trans or clutch (Borg Warner T5)?

 

I am having the same issue on my 69 C15. did you ever figure this out?

 

This may be caused by a rip or tear in a base gasket, air horn gasket, or adapter gasket or some foreign material stuck in an air passage of the carburetor. Inspect the gaskets to make sure you have no vacuum leaks of any kind. Check to make sure carburetor is seated correctly, and is fastened with the correct hardware. You can perform a quick check to find external vacuum leaks (such as a leaky carb base gasket) by spraying starting fluid on suspected areas while the engine is idling. If the engine speed changes for a second or two after you spray an area of the carb, you're found the leak.

 

 

This reply is long after the original post but I have experienced this issue on my sons C-10 and it had us guessing for a while as the noise was intermittent.
It was a vacuum leak between the carburettor (600 Holley) and manifold, it looked ok but the new gasket fixed our problem.