C3 Rough Start-UP, 427/400 hsp. With TI

[Jack Corso]

At cold start-up, the motor runs rough. I have to warm it up for quite a while before it idles good. Vacuum is good but get some minor hestitation in gears when I backoff on the throttle.Car runs good at higher speeds. could this be a fuel problem? I'm running avgas 100% Any thoughts? Thanks.

[Jim T.]

Re: C3 Rough Start-UP, 427/400 hsp. With TI

Jack the Holley carbs are known to develop ruptured power valves. A quick check that has worked for me for years is to remove the air cleaner top and start the car. Put a finger over the fuel bowl vertical vent of your center carb. If your engine dies immediately the power valve is ruptured. Easy fix, just a new fuel bowl gasket, metering block gasket, and power valve. I keep spares in a little plastic tool box that I take when going away from home, never know when you will have power valve rupture. These separate items are available from Auto Zone. If the power valve is good, putting a finger over the veritcal fuel bowl vent will not make the engine die immediately, but it will die with the vent air blocked off.

[Clem Z.]

Re: C3 Rough Start-UP, 427/400 hsp. With TI

holley sell a tool to retrofit a ball check valve to prevent the power valve from blowing out during a backfire thru the carb. all new holley carbs since 1992 have had this check valve

[Clem Z.]

i forgot the holley kit part # 125-500 *NM*

[Jack Corso]

Re: i forgot the holley kit part # 125-500

Thanks all.