Technical > Matt Shaff's Engine Shop

head gasket thickness how much is too much?

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crider:
They are short zoomies, I'll slip some pieces of pipe on them as extension,s. I've tried about everything else it's worth a shot

denverflatheader:
crider- since you’ve eliminated possible vacuum leaks, my guess would be the carb.  The first item I’d look at would be the power valve.  The power valve is an enrichment system with purpose to add additional fuel to the carbs main well when intake manifold vacuum declines either through high speed or heavy load.

There are two different styles of power valves, one with small rectangular holes and one with even smaller round holes located just above the threads.  The rectangular holes flow more so that is probably what’s in your dominator.  The two different styles of power valves use a specific gasket, make sure you have installed the correct gasket for your power valve or it could leak and cause a higher idle.  Secondly, if your power valve is bad and stuck in the open position, once you start the engine it will flow more gas instantly through the carb and cause higher idle, versus when it should open as it senses a decrease in intake vacuum, i.e. full throttle. 

Without starting the engine, just turn on your electric fuel pump and fill the bowls, then shut off the electric pump.  If your power valve has a bad gasket seal or if it’s bad and stuck open, gas will flow into the intake and slowly drain your float bowls.  For example, fill at night, check in the morning and if your float bowl has drained down, your power valve needs attention.  Alan

hemidakota:
My friend Scott's dragster is N/A injected alky and with zoomies it idles 2500 rpm, swap to headers and engine will idle as low as you want and also changes tune up quite a bit. We have to pretty much close throttle blades to keep idle at 2500 rpm with the zoomies. No real answer as why except for headers create a little back pressure and do not scavenge maybe? Camshaft could have a lot to do with it? It works so we have not been too worried about it.

Frontenginedragsters:
We run a S.B.Chevy with Enderle stacks on alcohol and zoomies.
Idles at 1500 RPM very smooth.

Paul New:
Do you have to have the idle cranked up to far that you are no longer in the idle circuit of the carburetor? I know years ago running a carb and I had to drill holes in the throttle blades to get it to idle low.

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