Blown power valve

[michael69]

Can someone tell me what the smyptoms of a blown power valve in a carb are. Does it cause hard starting, stumbling when driving or what.Thanks for any help.

[flyboy2610]

It pumps a lot of gas through the carb. You'll have cloud of black smoke following you, and you'll get very poor mileage. You'll also have a strong gas smell under the hood. It'll foul your spark plugs quickly, too.
To prevent blowing a power valve:
http://www.holley.com/125-500.asp
http://www.automedia.com/Holley_Power-V ... 011001cb/1

Quote from second link:
It doesn't take much to rupture these valves; just barely a perceptible cough or sneeze in the intake manifold will do. When ruptured, the power valves are essentially open all of the time, making the engine extremely rich at idle and part throttle. The easiest way to check for blown-out power valves is to gently turn the idle-mixture screws all of the way in. If the engine starts and idles without stalling, it's getting fuel from somewhere else—most likely a leaking, blown-out power valve.

[michael69]

Thanks flyboy2610 for the info. The problem I am having is it will start right up after setting all night with two quick pumps of the gas. then after driving when it gets hot when I turn truck off if I restart it in the next 4-5 minutes it will start right up but if it sets any longer I have to hold gas pedal to floor while cranking and it has to crank over for several secs before it will start. It acts as it is flooded and is hard to start. Any ideas ???

[george worley]

Sounds like a leaking needle and seat or the fuel boilling in the carb from heat coming up on the carb from the engine when it is not running.

[michael69]

I had thought about the heat getting carb hot after it sat. Do you think one of the phenolic carb spacers would help any? If so would a 2 inch one be better or the 1 inch spacer. The phenolic spacers are suppose to stop heat transfer from intake to carb.

[george worley]

I think a 2 inch would be the best if it doesn't interfear with hooking up your trottle linkage.I think the ones with the holes in them are better than the open ones. A two inchone will give you more low end torque. I have a 1 inch on mine because of linkage hook up and I have a tall air filter on it. If this doesn't solve your problem check your needle and seat.