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Discussion Starter #1
Will a power valve that's been backfired cause a bog or a hesitation when you attempt full throttle, but run normally just driving around?
Trying to tune a full throttle hesitation out but can't seem to get it. I suspect a blown power valve.

What else can I look for? I've ruled out vacuum leaks.
 

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A blown power valve will give a bad running engine at idle, lots of black smoke from the exhaust due to rich fuel. However, doesn't mean its bad, a check of the valve itself would be the order of the day, I think.

A bog is usually caused by not enough initial timing, idle mixture screws too lean, a vacuum leak, too small of squirter size on primary side, or secondaries opening too soon.
 

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Discussion Starter #3
Well, the timing is a guessing game right now..... the engine this carb is on doesn't have a timing tab. My next step was going to time it from scratch, watching the valves and using a piston stop.
I wanted to take another look at the distributor.... points type. Might be gunked up.
I think I can eliminate the power valve then, because it idles and runs fine... not too rich and no smoke.
Thanks Everett
 

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If this engine is a 68 and older SBC, then the balancer timing mark will be coplanar with #1 cylinder, i.e., point in the same direction, but parallel to #1 cylinder centerline.

This is where a metal coat hangar comes in handy, a pointer for TDC.

I myself use a vacuum gauge for timing and tune for max. Then, I back off at 2* increments until the hot engine starts without starter kickback from over-advanced ignition timing, and there is also no pinging at WOT.

You're welcome.
 
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