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Does it start right up after staling or do you have to crank it to clear any flooded gas. Also, does it do it every time under the conditions you listed in your original post or intermittently. I would look at the wiring for a break or loose connection. I had a similar issue a year ago. Drove me nuts for a couple months. Turns out it was a broken wire in the magnetic pickup. Pickup tested fine with ohm meter till I wiggled it. Wiggling every wire I could get access to with the car running would be my first move.
Good luck Fred |
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If all else fails, then I would suggest you look into Holley Part #11-4 DASHPOT this is a universal model Holley now provides, there website provides a number of brackets to support this dashpot. Dashpots were standard on the 60"s era Holley four barrels on Shelby GT-350"s and while Holley site says for manual shift cars, Shelby had them on automatics as well. If you could find one of those, they are the best, vacuum operated. The dashpot when adjusted correctly cushions the closing of the throttle in the last 4-500 RPM to idle. They are designed to eliminate the problem of sudden throttle closure shutting the engine off.
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bkozlow's post reminds me that carburetors with mechanical secondaries require more nuanced operation by the driver than standard street carburetors with vacuum secondaries. Their advantage is that they can give full open throttle quicker than vacuum secondaries but require the driver to control the rate of opening and closing to manage the air/fuel ratio during the transistion to and from wide open throttle. IF you have limited experience with a carburetor with mechanical secondaries your solution may require little more than adjusting your throttle technique to match your hardware. In other words, think of squeezing it more or less rather than flipping a switch from off to on.
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Tommy 'splains it better than me:)
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This issue is more common on Holley modular carbs than many other makes, simply because of the two separate fuel bowl volumes, one each for primary and secondary bores.
Accelerate hard, g-force allows the fuel in the secondary bowl to rush to the rear of the bowl, AND allow more fuel in. (The Primary can act in the opposite manner.) Get off the gas abruptly and the momentary high fuel level rushes out of the booster venturis, flooding the engine rich. The OP has stated the engine runs rough after restart, and then smooths out. I would like to know whether the exhaust blows any puffs of black smoke on restart. |
It almost sounds like you have two different problems. A couple of questions if you please.
1. does your carburetor set at a downward slope in your car? Front lower than the back. 2. Try this please. go out and start your car. Don't drive it. Warm it up just enough to allow it to idle on it's own. rev the engine to about 3000 RPM and hold it there for about 3 seconds. Left off the throttle quickly. does the the engine die? |
interested to see how the carb switch goes. I'm thinking the engine is sucking an idle circuit dry. Just a theory. Mechanical secondaries can be tricky.
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It is most likely that you have the idle set to high....with the idle screw that adjust the plates.......set the throttle plates first.....they should just uncover the transition slot.....and then you are supposed to adjust the idle via the idle screws .... The main idle ...screw ...is know used to get it final......if the idle mixture and transition circuit is set correctly it will not do that......1100-1200 is too high...it should still idle under 1000.
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A trick I have used successfully for fuel slosh out of the rear bowl on a holley is taking a piece of rubber hose and connecting the front and rear bowls and allowing the hose to arch up as high as the air cleaner allows. At the top I cut a notch in the fuel line so the bowls can still breathe. This will prevent fuel from sloshing out the short vent pipe and flooding your motor.
Tom |
I appreciate all of your responses, but this car has me more confused now than before. Three times now over the past weeks I've taken it out for a run, and have tried everything to get it to replicate the problem so I could decide which suggested diagnostic path to follow first, and each time, it has run like a top. Not even a burp where before it was dying. I guess for now, I'll accept that it runs fine, and not mess with it. If it acts up again, and I have a sneaky feeling it will, I'll try some of the suggestions you've given me and if I can identify the problem, I'll be sure to post it here. For now though, cross your fingers for me that the gremlin fell out and is laying on the road somewhere.
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