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Old 02-04-2012, 08:50 PM   #1
Arl37
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Truck stumbles and almost dies after carb rebuild

69 Chevy 307. It had a two barrel and ran fine. In a fit of being adventurous I bought a performer manifold and rebuilt a old Holley 600 CFM barrel. vacuum secondary.
Truck had new plug wires and HEI before the 4 barrel installation. Runs smooth at idle but when you try to accelerate, even mildly, it backfires and almost dies. When it does pick back runs fine. Cant imagine it is timing. Checked timing and it is 4 BTDC.
Must be carb. Where do I start looking?
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Old 02-04-2012, 08:58 PM   #2
geezer#99
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Re: Truck stumbles and almost dies after carb rebuild

It's timing!! Try 12 degrees. Set it with the vacuum line to the distributor plugged.
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Old 02-04-2012, 09:27 PM   #3
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Re: Truck stumbles and almost dies after carb rebuild

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Old 02-04-2012, 09:28 PM   #4
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Re: Truck stumbles and almost dies after carb rebuild

Really! I will give it a try tomorrow
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Old 02-04-2012, 11:30 PM   #5
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Re: Truck stumbles and almost dies after carb rebuild

Make sure your accel. pump is working good. With the engine off, look in the carb & work the throttle linkage. 2 squirts of gas should come out the nozzles each time. I agree a little more timing might help but I think you have a carb problem. Did you check the float levels after you installed & ran it. The level of the gas should be at the bottom of the plugs on the side of the bowls. You can adjust the level with the adjs. on top of the bowls.
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Old 02-05-2012, 12:43 AM   #6
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Re: Truck stumbles and almost dies after carb rebuild

Quote:
Originally Posted by Wrenchbender Ret View Post
Make sure your accel. pump is working good. With the engine off, look in the carb & work the throttle linkage. 2 squirts of gas should come out the nozzles each time. I agree a little more timing might help but I think you have a carb problem. Did you check the float levels after you installed & ran it. The level of the gas should be at the bottom of the plugs on the side of the bowls. You can adjust the level with the adjs. on top of the bowls.
X2
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Old 02-05-2012, 01:24 AM   #7
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Re: Truck stumbles and almost dies after carb rebuild

I will double check the accelerator pump tomorrow. Think I have the floats set right
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Old 02-05-2012, 04:51 PM   #8
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Re: Truck stumbles and almost dies after carb rebuild

Agree with the accelerator pump adustment. I would start there first.
As soon as the throttle is moved it should begin to squart gas in the carb.
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Old 02-06-2012, 07:20 AM   #9
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Re: Truck stumbles and almost dies after carb rebuild

I would check for major vacuum leaks first, probably at the carb base. With it running, spray carb cleaner around the carb base and even along the intake runners. If it picks up idle speed when you spray, you found a leak.

I'm not familiar with Holleys but if it's a square bore base, you might need an adaptor plate if going to a spreadbore intake.
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