Holly 650 DP Spreadbore 4175 - Team Camaro Tech
Engine General Engine Discussion.

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post #1 of 5 (permalink) Old Sep 11th, 03, 07:50 AM Thread Starter
Join Date: Feb 2000
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Running rich. Bogs down off the line, runs fine mid to high end. Backfires when I let off the gas. Have instruction manual that came with it to install, but doesn't explain how to lean it out. Second question, secondarys open too late if at all. Is that just a spring change? First time I've ever put on a carb for myself. Any help would be great!

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post #2 of 5 (permalink) Old Sep 11th, 03, 11:43 AM
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Location: Concord Cal. USA
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Which carb? Rest of engine specs? 4175 is a vac, sec. carb.
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post #3 of 5 (permalink) Old Sep 11th, 03, 04:33 PM
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Location: skiatook, ok
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Sounds like a combination of an incorrectly adjusted float and a vacuum leak. I put one on my truck a few months ago and have been very pleased with it.

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post #4 of 5 (permalink) Old Sep 12th, 03, 04:01 AM
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If it is a vac secondary carb, how do you know the secondaries aren't opening? It is common for a racer to pull the air filter off and rev it in neutral while watching the secondaries and wonder why they don't open. well, they will never open when in neutral because they only open under high load when the engine needs the air. I think Holley sells more double pumpers this way . . .

Anyway, like travis said look for a vac leak and check the float levels. The float level should be set so that the fuel just barely drips out of the site plug. Make sure th car is parked on a level surface when you check the adjustment too

ps. The secondaries will open sooner WITH an air cleaner installed.

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68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
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post #5 of 5 (permalink) Old Sep 12th, 03, 05:21 AM Thread Starter
Join Date: Feb 2000
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Oh its a great carb Travis. This is the one with choke delete and mechanical secondaries, Oger. I put it on with out adjusting anything. Seemed to run fine, just adjusted the Idle. Then almost immediately I noticed I was backfiring. My old carb was a single pump Holley 600. It only backfires on the highway, and only when I am decelerating. I have a muncie 4-speed. Other than the occassional "fart" the power is fantastic (w/the exception of off the line, where I bog). Could it be too, a fouled plug? I am doing ignition upgrade (MSD) this Winter. How you doing Eric68??

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