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Old 04-13-2013, 11:57 AM
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backfire

Built 302 Ford 670 Holley Truck Avenger. Off Idle stumble, and backfires through the carb sometimes. Why? 700 RPM, 6 degrees BTDC.

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Old 04-13-2013, 12:42 PM
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try more static timing
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Old 04-13-2013, 02:44 PM
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What do you mean by built? Give your cam specs, trans type, stall speed if auto and so on. I am sure off the top you will need more intial timing as Vinniekq2 stated.
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Old 04-13-2013, 04:13 PM
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30 over 2 valve relief pistons, 160 150 on the valves, 262 512 comp cam roller tip rockers, weiand intake shorty headers, stock converter, c6 automatic, 456 gears, 4-wheel drive. Seems to pull down flat spot until you nail the throttle but when crawling that's when I get the burp out of it. Not really sure where valve adjustment is now it's been a long time.
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Old 04-13-2013, 04:14 PM
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How high does it need to be?
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Old 04-13-2013, 05:03 PM
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Is that 262 advertised duration with 512 lift? Solid, hydraulic, roller, flat tappet? Do you have a grind number so we can see the specs? What is your compression ratio? Wieand intake... but dual or single plane? So far, it may just be a simple lean tip in. Is the pump set correctly too? I can't tell you much for intial timing yet, but I would think 12-14 would do much better. How do you have your curve set on the distributor? Using vacuum advance or mechanical?

There, answer these any we may have a little better picture of what you have.
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Old 04-14-2013, 08:21 AM
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Quote:
Originally Posted by 57 willys View Post
Built 302 Ford 670 Holley Truck Avenger. Off Idle stumble, and backfires through the carb sometimes. Why? 700 RPM, 6 degrees BTDC.
Ayuh,.... Sounds like it's goin' Lean,....

Richen up the fuel abit...
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Old 04-14-2013, 02:18 PM
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Quote:
Originally Posted by 33Willys77 View Post
Is that 262 advertised duration with 512 lift? Solid, hydraulic, roller, flat tappet? Do you have a grind number so we can see the specs? What is your compression ratio? Wieand intake... but dual or single plane? So far, it may just be a simple lean tip in. Is the pump set correctly too? I can't tell you much for intial timing yet, but I would think 12-14 would do much better. How do you have your curve set on the distributor? Using vacuum advance or mechanical?

There, answer these any we may have a little better picture of what you have.
xtreme 4 x 4 flat tappet hydraulic cams
INT. 262 EXH. 270 INT. 218 EXH. 226 Lift INT. .493 EXH. .512 lobe sep. 111 degrees Roller lifters compression ratio 10 if I remember right. Weiand intake dual plane Set from Holley probably should check I'll try 12 -14 on timing and to fatten up the carb that would mean to turn the screws in? And not really sure how to adjust the rockers. I never had rollers before. Thanks for the help. It is in a 57 Willys Wagon with 456 gears and an automatic. Pertronics distributor vacuum advance
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Old 04-14-2013, 02:44 PM
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mixture screws out will fatten idle only. do you know how to change jets?
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Old 04-14-2013, 03:04 PM
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mixture screws out will fatten idle only. do you know how to change jets?
will that make idle go up
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Old 04-14-2013, 04:25 PM
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everytime you change something in the carb,tweek the mixture screws
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