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416 high rpm backfire #998521
05/23/11 06:35 PM
05/23/11 06:35 PM
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maxwedge1 Offline OP
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416 sb been running same combo for a few years.
no previous poblems maybe 1500 miles on motor.

has developed a high speed hesitation and backfire out exhaust.
pulls good threw the gears but once in high gear at full throttle for a few seconds, feels like key is shut off then backfires out exhuast. then recovers as long as you get out of the throttle and runs fine at part throttle.

plugs/wires/cap seem good no sign of a lean cylinder.
mech advance not stuck, cant find vacuum leak.
new carter hi-po mechan pump, fuel pressure/float set ok.
carb cleaned.
havent pulled valve cover to look for broke spring but wouldnt expect that with low miles.

got me stumped.....mallory ready to run dizzy and msd coil.
only does it after going into high gear(4 spd tranny) at full throttle, i dont feel it 1st threw 3rd.

Re: 416 high rpm backfire [Re: maxwedge1] #998522
05/23/11 06:38 PM
05/23/11 06:38 PM
Joined: Oct 2004
Posts: 6,293
Northeast, Alpine, NY
9
9 Sec Phill Offline
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9 Sec Phill  Offline
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Northeast, Alpine, NY
Sounds like your starving for fuel.

Re: 416 high rpm backfire [Re: 9 Sec Phill] #998523
05/23/11 06:43 PM
05/23/11 06:43 PM
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maxwedge1 Offline OP
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added new pump and filter after problem began....underhood gauge, may have to run temporary gauge inside check pressure under load

Re: 416 high rpm backfire [Re: maxwedge1] #998524
05/23/11 09:35 PM
05/23/11 09:35 PM
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert Offline
Circle Track
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
Set a small can of gas in the eng compartment plumbed to the mech pump inlet w a 5/16" neoprene line & check/replace the filter(s) between mech pump/carb including carb inlet screen & take her back out. Still bad, I'd sub in a diff coil & repeat & if still bad I'd sub in a diff dizzy & repeat


live every 24 hour block of time like it's your last day on earth
Re: 416 high rpm backfire [Re: maxwedge1] #998525
05/23/11 10:33 PM
05/23/11 10:33 PM
Joined: Dec 2008
Posts: 176
Rome, GA
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GTXX Offline
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Rome, GA
most likely ignition, not fuel. coil would be my first guess. backfiring out the exhaust usually means that it did not fire and unburned fuel in the exhaust is igniting when the ignition comes back.

Re: 416 high rpm backfire [Re: GTXX] #998526
05/24/11 07:51 PM
05/24/11 07:51 PM
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maxwedge1 Offline OP
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coil is 6 yrs old probably time for new 1

Re: 416 high rpm backfire [Re: 9 Sec Phill] #998527
05/24/11 09:41 PM
05/24/11 09:41 PM
Joined: Mar 2011
Posts: 27
Virginia
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hokies1 Offline
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Joined: Mar 2011
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Virginia
check BALLAST Resistor







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