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six pack back fire

Cratos

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my 383 sixpack has an annoying back fire issue only under load I get single back fire??? I have played with the timing and changed to lower power valve.
running about 12:1 on the AFR

sixpack spec cam,and springs, roades lifters and new sixpack set-up 355 rear and 727
 

fasjac

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Is it popping out of exhaust or carbs? Did it just start doing this? Only reason I’m asking is that I’ve seen this happen when buddies change plugs, wires cap and rotor. I’m not implying anything but, could be a plug wire crossed, cracked cap etc. I’m sure you’ve already checked the simple stuff. What did find when checking the timing?
 

Cratos

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timing is@10btdc motor has about 120 miles on it only dose it if you jump on it. just driving around its ok???AFR runs 12-14, in till about 2500-3000 rpms then drops to 16. distributor is the old one, that was in the car when I got it. . new plugs, wires, cap and rotor, pops out intake but found blown exhaust pipe gasket so fixed that. very annoying.
 
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fasjac

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It sure is annoying. When you the say the distributor is an old one, as in the oe? You are running electronic ignition right? It’s easy to go down the rabbit hole on these six packs, that’s why checking and double checking the easy stuff is so important. If you get time, there’s a member on abodies only (monkstur) I believe, that has a really good post IMO.
Because after this stuff, we’re possibly looking at a leak down test, push rod inspection, cam etc.
 

fasjac

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One other thing to check, squirter size and condition. Also, adjust gap on the leaver arm to .015.
 

fasjac

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Good, what plugs, gap did you use and just make sure the gap didn’t close up on one (accidentally).

A33E7B5E-A526-424B-ABD1-216CC4FCBEAA.jpeg
 

fasjac

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The autolite on the left is new out of the box. The champions is what I currently use gapped at .045. I’m not an autolite fan but, a lot of friends have good luck with them. They may go in mine when needed, as the champions just don’t last long.
 

Cratos

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champions gapped @035
center carb jetted @ 62 outboards @82

took it back out and about 2500-3000 leans out to 16
thinking I need to rejet the center to 70??

your video wont open
 

Chryco Psycho

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Just to be clear the accelerator pump arm should have preload at all times , any play will cause a bog , what Fasjac is reffering to is at wide open throttle the pump arm should still have a at bit more travel left & not bottom out
 

fasjac

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It was just a video from yotube. I think you’re past all that anyway. It was just the basic stuff.
I’m running out of the box carbs from 10 years ago with no problems. My center jets are #62 I think the outboards are #84 ( would have to confirm). My power valve has a”6” on it. I know the auxiliary diaphragm is a 31. Had to replace due to dripping fuel.
I’m running a comp cam .545 hydraulic.
Eddy 84cc heads. Rotating Assy is 500 C.I. stroker. I mix 93 oct ethanol free with 100 AV gas. No bogging or popping. WOT pulls really hard. Didn’t mean to bore you with the simple stuff but, been down that road, after over thinking it. Sounds like you’re about to get it. My total timing is at 36 degrees.
My distributor is MSD pro, 6AL box and blaster 2 coil. Please keep me posted.
 

Cratos

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will do I am checking with a bud to see what jets he has laying a round hoping he has some 65-67's before I order a kit. I need to get this corrected show season is going strong here in FL plus I need to feel comfortable before going on any distance rides with it.
 

fasjac

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I’ll tell ya, the out of box did really good on mine. I have two center carbs.
Here’s what in them.
47B628A0-3993-4E9A-A29E-623C151D58BB.jpeg
8A9FC690-8AFD-4B1B-A447-7648C3A6EB03.jpeg
 

fasjac

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Here’s what’s in mine. The 6 is all I can see on the PV, but 62 for sure on the jets.
 

Chryco Psycho

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61 or 62 is normal in the center carb , accelerator tunign may get rid of a stumble but often low intake vacuum & air bleed that are typically too big can cause a problem too , inserting a piece of welding wire usually .035 into the bleeds can tell you if that is part of the problem , I make a horse shoe & slide it behind the squirter to trap it with both ends into the bleeds
 
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