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Discussion Starter · #21 ·
Checked the driver side exhaust this afternoon with the shop vac blowing air into it and soapy water again....no leaks. Took the truck for a long cruise and it still backfires out of just the 1 side. Other than the backfire it seems to idle and run well.

I didn't have time to let it cool down and pull the plugs again before work tonight but I'll inspect them tomorrow. I cleaned the carbon off all 4 driver side plugs before I left today and took a 40 mile ride of primarily highway and some stop and go local. The plugs looked a little rich before my drive but this is the first highway cruising it's seen. If the plugs still look rich upon inspection tomorrow I'll probably try stepping down from a 60 jet to 59s or 58s. Maybe when the throttle snaps all the way shut that last instant rich mixture doesn't have enough air to ignite in the cylinder and when it hits the header there's enough scavenged oxygen from the lake pipes being so short to ignite it? If I really ease out of the throttle on my shifts or feather it so it barely stays open I get no backfire.
 

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Discussion Starter · #22 ·
Just pulled my plugs....pics below. I'm not fouling anything but seems a bit rich still right? This was after about 40 miles of mostly highway driving. I have 60s in my center carb right now....I think I have 57s and 59s on hand. Worth leaning it out a bit and seeing if less fuel helps the backfire and overall combustion I suppose?
Wood Grey Finger Thumb Nail
Finger Thumb Wood Auto part Nail
Fluid Gas Audio equipment Auto part Automotive tire
Azure Wood Grey Flooring Pattern
Wood Grey Finger Thumb Nail

Fluid Gas Audio equipment Auto part Automotive tire

Finger Thumb Wood Auto part Nail

Azure Wood Grey Flooring Pattern
 

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Discussion Starter · #24 ·
So I went down 2 sizes but didn't change idle mixture or timing....backfire seems to be worse instead of better....I'm stumped. I'm going to try to get another highway run in later or tomorrow and see if the plugs at least look like they leaned out with less black deposits. Then maybe bump the timing to see if it helps?
 

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Discussion Starter · #27 ·
Just went for another cruise....backlash with the occasional loud backfire out of the driver side is still there. Other than that it feels like it's running good. I tried bumping timing up during the ride by several degrees with no change. Pulled 2 plugs when I got back and they were slightly cleaner than before. Ground straps have no soot....faces have some still but not as much as before the jet change. Wondering if I still need to go down another size or two....although I don't think it'll effect the backfire. At this point I'm about ready to give up and live with it as being the nature of the combo
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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Are these carburetors from a dedicated tri-power set up or did 3 of the same carburetors go on a tri-power intake?

From what I can tell, the 2 outer carburetors on the factory set up didn't have idle circuits and had special butterflies to permit better closure of the outer carburetors at idle. Do the outer carburetors have idle circuits?
 

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Discussion Starter · #30 ·
Are these carburetors from a dedicated tri-power set up or did 3 of the same carburetors go on a tri-power intake?

From what I can tell, the 2 outer carburetors on the factory set up didn't have idle circuits and had special butterflies to permit better closure of the outer carburetors at idle. Do the outer carburetors have idle circuits?
These were built to be end carbs...no idle circuit and heavy butterflies. I've had the ends completely blocked off with plates I made and it didn't stop the backfire

I'm going to completely swap the wires between both sides today and see if the backfire follows. Going to call Pertronix and see if there's a good stock application cap and rotor I can replace with locally as well.
 

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Discussion Starter · #31 ·
Swapped wires with no change...still backfiring on driver side. I also feel a hesitation now when I punch it at part throttle so stepping down 2 jet sizes yesterday may have been too much.

On the issue of timing advance....like I said bumping initial didn't seem to help. The Pertronix distributor comes with a few sets of springs.....I'm running the silvers since they seemed to be fairly non aggressive as a base point. Wondering if stepping up to the next set would help or hurt? The advance chart is below...
Blue Font Line Parallel Rectangle
Blue Font Line Parallel Rectangle
 

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Discussion Starter · #32 ·
I went up to the next advance curve setting ....once I bumped the jets back up to the 60s the truck feels snappier with more power but still backfires. May just live with it at this point after I do a few more plug chops for the air fuel ratio. Then I may put an undercarriage exhaust on this winter because honestly it's a bit too loud for me....I must be getting old
 
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