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Discussion Starter · #1 ·
guys a little help i'm pulling my hair out.
car keeps backfiring through carb LM1 shows a lean spike but hell i've tried bigger squirters,jets ,timing up and down, just cant get it figured out.
combo is a 355 sbc with a F1c 750 quick fuel blow thru
74pri/84sec
40pri/37sec squirters
26* timing
pump gas
does it sometimes but really does it when plugs start to go. car shows rich at a cruise 12.0, but when you go WOT its about right 11.2-11.8 after it backfires of course!
it backfired so bad tonight it blowed the inlet tube off?
can someone enlighten me with a fix please before i go insane or back to nitrous cause this blow thru shit is getting on my nerves!
 

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Did you TDC the motor ? Sounds like it could be running out of fuel. What needles and seats,pump and pressure are you running and what is your base and total timming. Could be the ingnition can't keep the motor lit.

However big sneezes that blow stuff off are usually overrich conditions snuffing out the sprak plugs.
 

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The wideband may show lean if the O2 is flooded with gas.
What are the AF's before the sneeze.
 

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Discussion Starter · #4 ·
.120 needle & seat
magna fuel 500 pump
6psi base pressure
base is at 40 then i pull it back to 26 with the dial before i boost it

what gets me is sometimes the damn thing does fine and just flat out hauls ass and blows the tires off doing it, thats what is getting to me why dont it do it everytime????????
 

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NEEDS MORE TIMING UNDER BOOST!!! TRY A BOOST RETARD SYSTEM.. THAT TAKES TIMING OUT AS BOOST COMES UP.... I HAVE RUN 40 DEGREES LOCKED IN WITH A BLOWTHRU, AND NOT REMOVE ANY TIMING ON BBC...9.0:1 COMPRESSION ..
 

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Two things I would consider first.
Pulling 14 degrees out, check your dist rotor phasing, could be getting to far off were you have it phased at.

The carb could be having a problem going through the transistion from vacuum to boost.

Blessings.......Ron.
 

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NEEDS MORE TIMING UNDER BOOST!!! TRY A BOOST RETARD SYSTEM.. THAT TAKES TIMING OUT AS BOOST COMES UP.... I HAVE RUN 40 DEGREES LOCKED IN WITH A BLOWTHRU, AND NOT REMOVE ANY TIMING ON BBC...9.0:1 COMPRESSION ..
26 degrees is a bit low, but I don't think it's going to cause a carb backfire. Maybe an exhaust, but not a carb.

I'd tend to agree there's a sealing issue in the valves.
 

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Discussion Starter · #9 ·
Two things I would consider first.
Pulling 14 degrees out, check your dist rotor phasing, could be getting to far off were you have it phased at.

The carb could be having a problem going through the transistion from vacuum to boost.

Blessings.......Ron.
hey ron thats something i didn't think about, does it matter where you phase it at .... base or the 14 degrees out?
on my nitrous set up i always did it at base assuming that was right.
do you think 14 degrees is to much to take out on pump gas
 

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I don't know if it's too much or not for your particular engine on pump gas. And I also don't know if rotor phasing is your problem or not, but I would certainly check it as a possiblity. Pulling 14 degrees the rotor phasing is important that's for sure.
My suggestion is to make sure you have one of the wide rotor tips (racing type), not the pointed ones. The leading contact edge will be radiused or curved. The trailing edge should be a 90 degree corner at it's end. I set mine up so the trailing edge of rotor at base timing is right at the passing edge of the cap contact. Then check it at full retard and it should have the leading edge of rotor at the approaching edge of the cap contact. This is the general idea to make the rotor and cap happy under load.
Hope this makes sense.........blessings........Ron.
 

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Discussion Starter · #11 ·
I don't know if it's too much or not for your particular engine on pump gas. And I also don't know if rotor phasing is your problem or not, but I would certainly check it as a possiblity. Pulling 14 degrees the rotor phasing is important that's for sure.
My suggestion is to make sure you have one of the wide rotor tips (racing type), not the pointed ones. The leading contact edge will be radiused or curved. The trailing edge should be a 90 degree corner at it's end. I set mine up so the trailing edge of rotor at base timing is right at the passing edge of the cap contact. Then check it at full retard and it should have the leading edge of rotor at the approaching edge of the cap contact. This is the general idea to make the rotor and cap happy under load.
Hope this makes sense.........blessings........Ron.
yeah thats how i was doing it so i guess i wasn't to far off with the nitrous set up before. i'll try it and see what happens you never know i have seen crazier things before!
 
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