89silverado283

ok it a 1980 chevy scottsdale 20, so a 3/4 ton, with a 4 speed tranny manuel, long bed, with a stock 350... ok i have been having problems with it popping out the exhaust. let me explan, i have a 4 barrol speard board carb, both of the air/fuel mixture screws are 1 1/4 turns from all the way in.. k the timing is on, atleast it says it is.. i just put dual exhaust on the old girl 7 feet of exhuast with a glass pack up to headers, when i rev it up or if im shifting gears it will either back fire on the left or the right bank or it will back fire on both banks, i have tried timing, i cleaned the carb and rebuilt it, i put the float and the other setting back to what they was when i pulled it apart, and it still back fires..

Mike Sigmond

Sounds like you dont have enough back pressure in your exaust system.

lukemoore646

sounds like unburnt fuel in the exhaust catching fire, watch a nascar race and in the turns some of the cars shoot flames out the exhaust, its just unburnt fuel getting ignited, did it do it before you put the exhaust on and are there any drivability problems

89silverado283

it did the with the old exhaust as well, before i cleaned the crab out it would blow black smoke when i would rev it up,, and it almost acts like its trying to hydro lock when i go to start it... like it will turn over just fine and i turn the truck off it will turn over just fine and it wont start so i pump the gas peddle 2 times and it some times fires right up but it normaly just makes it turn over treally hard... or it acts like the starter cant turn the motor.. i tried changing the starter but it still does it... i cant figure this one out, its kinda starting to bug me..and yes when i drive it it cuts in and out enough you can feel it in the tranny but not enough to really hear the motor change pitch, but i have had a few people tell me it sounds like its missing i have replaced the cap, coil, and plugs i havnt had money for the wires

mudmaniac

Try retarding the timing a little.

therewolf

Carefully and gradually start reining in your gas mixture. Sounds like it's very possible you're pumping way too much.

I'm going to beat the transmission filter drum here, too. After @ 50K, they start to bog down your whole system if they're not changed.

89silverado283

do what with the mixture?? lol reining?? i dont get it.. and i have a manuel tranny so i dont think it has a filter... could it be my float?? causing the getting to much gas thing??? and the timing thing it actis like its hella addvanced on the timing marks, but when we retard it to the point it says its on (with the vacuum addvance off) it dies, if i leave the vacuum on it, it says its dead on the markk so i dont know what thats about... maybe one tooth off???

89silverado283

or maybe its got a different harmonic pully...

jestam77

sounds to me like you have your fuel air mixture off,, getting too much gas and flooding at low rpms while setting timing

89silverado283

ok if i screw both of the air/fuel screw all the way in i have them 1 1/2 turns out, it kinda clears up around 3 turns out but then i have to choke it... i also noticed that the guy i got the truck from didnt put any grounds from the engine to the frame, and body, could this be a problem??? all my lights work, all my gauges seem to work, heck even the seat belt warning goes off...what should i try???