big backfire problem

[75_chevy]

I have a goodwrench 350 rated at 260hp with about 50k miles on it. recently I've put headers 2.5" pipes glasspacks and turndowns. was running pretty good. also have anew 1406 600cfm carb.
the other day I replaced the spark plug wires and took it for a test drive. on the test drive my truck completely died on the freeway. get towed home and we find the fuel pump had basically fallen apart. so we put the old gm one back on. one that works and we mistakenly replaced about a year ago.

now when I drive it it drives terrible. it's fine from idle up to about 2100 rpm.
if you rev it up it immediately starts backfiring extremely bad and the whole motor loses power. it sounds like a fully automatic gun of some sort. very obnoxious and not making me happy to have this happen. what could possibly cause this? I adjusted the timing and I've eliminated the charcoal canister but it was popping before that. anyways adjusted timing it's at 12' btdc give or take a degree. still popping. I gradually gassed up to 2300 rpm and it started surging and dieing. please help. this is my daily driver and I am only 19 and learning as I go. I can limp it around town to work for the upcoming days but I need to fix it as soon as possible in case I need to use the freeway. thanks everybody


Sent from my iPhone using Tapatalk

[75_chevy]

also I've adjusted my idle screws and got them pretty dialed in. my regular idle is around 1k which is ok with me I may tune it down to less, but when I shift into gear it drops to about 400 rpm which is way too low usually it's around 6


Sent from my iPhone using Tapatalk

[75_chevy]

mechanical fuel pump is pushing 8 to 8.5 psi


Sent from my iPhone using Tapatalk

[75_chevy]

I'm really stuck what other info can I give you guys


Sent from my iPhone using Tapatalk

[jaredts]

Look for vacuum leaks, burned spark plug wires, wires not plugged in all the way.  Don't crank them down, but see if the carburetor bolts have loosened by snugging them a little.  Using insulated wire pullers or something to protect you from getting shocked, you can pull the spark plug wires off the plugs one at a time with the engine idling.  If one doesn't cause an rpm drop then that cylinder is a problem for some reason.  If you suspect fuel then you can get a few feet of fuel hose and use it to extend the fuel line from where it hooks into your carb. into a bucket.  Have someone crank the engine and see if you get a good flow.  A trickle won't cut it.
Have you done anything to your truck just before the problems?  I always start with the last thing I worked on just in case I screwed something up or knocked something loose.

[bake74]

     Edelbrock 1406 carburetor has a maxim fuel pressure of 6.0 at idle.  Please see page 8 of the following manual.  owners manual
     Under  Fuel Pumps and Pressure, it says to set the fuel-pressure regulator (if equipped) to 5.5 psi.  Minimum pressure is at WOT which should not drop below 2.0 psi, if it does you will need a higher flow fuel pump.
    Continue reading and it will give instances of what happens with more than 6.0 psi of fuel pressure and what to do to correct it.  Good luck and keep us informed.

[Captkaos]

Another thing to check is if there is water in the gas tank...  Remove the line from the carb and pump some gas into a jar and let it settle...

[75_chevy]

jaredts: only things I did before it started was 1put the old fuel pump on2 replaced plug wires 3removed charcoal canister.

bake: thank you I just printed out that manual and I'm going to get a regulator tomor.

capt: I'll check that out tomorrow, but if there was water in the gas wouldn't it backfire during idle or at any rpm? my real problem area is high acceleration around 2200 rpm. also I was Reving while idling and it didn't pop at high rpm, but it backfired as soon as I hit high rpm while in drive.. thanks guys !!


Sent from my iPhone using Tapatalk

[Captkaos]

If there is water in the gas it will probably run out of gear at high rpm (relative) but once under load it will start missing and backfiring.

[75_chevy]

ok gotcha. and to clarify it is not like one or two cylinders missing, at the high rpm or wide open throttle every cylinder starts popping and backfiring badly. which I think rules out bad wires, especially since I just got new ones


Sent from my iPhone using Tapatalk

[Irish_Alley]

hows the fuel filter?

[75_chevy]

it had a small amount of black crud floatin around last time I saw it (within the past week)  I saw it right before work and didn't have time to clean it and forgot
about it


Sent from my iPhone using Tapatalk

[Irish_Alley]

i would check that it might not be clogged but may be restrictive and causing you to run out of fuel.

[75_chevy]

I'll go check that out right now


Sent from my iPhone using Tapatalk

[75_chevy]

k it was worse than I thought but I don't think they're was enough stuff in it to block the gas too bad. I also found out my fuel line is shredded where it meets the filter on both ends. I will get new line tomor and for now I put the plastic inline filter that came with the carb on. thank you Irish



Sent from my iPhone using Tapatalk