Backfiring through the carb

[t-bear95]

Here's what's going on, I recently bought a 1979 K20 Chevy longbed, and on its maiden voyage over the hills and through the woods it decided to stop working. But let me back up, I live it Utah and as I was traveling up a canyon at highway speeds my truck starts to lurch back and forth backfiring very heavy and losing all power. I let off the gas and bring the speed down 5mph and it stops yet as soon as I try to speed up again, it backfires. Then at my new speed of 5mph less it backfires again and I continue through the cycle until i'm crawling up the pass at 5mph at which time she dies. Now I noticed this happened at even the slightest of inclines but really stood out on the steeper ones. I had 3/4 tank of fuel. I pulled off the road and had a buddy of mine come and help me diagnose it afterwards. We came to the conclusion it was the fuel pump, but even after replacing that the problem persisted. On the side of the highway we noticed no fuel was coming out of the line between the pump and the carb hence leading to us replacing the pump. We then tried to used some quick start aerosol spray into the carb, after spraying some in and putting the air cleaner back on without the wingnut we turned it over and to our amazement we saw the air cleaner lift about 6 inches off the ontake ? I am looking for anybody and everybody that could help me with this diagnosis! Thank you and I will answer any questions you have!

[Boone83K10]

Backfire is a lean fuel situation plus timing. Check your timing, 10-16 degrees advanced is normal for sbc. Then tune you carb mixture screws with vacuum gauge. Try to get the highest vacuum possible. Im posting this from phone so thats why its short. I can get more detailed if you need more help.

[VileZambonie]

Make sure the distributor didn't spin.

[bake74]

     Timing is important, another problem might be blow by of the rings.  Blow by will cause back fire in the carb and exhaust depending on what stroke your engine is on.
     A compression check will tell you worlds about your engine, but do the easy steps first, timing and also check all the regular tune up parts such as spark plugs, wires, dist. etc to make sure they are in good/proper working order.
     Very first step is make sure you are getting a good supply of gas to the carb though.

[454Man]

What kinda carb do you have? If it's a a jet does it still have the filter in the fuel inlet? 

What's under the hood??? If you have to ask maybe we shouldn't race...

[t-bear95]

I brought it to a mechanic and he said my timing was good and mu distributor was also ok but I have my doubts that he actually checked the distributor. I can do the compression check but what psi should I be looking at? I also think I'm getting a good supply because when I disconnect the hose between the pump and carb and then crank the engine, fuel shoots everywhere. I believe the carb is an Edelbrock 1406 performer, it has given me some trouble but I have no idea how to tune a carb and seemingly no one else around my town does either. So With that being  said what would be a good resource to find how to do all these different diagnosis? Thank you for the replies too, I'm definitely lost..

[bake74]

     First off we would need to know what engine you have before we can tell you what your compression range should be.
     As far as your carb. goes, this on-line manual for your carb.  http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf  would be a great read for you to understand your carb. and how to tune it.
     Carbs can be tricky, but try to keep to the basic design, if and when you go to tune it, if for some reason you can not get it to adjust the way you want, then most likely something is leaking or allowing blow-by internally and it just needs rebuilding.  There are also books out there just on carbs., I have and have used the ones for Edelbrock  and Rochester's and found them invaluable.

[t-bear95]

It is a modified 350 which has had some questionable workmanship done to it. Other than that I can't tell you any specifics.

[bake74]

    A stock 79 350 should be between 150 - 170 PSI on each cylinder.  Since it is modified you would have to find out how it is modified and what numbers you should have.  But if you do not get a least 150 PSI on each cylinder I would say the next step is to do a leak down test to see what is wrong.
     Here is a good article on leak down testing, but the internet is full of how to do a leak down test.
http://www.carcraft.com/techarticles/116_0406_cylinder_leakdown_tester/viewall.html

     Good luck and let us know what you find.