Needing expertise, hands & eyes on this truck before I go crazy

[rustytruck50]

I'm knocking on the door of my wits end. I cannot get my '72 to run like I know it can. It seemed to start last fall when the electrical gremlins visited. Got that fixed by a friend, who has gone off the grid & can't be reached for any more help. Next up was the fuel pump going out. Got that taken care of and it's not run completely right since. I figured the problem was the incorrectly installed HEI distributor. I attempted to fix that when I resealed the massive intake leak. The battery lead on the coil was broken at the wire & replaced the coil along with the crusty ignition module, cap & rotor. Worked & worked at setting the timing and found that the balancer was wrong and in bad shape. To the best of my understanding after a lot of reading on the forum, I think it's timed correctly, but I'm beginning to have doubts. It does a bit of bucking and surging above about 30 mph, labors between 50-60, cuts out entirely when it is put to the mat, comes back when I'm off the gas, pop's & backfires a bit through the carb on hard acceleration...wondering if my fuel pump is bad or wrong, but i matched it up to the old one first...pretty much a exorcism may be next. If there is anyone in the Omaha area that could come over and help me sort this out, I'd be forever indebted to them. The last thing I want to do is throw my hands up get rid of the truck because I am pretty frustrated. I did that one time before and later saw the car out and driving perfectly fine after I let it go. I'm officially outside of my pay grade, experience wise!

[harpo231]

What did your friend fix ? ... mech. pump ?

[kwmech]

Sounds like a partially plugged fuel filter

[Shinysideup]

Sounds like a fresh carb or a good rebuild would fix the fuel starvation.

[rustytruck50]

My friend found a bad blower motor relay that was causing a draw on the electrical.....I have a mechanical pump. The truck still has the charcoal canister, but the fittings are broke off and the hoses aren't connected. I tried to block off the hoses, but it made it worse. I have thought about trying to go to a pre- '72 fuel pump and get away from the 3 port pump. Can I do this or am I just adding another unnecessary piece to the puzzle?

[harpo231]

sounds like ya got a bad pump ...

[bill3rail]

Is the firing order correct? I have seen it before where someone is at their wits end and it was the firing order.

Bill

[tutone]

It's been my experience that backfiring through the carb almost certainly is a timing issue. Through the exhaust generally spells fuel delivery problems.

[rjs53]

You reinstalled the HEI, it sounds like your off a wire. 18436572, is the firing order. You can have 2 wires crossed and it will run just not real well.

[stsalvage]

best thing to do is look on here and find some one that is close to you.See what you can barter with case of beer rent a hot girl for 1 hour only after he helps you fix your truck or see if some one had a heart that will come by and help another chevy guy out

[Robznob11]

Originally Posted by tutone

it's been my experience that backfiring through the carb almost certainly is a timing issue. Through the exhaust generally spells fuel delivery problems.

x2

[ElKotze]

Originally Posted by rustytruck50

It does a bit of bucking and surging above about 30 mph, labors between 50-60, cuts out entirely when it is put to the mat, comes back when I'm off the gas, pop's & backfires a bit through the carb on hard acceleration..

That right there sounds like timing to me. Start back at square one and get your timing 100%, or have somebody do it for you.

[rustytruck50]

Thanks guys...I will try all of that....I do have a cracked exhaust manifold and blown out donut seal and id read something about it causing problems similar to what I have been dealing with.....any thoughts on that?

[drewbert41]

That cracked manifold can melt plug wires and cause backfiring through carb. At least it happened to me.

[rustytruck50]

Well, I spent some time this weekend and replaced the totally crumbling exhaust manifold & donut seal, rebuilt the carb and still have some of the same problems...did get better off idle throttle response but still coughs and chokes under moderate acceleration. Thinking about getting a new pump under warranty from O'reilly. Also thinking that I may not have the timing totally right...thought I understood how to get there, but pretty sure I need some help. Good news is I feel like I'm making a bit of a move in the right direction.

[panhead59]

That's gooood news. We all get problems that seem "out of our paygrade" every now and then. Just keep at it one problem at a time and eventually you'll get it right. Do the easy and least expensive stuff first. Definitely change that new fuel pump, especially if still under warranty. New "solid" fuel filter also. Remember ethonal laced gas breaks down fast, as fast as a month or two, so have fresh gas. Most of us overthink these gremlins. Just get down to basics, go over everything and you"ll get it|!|!|!|! Timing is not that complicated, but does seem like your biggest problem. Check wires for correct location and then turn off the lights and look for spark to ground. . Just some thoughts, keep us posted. We all learn from this.

[rustytruck50]

Thanks panhead....the timing definitely shouldn't be that difficult... I've replaced everything on the distributor... So there really shouldn't be much of anything else except for maybe the distributor being worn out. I replaced the parts with things listed in O'Reilly''s catalog for a '78 Camargo since I don't know the origins of the distributor.

[Coley]

One thing about the timing is to make absolutely certain that the HEI distributor is inserted correctly and not one tooth off.
I have seen this happen before.
....this goes beyond just using a timing light because it involves checking the distributor's inserted position vs. TDC.

Once your timing is dead on...then the carb can be adjusted or checked for problems.

Coley

[demian5]

Secondary butterflies too lose? Is it a Q-jet?

I had a poorly running, but drive able truck for a while, and I put a new carb on it and it was a new beast and hauls the mail quickly.

[rustytruck50]

Thanks Coley....I will recheck that...wouldn't surprise me ifor it was off...
demian5...it's a qjet...I wish I could put something else on there...just not in the budget right now

[demian5]

Originally Posted by rustytruck50

it's a qjet

Adjust it, its a good carb, just check the fuel filter and if the secondary butterflies are opening too soon (fast, you can flop them open easily with your fingers), you will get a flat spot, bog, backfire, dying feeling or a flutter right about when they are supposed to open under light or moderate load.

https://ericpetersautos.com/forum/sh...lve-adjustment

https://www.youtube.com/watch?v=QhNYMftwNUo

[Steeveedee]

I looked at that first link. You do not have to remove the air horn to adjust the spring tension on the secondary air valve. You can put the Allen wrench on set screw and loosen it on the vehicle. I've done it hundreds of times, I think- many dozens, for certain. I worked as a mechanic for about 20 years, either for a shop or on my own. I think that the spec is one turn clockwise on the screw after the flaps close. If that isn't absolutely correct, it'll at least get you in the ball park. While you are in there, make sure the secondary metering rods are lifted up when the air valve opens. The nylon cam could be worn or missing, and you'll get a massive bog when the air valve opens and no fuel is added.

[rustytruck50]

Great info in the last two posts....that YouTube video was the money shot....massive improvement! Holy Cow!!! I noticed the secondary doors were not shutting the way I remembered they should when I was putting the carb back together yesterday, noticed the set screw and had no idea what it did. I went a bit far on tightening the spring when I first started and straightened it out where it grabs ahold of the little rod. So, I took the carb off again, flipped it over, pulled the pin & spring and fixed the hook end of the spring. Once I got it back together, I noticed the idle was a bit high, so i'll need to recheck my work. Feeling much betterer!

[rustytruck50]

Could someone explain the EEC system? I think this may be causing me some problems as well. Can I block the canister lines and run a vented gas cap?

[Steeveedee]

Do you mean ECS? Vapors from the gas tank are collected in the charcoal canister- adsorbed onto the charcoal. When the engine is running, vapors are pulled off the charcoal into the PCV system and burned.