'86 C10 350 5.7 w/ Edelbrock 1403 carb bogging on hills & quick acceleration

[fatastronaut]

Hey folks - truck is an 86 Silverado/C10. I bought it with a Q-jet, has a brand new Edelbrock 1403 on there now. Had been running great with the new carb, best it's run in years (if you saw the Q-jet I'd be banned from this forum). Lately it's having trouble getting up hills or accelerating quickly. Feels like the carb is bogging down. Example: on a hill it goes & goes, then it'll start to die, then it'll start to buck between revving and bogging down (in rhythm), and if i push too hard on the throttle, it totally stalls on me. Runs great at idle, runs & drives great otherwise.

First thought was a clogged filter. Has a brand new in-line filter going into the carb, pulled it off and it's totally clean. Next idea was the fuel pump. Bought a cheap fuel pressure kit at Harbor Freight, attached it to the line coming from the pump, started the engine and...well it's all over the place. Swinging rapidly between 2-8psi at idle, occasionally hitting 0 or 10. Cut the engine and it immediately drops to 0. Fuel pump is relatively new, but it's a cheap OEM one from ACDelco, and it lived through a lot of me learning my way around the truck when it wasn't running.

If it's not the pump, last idea I had was the fuel sending unit in the tank. It's the original tank, and I haven't dropped it to take a look in there yet. Could be an issue back there?

Thanks in advance for your help!

[bd]

Next idea was the fuel pump. Bought a cheap fuel pressure kit at Harbor Freight, attached it to the line coming from the pump, started the engine and...well it's all over the place. Swinging rapidly between 2-8psi at idle, occasionally hitting 0 or 10. Cut the engine and it immediately drops to 0.

Sounds like you found the issue.

[fatastronaut]

Sounds like you found the issue.

I figured the needle jumping was a bad sign, but I'm still a novice and wanted to make sure there isn't something I'm overlooking. I have a bad habit of assuming.

New fuel pump is on the way, I'll start there & see what happens. Thanks for the help bd.

[fatastronaut]

Update:

Installed a Carter M6626 fuel pump, carb was getting no gas to speak of. Pulled the output line off the new pump and it's dry - maybe a faulty pump? Put the old ACDelco one back on, and it fired back up. WTH. The ACDelco pump seems much lower quality than the Carter one, but the truck is running great now. Not even stalling on hills anymore (see below). With that pressure readout earlier, I'm definitely gonna put a new pump on there sooner rather than later, but maybe I'll try another brand.

One note: I did adjust the idle mix screws a half-turn richer, and set the choke one notch richer. Maybe I was wrong and the carb wasn't getting enough gas - not bogging down.

[bd]

Did you verify that the tank contains an adequate supply of fuel?  Check all of the rubber fuel hoses connecting to the fuel pump and the fuel tank(s).  Make sure none are pinched, cracked or split.  Make sure all of the hose clamps are suitably tight. 

[Chevygold]

Regardless of how the hoses look I'd replace them all for ethanol resistant ones, R4? too many of our older vehicles have gone up in flames to skimp on them!
Your problem could be in the tank, when I dropped mine off for cleaning the mesh on the suction pipe inside the tank was a mess, corroded and blocked.
One of my tanks had a white powdery residue in the bottom, looked like cement when dry, caused no end of filter problems!
If you run the fuel down it's not hard to drop the tanks for a thorough clean and well worth the effort.
Graham

[Mike81K10]

I had a lot of corrosion and rust in my fuel system and my fuel sending units were in very bad shape as you can see from the pics. I have actually replaced or in the process of replacing my whole fuel system to include stainless steel fuel lines. Ethanol in the fuel will do much damage to older vehicle fuel systems.

[TexasRed]

Since you've tried two pumps, it's doubtful that the problem is the tank. However it's possible that it's a new bad pump from Carter.

You could use a fuel hose into a fuel canister. Plumb that into the intake part of the pump. That'll help isolate the issues a little. You may end up needing to clean the tank and replace some of the pieces, but I would take it one step at a time. The pump should be able to suck the fuel out of the canister because it the diaphragm should be putting vacuum to the fuel. Just be careful.

You can then look at the pressure gage to see if it's still going crazy like you were reading before. Remember that edelbrocks and holleys don't like a bunch of fuel pressure too.

If the hoses are original. It's probably time to replace some of them with newer ones that as advised above would be ethanol complaint.

[JohnnyPopper]

Mike! What a mess!

Wait till your father gets home!!!

[fatastronaut]

Really appreciate the advice y'all. I've had a hunch that the fuel sending unit could be part of the problem, but nothing confirmed. Pulling the tank is on my ASAP list, it's all original and likely needs a good scrub and/or replacement. Fuel tank is topped off.

Checked the lines & hoses and they seem fine - no cracks or pinches - but they are original so it's probably time for an upgrade. Did not know about the ethanol thing, I'm sure that isn't helping either.

Mike - I'll send pics when I pull the sending unit and if mine is as bad as your K10, I'm sending you some beer so we can yell about it together