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- - Running rough (https://67-72chevytrucks.com/vboard/showthread.php?t=770095)

So I'm getting kind of clueless with this problem. My truck, 71 GMC c15 with a 350, runs super rough out of nowhere for no reason, at first I thought it was a spark issue, I replaced the distributor, plug wires and plugs. It ran great for a few seconds then rough again. Fuel maybe? So I checked my fuel filter, it is glass so I can see if there is no fuel, and sure enough, a lack of fuel. Bought a factory replacement and she ran great for a few days then back to square 1. Replaced all fuel lines, filter seems fine, it is a mechanical fuel plump and it seems to work fine, I don't see why it would break after a few days.

I moved on to see if the fuel sending unit gas line was clogged and it's clear. No vaccume leaks that I am aware of, the carb isn't even a year old, the new Holley street demon. Never had to tinker with it. Jets seem to work fine. I've replaced the whole fuel line and I'm completely lost.

The engine is timed, 8° past top dead centre. Harmonic balancer is a bit wobbly but I doubt that would cause the issue.

Any ideas? I just want my truck to work again...

Re: Running rough

Timing!
Do you mean 8 degrees before tdc? Or 8 degrees after tdc.
You likely need it at 16 degrees before tdc.
Especially at your altitude.

Besides the. Carb, what other mods.
Headers,cam?

Re: Running rough

Quote:

Originally Posted by geezer#99 (Post 8330024)

Timing!
Do you mean 8 degrees before tdc? Or 8 degrees after tdc.
You likely need it at 16 degrees before tdc.
Especially at your altitude.

Besides the. Carb, what other mods.
Headers,cam?

8 deg before is what I meant yeah. But it's been set at 8 for months, why would I need to set to 16 all of the sudden?

Re: Running rough

Quote:

Originally Posted by geezer#99 (Post 8330024)

Timing!
Do you mean 8 degrees before tdc? Or 8 degrees after tdc.
You likely need it at 16 degrees before tdc.
Especially at your altitude.

Besides the. Carb, what other mods.
Headers,cam?

Stock headers, stock cam, only mods I have is valve covers, carb, intake manifold, water pump, radiator, rad fan, exhaust, distributor, plug wires, plugs, fuel pump. I think that is all

Re: Running rough

Clogged pickup in the fuel tank? You mentioned checking the fuel line from the sending unit but not the sock on the sending unit.

Re: Running rough

Quote:

Originally Posted by Fbks_Cruiser (Post 8330730)

Clogged pickup in the fuel tank? You mentioned checking the fuel line from the sending unit but not the sock on the sending unit.

Sock had some buildup in the corner but didn't interfere with the line. Will try a new sock

Re: Running rough

16 degrees because you should be at 16 degrees!
Have you looked in the carb to see if it’s flooding?

Re: Running rough

x2 on the timing. Which carb are you running? Which distributor?

Re: Running rough

Quote:

Originally Posted by 68 P.O.S. (Post 8330802)

x2 on the timing. Which carb are you running? Which distributor?

The new Holley street demon and a msd distributor

Re: Running rough

Did you ever get this squared away?