'86 C70 427 Ci - Running too rich?

Hey everyone, I know it's been a while but I've been working on an '86 C70 Dump Truck that decided it didn't wanna run anymore. Traced it back to the fuel tank switch. Anyways, as I was taking off the fuel inlet line, I got good flow. I wasn't getting any flow through the little inline filter inside of the big fitting that goes into the carb. However, after taking it out and playing with it, I managed to get flow through it again. It gushes out pretty good. So I put everything back together and she runs ok. Idled pretty good at first but now when it warmed up it sounded like it was on it's last breath. I'm not very good with carburetors, but I looked at the exhaust and saw black smoke so I'm assuming it's running extremely rich. Never had this issue before. Just hauled some logs with it today and it backfires really bad when letting off the gas and barely wants to idle when coming to a stop. I believe it's a 427 motor. PO installed a new Holley carburetor a few years ago. It always backfired a little bit and had an idle issue on very hot days. I'm more knowledgeable of diesels than I am of carb'd gas engines lol. I ordered a set of plugs for it since they look old and I'm sure they're fouled.

Any suggestions? I'm gonna try and adjust the lean/rich setting and see if that helps at all. Puzzles me how it does this after just taking off the fuel line. Maybe that filter is stuck open too much? Again, I don't have much experience with big carburetors

Being a Holley, I would start with checking the float, and when you say backfire, like backfire out the intake or the exhaust, if the intake, being a Holley, check that the power valve hasn't blown out.

legopnuematic said:

Being a Holley, I would start with checking the float, and when you say backfire, like backfire out the intake or the exhaust, if the intake, being a Holley, check that the power valve hasn't blown out.

Click to expand...

I second this 1 backfire through the carb and the poervalve is done.

legopnuematic said:

Being a Holley, I would start with checking the float, and when you say backfire, like backfire out the intake or the exhaust, if the intake, being a Holley, check that the power valve hasn't blown out.

Click to expand...

Backfires through the exhaust

Holley carbs made in the last couple decades have what they call "power valve blowout protection" and it seems to work.

I'd say good advice so far, but if you think the plugs are worn out replace them before you do anything with the carb. Some* Sometimes lack of good enough spark can cause an engine to appear to rich as the fuel just isn't getting burned properly. Start there and see what happens.