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Calling Small Block Chevy experts

catch2otwo

catch2otwo

Active member
Joined
Feb 1, 2009
Location
Vacaville CA
Moto(s)
Multi
Name
Cedric
Out of the blue the truck started getting a very low idle. Sounds like its got a giant cam in it. It seems to run ok as soon as the truck picks up some speed but at idle it pretty much wants to die. At this very low idle, I can see black smoke coming out of the tail pipe. Not a lot but noticeable. I can smell it too. ALSO, if i coast it fast enough, for example if I go completely off throttle in order to exit the freeway, it will pop a bunch of times.

I started with all the easy stuff, distributor is tight and doesn't move. Plug wires are all connected. I changed the two fuel filters, all plugs, and gave it a new air filter. After I changed everything, it ran good for my trip around the block. Idled great at two stop signs. As soon as I pulled into the driveway, it went back to its crappy idle.

A friend suggested fuel pump not moving enough fuel at 0% throttle. Any input?

Oh its a 68 c10 with a 350. Carbed, hei distributor, stock as far as i know. All I know is it ran fine last week haha.
 
maybe a plug wire bad? you should narrow down which cylinder is missing, an easy way is to put some spit on your finger and touch each exhaust tube near the cylinder very quickly, if the cylinder is firing the spit will sizzle off, the one thats not firing it will linger
 
catch2otwo said:
A friend suggested fuel pump not moving enough fuel at 0% throttle. Any input?

Oh its a 68 c10 with a 350. Carbed, hei distributor, stock as far as i know. All I know is it ran fine last week haha.
Click to expand...

Other way around. Black smoke plus crap idle means it's dumping too much fuel through the idle circuit. $1 says the problem is in the carb, specifically the float bowl (sunken float, crap keeping the needle from sealing, needle itself is compromised, etc)
 
vacuum leak?
 
You said the dizzy doesn't move, does that mean you checked the timing? Guessing it's avacuum advance, it working right? Every cylinder is getting spark?

The big cam sound thing has me thinking you put at least 2 plug wires on the wrong cylinder. 1 8 4 3 6 5 7 2

Also don't do anything the guy who said there's not enough fuel pressure at idle tells you to do.
 
I always suspect #7 cylinder and flat cam lobes in a motor I have suspicion about the history. Hope it is something simple like. Carb issue, at least give you a r aeon to install a Holley truck avenger carb on it.
 
catch2otwo said:
Out of the blue the truck started getting a very low idle. Sounds like its got a giant cam in it. It seems to run ok as soon as the truck picks up some speed but at idle it pretty much wants to die. At this very low idle, I can see black smoke coming out of the tail pipe. Not a lot but noticeable. I can smell it too. ALSO, if i coast it fast enough, for example if I go completely off throttle in order to exit the freeway, it will pop a bunch of times.

I started with all the easy stuff, distributor is tight and doesn't move. Plug wires are all connected. I changed the two fuel filters, all plugs, and gave it a new air filter. After I changed everything, it ran good for my trip around the block. Idled great at two stop signs. As soon as I pulled into the driveway, it went back to its crappy idle.

A friend suggested fuel pump not moving enough fuel at 0% throttle. Any input?

Oh its a 68 c10 with a 350. Carbed, hei distributor, stock as far as i know. All I know is it ran fine last week haha.
Click to expand...

What did the old plugs look like? were they consistent in appearance?

sounds like fuel, but could be electrical...weak spark could foul the new plugs going around the block.

running rich or weak spark.

B-12 the idle air bleeds, maybe, and check the coil resistance.
 
First off.. Is it Quadrajet carb? Did you check electric choke operation?
 
If the choke stays closed i don't see how it can't be under powered off idle
should be under powered if it's ignition related too

u suck OP :twofinger
 
Last edited:
So if you didn't change anything, did it get water under the distributor cap, somehow ?
 
haha thanks guys. so old plugs were sooty black but i attributed that to a way over due air filter. Looked into the top of the carb and didnt notice much. It was dirty so I was planning a rebuild at some point, just haven't gotten around to it yet.

Just now got back from taking my dog to the vet. San pablo to oakland and back. Truck runs like shit, wont idle anymore. Pulled the air cleaner off, secondaries (the two bores closest to the cab) were dripping fuel even with the truck off. Turned the truck on to move it to the side of the driveway. Re-opened hood, gas is more than dripping from the same area and now its "overflowing" out of the carb.

Looks like its rebuild time. Guess it moved up a few spots on my priority list.
 
The squid has got it right it's the carb, I'am just guessing but the carb is probably a ROTTEN CHESTER with crappy floats and a peanut butter needle and seat!
 
But hey I've been wrong even after 30 years of wrenching.
 
well, at least you've got positive diagnosis.

light a match to it. that will eliminate the problem.:teeth
 
injun said:
The squid has got it right it's the carb, I'am just guessing but the carb is probably a ROTTEN CHESTER with crappy floats and a peanut butter needle and seat!
Click to expand...


Its a holley 1850-11. Where are you guys going for rebuild kits?
 
JesasaurusRex said:
Every carb problem always turns out to be ignition
Click to expand...

JesasaurusRex said:
If the choke stays closed i don't see how it can't be under powered off idle
should be under powered if it's ignition related too

u suck OP :twofinger
Click to expand...

catch2otwo said:
haha thanks guys. so old plugs were sooty black but i attributed that to a way over due air filter. Looked into the top of the carb and didnt notice much. It was dirty so I was planning a rebuild at some point, just haven't gotten around to it yet.

Just now got back from taking my dog to the vet. San pablo to oakland and back. Truck runs like shit, wont idle anymore. Pulled the air cleaner off, secondaries (the two bores closest to the cab) were dripping fuel even with the truck off. Turned the truck on to move it to the side of the driveway. Re-opened hood, gas is more than dripping from the same area and now its "overflowing" out of the carb.

Looks like its rebuild time. Guess it moved up a few spots on my priority list.
Click to expand...

:loser
 
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