idle/popping issue - The 1947 - Present Chevrolet & GMC Truck Message Board Network

catch2otwo · 02-10-2015, 06:42 PM

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. No details on the 350, PO did all the work. All I know is it ran fine last week haha.

octanejunkie · 02-10-2015, 06:50 PM

Timing sounds retarded

catch2otwo · 02-10-2015, 06:57 PM

Quote:

Originally Posted by octanejunkie

Timing sounds retarded

Could you elaborate on it? How would it change if the distributor is tight? Could there be an issue with the internals of the distributor?

thanks

octanejunkie · 02-10-2015, 07:08 PM

I won't speculate as to how that could have happened but if you have a timing light you should check the timing. Based on the symptoms you are describing "very low idle" and "popping when coming off throttle" it sounds like retarded timing.

It's going to an issue with either timing or fuel delivery, and in my it's best to confirm and rule out timing first. Since you also worked on the fuel filters, I'd throw a T in the fuel line and confirm fuel pressure while driving, AFTER you've confirmed your timing is correct or at least close.

Hope this helps

catch2otwo · 02-10-2015, 10:27 PM

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 ****, 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.

GASoline71 · 02-11-2015, 12:06 AM

Stuck floats or a hung needle...

Gary

cadillac_al · 02-11-2015, 07:57 AM

Probably time for new points and condenser.

catch2otwo · 02-11-2015, 08:13 PM

picked up a rebuild kit today, will have a go at freshening this thing up.

GASoline71 · 02-11-2015, 09:59 PM

If it's a 40 year old Quadrajet, it will need the throttle shafts rebushed or you will have vacuum leaks.

Gary

02-10-2015, 06:42 PM	#1
catch2otwo Registered User Join Date: Mar 2013 Location: SF Posts: 345	idle/popping issue 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. No details on the 350, PO did all the work. All I know is it ran fine last week haha.

02-10-2015, 06:50 PM	#2
octanejunkie Registered User Join Date: Jan 2015 Location: Santa Monica Posts: 264	Re: idle/popping issue Timing sounds retarded __________________ Déjà vu. It's that feeling you get when you hit your thumb with the hammer a second time '59 Chevy 3100 Stepside

02-10-2015, 07:08 PM	#4
octanejunkie Registered User Join Date: Jan 2015 Location: Santa Monica Posts: 264	Re: idle/popping issue I won't speculate as to how that could have happened but if you have a timing light you should check the timing. Based on the symptoms you are describing "very low idle" and "popping when coming off throttle" it sounds like retarded timing. It's going to an issue with either timing or fuel delivery, and in my it's best to confirm and rule out timing first. Since you also worked on the fuel filters, I'd throw a T in the fuel line and confirm fuel pressure while driving, AFTER you've confirmed your timing is correct or at least close. Hope this helps __________________ Déjà vu. It's that feeling you get when you hit your thumb with the hammer a second time '59 Chevy 3100 Stepside

02-10-2015, 10:27 PM	#5
catch2otwo Registered User Join Date: Mar 2013 Location: SF Posts: 345	Re: idle/popping issue 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 ****, 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.

02-11-2015, 07:57 AM	#7
cadillac_al Registered User Join Date: Oct 2013 Location: Maine Posts: 2,344	Re: idle/popping issue Probably time for new points and condenser. __________________ 76 Chevy K20 76 GMC K15 77 Chevy C10 77 Chevy K10

02-11-2015, 08:13 PM	#8
catch2otwo Registered User Join Date: Mar 2013 Location: SF Posts: 345	Re: idle/popping issue picked up a rebuild kit today, will have a go at freshening this thing up.



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