Stalling and shifting help? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

skyreep1 · 10-24-2010, 05:40 PM

Okay, a few weeks ago I rebuilt my 2bbl carburetor on my 71' 307 c-10. Being stupid I didn't count the turns on my air and fuel screws. Now it runs but seems like it's running at high rpms. Also, when you just depress the gas a little it'll start to lose rpms and sputter out unless you pump the peddle some like you're revving it. Secondly, when I shift into any gear (it's an automatic) it acts like it's in park, the shifter moves very smoothly but it just won't move when you gas it. Help please? Thank you guys
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ray_mcavoy · 10-24-2010, 08:22 PM

Hi skyreep1,

Standard procedure with most carb rebuilds is to turn the idle mixture screws all the way in until they lightly seat (don't tighten them or you'll damage them). Then back them out an equal number of turns (usually about 2 or 3). That'll give you a baseline setting where the engine should idle decent enough for you to fine tune the idle mixture. Note that you might have to back off the idle speed screw (over on the driver side by the throttle lever) if the engine is idling too fast.

The hesitation/sputtering could be due to a number of problems. Like a vacuum leak, retarded ignition timing, stuck/inoperative advance mechanism in the distributor, bad condenser, passages in the carburetor that didn't get thoroughly cleaned during the rebuild, and so on.

Check the shift linkage to make sure something didn't come loose or unhooked. The movement of the shift lever shouldn't be overly smooth/easy. You should feel a bit of resistance as it "clicks" through the detents in the transmission.

Also make sure the transmission is full of fluid and that the fluid doesn't smell burnt.

ChevLoRay · 10-25-2010, 11:04 AM

[QUOTE=ray_mcavoy;4258096]Hi skyreep1,

Standard procedure with most carb rebuilds is to turn the idle mixture screws all the way in until they lightly seat (don't tighten them or you'll damage them)..... QUOTE]

Good point, and one I've made before....

I have seen a bunch of those screws that have been bottomed-out and that will form a groove in the taper. That groove increases the amount of air that flows and makes your adjustment difficult.

ray_mcavoy · 10-26-2010, 08:32 PM

Hi skyreep1,

Yeah, check the vacuum hoses going to the vapor canister to make sure they're not cracked, split, cut, or anything that'd cause them to leak. The canister being old shouldn't be a problem. But give it a good looking over to make sure the plastic isn't cracked or anything.

There's also a vacuum hose going to the ThermAC air cleaner (if it's still on there). And a vacuum hose going to the distributor vacuum advance. That might be routed through a solenoid valve if your engine has TCS (transmission controlled spark). Check all those hoses and parts for vacuum leaks. Also check the hose going to the PCV valve and the one going to the brake booster if your truck has power brakes.

Unfortunately, even with new ignition parts, you can't totally rule out an ignition problem. A couple months ago I had an experience with a new condenser that was defective right out of the box. It made for a weak spark that was just strong enough to start & idle the engine. It'd bog, sputter, and want to stall out if you gave it too much gas.

skyreep1 · 10-25-2010, 08:24 AM

Thank you for answering so many questions, I have a feeling it's probably vacuum hoses because it sat without a hood on for a year or more before I got it. I don't think it's my linkage though because you can still will it pop into park etc. I'll check the fluid too though, do I check it with the engine running or off?
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KEL · 10-25-2010, 08:52 AM

warmed up and running. might even say that on the dip stick
good luck

skyreep1 · 10-25-2010, 09:22 AM

Okay, are my vacuum hoses all the ones running to and from my vapor canister? And coul it have anything to do with my vapor canister being old? I don't think the hesitation is from my electrical, when I bought it I replaced my coil, points, plugs, wires etc because it wasn't firing. Turned out it was a pinched wire in my distributor, but I gapped my points to factory spec with a feeler gauge.
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10-24-2010, 05:40 PM	#1
skyreep1 Registered User Join Date: Oct 2009 Location: Peidmont, North Carolina Posts: 97	Stalling and shifting help? Okay, a few weeks ago I rebuilt my 2bbl carburetor on my 71' 307 c-10. Being stupid I didn't count the turns on my air and fuel screws. Now it runs but seems like it's running at high rpms. Also, when you just depress the gas a little it'll start to lose rpms and sputter out unless you pump the peddle some like you're revving it. Secondly, when I shift into any gear (it's an automatic) it acts like it's in park, the shifter moves very smoothly but it just won't move when you gas it. Help please? Thank you guys Posted via Mobile Device Posted via Mobile Device

10-24-2010, 08:22 PM	#2
ray_mcavoy Registered User Join Date: Nov 2009 Location: Sherman, ME Posts: 2,363	Re: Stalling and shifting help? Hi skyreep1, Standard procedure with most carb rebuilds is to turn the idle mixture screws all the way in until they lightly seat (don't tighten them or you'll damage them). Then back them out an equal number of turns (usually about 2 or 3). That'll give you a baseline setting where the engine should idle decent enough for you to fine tune the idle mixture. Note that you might have to back off the idle speed screw (over on the driver side by the throttle lever) if the engine is idling too fast. The hesitation/sputtering could be due to a number of problems. Like a vacuum leak, retarded ignition timing, stuck/inoperative advance mechanism in the distributor, bad condenser, passages in the carburetor that didn't get thoroughly cleaned during the rebuild, and so on. Check the shift linkage to make sure something didn't come loose or unhooked. The movement of the shift lever shouldn't be overly smooth/easy. You should feel a bit of resistance as it "clicks" through the detents in the transmission. Also make sure the transmission is full of fluid and that the fluid doesn't smell burnt.

10-25-2010, 11:04 AM	#3
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Stalling and shifting help? [QUOTE=ray_mcavoy;4258096]Hi skyreep1, Standard procedure with most carb rebuilds is to turn the idle mixture screws all the way in until they lightly seat (don't tighten them or you'll damage them)..... QUOTE] Good point, and one I've made before.... I have seen a bunch of those screws that have been bottomed-out and that will form a groove in the taper. That groove increases the amount of air that flows and makes your adjustment difficult. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

10-26-2010, 08:32 PM	#4
ray_mcavoy Registered User Join Date: Nov 2009 Location: Sherman, ME Posts: 2,363	Re: Stalling and shifting help? Hi skyreep1, Yeah, check the vacuum hoses going to the vapor canister to make sure they're not cracked, split, cut, or anything that'd cause them to leak. The canister being old shouldn't be a problem. But give it a good looking over to make sure the plastic isn't cracked or anything. There's also a vacuum hose going to the ThermAC air cleaner (if it's still on there). And a vacuum hose going to the distributor vacuum advance. That might be routed through a solenoid valve if your engine has TCS (transmission controlled spark). Check all those hoses and parts for vacuum leaks. Also check the hose going to the PCV valve and the one going to the brake booster if your truck has power brakes. Unfortunately, even with new ignition parts, you can't totally rule out an ignition problem. A couple months ago I had an experience with a new condenser that was defective right out of the box. It made for a weak spark that was just strong enough to start & idle the engine. It'd bog, sputter, and want to stall out if you gave it too much gas.

10-25-2010, 08:24 AM	#5
skyreep1 Registered User Join Date: Oct 2009 Location: Peidmont, North Carolina Posts: 97	Re: Stalling and shifting help? Thank you for answering so many questions, I have a feeling it's probably vacuum hoses because it sat without a hood on for a year or more before I got it. I don't think it's my linkage though because you can still will it pop into park etc. I'll check the fluid too though, do I check it with the engine running or off? Posted via Mobile Device

10-25-2010, 08:52 AM	#6
KEL 72 GMC Join Date: Feb 2008 Location: Wells, Maine Posts: 534	Re: Stalling and shifting help? warmed up and running. might even say that on the dip stick good luck

10-25-2010, 09:22 AM	#7
skyreep1 Registered User Join Date: Oct 2009 Location: Peidmont, North Carolina Posts: 97	Re: Stalling and shifting help? Okay, are my vacuum hoses all the ones running to and from my vapor canister? And coul it have anything to do with my vapor canister being old? I don't think the hesitation is from my electrical, when I bought it I replaced my coil, points, plugs, wires etc because it wasn't firing. Turned out it was a pinched wire in my distributor, but I gapped my points to factory spec with a feeler gauge. Posted via Mobile Device



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