NOW WHAT??? carb problems are killing me - The 1947 - Present Chevrolet & GMC Truck Message Board Network

nejeff · 08-03-2003, 08:25 PM

I just swapped in a 307 2-barrel into a auto truck (72) and now all I have are hassles. Barely started ( had to hold foot to the floor) and then realized it was missing two carb bolts. Replaced them and now can't do anything but backfire or flood this pig! I think I hooked all the linkage back up correctly (the 307 was a Manual) but I never had starting trouble when it was in the manual truck but it did hesitate a lot when you stomped on it.

I can't adjust carbs well at all and can't figure this s@it out!

Help if you can

70c10 · 08-03-2003, 08:26 PM

Could be the accelerator pump gone bad.

ChevLoRay · 08-03-2003, 09:56 PM

Basic carburetor adjustment: There are two idle air screws on the base of the carb, at the front. Turn them in until the just barely seat (stop turning). Then, back them out 2 full turns. This is the basic adjustment, and assumes that the rest of the carb is working properly.

Fine tuning the carb may require a vacuum gauge, a tachometer, or both, since you will be making that same idle are adjustment but tweaking them to get the highest vacuum and a smooth idle, probably about 700 RPM's in Neutral, or about 650RPM's, in Drive at idle.

These are just ball-park figures. If you truly are not comfortable making the adjustments, by all means let someone do who is capbable. OH, make sure the ignition system is up to snuff. Carbs get the blame for ignition problems, and ignition systems get blamed for carb problems. If you don't know which one is the problem, get someone who is capable, to help.

71elect · 08-03-2003, 10:26 PM

nejeff,
Man I know what you are going thru now! I have a 71 GMC w/ 307, 2 barrel carb & manual 3 speed. It started with the simple, hey I'm gonna change the plugs and wires. Got the plugs & wires changed but for some fluke when I started up the truck the needle got stuck in the carb and now it flooded all the time. Rebuilt the carb and set it up to the rebuild specks, including turning the idle screws both back out 2 full turns. But all I got was a crappy backfiring idle that sometimes stalled. Well I set the timing, set the dwell, adjusted the idle, replaced the points,the condenser, the cap, the rotor, heck I even thru in a hi performance coil out of the camaro. But still no luck. Finially I tinkered with the idle screws one at a time by slowly backing them out further than the recommended 2 full turns. Man I was happy that now it was running smooth and had no hesitation at instant throttle. Kind of an expensive lessen to learn though. Hope this helps in the fact that man I hear you. PS watch out for fouled plugs also.
Josh

nejeff · 08-04-2003, 12:15 AM

Thanks guys. I'll try all that stuff tomorrow. Did not know if I screwed up the linkage or something

Thanks again

08-03-2003, 08:25 PM	#1
nejeff Registered User Join Date: Jun 2003 Location: Nebraska Posts: 63	NOW WHAT??? carb problems are killing me I just swapped in a 307 2-barrel into a auto truck (72) and now all I have are hassles. Barely started ( had to hold foot to the floor) and then realized it was missing two carb bolts. Replaced them and now can't do anything but backfire or flood this pig! I think I hooked all the linkage back up correctly (the 307 was a Manual) but I never had starting trouble when it was in the manual truck but it did hesitate a lot when you stomped on it. I can't adjust carbs well at all and can't figure this s@it out! Help if you can __________________ 72' Chevy Super Cheyenne LWB 72' Chevy C-10 (307 Parts Truck)

08-03-2003, 08:26 PM	#2
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,856	Could be the accelerator pump gone bad. __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

08-03-2003, 09:56 PM	#3
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Basic carburetor adjustment: There are two idle air screws on the base of the carb, at the front. Turn them in until the just barely seat (stop turning). Then, back them out 2 full turns. This is the basic adjustment, and assumes that the rest of the carb is working properly. Fine tuning the carb may require a vacuum gauge, a tachometer, or both, since you will be making that same idle are adjustment but tweaking them to get the highest vacuum and a smooth idle, probably about 700 RPM's in Neutral, or about 650RPM's, in Drive at idle. These are just ball-park figures. If you truly are not comfortable making the adjustments, by all means let someone do who is capbable. OH, make sure the ignition system is up to snuff. Carbs get the blame for ignition problems, and ignition systems get blamed for carb problems. If you don't know which one is the problem, get someone who is capable, to help. __________________ 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.

08-03-2003, 10:26 PM	#4
71elect Registered User Join Date: Nov 2002 Location: Southern Idaho Posts: 59	nejeff, Man I know what you are going thru now! I have a 71 GMC w/ 307, 2 barrel carb & manual 3 speed. It started with the simple, hey I'm gonna change the plugs and wires. Got the plugs & wires changed but for some fluke when I started up the truck the needle got stuck in the carb and now it flooded all the time. Rebuilt the carb and set it up to the rebuild specks, including turning the idle screws both back out 2 full turns. But all I got was a crappy backfiring idle that sometimes stalled. Well I set the timing, set the dwell, adjusted the idle, replaced the points,the condenser, the cap, the rotor, heck I even thru in a hi performance coil out of the camaro. But still no luck. Finially I tinkered with the idle screws one at a time by slowly backing them out further than the recommended 2 full turns. Man I was happy that now it was running smooth and had no hesitation at instant throttle. Kind of an expensive lessen to learn though. Hope this helps in the fact that man I hear you. PS watch out for fouled plugs also. Josh __________________ 72Chevy swb 4x4 71GMC swb 2x4

08-04-2003, 12:15 AM	#5
nejeff Registered User Join Date: Jun 2003 Location: Nebraska Posts: 63	Thanks guys. I'll try all that stuff tomorrow. Did not know if I screwed up the linkage or something Thanks again __________________ 72' Chevy Super Cheyenne LWB 72' Chevy C-10 (307 Parts Truck)



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