HELP, my truck's choking - The 1947 - Present Chevrolet & GMC Truck Message Board Network

67Fleet · 10-17-2006, 02:08 PM

I think it's an exhaust issue, but am not certain. My truck recently has been running rough. It idles fine, but seems like it's falling on its face at top end. It sounds as if it has an exhaust blockage or something. I checked the other day, got up underneath it and put my hand up behind both tailpipes to chk pressure. The pass. side was definitely blowing a lot harder than the driver side. A few weeks ago I noticed one of my pipes at the manifold was loose, and a nut was missing, so I put a new nut on and tightened everything down. Now I'm noticing this. What gives? There's some kind of spring actuated lever on the stock manifold, I checked that and it moves freely. Could it have broke and maybe be in the partially closed position? My low end is great, top end sucks.

**VetteVet** · 10-17-2006, 04:51 PM

This the little bugger. If you can't move the lever then it's froze and causing you too much back pressure giving the symptoms you describe. You should be able to pull the block off and free it up or just knock the butterfly out and put it back as a spacer. Being in Fla. you don't really need it for cold engine warm-up. If you can free it up and use it, all the better.

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67Fleet · 10-17-2006, 05:27 PM

Well, I don't think it's that butterfly mechanism. I can move it freely and I just double-checked it in case, and I can hear it moving inside the manifold. Any other ideas? I gave the entire exhaust system a visual inspection and I can't find any dents or crimps in it from hitting anything. I'm stumped.

zden · 10-17-2006, 05:34 PM

check the plug wires for a burn or make sure they are all firing. mine did about the same it ran great until you put a load on it and then it ran like crap. its worth a look maybe.

Werewolf · 10-17-2006, 07:00 PM

That "spring actuated lever" is a heat riser. I think it's supposed to sort-of block some of the exhaust gases from leaving the manifold so that it causes the manifold to warm up faster, which in turn forces the hot air pickup tube to get hot air into the intake sooner. It's an emissions device, essentially, and if you have an open air filter, there's no point in having it. I'm not positive on this, but it's what my dad told me years ago. You know how those old memories stick with you.

What size exhaust are you running? 2" duals should be enough for a mild 350. You'd need bigger for a more powerful engine. Is your carb giving you enough CFM's? Do you think maybe you're running lean at the top end? Where's your redline?

10-17-2006, 02:08 PM	#1
67Fleet Outlandish Trends - FL Join Date: Jul 2005 Location: Orlando Posts: 1,396	HELP, my truck's choking I think it's an exhaust issue, but am not certain. My truck recently has been running rough. It idles fine, but seems like it's falling on its face at top end. It sounds as if it has an exhaust blockage or something. I checked the other day, got up underneath it and put my hand up behind both tailpipes to chk pressure. The pass. side was definitely blowing a lot harder than the driver side. A few weeks ago I noticed one of my pipes at the manifold was loose, and a nut was missing, so I put a new nut on and tightened everything down. Now I'm noticing this. What gives? There's some kind of spring actuated lever on the stock manifold, I checked that and it moves freely. Could it have broke and maybe be in the partially closed position? My low end is great, top end sucks. __________________ -Bret 67 short-fleet sold!

10-17-2006, 04:51 PM	#2
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,717	Re: HELP, my truck's choking This the little bugger. If you can't move the lever then it's froze and causing you too much back pressure giving the symptoms you describe. You should be able to pull the block off and free it up or just knock the butterfly out and put it back as a spacer. Being in Fla. you don't really need it for cold engine warm-up. If you can free it up and use it, all the better. -------------------------------------- Attached Images __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

10-17-2006, 05:27 PM	#3
67Fleet Outlandish Trends - FL Join Date: Jul 2005 Location: Orlando Posts: 1,396	Re: HELP, my truck's choking Well, I don't think it's that butterfly mechanism. I can move it freely and I just double-checked it in case, and I can hear it moving inside the manifold. Any other ideas? I gave the entire exhaust system a visual inspection and I can't find any dents or crimps in it from hitting anything. I'm stumped. __________________ -Bret 67 short-fleet sold!

10-17-2006, 05:34 PM	#4
zden Registered User Join Date: Apr 2006 Location: Montgomery, TX Posts: 72	Re: HELP, my truck's choking check the plug wires for a burn or make sure they are all firing. mine did about the same it ran great until you put a load on it and then it ran like crap. its worth a look maybe. __________________ 1966 Chevrolet Suburban 1955 Chevrolet Bel Air

10-17-2006, 07:00 PM	#5
Werewolf Woof? Join Date: Jun 2005 Location: Raleigh, NC Posts: 276	Re: HELP, my truck's choking That "spring actuated lever" is a heat riser. I think it's supposed to sort-of block some of the exhaust gases from leaving the manifold so that it causes the manifold to warm up faster, which in turn forces the hot air pickup tube to get hot air into the intake sooner. It's an emissions device, essentially, and if you have an open air filter, there's no point in having it. I'm not positive on this, but it's what my dad told me years ago. You know how those old memories stick with you. What size exhaust are you running? 2" duals should be enough for a mild 350. You'd need bigger for a more powerful engine. Is your carb giving you enough CFM's? Do you think maybe you're running lean at the top end? Where's your redline? __________________ 1968 LWB CST BB 2004 Avalanche Z71 LT3. 2003 S-10 ZR2 (hers). 1997 Astro 1992 Caprice wagon, 500k stock miles. Nursing wounds after a bad wreck. 1997 Saturn - need gas mileage from something!



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