carb question from a newbie - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mhorning · 07-16-2003, 08:50 AM

Hi, I am new to this list. I currently have two Chevys- a 63 stepside and a 86 Silverado. The stepside is going to be a long project, as I get the money to restore. However, I wondered if you guys could give me some suggestions for the 86 SIlverado. It has a Rochester Quadrajet M4MED carb on it and a 350 Engine. Summit Header with 224 duration and 245 lift and exhaust. I bought the truck recently as something that I thought I could fix and drive a little more quickly than the 63. The guy before me took out the old 305 and put in the 350. I got the truck in less than perfect condition. It would run, and then stall, the timing was off so it wouldn't start, etc. I did a compression check and found one of the valves to be a little tight, so I corrected that. Also he had failed to connect the idle stop solenoid on the carb. Now the truck starts and runs pretty well. However, when I put it in drive it dies. I already have the rpms at about 900 which I'd like to lower, so I don't think that is the issue. Also, I checked for vacuum leaks. I noticed that this diaphram on the back of the carb called a vacuum break assembly doesn't seem to pull back the linkage when vacuum is applied to it. Could this be the problem? I thought I would ask those in the group who were more knowledgable on the qudrajet if they had any suggestions. Thanks.

BigRed · 07-16-2003, 09:20 AM

Welcome to the board. It sounds like you have your hands full. There are several Quadrajet guys around here that will hopefully chime in and offer you some suggestions. I'm clueless, so I'll keep my mouth shut.

Got some pictures of your trucks?

**old Rusty C10** · 07-16-2003, 09:36 AM

hey im not a carb expert by any means, and lol like you i have an 86 with carb problems that is at the rebuilder again trying to get straightened out. I just wanted to say hello and welcome to the board from NJ

**swervin ervin** · 07-16-2003, 12:52 PM

Hey, welcome to the board.

I know you say you've checked for vacuum leaks, but it sure does sound like you have one. How did you check for leaks? Besides spraying carb cleaner all around, try putting your hand over the carb to shut off all air. If it idles up, you have a leak somewhere.

Have you adjusted the carb idle mixture screws any? The vacuum break should retract when vacuum is applied to it. This won't cause a dieing situation though. All this does is open the choke slightly when the engine is started cold, and dampen the secondary air valve opening.

One more thing that will cause it to die when put in gear is the torque converter clutch. If you have a bad lockup solenoid, to where it's in the locked position, or the proper term, grounded, when put in gear, it will die.

mhorning · 07-16-2003, 03:22 PM

Thanks for the input guys. I'll have pics posted soon. When you refer to the lock up solenoid. Is that the electronic solenoid on the right side of the carb next to the throttle cable? Oh and about the mixture screws. Any suggestions on what to use for a tool? Can you buy it somewhere? I checked a few places and they didn't have a clue. By the way my names Mike and I'm in upstate New York. Looking forward to the discussions.

**swervin ervin** · 07-16-2003, 05:38 PM

The lockup solenoid is inside the tranny. This locks the tranny in overdrive. If it sort of acts like you are letting the clutch out, like in a manual, when put in gear, this could very well be the cause.

You can buy a tool to fit the mixture screw heads. Someone on here bought some from I think Pepboys. I can't remember what they are called though. You more than likely will have to remove the hardened plugs covering the screws first.

I made a tool to fit mine. I used a piece of steel tubing, I think it was 1/4" or so. I bent the two opposing sides flat. Works great.

Hey, us Mikes are good people.

07-16-2003, 08:50 AM	#1
mhorning Registered User Join Date: Jul 2003 Location: Corning, NY Posts: 158	carb question from a newbie Hi, I am new to this list. I currently have two Chevys- a 63 stepside and a 86 Silverado. The stepside is going to be a long project, as I get the money to restore. However, I wondered if you guys could give me some suggestions for the 86 SIlverado. It has a Rochester Quadrajet M4MED carb on it and a 350 Engine. Summit Header with 224 duration and 245 lift and exhaust. I bought the truck recently as something that I thought I could fix and drive a little more quickly than the 63. The guy before me took out the old 305 and put in the 350. I got the truck in less than perfect condition. It would run, and then stall, the timing was off so it wouldn't start, etc. I did a compression check and found one of the valves to be a little tight, so I corrected that. Also he had failed to connect the idle stop solenoid on the carb. Now the truck starts and runs pretty well. However, when I put it in drive it dies. I already have the rpms at about 900 which I'd like to lower, so I don't think that is the issue. Also, I checked for vacuum leaks. I noticed that this diaphram on the back of the carb called a vacuum break assembly doesn't seem to pull back the linkage when vacuum is applied to it. Could this be the problem? I thought I would ask those in the group who were more knowledgable on the qudrajet if they had any suggestions. Thanks.

07-16-2003, 09:20 AM	#2
BigRed Registered User Join Date: Jun 2002 Location: DFW, TX Posts: 1,680	Welcome to the board. It sounds like you have your hands full. There are several Quadrajet guys around here that will hopefully chime in and offer you some suggestions. I'm clueless, so I'll keep my mouth shut. Got some pictures of your trucks? __________________ Scott Shelbourne

07-16-2003, 09:36 AM	#3
old Rusty C10 Robert Olson Transport Join Date: Oct 2002 Location: recent transplant to NC USA Posts: 20,277	hey im not a carb expert by any means, and lol like you i have an 86 with carb problems that is at the rebuilder again trying to get straightened out. I just wanted to say hello and welcome to the board from NJ __________________ Bob 1951 International running on a squarebody chassis "If a man's worth is judged by the people he associates himself with, then i am the richest man in the world knowing some of the fine people of this board" http://67-72chevytrucks.com/vboard/a...t.php?f=25&a=9 (you can review the site rules here!) PM Me for your vehicle/parts hauling needs in the North East US or see my Facebook page Robert Olson Transport Live each day to the fullest.. you never know when fate is going to pull the rug out from under you... I hate cancer!!

07-16-2003, 12:52 PM	#4
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Hey, welcome to the board. I know you say you've checked for vacuum leaks, but it sure does sound like you have one. How did you check for leaks? Besides spraying carb cleaner all around, try putting your hand over the carb to shut off all air. If it idles up, you have a leak somewhere. Have you adjusted the carb idle mixture screws any? The vacuum break should retract when vacuum is applied to it. This won't cause a dieing situation though. All this does is open the choke slightly when the engine is started cold, and dampen the secondary air valve opening. One more thing that will cause it to die when put in gear is the torque converter clutch. If you have a bad lockup solenoid, to where it's in the locked position, or the proper term, grounded, when put in gear, it will die. __________________ Mike 1985 Chevy C-10

07-16-2003, 03:22 PM	#5
mhorning Registered User Join Date: Jul 2003 Location: Corning, NY Posts: 158	thanks Thanks for the input guys. I'll have pics posted soon. When you refer to the lock up solenoid. Is that the electronic solenoid on the right side of the carb next to the throttle cable? Oh and about the mixture screws. Any suggestions on what to use for a tool? Can you buy it somewhere? I checked a few places and they didn't have a clue. By the way my names Mike and I'm in upstate New York. Looking forward to the discussions.

07-16-2003, 05:38 PM	#6
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	The lockup solenoid is inside the tranny. This locks the tranny in overdrive. If it sort of acts like you are letting the clutch out, like in a manual, when put in gear, this could very well be the cause. You can buy a tool to fit the mixture screw heads. Someone on here bought some from I think Pepboys. I can't remember what they are called though. You more than likely will have to remove the hardened plugs covering the screws first. I made a tool to fit mine. I used a piece of steel tubing, I think it was 1/4" or so. I bent the two opposing sides flat. Works great. Hey, us Mikes are good people.



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