Carb ID and adjustment info - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Shibbershabber · 10-05-2016, 02:29 AM

What am I looking for to ID which carb I have?

Also, where can I find info on proper adjustments?
Its been a long time since Ive payed with a carb'd engine.

The reason I ask...
Sometimes It feels like its idling high, well into my trip... already warmed up that is. Not quite as high as the high idle... but its seems high.

Other times it will start to stumble a little... Ive never let it continue to see if it will actually die, a little tap on the gas gets things going again. Once this happened I was looking in the side mirror when hitting the gas and I had some black smoke when I hit the gas.

Occasionally get a strong smell of gas when getting out of the truck, but I have no visible fuel leak.

Though even if its all unrelated, itd probably still be a good idea to know what I am doing and to have the carb properly tuned.

thanks

geezer#99 · 10-05-2016, 08:48 AM

Could be any carb.
Take a pic!

Shugalou · 10-05-2016, 12:55 PM

If it's a quadrajet check the drivers side of the carb for numbers running vertically.

Do you know if your choke is operating properly? Check to see if the choke flaps are open once it's warmed up and it's coming off the high idle cam on the choke side.

I had similar problems and after I replaced a dead choke thermostat I was dialing it in when gas starting leaking out of the side of the carb.

For more details search my post 305 dies when warmed up - there was some great advice from the guys on the board

D13 · 10-06-2016, 05:31 AM

Also the throttle shafts wear out the bore and create a random vacuum leak. There's a bushing kit to fix that.

Shibbershabber · 10-24-2016, 02:50 AM

Finally had a chance to check it out.

Its a Quadrajet R4-M4MEF #17085004

geezer#99 · 10-24-2016, 09:39 AM

A pic would still be nice!
With the air cleaner off, both sides and the front.

Could be something simple or major. Could be rebuild time!

jdl71 · 10-25-2016, 08:41 PM

I have an M4MED with some of the same issues. Part of my trouble was the EGR valve, but I am still idling higher than normal and my next step is to replace the base plate gasket, I'm fairly certain there is a vacuum leak there. Do you have A/C? If so there is a fast idle solenoid, or "throttle kicker" that kicks up the idle speed when the A/C or DEF is engaged. Unplugging that might help a bit. The mixture screws on these carbs are factory set and require knocking out some plugs to adjust. I'd try checking the choke as mentioned above as well as checking for a vacuum leak before you break out the "magic screwdriver". I do have an '86 factory service manual that covers these carbs, however I don't have a scanner but if I can look up something specific for you I'd be glad to help.

jdl71 · 10-25-2016, 09:46 PM

Found an online version of the FSM on another forum:

http://www.73-87chevytrucks.com/tech...ice_Manual.pdf

10-05-2016, 08:48 AM	#2
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,750	Re: Carb ID and adjustment info Could be any carb. Take a pic!

10-05-2016, 12:55 PM	#3
Shugalou Registered User Join Date: Jan 2013 Location: Toronto, ON Posts: 458	Re: Carb ID and adjustment info If it's a quadrajet check the drivers side of the carb for numbers running vertically. Do you know if your choke is operating properly? Check to see if the choke flaps are open once it's warmed up and it's coming off the high idle cam on the choke side. I had similar problems and after I replaced a dead choke thermostat I was dialing it in when gas starting leaking out of the side of the carb. For more details search my post 305 dies when warmed up - there was some great advice from the guys on the board __________________ Found my dad's old truck http://67-72chevytrucks.com/vboard/s...d.php?t=563321 Newspaper Article Publishing the quest find my dad's old truck http://www.theglobeandmail.com/globe...ticle12494281/

10-06-2016, 05:31 AM	#4
D13 Registered User Join Date: Feb 2007 Location: Memphis MI Posts: 1,851	Re: Carb ID and adjustment info Also the throttle shafts wear out the bore and create a random vacuum leak. There's a bushing kit to fix that. __________________ 1987 2 ton 1982 250/TH350 beater in progress Dad's 1981 3/4 L6 3 on tree posi and no options, awaiting restoration or scrapping Plus a mess o' tractors

10-24-2016, 02:50 AM	#5
Shibbershabber Registered User Join Date: Sep 2016 Location: Vancouver, WA Posts: 18	Re: Carb ID and adjustment info Finally had a chance to check it out. Its a Quadrajet R4-M4MEF #17085004 __________________ 1986 C30 3+3 454 w/3spd

10-24-2016, 09:39 AM	#6
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,750	Re: Carb ID and adjustment info A pic would still be nice! With the air cleaner off, both sides and the front. Could be something simple or major. Could be rebuild time!

10-05-2016, 02:29 AM	#1
Shibbershabber Registered User Join Date: Sep 2016 Location: Vancouver, WA Posts: 18	Carb ID and adjustment info What am I looking for to ID which carb I have? Also, where can I find info on proper adjustments? Its been a long time since Ive payed with a carb'd engine. The reason I ask... Sometimes It feels like its idling high, well into my trip... already warmed up that is. Not quite as high as the high idle... but its seems high. Other times it will start to stumble a little... Ive never let it continue to see if it will actually die, a little tap on the gas gets things going again. Once this happened I was looking in the side mirror when hitting the gas and I had some black smoke when I hit the gas. Occasionally get a strong smell of gas when getting out of the truck, but I have no visible fuel leak. Though even if its all unrelated, itd probably still be a good idea to know what I am doing and to have the carb properly tuned. thanks __________________ 1986 C30 3+3 454 w/3spd Last edited by Shibbershabber; 10-05-2016 at 02:45 AM.

10-25-2016, 08:41 PM	#7
jdl71 Registered User Join Date: Oct 2012 Location: Eldon, MO Posts: 1,753	Re: Carb ID and adjustment info I have an M4MED with some of the same issues. Part of my trouble was the EGR valve, but I am still idling higher than normal and my next step is to replace the base plate gasket, I'm fairly certain there is a vacuum leak there. Do you have A/C? If so there is a fast idle solenoid, or "throttle kicker" that kicks up the idle speed when the A/C or DEF is engaged. Unplugging that might help a bit. The mixture screws on these carbs are factory set and require knocking out some plugs to adjust. I'd try checking the choke as mentioned above as well as checking for a vacuum leak before you break out the "magic screwdriver". I do have an '86 factory service manual that covers these carbs, however I don't have a scanner but if I can look up something specific for you I'd be glad to help. __________________ Psalm 23 64 C10 66 K20

10-25-2016, 09:46 PM	#8
jdl71 Registered User Join Date: Oct 2012 Location: Eldon, MO Posts: 1,753	Re: Carb ID and adjustment info Found an online version of the FSM on another forum: http://www.73-87chevytrucks.com/tech...ice_Manual.pdf __________________ Psalm 23 64 C10 66 K20



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