Carburetor Help, please

[jpatters13]

I recently bought an 84, 4WD, K10, 305, 700R4 with the stock carb, intake, exhaust (except for old cherry bombs).  The thing has some carburetor issues especially when cold orheaded up an incline.  It also only gets about 10mpg in the city.  What should i do to improve gas mileage?  Do I need to replace the carb?  I have never rebuilt one and the Rochester has a ton of moving parts from what I've heard.  I am just trying to make the truck more dependable and improve mpg. Any help would be great!  Thanks.

[dvdswan]

when was the last time the truck had a tuneup?  when I buy a used vehicle thats the first thing I check.  if someone is selling a vehicle do you think they want to put money into it?

your carb may be having issues and this would be a good time to learn about it.  if its your DD then you may need to just buy a new/rebuilt carb.  check your fuel pressure too. 

do you have a heavy foot?  does it take the truck a while to get up to speed?  how is the trans shifting?  a lot of things can cause poor mileage...

[rich weyand]

Tune it up first.  Then put a rebuild kit on the carb.  Poor performance when cold or headed up an incline can be a number of carb-related issues.  You want new floats and new valves on the float bowls (if the floats are sinking or the float bowl valves aren't shutting off, that will kill mileage and can richen the mixture enough to cause problems, particularly when -- surprise -- cold or headed up an incline), and new accelerator pump for sure.  Also, you need to clean it out in there.  If your air bleeds are dirtied up, that will cause a raft of issues.

[rich weyand]

BTW, you'll get better mileage from the Quadrajet than from the Edelbrock.  Carburetion is a compromise, since it is an open-loop system.  Fuel injection is a closed-loop system, which monitors the exhaust with an O2 sensor to adjust the mixture continuously, so it is exact.  Carburetion is an approximation, and, since a too-lean mixture will cause overheating or stall, all the errors are on the rich side.  The Qjet has smaller primaries, so it's running closer to design stack velocity, so it's errors are smaller, therefore better mileage.

Take the Qjet off, take it apart, clean it up good, clean out all the bleeds and such with carb cleaner, then put it back together with new parts: a rebuild kit, plus floats and accelerator pump if the rebuild kit doesn't already have them in it.

These books are essential to get.  Don't worry about how to tune all the air bleeds and such -- that's already been done for your truck from the factory since it's the stock carb.  Just do the rebuild.
http://www.amazon.com/Rebuild-Modify-Rochester-Quadrajet-Carburetors/dp/1932494189/ref=sr_1_1?s=books&ie=UTF8&qid=1388427376&sr=1-1&keywords=quadrajet
http://www.amazon.com/Rochester-Carburetors-Doug-Roe/dp/0895863014/ref=sr_1_2?s=books&ie=UTF8&qid=1388427376&sr=1-2&keywords=quadrajet

[jpatters13]

You guys are awesome. I ordered one of the books and I plan to attempt to rebuild the existing carb myself. Any recommendations on a source to buy the rebuild kit and pump? Any special tools needed?

Sent from my PC36100 using Tapatalk 2

[rich weyand]

Common tools. 

You have to be careful with rebuild kits because they vary by year and application.  This one looks right, but check your carb number to be sure:
http://quadrajetparts.com/rochester-quadrajet-parts-quadrajet-rebuild-kits-quadrajet-rebuild-kit-1979-q4009a-p-558.html

Also get the floats.  I don't think you need anything else, but you do need to plug the secondary metering wells with something.  The book shows how to do that, or you can get the plugs from these guys.  I think most people just epoxy them.

[jpatters13]

Great. Thanks.  Where exactly is the carb number located?

[jpatters13]

Nevermind. I found this link showing where to find the number: http://quadrajetparts.com/where-locate-carburetor-number-a-20.html

[jpatters13]

So I ordered the rebuild kit and a new float.  Also bought the Roe book but I honestly don't feel confident enough to do it myself.  A local mechanic offered to rebuild it for $80 if I supply the kit.  But I decided to order a remanufactured Quadrajet through Ebay. Found one from a national carburetor shop for $215 delivered with a 1 year warranty. http://www.ebay.com/itm/231101036896.  Thanks to everyone who helped me out! I love this forum. 

[SuburbanHunter]

Thinking about rebuilding my Qjet and have been looking at the links from this thread. I don't know much about the history of this carb. it was on a running engine (that's good)but it is very dirty and the engine didn't run very well. That may or may not have anything to do with the carb but it is off the engine so I thought I may as well.

When I order the rebuild kit should I go ahead and order new floats and accelerator pumps as well? I don't know if they are bad or not but they are not expensive it would be nice to have them on hand.

The float choices are Nitrophyl or brass. They say both are direct replacements and are the same price. Is brass better than plastic?

Thanks
 

[bd]

Rebuild kit, fuel filter, and float; the accelerator pump is part of the kit.  Check the choke pull(s) ahead of time and if they are sticky or won't hold vacuum, replace them (note: some secondary pulls incorporate an air bleed and won't hold a vacuum).  If the accelerator pump cup in the kit is black rubber, replace it with a pink or blue Viton pump service kit, such as Delco P/N 17110591.  Float selection is personal preference.  I use the OEM closed cell foam, because some of the replacement brass floats have different buoyancy properties that can affect the float level setting.  Brass has the advantage of not being as affected by alcohol enriched fuels.

[12gaige]

In my opinion a q-jet is the best carb to have for a dd. They are reliable and they give you "good" fuel mileage. That carb would be an excellent candidate for a rebuild. I live in lower michigan near detroit and alot of older shops will rebuild your carb fast. Ive had mine rebuilt while i wait if it has no heavy gunk build up.