Poor MPG's

[tony79gmc]

I inherited my dad's 79 GMC Caballero with a 4.3 V6 we put in several years ago. It has a Q-jet 17084226 on it right now. It gets very poor gas mileage with a lot of black sout in the tail pipe. What would you recommend to lean this carb to improve gas mileage.

[Cliff Ruggles]

What is the history on the carburetor, rebuilt, when, by whom, unknown, etc?.....Cliff

[tony79gmc]

It was orgianaly on a 305 that was in the vehicle when dad purchased it, then we put in on the 4.3. I tried to rebuild it about 4 years ago. Dad wanted larger main jets so we changed them. I don't remember what size. I have the original jets they are 73, everything else is stock as far as I know.

[Cliff Ruggles]

I would put the original 73 jets back in it.  I would install one of our kits while it is apart to insure the internals are up to par for this new fuel.  While it's apart remove the aluminum plug over the APT screw.  Tap it for a 3/8" set screw (provided in our kit by request).   Make sure the primary power piston metering rod hanger arms are level and EXACTLY even.

Then you will have full control of part throttle A/F from rich to lean.  The carb should be using "M" series primary metering rods which are tapered .010" on the upper section

This will restore the carb to correct working order and get the fuel mileage back where it should be.....Cliff

[tony79gmc]

What is the correct float level for this carburetor?

[Cliff Ruggles]

The float level is listed in the instructions that are supplied with our kits, but keep in mind that each carburetor was set-up for the original application.  If using it on something else that what it originally came on, it may require a different float height.......Cliff

[tony79gmc]

I bought your HP kit and book for the Q-jet, but I didn't see any instructions in the box.  What's a good starting point for the float level? I plan on starting the rebuilt tomorrow.

[omaha]

i think the book recommends 1/4 inch for a starting point.  {Good luck on the knee surgery Cliff.}

[Ethan1]

 13/32" is the correct float level for that carburetor number.

 EDIT: Yes, a good starting point is 1/4". 13/32" was the original float level setting for the 305cid engine.

[tony79gmc]

I set the float to 15/32, I found an instruction manual from the rebuild I attempted about 4 years ago.  For the 4.3 V6 it listed 13/32 for 1985 and 17/32 for 1986 Astro van. so I just slit the difference.  I have been driving it a couple of day and it appears that the MPG have improved.  I think the main reason it was poor to begin with is that the hanger arms for the main metering rods were bent up ward and were not letting the rods go down in the jets very far and was letting a lot of gas thru.  Is the 17084226 carb supposed to have the plastic filler cup on the passenger side of the carb?  If so mine is missing, does anyone have one if its supposed to be in this carb?

[429bbf]

you ask a good question i can't answer the plastic filler i believe i was able to buy from cliff . i tried running one with and the same carb without. i thought i could get more fuel capacity in the bowl because i was running out of fuel on top end. problem was fuel supply . to small of needle and seat arrangement and also kinked fuel hose between tanks . hth