Author Topic: Not sure what my Carb problems are  (Read 467 times)

Offline AdamC

  • Newbie
  • *
  • Posts: 1
Not sure what my Carb problems are
« on: February 23, 2025, 12:50:30 PM »
I recently bought a 1970 c10 with a 7045228 quadrajet.  The truck ran awful, so we pulled the carb and cleaned it out.  Before finding this place, I had bought a rebuild kit online, so has all new gaskets, piston pump, and vacuum "covers".  I also added an electric choke since the previous owner had removed all choke components and just hand fed fuel to the primaries until it was up to temp.  Since putting everything back together, it runs fair at idle, but if you do more than ease on the accelerator, it stalls.  I tried tuning with a vac gauge and the highest reading I got was 3 in Hg.  when adjusting the right side idle mixture screw, no turns either direction changed the reading.  I also noticed that after running a bit, if I shut off, the left side primary looks wet, but the right side looks dry.  I am a total newbie, but my daughter wanted her first vehicle to be a project truck for us, so any and all help would be greatly appreciated.

Offline Kenth

  • Qjet Hero
  • *****
  • Posts: 500
Re: Not sure what my Carb problems are
« Reply #1 on: February 24, 2025, 12:51:32 AM »
3 in/Hg in intake manifold at idle is a sign of a massive vacuum leak.
Should read at least 18 in/hg @ 750 rpm.

Offline Cliff Ruggles

  • Administrator
  • Qjet Hero
  • *****
  • Posts: 5479
Re: Not sure what my Carb problems are
« Reply #2 on: February 28, 2025, 04:20:23 AM »
1975 passenger car carburetor with the APT adjustment under the brass cup the left front of the airhorn (as viewed from the front).

Those aren't that great as mentioned in my book and their existence was very short lived.  I had so many problems with them in the shop back when we were doing rebuilds and restorations I quit taking them in. 

Not saying you can't make it work, but I've ran into just enough of those that don't work well no matter what you do to them to avoid them completely.  Rochester knew there were flaws in the design and very quickly discontinued them in 1976 and went to the far superior late style units with the APT screw in front of the power piston that raised/lowered tapered metering rods for fine control of the primary side A/F.

Your symptoms indicate going WAY lean right off idle, which could be many things, but I'd start by putting one of my rebuild kits in the carburetor as the accl pump in the kit you bought isn't worth two squirts of duck poop, plus the N/S assembly is incorrect with a pretty small hole in it which effects the fuel level in the bowl and overall metering to the engine.  Also verify that the PP hanger arms are level and EXACTLY even, which seldom happens with these things.

You also mentioned "adding an electric choke".  Did you do the conversion correctly by blocking the vacuum BEFORE the choke housing or using a later choke housing designed for an electric choke. 

I see a LOT of carburetors that have had electric chokes added to them, and maybe one it fifty was done correctly......FWIW.....