I have a few questions about feedback carbs, I am helping a guy with his s10 conversion and we used a feedback controlled engine from a 85 or so fullsize truck. This thing starts runs and drives perfect with light to moderate cruise condtions, Under hard acelleration it bogs down hard and fells like it is on a power on of switch anything over half throttle. But at 1/2 throttle it pulls good and feels strong. I just unpluged the feedback wiring and replaced the distributor from the car with a older vaccum advance unit during the swap. Would the feedback carb work correctly with out the electronics in place and could it cause a problem such as this? I guess I could explain it as driving a car with a closed choke after warm up it starts losing power and bogs and almost dies. I am confused here and any input would be great. This is a 4 barrel quadrajet unit.
Thanks again
Elec

 

You can't run a computer controlled QJet without the computer. As soon as you unplug the 2 wire mixture control solenoid plug it defaults to full-rich and run like a pig.

From the symptoms you describe it sounds like something is just WRONG inside that carb. Probably on the secondary side, since it just starts to open up from about 2/3 throttle on up. Maybe a rod has fallen off it's hanger and is stuck down in the jet, maybe a lot of things. Not many people know what they're doing with a QJet and almost nobody knows the computer controlled ones (I know both extremely well, having worked on them for 20 years worth of weekends).

Suggestions:

1. Get the computer controlled QJet fixed by somebody who knows what they're doing and put all the computer controlled stuff back on (including the distributor).

2. Ditch all the computer controlled stuff. This means putting on a non-computer controlled QJet in place of the original and a non-computer controlled distributor such as you already installed.

 

Yeah you cant run the controlled carb without the computer and distributor. If it were me I would ditch it and get a manual secondary holley and drop in a HEI, or MSD if your budget allows. When the Q-jet works its great but save yourself the headache and get a holley!

 

Another consideration is the fuel line size from the tank. It may not be large enough and you are simply starving the engine for fuel.

 

Thanks for the input guys, The funny thing is this unit runs excellent at idle and part throttle. It seems to starve and die under full load (or anything past 1/2 throttle). I figured as much about needing to ditch the carb it's just to bad since the carb seems to run and drive excellent aside from the full throttle problem, it even starts with the slightest tap fo the key.

Thanks again for the input guys I will change a few things and repost what I find.
Elec

 

If the vacuum controlled plate over the secondaries doesn't open you will get this also. See if you can find someone in your area that likes to work on these carb's and have him look at it.

 

is this internally controlled with vaccum then?

 

Yes, it's vacuum controlled. And there is a counter spring with an adjusting screw, but I've never been very good at tuning these, don't like them.