Hello all. I'm the proud owner of an 85 f150 300 I-6, manual trans shortbox stepside and for the last couple of months it has been blowing black smoke from start, through warmup as long as it runs and is consuming a ludicrous amount of fuel. I'm getting less than 8mpg!!!
It idles rough and If I drive part throttle it starts losing power and feels like it's choking out but when I punch the accelerator it stutters, blows out a giant cloud of black smoke then regains power. Once shut off if I try to restart it within 15-20 minutes I have to crank it for a while with the gas to the floor then it starts up rough and blows out lots and lots of black smoke and it won't take off unless I rev it up for a while to blow out all the excess gas.
Unfortunately I have the electronic carb, O2 sensor, ECM model with TFI Ignition. I know as these vehicles age they get more and more tempermental.
The choke seems to function properly, the carb is theoretically new (I bought the truck from a dealer who said he replaced it, it looked new at the time). The only modifications to the truck is the charcol filter box was removed and lines to it plugged which made no performance difference at the time.
Any ideas on what might be going on? The truck did not do this when I bought it.

Thanks in advance for any help!!!

 

I strongly suspect that the accelerator pump diaphram is blown. You can rebuild the whole carb, or just replace the pump. It is sold separately for less than ten bucks, or the kit is about 30 bucks. Have to disassemble the carb either way. Also, disconnect and block off the mixture solenoid on the front of the carb. These things are useless. This will solve your problem.

Robbie.

Let me know how it turns out. Sure fire way to tell if the pump is leaking is to back out the mixture screw and if it runs smoother the further you back out the screw, you got it!

 

after I posted that I was messing with it and decided to play with the mixture screw, I backed it out almost six turns and it runs much better, but still rough and smokey. I'll try rebuilding it, thank you very much for your answer!! I'll let you know how it goes.

 

Well, I rebuilt the carb and found several thing missing, yup, missing. The spring for the inlet needle was missing, the small filter inside the inlet seat was missing, and the accelerator pump diaphragm washer was missing. So I replaced all of that with the new parts except for the filter 'cus the new kit didn't have one and it runs much better and has more power off idle and doesn't run nearly as rough.
Now for the problems, I adjusted the float and main jet metering rod along with the choke thermostat and idle mixture but it still runs a bit rich and it still dumps excessive amounts of gas into the cylinders after it's shut off. Just as before when I start it up after it's been warmed up, it's very hard to start and I have to hold the gas to the floor, then it fires up with a giant cloud of black smoke. The only things in the carb I did not mess with it the main jet, everything else was cleaned/replaced/adjusted.
As for the solenoid you spoke of, is it the black one hanging next to the float bowl with the wireing harness on the bottom?

Thanks for the help