Hello all, this is my first post to this site but sure it won't be my last. I have an 83 F250 2wd with, you guessed it, a 300ci straight six manual tranny. I replaced the motor with a rebuilt long block about 3yrs ago and have been very satisfied with how it has be running. But the motor has seemed to have developed a small problem. There is a slight stumble while idling. This stumble is present at idle and just partial throttle. Once the clutch is out and above about 1200rpms the motor runs normally. I've tried playing with the timing by advancing and retarding it but no change. I've checked for any vacuum leaks and none are present. All the plugs look fairly good, or at least all the same, white to slight brown. I'm thinking that it is a lean fuel related problem and am thinking of rebuilding the carb. It is a 1bbl but not sure of type but guessing holley.

With this description would you all agree that it's fuel and is there a way I could verify this before going through the hassle of rebuilding what could be a perfectly good carb??

Secondly, how do I identify the carb?? I've looked all over the carb but can't seem to locate any id marks what so ever.

My family keeps kidding me about traiding it in for something new but this truck has been such a solid runner for me and I just put over a grand into the rearend that I'd really like to hang on to her.

 

Hook up a vacuum gage to the manifold, then adj the idle air/fuel screw till you get the highest rpm. Also have a tack connected so you can see the rpm change. May need to readjust the idle speed.

Bad plugs can cause a rough condition too. But from what you describe I would lean toward the carb. Carbon build up on the pistons and head can cause rough idle too. I would give it a drink of water. Bring your RPM up to 2000 and slowly add water. As you add water increase throttle to maintain the rpm. Water will not burn and will be hard to restart if you kill it. As for volume about 12-16 oz should be enough.

You may want to add some RXP to you gas. It's what we use if a car is having problem with emission. I also use Barymems Chemtool B12. It's good for shooting down a carb and help clean the intake.

 

I believe I read from some of the other guys on here, that the carb for the six is famous for the screws loosening up that hold the carb together.

 

That is true, the 300-6 is quite a shaky little beast. The four main body screws are known for coming loose as well as the mounting nuts/bolts. Also I know you checked for vacum leaks, the 300 is known for the rear intake bolts coming loose too.

 

Thanks for the info and I'll definitely check for loose bolts and screws. If it comes down to a carb rebuild, where do I find the carb id plate?

 

It should be screwed to one of the main body screws...