I have a 1973 f 250 with a 390 2100 series 2bble Motorcraft carb. I was checking for vac leaks today and found out I have leaks around the throttle shaft. Spray carb cleaner around the mounting gasket its fine but when i spray around the throttle shaft it changes engine speed. Is that normal and how much is allowed?

 

It's absolutely normal-after all, those two dissimilar metals have been rubbing against each other for over forty years! There's no "acceptable amount" for measuring the slop. Basically, you can run it till you either can't tune it any more, or the leak is too great.

Then you replace it

 

2x ..no unmetered air is allowed.

That carb is worn out. Could get it rebushed but it's typically more cost effective to get a different carb and rebuild it.

 

Thank you that confirms my thoughts on carb! Napa has a Rebuilt one for $250

 

Pick up a used one for $20 and rebuild it for $25. Super easy.

 

Rebushing or replacing are preferred, but sometimes cash flow limits what we can do. A quick 'field expedient' fix: smear oil on the shaft - only on the shaft - where it comes out of the carb. Clean the carb surface around the shaft with alcohol or acetone to make sure it is contaminant free, then apply a small bead of gasket sealant to the joint between the carb body and the shaft. The oil will keep the sealer from sticking to the shaft and but you will significantly reduce the amount of air getting sucked in. Not a permanent fix, but it will reduce the air leakage and may make the difference between the truck running poorly and running acceptably, and will buy you some time to save up for the more expensive repair. T