my 78 f-150 passed all but the hydro carbon test at 2500 rpm. It passed the curb idle with no problems. they want to charge me $72 just to find out what is wrong with it. If I'm not mistaken this can be fixed by leaning out the carb. Has anyone had this problem. I want to make sure a carb adjustment will cure it before I spend another $30 on another test. thanks

 

I'm not sure if leaning it out would help. You may want to check the thermactor system for proper operation? You may want to look around for a "tune up" that's cheaper than $72 that would include adjusting the carb.

 

Without an HC/CO tester it’s hard to tell the results of your adjustments. I have a couple of commercial infrared machines and you’d be surprised at the difference a small adjustment makes. You can try adjusting it leaner but make sure it does not miss at all, ever. Before making any adjustments though, count the number of turns on the needle valves first so you have a reference point to go back to. When you were testing at 2500 rpm, was it running smooth or surging, missing? If your exhaust system is partially clogged up, the back-pressure regulated EGR valve will dump too much exhaust back into the engine and cause a surge/miss condition at 2500 rpm. Check this by running the engine up to 2500 rpm and then disconnect and plug the vacuum hose to the EGR. If it runs a lot smoother then that’s your problem. Also if you have a lot of miles on the engine the excess crankcase blow-by will cause you to fail. If that’s the case, change your oil to straight 40W and throw in a can of CD-2 (thick stuff not the thin). I’m sure you already checked the timing and changed your plugs. When you retest, make sure the engine is not cold, it takes a couple of minutes for the converter to fire up and start working.

Barry