Hey guys, I got a 300 in a 78 f100 that is missing at idla and just off idle. If you get the revs up it smooths out pretty good. Engine is completely stock, and is carbed. Any ideas what the problem might be? Thanks for the help.

 

when was the last time she had a tune up?

 

Hasn't had a tune up in quite a while. Doesn't get used a whole lot. Could it just be that it needs one?

 

yeah that could be your problem right there.

Check the timing while you're at it also.

 

those are also classic vacuum leak symptoms- one more thing to check, especially with that mile long intake gasket!-good luck!

 

How do I check for a vacuum leak? And how do I fix it? Is it very dificult?

 

first off, im gonna agree with the other guys here- tune that truck up first! plugs, cap and rotor, (i'll assume that truck has an electronic ignition, so it doesnt need points, but check!), etc. next, spray some soapy water in a spray bottle around the ignition wires, to check if they are arcing. one other quick, down and dirty test while your under the hood- before you pull everything apart, disconnect one of the wires from the coil, and CRANK THE MOTOR OVER FOR @ 10 TO 20 SECONDS. what this does is let you know if youve lost compression in one or more of the cylinders. as the motor turns over, it should make a nice even sound. if you have low compression in a cylinder, it will 'speed up' for a moment- if you want a good example of how this sounds, pull JUST 1 of the sparkplugs out and crank it over- you'll hear what i'm talking about. post back and let me know how this stuff works out! as for looking for a vacuum leak, its pretty simple on your truck- get a can of wd 40, start the truck up and let it idle, and spritz the wd40 around the intake where it meets the head. small bursts will do it- try to spray around each one of the intake runners one at a time- then spray at the base of the carb, etc- any place that the intake manifold would join something or have something plugged into it. if the motor smooths out or revs up alittle, thats where your leak is. one warning, DONT SPRAY THE EXHAUST MANIFOLD! also, listen while the motor is running- a vacuum leak will make a 'hissing sound', caused by air rushing into the leak area- a 12" piece of vacuum or garden hose, held up to your ear, can help you hear- just move the end of the hose around the manifold seal areas-if there is a hiss, you'll hear it! ok, that should make enough trouble for you- remember, TUNE IT UP FIRST, before you horse around with this other stuff. -post back if you need more help!-good luck, cave

 

I have never really done too much to an engine, it is dificult to do all that is required for a tune up? How much will new parts cost? I am in college, and on a pretty tight budget. Thanks for all the help. I will post if I am able to find time to do all this. Finals are coming up and things are getting really busy.