I've got a '74 F100 with a 302 and motorcraft carb. I installed a petronix and set the timing to 8 BDC (it doesn't start at 10 or 12), and I can get it to start and it seems to run pretty well. But it's always been really hard to start since I reset the timing.

There was hesitation just off idle occasionally so I cleaned and rebuilt the carb. I didn't change any of the settings but reset the float (it was really low). Once I reset the float to factory specs (7/16ths) the carb started overflowing out of the top of the airhorn. I nudged the float back down a little until it stopped overflowing.

Now it's really hard to start (like before) and when I shut it off I hear a bubbling sound and smell raw gas. I took the air cleaner off, and it sounds like raw gas bubbling into the carb throat, and i can see vapors coming up. It appears that there is a leak of raw gas around the back of the carb from the large vacuum port for the PCV hose. I took the hose off and a lot more vapors came pouring out of that port.

I'm new to fords so this is all kind of a mystery to me. Any pointers on what might be wrong? Thanks.

 

Sounds like you are flooding out the engine. Floats might need to be adjusted still. I would set them using the site plugs (if it has them, I've always had holleys) someone else may be able to help more on the specifics of a motorcraft. Concerning the timing, does it sound like the starter is having a hard time turning over the engine? This could indicate too much timing or a starter going out. But 8 btdc sounds correct for a stock engine.

 

I agree; sounds like the float is still set wrong. Motorcrafts don't have sight plugs; you have to measure the float height.

 

Ok I've adjusted the float again. It's lower than the carb instructions say it should be and things seem better. I no longer hear bubbling, or smell raw gas. It seemed to start easier as well, but we'll see how it does tomorrow.

As far as starting, it turns over fine. The battery is reasonably new, the starter was replaced not long before I got it, and I replaced all the battery cables and ground straps. The alternator checks out as well. When I start it, it spins the motor but doesn't want to catch unless I pump the gas a lot, and then it runs rough for a second or two until I rev it lightly.

When I got the truck, with a blown transmission and really worn points, it would start instantly, and idled smooth right at start up.