I have a 78 F250 with a 351M and C6. I recently within the last month or so put a newly rebuilt carb bought from autozone on. I have only driven it maybe 200 miles since I put the new carb on, and yesterday I loaned the truck to a friend to tow a car.

When I got the truck back it was running horribly (lesson learned about loaning one's truck). It had a very bad miss, at least one cylinder, but when reving it to very high RPM's, it would do "ok", but still not run nearly as good as it did when I first put the carb on.

I started pulling spark plug wires while it was running and on my first try found a wire that made no difference to the way the engine ran when I pulled it off, but I could hear/see it jumping spark to the exhaust manifold, so I know it was getting good spark.

I pulled that plug and it was very wet around the threads, black oil wet. It smelled kinda like gas, but I don't have the best sense of smell. The gap itself appeared ok, and the end of the plug was black, but not wet. (should be grey shouldint it?).

Also, the oil is now black, when a couple of weeks ago it looked brand spanking new. I thought maybe the choke was stuck so I pulled off the air filter and was holding the choke open 100% to see if it would make any difference (it was open almost 100% anyway), but it made no difference.

The kicker here is that it died on me, and when it died it squirted a ton of gas out of the carb SOAKING my hand. I started it back up, reved it a few times and watched it for a few seconds and when it died again I saw it squirt a stream of gas up and out of the carb, soaking the top of the carb.

Soooo, anyone have any tips on exactly what it could be? I ordered the carb online from autozone.com, don't think they have any in stock in the stores. I would like to do some kind of a temp fix before I exchange the carb for a new one so I have some transporation. It is my only way to get to work or go anywhere right now.

I am thinking the float is stuck, and because of the amount of gas getting poured in, it runs better at high RPM and the excess gas is working it's way into the oil through the rings. Is there an easy way to temporaily unstick the float if that is infact the problem so I can get around while a new carb comes in?

Thanks for your help.

 

Either the float has a pin hole in it or there is a small piece of debris in the needle and seat. Just remove the top and check these items.

 

The power valve may be blown also.

When was the timing chain replaced? The timing chain should be replaced at 80K miles. Check for play in the timing chain. Your repair manual should have the diagnostic procedure listed.

 

Hi, thanks for the replys. The engine was rebuilt recently and had quite a few new parts, including the timing chain. I called up Auto Zone this morning and they have one in stock in a different town which will be delivered to my store this afternoon. I am going to swap out the carbs, hopefully it will fix my problem.

 

Good call on swapping the carb. Also most carbs need to be adjusted out of the box to your application. Sounds like you may have a fouled plug. If your carb was overflowing you may want to start out with a fresh set of plugs while your at it