Hello all. I have a '68 F-250 I bought from a guy in Van Nuys California with a stock 360 and a Motorcraft 2100. The truck was in storage from '89 to '14, has 135,000 miles on it and the motor has at least one rebuild on it. I think the carb was rebuilt at some time before I got it in '14.

It has a couple of burnt valves (rebuilt heads with hardened seats are on the way):


The plugs from the cylinders with the burnt valves look like this:


The rest look like this:


The guys over in the '67-'72 section of the forum are telling me my fuel mix is too lean and one guy says I should post a question here. Van Nuys is about 750 feet above sea level and I live in the SC lowcountry, so I'm very close to sea level. Should I re-jet the carb? Any advice would be greatly appreciated.
Thanks!
C

 

Hi,

Since no one else has chimed in I will throw my .2ct in.

It does appear from the pic's that you are running alittle lean.

The rule of thumb I have been taught when changing jets (where leaning or riching) is to change at least 2 maybe 3 jet sizes from the current ones in the carb.

The jet number should be stamped on the side of the jet.... so pull the bowl, then un-screw the jet and see what you have,... order replacement 2-3 sizes larger.

Don't forget to post a follow up so we all can learn more about tuning.

 

Thanks for the reply! I changed the jets weeks ago. Motor still coming back together. I'll check the package the new jets came in to verify, but I believe I went up one size. Hard to know since I can't tell what was in there before (someone else's rebuild).

I'll probably have to run it around a bit to get the kinks out after the rebuild before I know what's going on with the fuel mix. Will post more info then.
Thanks,
C

 

Okay, got the truck back on the road. The jets that were in the carb were marked 53F. I replaced them with 55s and the exhaust still stinks with the idle screws adjusted at 1-1/2 turns out. Idles a little rough, as if it has a somewhat lopey cam.

 

Hi,

What method did you use to set the idle mixture? Best way is to use a vacuum gauge hooked up to manifold vacuum. Adjust the screws for the highest vac reading. As you adjust both idle screws you may also have to adjust the idle speed screw as the idle speed may change with the mixture screws.

Just to be sure, I have to ask: You are aware that the main jet size doesn't have anything to do with the idle exhaust smell. Right? Main jets generally only come into operation after the throttle is opened past the idle position.

Have you checked the fuel level in the bowl? That and the idle screws settings affect the idle smell. Also, is the choke opening up all of the way when warm? If not that could cause rich idle.

 

Couple things to keep in mind, after 50 years almost anything could have been done to an engine or carburetor. It may be an entirely different carb as well! While 50 something size jets sounds correct, what I'm getting at is it's a bad idea to assume that whatever is installed after all this time is correct. They can also have been drilled out, so the #s stamped don't really mean anything as far as that goes unless you check.

Always use the manual to determine the proper size jets, it will indicate the stock factory jetting for that particular carburetor and engine combination and altitude. Also lists the venturi size and cluster and power valve size (color), fuel height, and setup and tuning instructions.

This 1.5 turns out business on the idle mixture screws is just to get the damn thing close enough to start and stay running, it's just a ballpark setting. May end up turning them in almost a full turn say, about 1/2 turn out, for best idle "lean drop". A vacuum gauge works good for carb and engine tuning.