79 cj5 running rich

I have a 79 cj5 (73k miles) with an amc 304 cubic inch V8 which still has the original 2BBL carburetor. The carburetor has been rebuilt 4-5 times, and everytime the engine runs great for about 2 weeks - 2 months worth of driving. I live at 7200' so the last time I had it retuned, I made sure the mechanic knew to adjust it for high altitude. Ran great for a while, but now it is running rich. I am surprised the people behind me don't get high from the fumes...

Does anyone have any suggestions on what else I could try, or do I have to live with this?

Thanks a lot.
Brian

 

Can you lean the carb out yourself? Adjust it until it runs correctly? If it has just been rebuilt, I would think the internals were replaced... Sorry, just thinking out loud here.

 

If it runs OK for 2 weeks, then starts running rich, do a spark plug check.
Based on the plug check, I would try running a hotter plug & also take the time to index them. If you're not familiar with indexing, it involves getting the plug gap to face the intake mixture by using different size spark plug crush washers.

gj

 

Thanks for the reply guys! Wow, never would have thought about the spark plugs. Thanks for the tips on how to check them, I did not know that.

Brian

 

You're welcome.

When i was riding at many different elevations on my Shovelhead, I found an adjustable main jet kit. It was the best $30.00 investment I ever made. Just a turn on the t-bar would lean out high altitude rich conditions. Of course, even though the kit was spring loaded, I had to constantly check that it did not turn itself from engine vibes. Most BMW's would struggle through the hills as I putted along.
It's a shame that nothing could be adapted to automotive applications.
You'll be surprised at how much difference plug changes & indexing will make.
I don't know if NGK makes plugs for automotive use, but I found the best of luck with them on my scooter, especially the copper-cores. Mayhaps some brand of Splitfire (overrated IMHO) could help. A good parts store will have a list of different heat range plugs, but you may have to go to a performance shop for the varying thickness crush washers. Be careful checking the distance that a potential plug
will extend into the combustions chamber.

Good Luck,

gj

 

Does a '79 have a 2100 or 2150 Motorcraft? The 2150 is basically a 2100 with an altitude compensator. If you have a 2150, the compensator may not be functioning properly. I think you have a 2100; the 80s Wagoneer 360 certainly used the 2150.

Once the carb is together, the mixture shouldn't "drift". The mixture is controlled by fixed jets and the float level. If the mixture seems right following a rebuild, I'd be more suspicious that the choke isn't opening properly, or something wrong with the compensator (if a 2150).

My favorite option would be fuel injection - the modern way to get adjustable mixture. Several aftermarket setups are available, though not cheap.