[77newell]

I'd say what Joseph said and add some further thoughts as to causes. Unburned fuel can result from either poor atomization by the injector or by low compression. Given the time it takes for this problem to go away I suspect the engine has to thoroughly heat up before the fuel is inclined to burn.

Here is how I would proceed if this were my situation; I would get an infrared temperature gun (cheap will be ok for this use), start the engine and measure the exhaust temperature right where it exists the cylinder. This will tell which cylinder(s) are not firing. Then, assuming you have a Detroit V92 series engine I would pull the air box cover for that cylinder and have a peak in that cylinder with the piston all the way down. If the cylinder looks troubled then you are probably on the road to an inframe, but before you went there I would do a compression test. If the cylinder looks just fine then it is likely the injector. Thankfully, mechanical engine injectors are cheap. I think I paid about $75 a few years ago for one. Installing it is a bit tweaky and requires a special gauge that isn't expensive, but you need to know your injector number to know what gauge to buy.