I am still a newbie and I am running a OS 40LA in a Sig LT 40 that I have had for the past 3yrs. First time running since last season was today, put in new plug and fired her up, no problem at first, at least I hope not, her exhust smelled burnt and her run out was black. I never had this type of problem before she has always run well and clean. I also noticed that while throttling down it was missing just on this one notch before shutting it off, so I waited a few mins and it took quiet awhile to start it back up, and it did the same again blowing black fuel and smelling like it's burnt fuel and only missing on this one notch down, what do you think the problem is?

What type of fuel/oil are you using? Caster based fuel may leave slight blockage in carb (dried out caster) and the engine will run slightly leaner than it should, especially if it was orignally set on the lean side.

Cheers.

The black fuel residue sounds like the muffler to the engine connection may be a little loose. Check the bolts and make sure they are tight. While you are at it check the other bolts on the muffler also. Many people have lost mufflers from them comming loose/off in flight.

If the muffler is loose, that may also be the cause of "the miss".

I would follow Campy's lead. The screws to the muffler at the side of the crankcase could be loose, letting air in to the exhaust.

Anytime you see really black oil, something metal is rubbing in a way it shouldn't. Do not ignore it. Find the cause and fix it before you run the engine again.

Jim

Over lean mixture/black aluminum residue, engine eating itself!