I replaced the stock airbox and filter on my Mojave with a UNI pod filter a few days back. I also started using 112 octane (mixed about 50/50 with 92 pump gas) fuel around the same time, I was using the fuel a couple days before the filter actually. Heres what seems to be happening.

It feels like it lost a little bit of bottom end and it also misses around half throttle as well, it doesnt seem as bad at around half throttle. It not a real bad miss, pretty mild if that makes any sense. It will give you some small back fires, pick up, die off and repeat the process but it isnt really pronounced.

Would the higher octane fuel itself play a role in the air/fuel mixture or is it solely the air filter? The plug looks like its been running a bit hot, it had a grayish yellow appearance but there also was some deposits on it (mostly yellowish in color) that looked like glazing possibly. Before the fuel and filter change the plug was always dark (black) so I know it was running pretty rich before (I actually thought that maybe the rings were getting tired), quite of bit of carbon was on it. Now I'm pretty sure the engine is in great shape but I was just wondering if it had something to do with the fuel. I dont run it all the time so I dont know what it looked like with 92 octane and the UNI filter.

 

If you are running VP C-12 the yellow spark plug color is normal. This is the fuel I use and mine is jetted perfectly with the same plug color. You can also check on VP's web site because I saw an article on this in there before. As for the half throttle miss you need to richen(raise) your needle. If you have a jet kit just move the clip down a position or two. If not just find a realy small nut to shim the stock one about 1/16".

 

Its actually helo fuel that a friend of mine got from work. He brings a couple gallons home now and then. I agree that the yellowish color is good but it looks like there may be just a little glazing on it. I drained the fuel a couple hours ago and went for a ride with straight 92 pump gas. It did exactly the same thing so it obviously had nothing to do with the fuel. I'm surprised that the UNI pod filter made such a significant difference in air flow, I didnt expect it to really do anything. Thanks for the help, Aaron.