2008 Suzuki rmz250. I live in Connecticut so it has gotten colder here (usually 40-55 degrees now). I don't plan on riding/racing the bike much more but I do have an arenacross race in a few weeks in Albany New York, which should be cold.

Ever since it got colder out, the bike runs poorly. Basically, it backfires and pops, it will bog if you wack the throttle hard. Out on the track if you get on the gas quick it will pop before it "catches itself".

I tried opening up the fuel screw, it helped a tad but I am at the end of adjustment (about 2.5 turns out).

If I let the bike warm up for a LONG time, it does run better, the backfiring will go away but it will still give a pop/bog if you wack the throttle.

It's obviously a lean condition. Specs are: #162 main jet, #42 Slow jet, Jet Needle NLCT at the 3rd clip position, pilot screw from factory should be 1.5 turns back (I have it a 2.5 now).

Suzuki supplied a #165 main jet. Should I try this first? Maybe lower the clip a position? Or, is this a pilot jet issue and go bigger on the pilot?

Thanks, I will check to see if the local shops have the next smallest leak jet. Curious, will I have to go back to the stock leak jet in the summer months? Or, will adjustment of the fuel screw compensate?

Reason being, I will only be riding the bike a few more times this year and then store it until spring.

Colder temp means more dense air, so your bike will run lean. I'd say rejet the bike for the temp by going one up on main and pilot jets depending on throttle position where the problem occurs, first.

Ok, I went from a #42 pilot to a #45. The bike runs so much better now, no more popping at 1/4-1/2 throttle. But now, the bike bogs out if I wack the throttle wide open.

The bike has a #162 main jet. I have a #160 and #165 jets to play with. What is causing the bike to bog when I wack the throttle wide open? I rode it yesterday on the track and it seemed to ride really good so I'm not sure.

I would listen to edward cissners

listen to eddie