KTM Duke II modifications - the easy stuff

Step One - Let it Breath

The first thing you'll hear on the various lists is that the bike is extremely lean from the factory. It's not actually, just restricted. The tip is to remove the airbox lid and throw it away and change the main jet from the tiny 145 to something like a 175 (assuming sea level). The KTM power-up kit (part # 58705060044) is basically this with the addition of a Y-pipe to even the exhaust distribution between the two pipes. We thought we'd run the bike stock and see what it made for a baseline - 46.6rwhp (blue trace). Not bad but it felt a bit anemic.

First we did the cheap fix - we replaced the airbox cover with the "racing" cover (you could also just remove it but I was suckered by the word "racing" - save your money), installed the 175 main jet, drilled the slide holes out to 3mm, turned the mixture screw out 2.5 turns and replaced the spring (red trace). You can also cut four turns off the stock spring. Anyway, that's about $10 worth of parts. This gave us 49.3rwhp. It read a little rich so we thought we'd just add the Y-pipe and see if that helped flow a bit more air but it didn't as the power actually dropped to 48.9 (green trace)- only half a horse but we expected something since the bulk of the kit's cost is the Y-pipe. We went to the 170 since it still read rich but that dropped us to 48.6 (purple trace). While these gains sound modest they are across the whole powerband and really affect the bike.

We're guessing that the Y-pipe will help when the restrictive mufflers are unrestricted but if you plan on keeping your exhaust stock you should save yourself some cash and just remove the airbox cover and rejet the bike. As it was we ran out of time and so I thought I'd just live with the bike for a while with the power-up kit in it and the 170 main and see what it was like on the street.

Much better. I'd swapped the countershaft sprocket from the stock 17 to a 16 as so many recommend but I didn't like how short and useless 1st gear became. I did like the ability to get the front wheel up in second though. With the jetting changes I thought I'd go back to the 17 and see what it was like. It felt like the 16. The bike lifts the front effortlessly in first and then in second with a gentle tug. Power is crisp and clean and the bike feels like it's breathing as it should. This is a really fun bike and the simple change of jets makes it run cleaner and smoother and with a very useful 6% power increase. Don't waste time in doing this if it's all you end up doing to your Duke - it's cheap, easy and worthwhile.

Next we'll take apart the stock exhaust to see what's inside and then see what a straight through exhaust does for the bike but first a little cosmetic surgery. That plate is rather ugly hanging out in the breeze despite the pretty trellis bracket.

Peter demonstrates how to coax power from the Duke II mill. Form is everything on the dyno...

The KTM Duke Tuning Kit - Y-pipe, jets, shim for the needle, drill bit, and spring.

The mixture screw gets turned 2.5 times from (gently) closed and the main jet is replaced by a 175.

Drill the two outside holes of the plastic slide to 3mm. Not the center one which is for the needle.

This photo has no redeeming value other than it's cool looking. Backfires on decel as we sort the jetting...