high(ish) rpm, low throttle input, jetting issue. DRZ400SM

I posted this in the DRZ400 section, but thought I'd post it here in the jetting section as well:


So, I have an issue. Might be jetting, might not be jetting. This is gonna be long, but please bare with me and read on. I'll try to describe the issue best I can.


Bike is a 2014 DRZ400SM with just under 5,000 miles. Mods are 3x3, Powerbomb header with the Powercore 4 muffler, and a JD jet kit on the stock BSR36 carb. Current jetting is 160 main, blue needle 4th clip, stock pilot, and the extended fuel screw which is currently at 3 turns out. I've tried the fuel screw at anywhere from 2.5 to 3 turns out. Temp today was mid 40's and sunny. Elevation is sea level to maybe a couple hundred feet above it. 


The issue I am having is at higher rpms with low throttle input. A perfect example was tonight I was going 52mph around a corner in 4th gear just holding a steady speed through the corner. It started doing it, I then looked down and the speedo showed 52, I looked back up to continue through the corner. The throttle position was about 1/4 throttle, maybe 1/3rd throttle at the very most. I don't have a tach, so I'm not sure what rpm a DRZ400SM with stock gearing is doing in the low 50's in 4th gear. My best guess would be maybe 6,000 rpm. It's definitely not near the limiter, but right in the thick of the powerband.


The best way to describe the issue would be that it feels like it's running out of gas. The same kind of feeling you get when you have to switch to reserve on the tank. If I give any additional throttle input it'll accelerate right through it perfectly fine. I wouldn't call it a bog, because if I roll on the throttle or crack it open to full throttle the response is instant and it just accelerates right through it. It just feels and sounds like it's breaking up when trying to hold the throttle at a steady position. The first time this happened was in 5th gear at about 70mph So I originally thought that I had the dreaded 70mph stutter that many people have complained about. Then I started to notice it in other gears at other speeds. 


Tonight I checked my spark plug. I think it looked fine, I'll put up a pic, but I went out and grabbed a new one anyway since they only cost 4 dollars and change. I also turned the fuel screw out to 3 turns instead of the 2.75 turns it was at. Also put some Lucas brand fuel system cleaner in my tank. The issue I just described is still happening after the new spark plug and the screw being turned out the extra 1/4 turn. 


The bike runs perfectly otherwise. Starts up instantly, even starts up cold without any choke anytime it's above 40 degrees outside. Idles perfectly smooth. Throttle response is crisp and instant. Bike pulls strong and hard. The top end pull isn't anything special, but it's a mostly stock DRZ. It'll pull 3rd gear power wheelies at around the 30mph mark with just a slight tug on the bars. Decel popping isn't anything out of the ordinary, but it does do some light popping sometimes, but nothing I'd call excessive.  The bike runs great otherwise. This issue isn't stopping me from riding it, but it's kind of annoying.


Sorry this got so long, but if you have any ideas or suggestion I'd like to hear them. I'm out of ideas.


Needle flat spot common to that bike


You have to live with it or get a 'real' carb.

Needle flat spot common to that bike

You have to live with it or get a 'real' carb.

Really? I've never heard this before.

CV carbs don't work so hot once you start de-restricting the motor.

This is the single weakest link on all DRZ's.

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