wide open stumble

When I open the throttle I get a stumble/bogging, if I gradually open the throttle it runs and pulls fine. I am brand new to the drz world so any info would be helpful. I was going to adjust the pilot screw but I don't know were to start. The bike idles at approx. 1500 rpm I don't know if it is running rich or lean that will be the next thing I check.

Yeah , start with a clean carb . Jetting next

What carb ?

sorry it is a  Mikuni BSR36

The pilot screw won't change anything since your problem is at wide open. Any modifications to this bike?


If the carb is stock, the fuel screw will still be covered with a cap, so you can't get to it without drilling a hole in the cap to remove it.


If you have mods, you need to figure out what your current jetting is. It sounds like your carb is just clogged / dirty, not getting enough fuel. My guess is that it is running lean.

When cleaning, pay good attention to the main jet.

Well a big morning for me...First thing I did was pull the plug, it was more grey than black. I figured I would fart around with needle setting, the needle "c" clip was in the second position(from top). I set  it in the 4th position and took it for a ride. The bog was still there but not as bad...so back home and pulled the needle again and put it in the 5th position. This time the bog was worse..so back home. I pulled the needle and ran it in the 3rd position it was better but a WOT  it would bog. At present I left it at that I may try a new needle and main jet, I will get a couple of different sizes. The bike has been apart before, the fuel screw is not plugged and it was obvious that the carb was apart. The bike is piped with a Yosh, the idle is at approx. 1500 to 1800 (idles very nice). So my way of thinking is that the idle is set properly but my main jet is the one giving me grief (WOT)...it would be nice if I knew what main jet I had.

I will clean the carb prior to re jetting..I may have to enlist a mechanic this next round.

Have you pulled the carb off the bike? 

Or only changed the needle while still on the bike.

WOT bog could be water or some other contaminate in the fuel bowl.

yes I had the carb off the bike ..I dropped the tiny O ring and had to remove everything to find it. I did drain the bowl and also blew air through to carb. The bike has had the 3 x 3 mod done to it..I also ran the bike with out the side plate so for sure the bike has lots of air. What jets are a good starting point?......thanks for your help by the way.

I would start with either a 150 or 155 main jet.

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