Flat Spot from 3/4 to WOT

Hi i wanted to ask about my jetting problem i'm sorry if my english is not quite well :thumbsup:

My bike is a 2008 kawasaki 150 rr two stroke (I know it is not a dirtbike but I hope someone here might be able to give me answer with my problem)

it has SKIPS which is operating at 7000-8000 rpm

the temperature in my area is 29-30 day 23-25 night, 3000-3300 feet above sea level

DBS exhaust(free flow the silencer replica of tz 125),polished machine port?!?(I don't know the exact term in english it is below cylinder head and above the crankcase),stock air box filter

my pilot jet right now is 22,5 main jet 270 clip #2 (the needle only has 3 notch)

1 turn air screw, mikuni vm28 carb, float height 20 mm )the factory setting float height for is 16 mm my mechanic bend it because he think it would run too much gas because the carb position not standing straight the carb stand like this "/")

my problem is when i open throttle slowly but sure cruising through the gear, there is a flat spot at 3/4 and before WOT it happen only in 4-5-6 gear in slight uphill as well as flat road

it feel worse in the 5-6 gear even if I widely open the throttle until the throttle end point it won't go up further than 7000 rpm but if I aggressively wack open the throttle from gear 1-2-3-4-5-6 and constantly shifting gear at 9000-10000 rpm it would go up to 12 rpm without no hesitation:bonk:

i've been trying to change the jet combination and needle position

1. pj 22,5 mj 250 clip #2

the flat spot only appear at 6 gear WOT

2. pj 22,5 mj 280 clip #2

the flat spot appear at 5-6 gear before WOT

3. pj 22,5 mj 270 clip #3 (the lowest)

sputtering like it has to many gas especially feel when going uphill

so what is the problem of my jetting it is too rich or lean?

which circuit should I fix?

i have been gone to many mechanic at my town and neighbour town but the problem is still exist so if anyone here have a clue please tell me:worthy:

Set your float height back to factory setting. Put your needle in the position u think runs best. Start tryingdifferent main jets w/o changing the needle

so the fuel float have effect on jetting?I never think about it :thumbsup:

thanks for your reply I'm going to try it this afternoon,

by the way the best needle position for me is the #1 but if i put it there the bike wouldn't take off immediately it bog first waht do you think?should i put it on #1 or stay on #2 for safe?thank you mxtech

I would put the needle back at factory setting. Then start trying different main jets. Most factory bikes come jetted pretty darn good, however they are typically on the rich side to increase engine longevity. Generally, you can lean the jetting out and gain a little more performance. Don't get frustrated, without a dyno or exhaust sniffer, its a very tedious process. Make sure u ate only changing one key at a time so u can get a good feel for what effect that jet has. Your air mixture fuel screw may also have some effect in this situation so try adjusting that but only in 1/4 turns at a time.

thank you for your advice :smirk:

I have tried your advice about the float height yesterday and now my motorcycle run much better, now i'm searching for other MJ size to continue the jetting process to make the flat spot completely disappear

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