1200 bandit misfire

[George Mac]

Hi Guys a question for the carburation specialists. For the last 3 years I have had K and N pod filters and a stage 3 Dynojet with 150 mains kit on my B12 and it has run great, a slight hesitation mid-range , but nothing to worry about. Just recently it has started to miss fire badly at about 3000rpm and wont pull through it unless you are real careful with the throttle. I have cleaned the filters, checked the plugs several times and replaced them once and each time no1 is black and sooty. Can anyone think of anything obvious before I strip the carbs out. Cheers in advance George

[oldskool]

Your pilots are too big @ 37.5 you need to change them for 32.5 your hesitation will disappear and be replaced with power also you will not be running too rich at partial throttle, also 3 turns out on your air screws will fix it all up.
Hope this helps George.

[George Mac]

Thanks oldskool, I guess I am going to have to try and source some 32.5 pilots on the Sunshine Coast.

[Dynomutt]

Check the emulsion tubes are not worn oval, the Mikuni BST series of carbs are very susceptable to emulsioj tube wear. When this happens the needle can no longer meter the fuel correctly, and it usually manifests as a stumble around 3000/3500rpm, when the fueling is transitioning from pilot circuit onto needle jet/jet needle. Some Dynojet kits come with new emulsion tubes, there are a couple of companies offering plated tubes which don't wear as quickly, the problem is often excaserbated by the Dynojet needles which are titanium unlike the stock needles which are softer.

[80s freak]

^^^^^^What e said, particularly if the prob has come on without changing anything. You can buy tubes genuine for around $40 each. Also check the air jets in the back (filter slide) of the bore, make sure they are clean. A blocked intermediate jet will cause low end of mid range to draw to much fuel.

[oldskool]

quote:Originally posted by 80s freak

^^^^^^What e said, particularly if the prob has come on without changing anything. You can buy tubes genuine for around $40 each. Also check the air jets in the back (filter slide) of the bore, make sure they are clean. A blocked intermediate jet will cause low end of mid range to draw to much fuel.
good point

[oldskool]

I still think its your pilot circuit
GSXR's suffered emulsion probs more than GSF's if your bandit has don under 80+k its the pilots.

[George Mac]

Thanks guys, will order some 32.5 pilots today, that should help the hesitation. As the misfire has only started fairly recently and No1 plug is the only one that is fouling I will focus on that carb. As the motor has done less than 30,000k I would have thought it doubtfull that the emulsion tubes are worn, but I will definitely check them.

[80s freak]

Pods will accelerate tube wear as there is no airbox to spread/soften the pulse waves.

[oldskool]

I would have thought an air box to create more & constant pressure on the slides?
Might take that back now my gray thinks about it, thats why ya need stiffer springs with pods, Geoff your a musician.