Off idle hesitation following 1230 piston kit fitted to GS 1150

[John Kat]

My GS 1150 engine has been rebored 3mm to take the Wiseco 1230 piston kit.
Since this modification, the engine hesitates just over the 1/8 throttle opening.
Above that it will really fly.
My carbs have the OEM jets with the OEM air box and filter.
When decelerating it will also pop despite new exhaut gaskets.
Is the mixture too rich or too lean?
Will I have to change the idle jet?

[Big T]

It's more likely the needle than the pilot jet

Lift the needle a notch, or shim it

[Tom R]

Does it start up and idle fine? How much choke does it need? If it starts right up, doesn’t need much choke, idles nice and doesn’t have a raising idle as the bike heats up, you might want to look at the idle air jets.

[zed1015]

Going to 1230 accompanied also by what i presume is also a compression increase with the Wiseco pistons will require at least going up a size or two on the main jet.
The hesitation off idle is cause by a fueling gap so you may need to introduce some additional fuel in that area if the larger mains don't cover it.
Depending on the severity you may be able to do this on the mixture screws or by lifting the jet needle a notch or as already suggested with shims if a full notch is a touch too rich.

[John Kat]

It's more likely the needle than the pilot jet

Lift the needle a notch, or shim it

Thanks Big T!
It worked just fine by raising the needle one stop.
In fact I had done this beforehand but got mislead by a blocked main jet that made me revert to the previous setting.

[John Kat]

Going to 1230 accompanied also by what i presume is also a compression increase with the Wiseco pistons will require at least going up a size or two on the main jet.
The hesitation off idle is cause by a fueling gap so you may need to introduce some additional fuel in that area if the larger mains don't cover it.
Depending on the severity you may be able to do this on the mixture screws or by lifting the jet needle a notch or as already suggested with shims if a full notch is a touch too rich.

The problem got fixed by raising the needle by one stop.
I'll look into the main jet after running in the new pistons and valves.