Needle jet change on US import V Twin

[McTrucky]

I have an old US spec. Suzuki vx800 that I bought recently and now starts and runs OK, ish.

There is a flutter that corresponds to being lean in the midrange around mid throttle. Above 6k seems ok, below 3k is ok, but hesitates and surges between the two on part throttle.

The needle on the US model only has a single notch, so can't be raised, but I can investigate shimming to raise it.

The carb settings for different markets vary, I struggle to understand this beyond climate and altitude (and emissions control) variations. The UK spec is different to the French and very different to the US. They have different jets, and different needles, and some vary between carbs (bike is 800cc VTwin), which I guess is related to temperature between front and rear cylinders, but only in some climates(!).

So my question: are needles matched to needle jets? Do you think I should drop in a couple of UK spec needles with the original US spec needle jets? Or should I seek out a full set of UK spec jets? Or do I wait until it is warmer weather (currently about 1 degree C) and hope the US setup starts running smoothly.

[catman]

I believe that you would need the jets and needles to match, to run properly. If the carbs are set up correctly, the engine should be able to cope with the inherent temperatures of the country that it's in.

The emission control may also have an adverse effect on the running too. It may be worth speaking to a Suzuki Uk Dealer and running the problem by them.

[E-bmw]

On top of differences between emission control country-to-country there were also noise measurement issues.

For instance in the UK I do know that the Yamaha FJ1200 had to have a flat-spot engineered into the carb at a certain revs because the noise from the tyres spinning was at exactly the point at which the noise was measured for C & U regs.

So they detuned the carb at that point to stop it wheel spinning & thus make it quieter.

[McTrucky]

Yes, UK bikes traditionally had a flat spot around 4k due to drive by noise tests. Hence the success of dynojet kits that just richened the mix in the mid range.

The US models even seal the air mix screw to stop people richening closed to one eighth throttle. Seems counter productive because it forced everyone to use the choke for longer.

Pretty sure I can shim the US needles to raise them, and will do a plug chop to try to identify if both cylinders are running the same.

Will put in new plugs and run for four or five miles with the throttle and revs in the problem range then plug chop and hope for clear results. One cylinder giving a white electrode and the other a caramel brown would be perfect.