Carb (I think) problems, flat spots

[Globe]

Greetings from New Zealand. Great forum.

I have a franken-bike 2007 GN250. I have replaced the exhaust with an aftermarket reverse cone thing. I think it has a copy carb on it, TK is stamped on the side but it matches the mikuni exploded diagrams on the web.

(one of these http://www.vbsco.co.nz/product/motor...rse-cone-black)

It was running fine with this muffler on there. I serviced the bike, set the gaps, changed oil etc - no carb work - at it still ran fine except it would cut out at idle once the engine was warm.

Pulled the carb off, cleaned it out thinking the pilot may have been blocked. Since then it has run awful. When I ride it has a flat spot around 1/4 throttle and is unresponsive and then surges at WOT. I presently have the air/fuel screw out about 1.5 turns, riding around and adjusting yesterday this seemed to be the best setting.

Items that I think could be contributing,

- The main needle has the plastic thick washer (about 3mm) above the e clip. Should this be underneath it?
- The spring that goes around the main needle (not the one above the diaphragm) is between the e clip and the plastic holder/plug/cap thingy that limits the movement of the needle upwards. The exploded diagram shows this as it should be under the e clip but this doesn't make sense to me so am assuming it is a typo.
- I have replaced the coil and HT lead so unlikely to be that.
- Just general old and worn jets - again doesn't make sense since it ran fine before the clean. Unless I damaged one during the clean.
- The plugs are coming out as a bit rich, I haven't done a plug chop though
- It used to start fine without choke, now it needs choke to start.

All ideas and conversation warmly welcome, Cheers

[derbydave]

putting the spacer below the e clip raises the needle valve and richens the mixture. Putting the spacer above the clip would effectively accomplish nothing in the way of adjusting the needle valve height. Sounds like at 1/4 throttle (when the needle valve starts to work) it is too lean and the needle valve needs raised. See the attached picture showing when each component of a CV carb is functional.