CPI Racing 70cc Stage6 Sport Pro acceleration problem

[cpiracing]

Hi Guys,

Bought new CPI Racing GP scooter few years ago. In stock this thing doesn't move at all so I changed cylinder to 70cc Stage6 streetrace and carb to 19mm Stage6 dellorto racing black, main jet was 77.5. Scooter moved very well for few years until one of the piston rings snapped and damaged piston. Well this happened few months ago and decided it was time to upgrade a little.
So went with 70cc sport pro from Stage6 and some problems started.
I'm having trouble reading plug as it's always grey'ish (not white or brown).
I started with same main jet what I had on streetrace cylinder and moved step by step up. Around size 90 jet I noticed improved acceleration, but it was still problematic.

Main problem is that if I turn gas quickly to WOT then engine just stops. It doesn't start bogging down slowly, it's just like cut's off. It only happens if I turn gas quickly to WOT, if I turn gas slowly it can rev easily over 10k. This problem is not present when I'm revving on stand, only under load. It happens around 6500-7000rpm area.

What I have tried:
Changed main jet from 77.5 up to 122.0 step by step and problem is exactly same
Removed stock airbox and driven with out filter element, still same.
I had drilled some extra holes for streetrace kit( 2x 8mm holes in to filter housing). First hole improved acceleration, 2nd didn't do anything for streetrace kit. So just in case I added 4 more 6mm holes into filter housing, but no change in acceleration.
Exhaust is stock, no restriction in it.  
New plug PR8HSA, stock ignition box and cdi.

Any ideas anyone what to check or do change next?

Thank you all,
Tom
Changed needle position from 2nd to 3rd, no change.

[90GTVert]

Do you have any other needles to try? Have you tried to richen up the idle settings to see what that does?

[jdl357]

You've got a nice bbk and great carb but stock exhaust? You need to let that thing breathe! IMO! Probably see a hell of a difference!!!

[spaz12]

Is the copper disk still attached below the main jet? Get rid of it if it is. When you say you went all the way from 75 to a 122 and it does the same thing, it made me think of the copper disk. If the disk is installed upside down it will starve the motor of fuel, almost like the only fuel it gets is the fuel from the pilot.

[cpiracing]

Hi Guys, Thanks for all the responses.

So I started testing again.
1) Went back with main jet where acceleration felt best (90-100 size area). Started with 100 main jet.
2) Also changed pilot jet from 40 to 50
3) And changed needle position from 2nd richest to 1st richest

Result:
1) Idling was rich, easy to see blue smoke and quite strong fuel smell. Did test run and no change maybe even little bit rougher ride.

This was indicator for me that engine is running too rich.
2) Changed needle position to 1st leanest position and made another test run and Yuhuuu we have a progress. RPM cut off area has moved higher around 8k. Scooter accelerates quite quickly up to 8k and then starts cutting off down. Now this result is with W8 needle.

3) Tried W7 needle in 2nd richest positions and also W9 needle. Both made conditions too rich to start moving from start. Stayed with W7 and moved needle position to 1s leanest and changed main jet to 95. Test drive acceleration wasn't as good it was with W8 1st leanest needle position so moved back to W8 needle with 1st leanest position and main jet 90.

4) Test drive with W8 needle 1st leanest position and 90 main jet was almost smooth, there was some empty acceleration spaces, but there was no cut off area anymore. Checked plug and it was little bit whiter then I would like, but nothing major. I can definitely  say that with 95 main jet acceleration was faster and plug looks good. I would say I'm almost where I need to be so I will too some longer test drives over  a week and see how engine responds to this.

Stock exhaust for Aragon GP is quite good actually compared with other stock exhausts. Also I live in suburbs and go to work every morning at 5am so I can't change exhaust even more louder than it is now.
There is no copper disk under the main jet.
I'm wondering if this kind of cut off situation can happen if there is too much fuel going into cylinder?

Thanks guys!