Derbi GPR/Gilera SC, DT125 engine/carb fuel issue?

[crazycat109]

hi all, i have a 125cc sports bike with a 2t dt125 engine with what i think is a fueling issue.

problem is that it wont pull in 6th gear it actually decelerates so its pretty useless. the bike runs fine in lower revs/gears.

the previous owner has fitted a full arrow exhaust system to the bike thus leading me to believe that it maybe running lean?

my question is will increasing the main jet from #210 to #220 and 1 notch down on the needle potentially fix this? yes/no, not enough?
carb model is a Mikuni TM 28-92/1.

thanks for reading. adam

[SQL]

GPR?

[crazycat109]

[SQL]

[crazycat109]

thanks but i am already aware of this post.

i just want to know if rejetting will help the bike pull in top gear

i appreciate your reply though

[SQL]

Possibly however the first thing I would check is what gearing you have is it stock??

what speed do you hit on the clocks in 5th?

[crazycat109]

[crazycat109]

think i found the problem :/ the previous owner has drilled 4 12mm holes in the air box which i think is making it run lean. took the carb off anyway and its already up jetted to 220.

anyway ive fitted some carbon fiber reeds to help and gonna get a new air box or plastic weld the old one. if this don't cure it then maybe a 230 jet.

or seeing as these bikes supposedly cant pull top gear well i might just be too heavy for the bike (15stone)

bought this bike from the triumph dealer in Blackburn, you think they would've spotted the holes when they check it over

[SQL]

Also I believe these airboxes never did seal properly, I intend on using bathroom sealant to seal mine