Need help tuning my Vento GT-250 (Same as Hawk)

skirmich · 06-27-2023, 02:31 PM

Hi!

I need a little help tuning my GT-250 with these mods:
NIBBI P28FL Carb (I bought this before thinking going big bore)
Big Bore Kit to real 250cc (70mm piston)
Full SS Exhaust.

I did a little porting and polish to the head, I am running stock Camshaft on 91octane at sea level.

My current jetting is the last one I used with the stock piston:
115 Main, 38 Pilot, Needle on the 4th position from the top, Air Mixture at 1.5 turns.

My issues:
-Very hard to start when cold (I must use choke or it wont start, Prior it would start without choke).

-When hot and idling If I give it a quick turn to the throttle it would bog down hard, sometimes completely stall.

I am still breaking in the cylinder so I am not going past 5K RPM but the acceleration feels lazy not at all as before.

Any reccomendations for jetting or hints would be appreciated.. I have never tuned a bike before but I have messed with the jets for a little bit.. I got a full set of jets available for testing so what ever you ask me to test I can do it.

06-27-2023, 02:31 PM	#1
skirmich Join Date: Apr 2021 Posts: 21	Need help tuning my Vento GT-250 (Same as Hawk) Hi! I need a little help tuning my GT-250 with these mods: NIBBI P28FL Carb (I bought this before thinking going big bore) Big Bore Kit to real 250cc (70mm piston) Full SS Exhaust. I did a little porting and polish to the head, I am running stock Camshaft on 91octane at sea level. My current jetting is the last one I used with the stock piston: 115 Main, 38 Pilot, Needle on the 4th position from the top, Air Mixture at 1.5 turns. My issues: -Very hard to start when cold (I must use choke or it wont start, Prior it would start without choke). -When hot and idling If I give it a quick turn to the throttle it would bog down hard, sometimes completely stall. I am still breaking in the cylinder so I am not going past 5K RPM but the acceleration feels lazy not at all as before. Any reccomendations for jetting or hints would be appreciated.. I have never tuned a bike before but I have messed with the jets for a little bit.. I got a full set of jets available for testing so what ever you ask me to test I can do it.
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