3TB 44hp/4PT 40?
 

It seems like they have same bore x stroke and compression, what happend to the 4hp? Different carb, exhaust?

The secondary carb was smaller after the 89 us model, and jetting was different. THUMPTHUMP

Yes but iam talking about the 1990 vs 2002mod. The 96mod had 45hp, so what happend in 2001?

Theres several threads about, the only thing that seemed different was the ignition curve. But I wasn't able to jet my 2003 model, to suit the ignitioncurve.

Well its not easy to search and find threads like this, if you change to old ignition curve and use same jetting and still no good it must be something more different.

Unless you have put each on a dino, I would not be confident in the posted HP numbers. At some time in the past they used to put Hp numbers from the drive sprocket and later at the rear wheel. Drive train friction lowers the HP rateing. Emission requirements increased over time and they changed ignition timeing as stated in previous posts and also leaned the jetting to get by the emissions requirement. THUMPTHUMP