maybe the ports are blocked???

standard air box with snorkel removed

 

I have done a plug chop and it runs a real nice tan colour

 

I run a streetrace with a 17.5 dellorto, standard airbox and snorkel removed. It has an 84 main jet and the plug id a loveley biscuit colour. So I would have thought that a 19mm carb would need a bigger jet

 

Its nice to see the old premix arguments going on. I use a 26:1 ratio and that's the leanest I'll run. Alexander Graham Bell did several studies of different premixes and putting it simply, the less oil he used from 18:1, the less power he made. Understandably plugs get fouled a bit, but my pistons are always tidy and clean with next to no varnishing and no scoring. (Apart from the last one =/ Lotsa bits missin out of that piston haha)

 

I'm pretty sure Yamaha spent a fair bit of time and money in r&d, and their standard pump uses 50:1. I have first hand experience from motocross of too much oil causing boggin and excess smoke, and that's just from using 35:1 instead of 45:1.

My motocross pistons and my aerox ones are always immaculate and my cranks last very well in motocross, so I'm going to carry on doing it that way. That's using putoline MX9 ester-tech oil

 

I'm using Motul 800 Factory Line Road Race at the moment, All I'm saying is there is scientific evidence that proves the correlation between less oil and less power. I can take a scan of some of the pages if you want? Yes Yamaha did spend a LOT in R&D, they got that money by cheating in the 750 2 stroke races =P But remember that factories design the bike to suit as many styles of riding as possible, as well as as many environments. Then you have plug fouling to remember, A LOT of the oil:fuel ratio decrease has been driven by plug fouling.