I have a 690 raptor with porting dual exhaust and all the goodies to make it go fast and i am trying to understand just what effect head porting has on my jetting.I assume that because porting has an effect on flow characteristics that it would require different jetting than on the same motor without porting?I am probably just thinking too much but i like to know just why somethings works or doesnt.Right now i am at 170-175 mikuni mains with a dual exhaust system and it runs very strong top to bottom but would it be different without the porting that i have?

 

The better flowing your head is the more fuel it will take. Depending what size valve, what kind of bowl work was done, and how much bigger the exhaust ports were opened.
Becuase of your altitude your jetting sounds good, if you are running stock carbs are you using a dual feed into the carb? I would save money and get the 35 or 39mm FCR Carbs.[img]i/expressions/face-icon-small-smile.gif[/img]

 

Thanks for the response Ernie and although this may sound ignorant what exactly do you mean by dual feed?I have been doing quite a bit of drag racing at the dunes where i ride and another raptor that consistently beats me by two quads lengths in 300 feet has 35mm fcr,s and higher compression so would i gain the two quad lengths back with the 35mm carbs?My raptor is as fast as any four stroke that i have raced after 300 feet and in fact i come back to beat most but not all that i fall behind so if i could gain a couple more quad lengths initially then i would consider the carbs.What benefit would i see if i switched to alcohol and could i do it with my stock carbs.I will consider all mods to my raptor to make it go faster because it is the quad that i use mostly for racing so even though i want it to be reliable it is not as important as it is on my everyday dune quad.My exhaust valves are 1mm oversize.By the way the raptor that beats me by two quad lengths is the fastest four stroke that we see on our dunes and we have quite a few so i am not too far off from where i want to be.