thanks for all the good suggestions, turns out I had a crack in the spark plug even though it looked intact, but after seeing 720's reply, I went and down sized my mains, cleaned up my air filter, replaced the plug and its rocket time again in colorado

 

THe European boyz use the Kehin FCR 35/39mm combo on the MZ motorcycles and on the Yamaha SZR motorcycles. Both run the 660 engine and both are limited to 1mm overbore for most of the supermono classes. With a cam and proper head work (in some cases, they actually reweld the head to make it a down draft) they hit 70hp BUT that is at high rpm.

For me, after a real pain in the ars, I got the FCR 35/35 combo to work. That is really all the CFM any Raptor will ever need -- in fact, it is actually overkill.


1rap, glad to hear you are back in business!!!!

 

720, interesting point about the down draft head mod, I was in Oregon recently and went and saw the team at Powroll, and look see they had a Raptor head ready for the flow bench, they also had a YZ 426 head for comparision, The Raptor head is very restricted on the intake side with the stock port layout, they where pretty disappointed with the heads performance.

They where going to seriously look at machining the whole intake port arrangement off and starting agian... In there opinion the Raptor is running at about 2/3 it's maximum HP potential, and due to the restrictive intake setup it is why these engines just sign off at about 6500 rpm, they just can't get enough airflow........

Still like you say high rpm HP ain't much benefit either........ Powroll where also playing around with a 750 cc Raptor stroker..... after seeing their trick hand built Cr 80 / 150 cc four stroke engine, one cylinder carved off a CBR 600 engine and grafted onto a cr 80 low end, with enough trick goodies on it to bring a tear to any petrol heads eye..... I'd say that once they customise their Raptor engine stand back.........

Kiwi

 

Well at least they are trying.

My goal is to research cost effective methods of increasing performance without making a "new wheel." Want the down draft head, I can sell you one. What the 35/39mm FCR carbs?? got those as well. Want a 4mm stroke got that. 6 spring clutch got that.

I like the 686 for most applications and the 720 for extra performance. Too much head work is a waste of time in my book. BUT I would like to see what Powroll can do.

 

If you are 3 turns out on your screws you have the wrong size pilot jets.

On the plug, just unplug it from behind the radiator cover.