What size jets should be in a 99 670 ho..would it be OK to jet down a little, and what about the jet needle...what position should they be, can you set them too lean out the sled a little, like i don't want too lean it out too much, just curious too what you guys with the Ho's do for a little more performance.

Honestly, the 670 always liked to be run a little rich to make its best power.. Factory jetting is for around -20c so you could trim a bit off that provided your not out in really cold weather.

On the 670 I had I ran a holtzman Tempaflow. It worked a mirical on this engine. giving me perfect plugs, way better milage, and a much more responsive motor. If your sled has DPM then you dont need it, because DPM is the same thing. But if you dont, I would look into investing into it. It will pay for itself with the gas you save. And will always keep your jetting bang on.

carefull, big bore motors are piston eaters...and they make the same hp at one jet size over one that could burn down at 1500' or so. there where some folks burnin em down with stock jetting. the 670 is a great motor but i however would NOT push the realms of jetting with it.

Leave the stock jetting and make sure the DPM is functioning correctly. The HO has the best jetting range of all the type 669s and won't run much better when fiddled with. Once you start down that road it usually ends with finicky motor or seizure...your choice.

OK..no jetting changes..thanks