[RNM2399]

I have a 98 Formula Z 670. Stock engine running stock jets except for the pilots we bumped down to 50s from 60s. Throttle respense is much better now. That makes me want to take down the mains a little. Can I safely go down one size on the mains? What are the rest of you guys running? I ride in Michigan elevation 1-1000. I dont want to have to rejet all the time or worry when I ride when its cold. Thanks!
       Ryan

 

[Rocketman]

I jet mine so that the plugs are dark brown at about -20C because that is the temp that we sled at most often. If all depends on what your plugs and pistons tell you. Try it carefully. Right now my jetting is the stock jetting (300 PTO 280 MAG I think)

 

[kid rocker]

The only way to re-jet without burning it down, is to do a plug check and piston wash check.  I have an air density guage that costs $129.00 that measures the air density, not temperature.   Then I use a RAD wheel to determine the proper jet size.  Very accurate, and not a lot of money compared to pistons and cylinders.

 

[mr670]

Just leave it alone, twice I burnt a piston in my 670, with jetting that was one down from stock.

 

[RNM2399]

Thanks for the advice guys. I will look into one of those gauges. Maybe a buddy and I can split it.
                 Ryan

 

[AC]

I was running stock on my sled but the plugs were black as were pistons, I would of probably gone down 1 size but I now run 390-360 mains because of mods. Plug and wash color are the most important, go down 1 size at a time. I would doo like Rocketman, Jet at -20 and leave it alone unless you're planning to race

 

[RNM2399]

What kind of gas miage are you getting with that setup AC? What did you have done. Thanks!
                           Ryan

 

[AC]

I have carb bored out 42.5 and same setup as HO except for mains, 501 RV, shorty boots, trail ported head shaved 0.060 squish, Y pipe cut, gutted air box, cudney clutch kit without primary spring for trail, it raises engagement to 5000 and too much ski lift, 1.18 full lug track, ETS kit and rear springs rated for 380 pounds ( no I don't weigh that much but I like to pound the #**% out of my doo).  I've also have new pistons (after 10000 km) and a crank from HO that had to be slightly modified to fit but it's apparently better construction.I've only gone thru 2 tanks since mods and it was worth it. I went for my first real ride today and made about 100 miles on the tank (10 miles/gal) which is what I had before mods and the engine is still tight. I can't put as much throttle as before otherwise I won't be able to steer with the skis in the air