I have installed on my 2002 ZR 800 efi C/C a Black Magic Hearthrob clutch kit and R/T canister. First run with it, it would not pull over 7100 rpm. It was pullin harder than stock though. Played with the secondary spring and helix shims but still wouldn't pull the extra weight. B/M sent out a primary spring for this kit and once installed it brought the engagement up to 4300 rpm and peak upto 7500. Pulls hard out of the hole and has wicked accellaration. I removed the coupler blocks to get the thing to hook. Setup is a little soft for my weight but hooks great and hangs the skis for a long stretch. Haven't had the greatest snow conditions to ride in and as of today the snow is all gone . When we had snow we tested my stock ZR against a stock 2002 XC 700. Difference in weight between riders was 120 pounds (i'm a big dude) and we were dead even. Switching sleds, my ZR was 6 lengths ahead. After clutching the XC 700 i was 2 lengths behind. Now all the snow is gone and i haven't had a chance to run the XC with the new setup. Hoping to kick his a** with a huge weight diadvantage in my corner. Just want to know if anyone has tried the [email protected] setup and how it works.Oh yeah, anybody else having problems starting their 800 efi when the engine is warm. I have to hold the throttle open to get it to start. Sometimes it starts good when warm, and sometimes it will fire once then die. Then Ihave to hold the throttle open for it to start. I tightend up the throttle cable to spec but to no avail. Oh well, back to the dealer I go .