Carb setup/Spark plug heat range/Rotax Max

Terry Grau · Joined: 25 Jul 2001 Posts: 12 Location: Evergreen. CO

Just had my second DNF due to wet fouled spark plug at the completion of the warm up/pace lap. I was running a Rotax Max at the highest track in the US, 6880 msl. 150 main jet, full lean on the needle clip, three turns out/lean on the Idle bleed and a Denso Iridium 31 plug.
I have run NGK B9EVX for short periods and had no fouling problems but am concerned that it is 2 heat ranges hotter than the Denso 31.
Anyone have any useful input on solving this problem or thoughts on how many heat ranges hotter a Max can tolerate without burning a piston.
My best guess is that the main circuit is ok but the idle progression is way off with the stock idle jet and leaner idle jets are apparently not available.
Thanks
Terry

perfonic · Joined: 30 Jul 2001 Posts: 20

Hi Terry
I run a series 1 Rotaxmax motor, carb came with # 50 idle jet and # 60 emulsion tube
There are other jets and tubes avaliable from Delloroto

Terry Grau · Joined: 25 Jul 2001 Posts: 12 Location: Evergreen. CO

Trevor,
Thanks for the response, but the series II already comes with a 30 idle jet emulsion tube and the Dellorto parts list I have says that is the smallest made for the VHSB.
Terry