I am building a mini-buggy and have the frame almost built and plan on using a rotax 521cc engine to power it. I am using a honda civic radiator with an electric fan so she should stay plenty cool. I am just worried about the jetting. It ran perfect in the winter, but what will happen in warmer weather? I think it just may run really rich?

It will run real rich with winter jetting. You will have to lean out the jetting. If it was a well balanced set up before you may be able to get it running well by just reducing the main jet. Work your way down and check plugs and piston wash until you get things looking good.

That is what I was thinking, but wanted to make sure I was not backwards. This buggy is gonna hammer!

When I ran my 93 670 on grass I went back 10 jet sizes to get i to run.
I would go 5 sizes to start and then keep checking the plugs, when you get them running a nice mid-to dark brown stay there and you won't have any problems.

Cliff

BZZZZ, thanks for playing. If you are going to run that buggy for any distance, you may have to jet up. It has some to do with ambient air temp, but not nearly as much as you think. My tar sled is richer in the mid range in the summer vs the winter. I finally figured out why

Sure on some sleds that may be true!
But the 521 he's asking about, it's very close to the 440, 521, 670,583.470 and 617's we ran on grass for years.

Run them with winter jetting and they load up so bad they'll foil the plugs.

But then thats just 28 years of expeareance with rotary valve rotax's on grass.

Cliff Yeatman
Advanced Dyno

agree with that one been here all week just put 38mm mics on my 473mod sled and its been a jetting nightmare started off with 350 340 mains and now im down to 220 240 with my dial a jet set up i would also recomend that thunderproducts.com and go order a dial a jet kit makes jetting a million times easier for changing weather conditions they set those old rotary motors up just a tad rich!!