rotax 503 in a bigmax

[whitefisher]

put a 503 rotax in the big max lastnight all went well still need to set secondery up right preload....some wireing ....50hp.in a 72 big max 2...scary fun..... i need a 15 deg. mikuni flange to level carb 36 mm vm to 503 any ideas..? its a tight fit on clutch side ...

[jpswift1]

Contact 6X6World member techfx. He has a 503 Rotax in his Max II as well. There's also pics in the photo gallery in his album.

[whitefisher]

well wireing is done.....test run....wow.. will spin up tires for 40ft this thing scary ......topend 20mph.//driven spring to tight..i think..still need 15 deg. flange for a 36mm carb and intake......

[whitefisher]

Carb flange done ,,tub done,, driven done,,exhaust done ...belt adj ....alinement close ...now lets talk brakes.......any ideas. on up grades .... for 72 big max

[jpswift1]

The T-20 will be sufficient to slow the machine down. If you want additional stopping power you could add on a front foot disc brake setup from a 1996-present Max II.

[whitefisher]

Any pics of this setup will heip thanks..........

[whitefisher]

elec.....came with a jlo 400 60w chargeing system. 5amp recifirer ,for elec. start -----rotax 503 200w chargeing system no elec.start ,,volt reg.. out of snowmachine ..would like to add starter later...were to go with this???

[hydromike]

If you want to run an electric start on the 503, you'll need to use a stock Ski-doo drive clutch with the starter ring gear. The problem is, these clutches really aren't calibrated (or calibrat-able [easily...]) to use in an ATV. Of course it can be done, but you'll not match the performance of an easily modified Comet 102/108 (or even Salsbury) drive clutch.

The other option is to use a starter from an ultralight aircraft that mounts to the magneto-side of the engine. These get uber-costly REAL fast, though, and you might run into clearance issues with the tub on that side of the engine (they stick out from the recoil housing)

I don't know if TechFX is running an e-start on his or not, or if he's running the stock ski-doo clutch. If you want to try your luck with the snow machine clutch, give it a shot; you might love it. Other than that, there's no real big issue with the electrics. Run a small battery (get a good name motorcycle battery versus the lawn-mower battery...) and the stock voltage regulator and you should be fine. The stock Rotax Denso starters use an integrated solenoid on the starter, and are really robust units, so you won't need a remote solenoid. 16-17 amps (200 watts at 12 volts) isn't a whole lot of juice coming out of that charging coil, but if you're not planning on running lights it should be okay.

Besides, you can easily exceed the speed of light with the 503, so headlights shouldn't be a real deal-breaker.

[whitefisher]

Thanks but the stock skidoo clutch rocks......works better then the stock unit by far.. starter system, will use stock starter denso,. mounts ,gear ,375 amp battery for the 4000# winch ..the jlo had 60w charge to run two 18 w lights.. stock... the rotax 200w to run 2 -35w lights ,,and to charge battery 130w......but thats still close to a 10amp charge.....got the clutch close..30mph topend..but twice the power over the 400 jlo no creep at idle,, now to address ..driven clutch..these steel drivens are junk...time to upgrade maybe alum..artic cat free float secondrery......???

[hydromike]

got the clutch close..30mph topend..but twice the power over the 400 jlo no creep at idle,, now to address ..driven clutch..these steel drivens are junk...time to upgrade maybe alum..artic cat free float secondrery......???

Actually, the steel secondary clutches perform great on the T-20, and even ahead of the 503 Rotax. If you like your Ski-doo clutch you should keep it. When understood, maintained and calibrated correctly they work flawlessly in this sort of setup. Regardless, you need to find a way to squeeze the extra 25mph out of that Rotax that it's capable of in an AATV. I know where *I'd* start.....

It seems like you've got your charging issues all figured out, so I'll digress on that point.

[chris davison]

If I'm not mistaken Blower drives in whittier calif has done super chargers on the 500 rotax.

[techfx]

I ended up with a new Comet clutch on my 503 w/ a Rotax ring hear (they were a lot of help). It's adjustable by adding removing pucks (haven't experimented). I don't know if my "custom" exhaust is the best solution, but it isn't choking it out like the previous owner's hacked manifold. Sorry, I've been away for a bit... hectic work, school, etc.

[techfx]

If I'm not mistaken Blower drives in whittier calif has done super chargers on the 500 rotax.

That might be fun ... may need to cool that down somehow, though.

[whitefisher]

well how do u like your 503 in your max..? how is your driven set up i have yellow spring set at 120 deg. why did u change your clutch..bad.? i have 102c i mite put on to try..! on elec.did u use regulator or recifire ...?

[Bazooo guy]

I added the ring gear and starter to my rotax 372 and used the skidoo clutch off a 399cc.
The clutch engages around 3500 rpm and feels like it has a stall converter if I pin the sticks forward and hit the throttle.
The sticks on my Bazooo engage 2 clutch discs after the trans to drive each side so it will take off slow with lots of power on the trails.
Strange setup but it works well and is true 6 wheel drive.
Your 500cc will fly if you can get the power to the wheels and maybe a gear change on the T20 will give you more top end.