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Discussion Starter · #1 · (Edited by Moderator)
Hey all, hope you are all enjoying any snow you have for some riding!

I had a question about the motors in the MX and Formula plus and I'm hoping you can help. When I was a kid, I had an 88' Formula Plus with a 521 rotax motor. The seat and the hood had black and white striping. Not sure what the tag number was on the side of the tunnel (never bothered to look when I was a kid, darn youth!) I recently picked up another one from a guy at work who didn't want anything to do with it. At first glance I thought it was a Formula Plus, about the same vintage as my 88' so I gave him $100 and brought her home. Got her cleaned up, new fluids all around and 2 new carbs installed and my kids now think that they should be able to skip school and go riding all day!

Looking at the one I have now, the Manufacture Date is 1989 so model year 1990. The hood has the gold striping and says "Plus" on the front. The number on the tag on the side of the tunnel is 3742. Everything I can find online suggests that the 3742 denotes an MX, but the motor is tagged a 521. Did the MX ever have a 521 in it? I had thought it wasn't available in the MX but wasn't sure so I came here to ask the experts. The motor has a tag on it lists the following:

Bombardier-Rotax GMBH, Gunskirchen

Motor Number: 3626986

Bore: 2x72mm, stroke 64mm, capacity521.2 cc

Type 537 Made in Austria

Any help is appreciated! I'll post some pictures of the sled and the tags.
 

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I had a 90 Plus last season, didn't have decals on it like that. If my memory serves me correctly, the type 537 was the dual pipe version of the 521 and in 1990, they ran the type 536 with single pipe. My guess is that someone took a 90 MX and an earlier Plus and mated them together.
 

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# 3742 is a 1990 MX. No, the MX never had a 521 engine. The type 537 is the engine from a 85 to 88 Plus. Fairly peppy engine. Someone has for sure done a engine swap.
 
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Discussion Starter · #4 ·
Thanks! I figured someone picked and pasted the two sleds together. At first I thought maybe just a hood swap, but then saw the 537/521 Rotax motor. The gas tank has the sight glass which I know they added after the electronic fuel gauge, but the dash also has the electronic fuel gauge but currently it doesn't work.

Thanks for the reply!

I had a 90 Plus last season, didn't have decals on it like that. If my memory serves me correctly, the type 537 was the dual pipe version of the 521 and in 1990, they ran the type 536 with single pipe. My guess is that someone took a 90 MX and an earlier Plus and mated them together.
 

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Discussion Starter · #5 ·
Awesome, thank you! I let my Dad take her for a rip the other day. He said he didn't know it would pick the skis up lol. I said he put thousands of miles on snowmobiles back in the day, but he reminded me the last sleds he owned/rode were a 74' skidoo TNT and a 76' John Deere JDX 8. Thanks again for the reply!

# 3742 is a 1990 MX. No, the MX never had a 521 engine. The type 537 is the engine from a 85 to 88 Plus. Fairly peppy engine. Someone has for sure done a engine swap.
 

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I had a 89 MX. That is they year they added the sight gauge in the fuel tank and got rid of the electric one as stock. You could still get the electric one as an option. I did that on mine. From what I remember, the 90 MX was a copper color. The Plus was still red. They also got rid of the twin shock rear suspension and went with the single shock. I have never seen those decals either. From what I remember, they were black and white. I need to dig out the old sales brochure and take a look!
 

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Discussion Starter · #7 ·
Thanks for the reply! 89' makes sense for the sight glass. My 88 Formula plus didn't have one. And I think this sled does in fact have the single shock rear suspension. Trying to remember how many grease fittings I clipped onto laying upside down on the garage floor. I hadn't seen the gold graphics either. Aftermarket maybe? Below is the 88 Formula Plus I had back in 98-01. Had I known I was going to buy just about the same sled twenty years later, I would have just kept the 88! Thanks again!

I had a 89 MX. That is they year they added the sight gauge in the fuel tank and got rid of the electric one as stock. You could still get the electric one as an option. I did that on mine. From what I remember, the 90 MX was a copper color. The Plus was still red. They also got rid of the twin shock rear suspension and went with the single shock. I have never seen those decals either. From what I remember, they were black and white. I need to dig out the old sales brochure and take a look!
 

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