SRVIPER MTX TOP SPEED SEEMS SLOW

[Bigwood]

I just bought a 15 SRVIPER MTX 2 weeks ago and have been taking it out for a few test rides in the backyard as the ice on the lake wasnt quite thick enuff. Up till last nite i was happy with it. I was hoping it could keep up to my buddies 800 and 700's. But i took for its first real rip on the lake last nite and its top speed is 75mph on the hard pack! Is this to be expected with its 153" track? I as hoping it would go at least 90mph. But its hardly faster than my 250 bravo! Is there sumthing wrong with it?

 

[MrSled]

I just bought a 15 SRVIPER MTX 2 weeks ago and have been taking it out for a few test rides in the backyard as the ice on the lake wasnt quite thick enuff. Up till last nite i was happy with it. I was hoping it could keep up to my buddies 800 and 700's. But i took for its first real rip on the lake last nite and its top speed is 75mph on the hard pack! Is this to be expected with its 153" track? I as hoping it would go at least 90mph. But its hardly faster than my 250 bravo! Is there sumthing wrong with it?

What RPMs are you pulling?? Its no 800 thats for sure.

 

[shagman]

Put 1000 miles on then report back. It needs to break in.

 

[viperjeff]

Secondary bind?

 

[shagman]

Secondary bind?

Most likely. But most of all it need to get miles on it. I had gains up to 3000 miles. these sleds really get an increase around 500 miles. Nos-Pro changed his XTX to 153 and i think he is over 90 mph. Not sure of gearing and driver difference though vs. MTX.

 

[Bigwood]

Put 1000 miles on then report back. It needs to break in.

Will do thanks

 

[Bigwood]

Most likely. But most of all it need to get miles on it. I had gains up to 3000 miles. these sleds really get an increase around 500 miles. Nos-Pro changed his XTX to 153 and i think he is over 90 mph. Not sure of gearing and driver difference though vs. MTX.

Yah the mtx's have different clutches and clutch weights. Itd b nice to get a little more speed out of it though. I will wait till the break in before buying a turbo lol

 

[shagman]

It will need some clutch tuning. Read Clutching on the Cheap in SR Viper for info. there is a lot on info for viper clutching on this site or purchase aftermarkert kit for a vendor on here. Big gains are made. You will be happy.

 

[Natergd1]

I have a 15 viper mtx 153 with about 2000 miles and still tops out at 76 on hard pack hitting limiter at 9150

 

[PeeWee86]

You revived an old thread. At 2000 miles everything should be broken in. If you have stock clutching and gearing, 76 mph sounds about right. I believe the Ulmer gearing chart shows 85 mph with stock gearing. Yamaha calibrated the MTX for 10,000 feet elevation and deep snow conditions. At that elevation the naturally aspirated Viper produces a little less than 100 hp. At lower elevations the stock clutching will quite easily hit the rev limiter.

There are several vendors on the site that would be able to provide you with clutch calibrations. Of course their knowledge comes at a cost. For running at lower elevations and staying on a tight budget I had good luck adding one Yamaha 4.5g rivet and a button head bolt and nut that was about 5.9g to the stock 8BU10 clutch arms that come in the Viper mtx. (See photo) Off the top my head I do not remember the exact size but if I recall correctly it was a metric bolt. Grind off the end of the bolts with a belt sander so that they are flush with the nut and then verify the weight so that your clutch arms are in balance. I used red Loctite. Use a thin nut and verify that there is enough clearance when the arm is reinstalled in the clutch.

You may also need to increase the angle of the secondary clutch helix. Try anything you can get your hands on, but I would venture that a 46/40 would be close. Many aftermarket cams are cut to allow for additional shifting of the driven clutch which will help your top speed. After you get your rpm’s down off the rev limiter you can consider whether taller gearing maybe a benefit to you. However, there are limits to how fast you can spin a tall lug 153 inch track. Post again with your results. Welcome to the forums.
-Peewee