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Overview to Performance Mods

 
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DandyDan
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Joined: 17 Oct 2007
Posts: 1075
Location: Victoria, BC

PostPosted: Wed Oct 17, 2007 3:27 pm    Post subject: Overview to Performance Mods Reply with quote

Once I got my Beluga running normally (60 - 65km/hr) I turned my attention towards making it faster. My brother's 1983 Honda 80cc scooter (NH80) is radically more powerful than my Beluga and it seems like there are some easy gains to be had. Yamaha really didn't put any effort into making this scooter powerful (if anything they tried to make it unpowerful) so there are a lot of areas that can be vastly improved. In my opinion, Yamaha tried to keep the Beluga tame & friendly, but they went to far and made it completely gutless. Thankfully Yamaha recognized this and in mid model run ('83 Europe, '84 Canada, '85 USA) they made a number of engine improvements that raised the top speed to 70-75km/hr.

The following is my suggestions for the best order to mod your CV80. Besides the lighter rollers, you'll need to be fairly mechanically inclined.

Suggested Order of Mods:
1 - Install lighter rollers - Benefit: Significantly Improved Acceleration
2 - Retrofit Early Model ('81-'84) CV80 with late Model ('85-'88 ) Parts - Benefit: +10-15km/hr
3 - Install a Larger Carb - Benefit: +5km/hr?? on it's own but more in combination with other mods
4 - Replace Exhaust with an Expansion Chamber Exhaust - Benefit: Huge! Perhaps 10-15km/hr
5 - Shave Head to Raise Compression - Benefit: a couple km/hr?
6 - Modify/Replace Reed Cage (if possible) - Benefit: a couple km/hr?

Roller Weights: The roller weights in the CV80 are way too heavy. Roller weights control how fast our CVT's (continuously variable transmission) upshift and heavier weights mean faster upshifting (because there's more centrifugal force pushing you to a taller gear) so you get less revs as you accelerate with heavier rollers. Using my Tiny Tach I've observed that my '83 Beluga upshifts to pretty much the top gear ratio by 30km/hr and then after that your RPMs start to rise but they are only around 6000 RPM at 60km/hr so it's still pretty low to make decent power. The CV80 has a 'non-servicable primary sheave' (variator) but as you can see at the link below, disassembling it is not hard and lighter weights can be installed. The stock weights are 15x12mm and weigh 10.4g each. I first installed a set of 7.8g Malossi ones but this was still too heavy. I've ordred some 6.0g rollers which should be installed this week. This mod is likely the best mod to do first because it's cheap ($14-$25 for roller weights) and can be done in a few hours. I would expect dramatically improved acceleration for an early model CV80 with the right rollers.
http://cv80.phpbbweb.com/viewtopic.php?t=10

1985 Parts on a Pre '85 Beluga: Owners of 1981-1984 CV80's typically report top speeds between 60-65km/hr whereas 1985-1988 CV80's typically report speeds in the 70-75km/hr range. This seems inline with changes Yamaha made in 1985 to use a bigger carb (although still very small) and redesigned reeds, cylinder, intake and exhaust. Perhaps the easiest mod to make to an older Beluga is to watch eBay for a late model engine and toss the whole thing in. This mod is likely a great thing to do if you want to keep things reliable and not go too crazy. If you are going to go further and toss on an aftermarket exhaust then this mod is less effective since the late model CV80 pipe is likely the reason for most of the improvement. You can read more about this here:
http://cv80.phpbbweb.com/viewtopic.php?p=132#132

Larger Carburator: The stock carb is likely one of the biggest restrictions/bottlenecks in the Beluga (next to the exhaust). The 13mm carb in the pre '85 Beluga's is shockingly undersized and even the 16mm one is the '85-'87 models is really small. A typical 80cc 2-stroke dirt bike uses a 24-28mm carb. For more info on this option check this out:
http://cv80.phpbbweb.com/viewtopic.php?p=68#68

Exhaust: The stock exhaust is terrible. You can very likely add a ton of power with an expansion chamber exhaust but I would say a bigger carb is a prerequisite for doing this because the stock carb is tiny and likely would negate much of the gain. There are three potential routes I can think of for improving this situation which are:
1) Toss on the late model CV80 exhaust (requires also using the late model cylinder).
2) Modify a 70cc aftermarket scooter exhaust from another application to fit.
3) Heavily modify an 80cc dirtbike exhaust to fit.
You can see a more indepth writeup of these options here:
http://cv80.phpbbweb.com/viewtopic.php?p=66#66

Compression Ratio: The CV80 has a rather low compression ratio...I believe it's 6.8:1 whereas most 80cc dirtbikes are in the 8.0-9.0 range. Shaving the head down to raise the compression should be a fairly easy way to add a little power but it likely won't add much. The head and base gaskets are still available from Yamaha (and they're super cheap...about $1.50 each) so doing this mod would be rather straight forward as long as you have some way of knowing how much to shave off. Perhaps a good shop would spend the time doing the calculations for you. I'm considering this but it'll likely come after I do a bigger carb and expansion chamber exhaust.
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