Yamaha C3 Performance Upgrade – Exhaust

It turns out that the exhaust upgrade was fairly trivial once I knew what to look for.  I ended up choosing the Jiangwayne Performance Pipe III , which according to their charts offers a roughly 45% increase in horsepower over the stock pipe and increased torque.  It’s not clear to me if that involves any other tweaking, like intakes, but I’ll take it at face value for now and try it out.  I bought the III because it seemed quieter than the other two and that’s one of the reasons I bought the C3 in the first place.

I also did a couple days with the standard 6g roller weights back in (with the Boppers on).  Definitely better than before, but not as good as the 5g weights both in acceleration and getting to top speed.  For now I’ve settled on the 5g weights, though I may revisit that decision once the new pipe is in place and I’ve got more power.

I now have a phone that’s capable of doing GPS tracking, so hopefully I’ll get a chance to do some speed tests and get a reasonably accurate measurement of how fast the bike can go with the changes I’ve made.

Yamaha C3 – Performance Followup

I ended up ordering two new sets of weights – one 5g and one 7g (again, 15x12mm to fit in the stock variator) – in order to experience first hand how they altered performance.  The 7g weights caused the scooter to bog badly – at that gear ratio, the bike simply wasn’t generating enough torque to accelerate well or hold top-end speed.  The 5g weights worked well to improve acceleration up to about 30mph; after that, the acceleration drops off  but is functional to get me up to the peg (about 44mph) on a flat surface and faster on any downhill.  The 5g weights also hold speed better when going uphill.  I now have a better understanding of why that is  from www.scootnfast.com , which has a great explanation of the dynamics of the CVT in their 2-stroke section. Basically, there is a large spring, the contra spring, that pushes the rear pulley plates back together when speed falls off, essentially “opposing” the roller weights in the variator in order to reduce (increase?) the gear ratio to adjust for speed.  Now that the front weights are lighter, this spring will push back more quickly when speed drops off, which causes the gear ratio to change more quickly and give more power for maintaining speed.  This dynamic also explains the “floaty” feeling I was getting with the 4g weights, as they were not heavy enough to oppose the contra spring and thus could not maintain top-end speed.  I’m going to order a set of 6g Dr. Pulley weights and compare those to the 5g – I should have a phone with GPS today, so I should be able to take some speed measurements.  With the 5g weights, I was able to ride to my brother’s place in Raleigh in just over 30 minutes, which is a significant improvement over my previous time.

Tires – I ended up doing quite a bit of research on this, most of which was a fruitless search for rolling resistance specifications from manufacturers.  It came down to either the Michelin Bopper or the Pirelli SL26.  I decided to go with the standard 120/90-10 Bopper on both front and rear, as someone on a forum had graded the rolling resistance on those tires as “A”.  That person was absolutely right.  With the Reggae, I felt like the bike was fighting me, especially uphill – if you got slow enough, you could actually feel the tires bumping, and when you let off the throttle, the deceleration was swift and decided.  The Boppers are quieter and during yesterday’s ride I had to use the brakes much more than normal because the bike really felt like it wanted to roll.

Side note:  Michelin, you seriously need to work on your scooter tire branding.  I was riding a Giggle with Reggaes.  Now I’m riding a Giggle with Boppers.  Not exactly the most appealing branding ever, you know?  You’ve got good tires, but I bought them in spite of the name, not because of it – not the best marketing!

So as things currently stand, I’ve:

• removed the restrictor washer for a 4-5 mph increase in top speed
• replaced the variator weights with 5g 15x12mm Dr. Pulley sliding roller weights for better low-end acceleration and still decent top speed
• replaced the belt with a Malossi Kevlar belt, which eliminated a sluggish spot from 20mph to 30mph that was apparently due to belt wear
• replaced my Michelin Reggaes with Michelin Boppers, which probably gave me 1-2mph top-end and help maintain speed.

After reading scootnfast’s site, my next task is improving/derestricting the C3’s exhaust to gain power.  I’ve seen references to a Jiangwayne pipe that appears to work, as well as some homemade modifications.  Back to the Internet!