Personally, I would say upgrade the exhaust.. With that said, let me come up with a plan for you. It's gonna be similar to what I'm hoping to do with my spare SR tentatively, once I have funds. I will actually go farther in case you decide you'd like more out of her in the future.
And if possible, do in this order for best noticeable results
Part - Price (sh included) - Possible seller
1. R1 Exhaust $165 Daywot (or PG Short/Long if you wish..)
>>> Skip mod #1 if doing Mod #4, for now
2. Keli Pulley + lighter weights $48 Daywot
3. 9:1 Upgears $50 VT Cycles (May go lower ratio for future..)
4. Contessa bore kit $230 Daywot
5. Center Spring 1.5-2k $15 VT Cycles (Get now or regret later)
Tuned that should net near 50-55mph top, at ~$275-345 total
From there you can cruise or wheelie and start saving for whichever step you skipped, and also a bigger carb and manifold.
>>Skipped step here #1 OR #4
6. CT Manifold $50-60 Indycycleranch or ebay
7. 21-24-28mm OKO carb $90-120 VT Cycles
8. Adj Throttle Cable $10-15 Daywot or VT
9. UNI Airfilter $30 Local MC shop or VT (Do Not get KN gauze type)
Now RE-tune and enjoy a boost in midrange and increased top speed of ~60-65mph (higher if smaller initial drive gears) At total of about $700. At this point you may be contempt, if you'd like more, tires and misc essentials might be in order first:
10. Michelin S1 Tires $50x2 Local MC shop, cheaper online
11. New Honda OEM belt $40 VT Cycles
12. Malossi Rollers $20-30 ebay or VT? (worthy investment at this point)
Now you're at a cool $860, able to cruise 60mph somewhat safely thanks to better tires and ready in case you bust your belt due to too much hp! You daringly want more? With this foundation you can now port your bore, port the intake, upgrade reeds, raise compression and see beyond 70mph on a budget of 2stroke knowledge and skill!
Disclaimer: I have never done this exact path! It is only an educated guess of a good solid, reliable and fast setup that can be built over time and allows you to budget chunks at a time based on information I've gained and personal experiences with upgrading scooters! I am not to be liable for any misleading assumptions due to ignorance or lack there off in building a potentially risky liability prone vehicle. USE CAUTION, READ, RIDE, BE SAFE
All parts links (Note some are ebay, so temporary)
Daywot Store - Contessa bore, pipe, keli
CT Mani
VT Cycles - Bore, pipes, call for gears, OKO Carbs
Malossi Weights, possible source
Michelin S1 3.0-10 Tire, Can fit 3.5 on Rear
....
After putting this together I now realize I've probably spent MORE than I anticipated with my Corsa built SR72
And she's worth every penny
Also thinking this would make for a dang good sticky
