How to derestrict a Yamaha C3 scooter, 1 of 5
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Edit may 29th:
I tried derestricting with my new belt: Do not want.
Yes, in ideal conditions (downhill or on very long flats), I can pin the needle all the way to the top (probably more than 70 km/h) but the acceleration and midrange power suffers greatly. It would slow down more when climbing hills, and wind have more effect on speed than when left restricted. Top speed restricted is now 65Km/h (halfway into the Yamaha logo). That is more than enough for an urbanite like me.
I am not saying that you shouldn't derestrict. Maybe it would be better for you than for me (mainly because I'm on the heavy side, I weight 215 lbs). So try it for yourself, and if you don't like it, just revert.
Also: by now, I think that three or four persons sent me private messages asking me how to re-tighten the belt after loosening it. (In part four, remember: spread the rear pulley halves to loosen the belt so that re-assembling the front pulley is easier).
Once the front pulley is assembled, just start the engine. The belt will tighten itself almost immediately. Do this before replacing the trans cover to see for yourself.
Also: Goldvisaguy, a member of the c3rider.com forums, got a brilliant idea for a tool to replace the strap wrench. It was quite cumbersome and frustrating to use a strap wrench to remove the front pulley, so Goldvisaguy invented a homemade tool that cost less than 10 bucks. I built mine and it works fine, but I had to use three L shaped pieces bolted together because they were too thin. All bolts are 1/4 inch dia.
Check these pics for the wonder:
Edit May 25 2008:
If over 4000 Km on the odometer, I would suggest you to get a new transmission belt and replace it every 4000 km thereafter. Belt is rated to last 10 000Km, but you may lose a lot of top speed after just a few thousand Kms, because the belt gets narrower as it wears, thus changing the transmission range. I replaced my belt at 4500 Km. With a new belt, and with the restricting washer put back on, I get top speed almost as good as when unrestricted with the old belt, without the loss of acceleration. A new belt cost about 20 bucks, and if you can perform the derestriction as shown in my videos, you can also replace the belt by yourself. Just take off the rear pulley nut using the 17mm socket and the strap wrench. You can figure the rest by yourself. Just make sure the belt is put in the correct direction: The arrows on the belt shows the correct rotation.
But you may ask: why is it faster now, restricted with a new belt, than when it was brand new? I would say that it is because my C3 is now well 'broken in', the engine parts are less stiff, that is why it is faster.
Also in this update: performance parts are now being made especially for the C3:
New variator kit, price unknown:
New ECU without engine rpm limit 299$:
I haven't tried any of these yet. I plan to buy the var kit soon, though.
Edit 8May 2008: It seems that this derestriction, while increasing top speed, will also decrease the acceleration slightly.
This serie of five videos shows in all details how to derestrict the Yamaha C3 scooter. This derestriction will add 6-7 Km/h to the stock top speed.
A few word of warning: I can only take responsibility for the good results you may get. You may damage your scooter if you are too clumsy to perform this modification. Proceed at your own risks. Be also aware that the C3's suspension and brakes may not be designed to perform correctly at speeds above the stock limit. If you hurt or kill yourself riding a C3 that you have modified because of me, I will not feel sorry for you, nor will I feel responsible for your demise, because you were properly warned about the risks. Also, keep in mind that modifying your C3 will void your warranty and may also void your insurance. Always ride responsibly, and ride fast only on roads/streets you are very familiar with.
I know that there are other ways to make this scooter going faster or to have better acceleration, and these ways are: replacing the stock variator with a better one, using lighter roller weights to improve acceleration (but if those weights are too light, you will lose some top speed). And there are other, more advanced modifications that can be made to the carburetor, engine and Exhaust, though these mods may increase performance, they may also reduce the reliability of your C3, and will most probably cause premature wear.
I may experiment a little more on my C3 in the future. I will keep you informed.