Wednesday, July 23, 2008

How to throttle a throttle

I've said it before and I say it again, I am a speed addict. Typing my last post, I got a brainwave of limiting my throttle, in order to keep my speed under control. It's a kind of crude speed limiter, but effective, none the less. What I have basically done is that I've limited the amount that I can twist my accelerator, which is kind of like fixing a wedge under the accelerator pedal of your car, except this is not quite visible. Okay, so here's what I did :-

Remember the carburettor??? The one I had opened up in one my previous posts?

Well get it off. (Instructions in previous post, if you are new at it)

Now unscrew the top, the part where the accelerator cable goes in.

Take an small piece of plastic tube or something else that's rigid, and about an inch and a half or two long. I chopped off the back end of an old pen refill. Though I would have preferred to have used a long screw, filed off its thread, and sawed off it's head. That would have been a better thing to put inside a carb, but since the carb isn't supposed to heat up, I used the refill. Edit: The top of the carb is in fact really cold, especially during the rains. Also another thing you could put in here is one of those round PVC conduits, if you can get your hands on a small piece of it.

Now place the chopped off piece of the refill (or whatever you are using to restrict the movement) inside the spring.

Carefully put back the carb, making sure everything goes back in smoothly. Don't try to force anything in. If you are new at opening your carb, It'd be better if you went through how to open a carb explained in this older post.

Once you close your carb, you can check out how much you are restricting the bike by checking the amount you are restricting the air flow. The fuel being used is proportional to the air being allowed. This image shows the position during idling.

And this is the position with the full throttle, after adding the restrictor. Notice I have set my bike to run at 50% power (IMO that's 25% too much). Once again, you can see how much the full throttle opens up on 100% on my previous post. If the accelerater doesn't turn at all, the restrictor used it too large. If it opens up more than 50%, or the amount you want to limit it, it's too small.
Put the carb back onto the bike and you have got yourself a speed limiter. I have done extensive testing on my bike and have even had a fall in the process. At 50% restriction, the bike is still quite peppy with a solo rider, but a bit sluggish with a pillion. The initial pickup is compromised, and starting up an incline with a pillion could require more effort. The top speed attained on straight piece of road was 95km/hr (though it took really long to attain, I'd rate the crusing speed to be 75-80). Mind you my bike levels out at a 100-110 otherwise. With a pillion, the top speed drops to 85km/hr (Crusing speed of 60). Top speed with the pillion otherwise is the same, 100-110. Inclines with a pillion may require an upshift. I couldn't find a perfect dry road for the burnouts, since it has been raining. The only dry piece of land I found and the burnout left my bike 6 inchs below the ground level, which required me to take my weight off the bike to get it out. The gearwise speeds are as follows

Gear Top speed unrestricted Top speed restricted
1st 45 40
2nd 65 60
3rd 90 75
4th 110 95

I had tuned my bike to perform, so it is doing really well despite being restricted. You get used to the amount of power you have and eventually you start shifting gears better and you forget that you have limited your accelerator. All in all, I am quite satisfied with the restriction. I will be adding the average if n when I calculate it. My bike currently has a fuel economy of 22-25 kmpl.

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