Karting Update

As a sort of appendix to the last post, I figured I would update progress with the kart.

I got the carb all cleaned out and the float adjusted a tiny amount. I changed the main jet to a 155 rather than the 160 that was in it. Now it doesn’t idle well at all. I have a feeling the idle jet is too large. It didn’t really idle well before either, so I assume my cleaning and float bowl changing and main jet changing didn’t hurt that, but who knows. I have it adjusted to where it idles at about 1500-1700 rpm, which is what it should be at. But it does not like to stay there long and to get it there took some odd adjustments.

I cleaned out the clutch to see if that helped it work better as it had some grease inside the housing. On the stand I can now hold the tires at idle without it spinning them, I never tried that before I cleaned it. Also, I have not tried sitting in it with it on the ground either. So I do not know if it is cured. There isn’t much I can do about it anyway until I update to the new style clutch. And while I have the cash to do so, I refuse out of principal. That is, unless the old one is completely horked.

I did some calculations (and made a spreadsheet of course) and found I was topping out at 66.5mph. Mike in my kart was hitting 68mph with an 80lb weight advantage. So #1: I wasn’t doing too bad. #2: It was running poorly, but damn. #3: I think my gearing needs to change a bit. For reference on the “but damn” from #2, the 2nd place finisher in the shifters was hitting 85mph on the same track configuration. Unfortunately, I was unable to get the same data from one of the leading Rotax guys, but I assume they are 8mph or so slower. However, my biggest issue on track was RPM dropping too low and losing most of my acceleration. I realize a lot of this was me braking too much, but until I can improve my driving a lot, I need better gearing. So I bought one of these Kart Master engine sprockets:

I got the 12T, not the 11T

My current gearing is theoretically good for 78mph, which I assume is about where the class leaders are. The new gearing will only be good for about 72. But in my current state, I think acceleration out of corners will help me more than top speed. And I can always fine tune gearing with the driven sprocket of course.

I also discovered my tire pressures were off. I read that they should be about 16psi. Turns out when hot, they were only gaining about 1psi. I checked with Mojo (the tire manufacturer) and they say tire pressures need to be 9.4psi +4.6psi/-1psi cold. So 8.4-14psi is what the manufacturer wants to see. So 16 was obviously high, even when I lowered them to 16 hot which turned out to be 15 cold. I should have shot for more like 12 or 13 cold.

I still have not come up with a good way to mount my Contour GPS camera. I thought of a way to do it, but not a good way. So I still have not got video, but I will try to get that on Sunday while I am racing.

The ContourGPS

While I am on this subject, I can’t wait to try out the ContourGPS. It is a small camera that records up to 1080p video. It stores the video on a micro SD card. It has accelerometers and of course GPS. The entire camera can be rotated in the housing so that your video is always upright no matter what angle you mount it at, and that also corrects your accelerometer readings. The software for the ContourGPS only allows up to 2Hz on the data. However, the firmware allows up to 4Hz. You just have to manually alter a file to get it. Which I think I have done. So mine should be set at 4Hz. Also, another great feature of the Contour, is it has bluetooth. So I can use my Android phone to see what the camera is seeing. This should come in handy for aiming it since it does not have an onboard screen. I can also change all the settings of the camera from my phone as well. However I imagine that would also downgrade my GPS back to 2Hz.

Here is an example of the ContourGPS mounted on an R/C car. You can see the g-force and the speed overlay on the video which is data pulled directly from the camera:


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