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Yerf Dog 3203 |
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Yerf Dog 3203 |
The Yerf Dog 3203 came with a gutless Tecumseh 6.5HP engine.If there is one summary word to describe the Yerf Dog 3203 go kart we owned, it's that it was "gutless". True, I didn't realize how gutless it was really going to be when I saw it hanging on display from the ceiling of a local Sam's Club store. The price was around $900 and it looked like fun, so we bought it. Obviously, this sort of go kart is more of a kid's toy. It will go around 30mph, but it won't get there anytime fast! It's slow acceleration is fine for younger people learning to drive. So, in terms of a fun kids machine, it was not really so bad.
Only problem was that Dad was driving it most of the time since the kids were too young to drive it unsupervised at that time. The Tecumseh engine was rated at 6.5HP and that was optimistic! The way it drove, it seemed that about 2 or 3 of those "horses" escaped from the barn! On a good note, the Yerf Dog 3203 go kart did come with a Comet torque converter system that did help make the most of the weak engine. In addition to being gutless, the Tecumseh was a cheap throw-away engine design. It was an aluminum bore engine that was designed to last around 150 hours. That's right. Steel/iron piston rings rode in a soft aluminum bore! Hardly what I'd call a good engine design. Combine that with "features" such as a plastic camshaft, and I decided to get rid of the cheap Tecumseh engine and put something of better quality in there. It would have been nice to put in a much bigger engine, but to save money I wanted to continue to use the same Comet 30 series torque converter system, so I began researching engines with the same crankshaft size for use on my Yerf Dog 3203. I ended up deciding on a Robin Subaru EX21 7.0HP engine. It was not a huge increase in horsepower rating by any means, but it was a HUGE increase in terms of quality. The Robin Subaru EX21 engine came with forged rocker arms, forged crank and rod. The crankshaft was supported by double ball bearings. Engine design was more like a motorcycle, and I knew that it had much more potential to handle increased power output. Not to mention that the engine design gave it a rated life into the 1000's of hours, rather than the pathetic 150 hour rated life of the Tecumseh engine. In stock form, the superior design of the Robin engine did result in better performance. Even though it was rated at only 0.5HP more than the original Tecumseh engine, this Robin EX21 felt more powerful than that small difference. As usual, I began to try to find ways to increase the performance of our new Robin EX21 engine. One of the first things I did was to override the engine governor that limited engine RPM. I knew that the stout engine design could handle some extra RPM's with no problem. The intake was pretty choked off, so I decided to try to see if I could free up some power with a free flowing intake and air filter. I got rid of the restrictive stock airbox and filter assembly. I bought a short slab of aluminum round stock of the appropriate outer diameter. Using hand tools, I fabricated a simple intake adapter so I could clamp on a free flowing K&N style filter with an outer foam wrap (for extra dust protection). This did seem to help the engine rev up more quickly and easily.
Carburetor Adapter & Free Flowing Air Filter on Robin EX21 Even though the engine seemed to like the free flowing intake, the engine still could not rev up to the RPM's that I wanted. Part of the problem was that the Comet 30 series torque converter on the Yerf Dog 3203 was calibrated to upshift very soon and bog down the engine. The engine was loaded down so much, that it was not allowed to wind out. To try to address this, I made a couple changes to the torque converter and drive system. One of the things I did was to replace the 10T drive sprocket with a 9T sprocket. This gave me a slightly lower overall gear ratio. In addition, I found a stiffer spring to install in the driven unit of the torque converter. This combination of lower gear ratio and re-calibrated torque converter did really make a big difference. The go kart could now climb hills that would have made the stock Yerf Dog 3203 bog and stall out. Granted, the go kart was still not fast, but it was significant the transformation in it's torque and hill climbing ability. It would just chug right up some good sized hills.
Comet Driven Clutch with Stiffer Spring Even with these changes, I was looking for more power. I bought a Tillotson carburetor and was getting ready to modify the engine to run with a higher flowing carb. I was thinking about making a header and high flow exhaust for the engine. The camshaft was definitely mild and limiting max RPM's, and I knew that a good cam would really wake up the engine. Fortunately, because the Robin engines were just entering into the kart racing world, there was at least one company that I knew of that was working on a race cam that should have worked in a stock Robin EX21 engine. I never got that far. I discovered the Yerf Dog 3206 go kart (don't laugh... once again at Sam's Club), and I decided to sell the Yerf Dog 3203 and upgrade to a kart that I felt was already better equipped. Some may joke and think why waste time on a kid's kart like a Yerf Dog 3203. Yes, it's an underpowered kid's go kart, BUT the principles involved in trying to extract more power and performance from such a low performance machine are lessons well learned. These same "hot-rodding" principles can be applied to vehicles of all shapes and sizes. The Yerf Dog 3203 was a fun way to start off tinkering on off road go karts. It was quickly outgrown, but it did serve a good opportunity to learn something and have a little bit of fun with the kids along the way. Click links below to see some of the other machines I've played with:
Honda Odyssey Yamaha Rhino Twister Hammerhead Yerf Dog 3206 Yerf Dog 3203
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