After finishing my pit bike project, I began looking for something new to work on. My 150cc SSR pit bike is great for jumping and high speeds, but it is horrible to ride in any kind of sand. And around here, most of the riding is sand. So my goal is to build a capable sand vehicle.
I had seen a couple of decent adult go karts pass through Craigslist at low prices, so I started watching closer to snag one. After watching for several months, I was able to pick up a 2001 Murray Explorer go kart for cheap. The kart was good overall condition, with maybe 40 hours on it, but was not running due to a long sit. It needed the degraded gas cleaned from the carb, a lot of routine maintenance, front tires and an air filter. The motor is still solid, the previous owner did keep up on the engine oil maintenance.
Check out the neighbors dog looking for a nice place to take a dump in my yard. Just picking that prime spot. I swear I'm going to buy a crossbow soon.
The kart ran ok after getting everything squared away. Fair power all around. Ran fair in mid to high rpm. Ran rough in low rpm. Idled rough. The carb seemed rich on the mid to top end and lean on the bottom.
A lot of power was being lost in the primitive fuel delivery and rpm limiting. The carburetion and governor system is a nightmare of rpm control, government regulation and cost cutting. There was no adjustment for low or high fuel metering. There was no choke for cold days. I hated it and began looking for alternatives.
Tecumseh is the black sheep of the kart racing world. They canceled their karting performance program and angered the karting community. The end result is that there is not a lot of performance information or parts available out there. However, Tecumseh OHH motors are very common on fun karts and mini bikes.
Despite is paltry horsepower, the OHH60 motor is actually a 195cc motor. Getting more than 6 hp from 195cc should be pretty easy. However, the motor has some low end features like a thermoplastic cam and aluminum wall cylinder, so heavy modification is probably a waste of time. However moderate performance increases and higher rpm should be no problem.
I dug around in the archives of several go kart racing site for low cost ways to get some performance from this motor. Due to the fact that this is a used motor, I am not going to invest any real money into the internals of the motor. No cam, etc. Strictly "bolt on" type mods. When this motor goes, I'll buy an upgraded motor and move my parts over. For now, let's see what this will do.
Most of this info has originated from either David Ables of Dare Motorsports or John Davis of O-1 Racing. These gentlemen are keeping Tecumseh OHH performance alive. Look them up if you want to build a 14 hp monster engine.
Note: If you performing these upgrades, you should have some prior engine experience or the Tecumseh shop manual and a fair dose of common sense. You can easily destroy your motor or injure yourself.
First order of business is an exhaust. I ordered Robertson's Kart Pipes Torque Tube #T-OHV-LG-M and and the recycled aluminum muffler. The cost is $80 shipped. If you don't need to be quiet, you can get a straight header for about $45. Note that the muffler is made from aluminum energy drink cans and that is what it looks like when you get it. I brushed mine and shot it with an aluminum engine paint.
The exhaust is well made and looks great on the kart. The engine sounds much better with the pipe installed. In the photo, the exhaust is installed with the included bracket. I found that there was too much vibration and installed a custom bracket later.
The stock paint burns off of the exhaust in the first hour of use. Stop by your local hardware store and pick up a can of BBQ spray paint. This flat black paint can withstand the heat and is inexpensive. The exhaust will rust quickly if you do not keep paint on it. Go ahead and paint your rusty-ass BBQ too. You'll have plenty of paint.
Go to Page 2 for valve spring and carburetor information.
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