Friday, April 18, 2008

DR Hop Up

I am generally happy with the power characteristics of my bikes, but the Suzuki DR 650 is so mildly tuned and docile that I began to think it might be worth the expense to liven up the motor a bit. The big DR is much heavier than the smaller DRs and is somewhat hampered in the dirt by this weight. Mounting semi-knobby tires helps but it remains more impressive on pavement than in the dirt. While it has gobs of torque for off-road use, you can never have too much power on the street.

I ordered an FMF slip-on muffler from Jessie, the DR guru at His web site shows pictures of how to open up the air box for better breathing on the intake side. I simplified the procedure by using a hole saw to make a couple of large round holes in the box. I then rode down to Mike Kirkpatrick's Pro Tec Dyno to get the carburetion dialed in. This was my first experience with a motorcycle dyno and it is pretty impressive. Since all bikes come from the factory with lean jetting these days, opening up the breathing at both ends only makes things much worse and the carb must be re-jetted for maximum power and longevity of the motor.

What I didn't realize about modern dyno machines is that they have a sniffer that goes down the exhaust pipe to read the actual fuel-air ratio all the way up through the RPM range. The initial dyno run revealed lean burn that was off the chart. Mike's been tuning bikes as a hobby for decades and has such a feel for it that he picked the correct jet the first time on my bike. He says he got lucky but he obviously knows what he's doing. A couple of other tweaks to the carb and it was back on the dyno to check the result. Both he and I knew right away that this run was much different. Now the docile DR was really making power and spinning the dyno drum at a ferocious clip. The printout revealed a 7 HP increase and a truck-load of additional torque - especially in the mid RPM range - and my fuel-air mixture was now right where it should be.

I found it hard to explore all this new power in the city, as opening the throttle half way quickly puts the speed into the bad-ticket zone. Once on some twisty country roads it was plain that the old DR was now a bit of a beast. Whacking open the throttle makes a lot more noise with the aftermarket can, but there is also some serious muscle to go with it. It feels like it wants to tear the knobs off the tires. At first I was tempted to say that the 650 now felt like an 800 but that is not quite right. Before, it was a 650 with a pillow jammed into both ends. Now it feels like a hot 650 - at least by comparison. It really feels like a 650 version of my KTM 450 - still torquey and tractable but much more athletic than the dumbed-down stocker. I would say that an increase in power in the same bike pays out dividends in fun by a factor of two. A 20% increase in power yields a 40% increase in fun - and fun is what it's all about. I now have what amounts to a new bike for only a few hundred dollars. Money well spent.

There is another reason I went for the aftermarket pipe - weight, or lack thereof. My bike lost 7.8 pounds. I had my doubts that I would really notice the weight reduction while riding but I do. While roosting up the dirt road that links Cashmere's sewage treatment plant with Monitor's orchards, I felt the bike was handling better. It's not just the weight but where the weight is located on the bike that can make a difference. Sport bike designers are all aflutter over mass centralization these days. On the DR, those extra pounds were hanging high and to the rear - far from the center of mass - like an eight pound pan handle. When the bike wanted to twitch to the left, that old muffler wasn't done swinging to the right. The loss of weight can only benefit acceleration, deceleration and every other kind of motion. Money even better spent.

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