If you are buying a DRZ for performance, you are best off purchasing a 2000-2006 DRZ-400E (2000-2003 for California models). This model was equipped with a Keihin FCR 39mm pumper carburetor, higher compression base gasket, and performance camshafts. This will give you good bang for your dollar. Unfortunately, this model can not be made street legal in many states.
Some tuners claim that noise equals power; however, I feel this is an irresponsible statement for those involved in the motorcycle community to make. Loud pipes may gain a horsepower or two, but at the expense of closing trails and upsetting the general public. I could envision one buying a loud exhaust for closed course use only - but on a DRZ this is very unlikely!
The stock DRZ exhaust is a good compromise between low noise and power output. 400S/SM owners looking for better flow could consider purchasing the larger diameter 400E headpipe.
“But, Paochow, I seem to remember you running a Yoshimura RS-3” you say. I did run a full Yoshimura exhaust for most of my time with the DRZ, however most of that time I ran an old style TEC insert which kept the sound at reasonable levels. It did cut power from the wide open setup, but it stopped me from setting off the alarm on every parked car I drove by. Reinstalling the stock exhaust on the bike was a major revelation as it provided similar power to the corked up Yosh, but with even less noise. . Oh, well, maybe for my $400, I saved two pounds.
The stock Mikuni 36mm carb on the 400S/SM and 2007 and later 400E models is a major constraint, both in terms of throttle response and jetting. Rejetting this carb will alleviate the jetting issues, however it will not provide the throttle response of the Keihin FCR. This pricey carb can often be found on eBay for reasonable prices, and otherwise can be purchased new from vendors such as Sudco or Carb Parts Warehouse. Its accelerator pump gives a squirt of fuel when the throttle is turned, providing excellent throttle response. Despite the reputation of pumper carbs for being finicky with altitude changes, I found the FCR provided crisp carburetion from altitudes from 3500-10,000 ft.
At this point I don’t have any experience with the Edlebrock Carburetor, and reviews seem to be of the love it or hate it variety. One of my friends recently purchased one, so soon I will have some first hand feedback.
Numerous piston/cylinder kits are available for the DRZ ranging insize from 434cc to 475cc. These kits are fairly easy to install even for a home mechanic. To see what is required, see my how to guide here. These “big bore” kits will provide horsepower and torque increases across the board, with little decrease in reliability.
Adding a stroker kit can increase displacement by an additional 5mm of stroke for displacement in excess of 500cc’s. My personal opinion is that if you are looking at increasing displacement, I would recommend drawing the line with a piston/cylinder kit. Installing a stroker kit requires splitting the engine cases, and if you want to invest the time/money to do so, you may want to reread the second paragraph of the introduction and consider investing in a more powerful platform to begin with.
I’m hesitant to advise a switch to aggressivecamshafts as they can stress the two piece valves, which can cause valve failure. Sticking with the stock cams, 400E cams, or Stage 1 Hotcams will limit the strain on the valves allowing the stock valves to be run. More aggressive cams can be run but will require one to upgrade the stock valves - this is expensive and may not be worth the performance gain. Again consider the cost of modification versus buying another bike. Also note that leaving the valve train stock results in very infrequent maintenance intervals, a situation that I am envious of now with the rigorous demands of an Austrian maintenance schedule.
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