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Jon Sinclair

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  1. Hello everyone, I recently picked up an 04 Suzuki dr200se. I'm an experienced dirt bike rider and have owned many different models over the years. The only reason I dragged this one out of my neighbor's backyard was because it was in decent shape and I felt sorry for it. The carburetor that was on it was in horrible shape and I hate CV carbs in the first place so I tossed it. I replaced it with a Mikuni tm33 Pumper. I have removed the airbox from the bike completely and replaced it with a clamp on uni filter. Although I have tinkered with and tuned many different bikes over the years, I have yet to make such a radical change to a machine such as moving to this type of carburetor with no support from the riding community other than speculative advice. The TM33 is the first carb I've ever felt the need to mess with the air jets, but I'm glad I did because I believe I have learned something. It was a little confusing experiencing both lean condition and Rich conditions at the same time. I mean, I knew the carb came jetted way too lean when I first installed it on the bike and fired it up. I will normally start with the pilot circuit which I did in this case. I noticed that as I increased the size of the pilot jet, the spark plug told me that I had gone way too rich, but the bike ran with an off idle bog as if it were too lean. Turning the fuel screw in and out only added to the confusion. One quarter turn in the wrong direction either led to a black sooty spark plug or the bike spitting on deceleration as if it were running out of fuel. Before playing with the air Jets I decided to increase the size of the needle jet to the largest size available which seemed to help considerably. I had also increased the pilot jet by three sizes (#45) and the main jet by 2 and 1/2 (#145). I actually took the time and patience to work up slowly to those sizes only to find that the spark plug said that the engine was running extremely rich, yet the bike ran as if it was lean. After much frustration and taking the bike apart probably over a hundred times I decided maybe it was time to mess with the air Jets. I increased the pilot air jet from 1.1 to 1.2 and there was a dramatic difference in idle and low end response. The bike still idled as if it were a little rich, but when I closed the fuel screw by a quarter of a turn, it would act as if it were running too lean again. I got the pilot circuit to run okay at idle all the way through 3/4 throttle and then decided to change the main air jet. The bike made pretty good power through the mid-range with the needle on the third clip position, but there was a significant Rich burble between 3/4 and wide open throttle. I had gone from a 130 to a 145 Main Jet. I noticed that as I increased the size of the main air jet, the rich burble began to pinpoint at wide open throttle. I had increased from a .7 to a 1.0 main air jet and still noticed a slight burble at wide open throttle so I reduced the main jet by 1/2 size to 142.5. Voila! I was able to achieve near Perfection from 1/8 throttle all the way to wide open. At this point, the bike seemed to idle a little bit funny and seemed to miss a little bit around 1/8 throttle. Thinking that it might be a little rich, I turn the fuel screw in one quarter turn only to find but it made things worse. I decided to increase the size of the pilot air jet to 1.3 and open the fuel screw back up to 1 and 1/2 turns out and this thing runs perfectly! Power is almost perfectly seamless from idle to wide open throttle and the Improvement in mid-range power is the most profound part of it all. So I guess the overall point of what I'm saying is that I would have expected this bike and carburetor configuration to want more fuel, it seemed counterintuitive at first for this combo to want more air and fuel at the same time, but that's exactly what it wanted. At this point the spark plug says that it's about as perfect as it can be with the stock exhaust still on it. leave it to me to order another pipe and put myself through all this all over again. :-)
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