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Thread: '83 250R carb swap

  1. #31
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    Quote Originally Posted by barnett468 View Post
    I have never seen or used a 42mm carb on any single cylinder 2 stroke 250 no matter how much it was modified but I'm sure some people have installed them, but I would love to see a dyno sheet with the same type 38 vs a 40 vs a 42 on any model, but especially on an atc250r.
    All out high RPM monsters. At 9200 RPM with perfect porting for drag racing, looking for maximum power, 42mm is it.

    The stock KTM SX 125 uses a 39mm PWK. Little bitty guy with a carb half the size of the motor. lol
    I just wanna go fast. If your not first, your last!!
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  2. #32
    barnett468 is offline FACT ! I have no edit button Arm chair racerThe day begins with 3WW
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    Quote Originally Posted by RubberSalt View Post
    The stock KTM SX 125 uses a 39mm PWK. Little bitty guy with a carb half the size of the motor. lol
    Yes but you can't compare new technology to 40 year old technology. My 1980 YZ250 was the fastest 250cc production motocross bike ever made until the advent of the power valve engines that came a few years later, and my bike in stock form put out 32 hp. Mine has had some minor engine and pipe mods done so it puts out a little more than a stocker, so it's probably around 36 hp and I use the stock 38 mm carb. The KTM 125 puts out even more hp than my modified bike at 38 hp.

    There was a newer KTM 125 in the same race I was in a few months ago, and I am a very good starter, and this guy blew by me and everyone else on the start and had around a 3 bike length lead going into the first turn, and I got a very good start and was in second, lol.

  3. #33
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    Quote Originally Posted by barnett468 View Post
    Ok then it really might be best if you ride it again then tell us what you would like the engine to do that is different than what it is doing now before you go buying parts you may not need. You may also just need a different silencer instead of an entire expensive pioe to get the type of power you want so changes can be made in small steps one at a time to kerp from buying unnecesssry parts.
    I have to agree with this here. A couple of years ago, I rode a 1981 250R. Not long, just enough to get a feel for it. After yeagerb completely rebuilt the engine, ported it out, and the owner put a full DG exhaust on it (I have no idea what type of carb was on it), it was an entirely different machine, and it felt like it had almost twice the power. It was amazing engine work. I told the owner that while it was great, I'd actually prefer it stock for 90% or more of the trail riding that I do. It lost bottom end power after all of the mods. I usually ride tighter trails and not at race speed. It may just like Barnett said, you may not need many parts for it to run like you actually want it to. It's easier to modify your trike than it would be to put it back to stock, assuming that you have some serious engine work done.

  4. #34
    JacobMonster's Avatar
    JacobMonster is offline At The Back Of The Pack Arm chair racerFirst time rider
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    Honestly, I wouldn't think the DG would make that big of difference in the power. I have an 82 with a DG silencer and stock head pipe, with stock jetting I assume. The thing rides the same way you described your stock 83. Beastly low end, lift the front wheel anytime you tell it.

    With my woods build that I'm slowly working on, I'm just going to run the stock carb with a full DG. I'm just buying the header pipe because I have the DG silencer and my stock header is bent, so it leaks exhaust right at the engine. I want to run a Lectron carb on it. I've heard so many great things about them. You don't have to jet the carb, it does it automatically. But you pay a pretty penny. I think they were close to $500.

    I say if you want something good for the trails and low on cash, keep the carb you have and fine tune it. No sense in going through the hassle of making a carb fit and all that jazz unless it will significantly change the performance of the bike. You could do more by simply changing your gearing than messing with carbs.

  5. #35
    barnett468 is offline FACT ! I have no edit button Arm chair racerThe day begins with 3WW
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    Quote Originally Posted by JacobMonster View Post
    I want to run a Lectron carb on it. I've heard so many great things about them. You don't have to jet the carb, it does it automatically. But you pay a pretty penny. I think they were close to $500.
    Actually, contrary to the few positive reports there are out there about them, there is a very good chance you will have to "jet" it like many other people have, which may very well involve replacing the needle with another one, which consists of calling Lectron and telling them exactly what the problem is etc and then having them take their BEST GUESS as to which needle will work best, and if it still has a problem with the new needle they send you, you are back to square one.

    Do not believe the advertising/marketing hype and make the mistake that this extremely expensive carb will bolt on to your bike and work flawlessly. imo, if it does, you are extremely lucky, and if it doesn't and you have to start changing needles etc, you may be extremely unhappy.

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