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    Re: Re-engine Buggy with a (modified) Predator 670
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    I think I missed the video of you doing donuts in the dirt and drifting around corners.
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    Re: Re-engine Buggy with a (modified) Predator 670
    Senior Member darwinpayne2000's Avatar
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    Okay, now I have two excuses to go back to the sand dunes. Test out the new jet needle and get some video of the buggy doing donuts and drifting around the corners.
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    Re: Re-engine Buggy with a (modified) Predator 670
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    Nice! Glad I could help..lol
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    Re: Re-engine Buggy with a (modified) Predator 670
    Senior Member darwinpayne2000's Avatar
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    The new jet needle arrived in the mail a few days ago, so back to the sand dunes for some fun!!!

    The jet needle is a 6EN11-55. Two sizes leaner than the stock needle. I played with the clip settings at home using the vroom-vroom method and decided that the clip still needed to be at the very top to sufficiently lean out the mid-range. Once I got to the sand dunes, I would be able to confirm that setting.

    I loaded everything up for the trip and, just to make things interesting, I also brought along the Keihin 39mm Striker carb that I originally used on the buggy. I didn't have the AFR gauge at the time and I could never get it dialed-in. With the gauge, I should be able to quickly dial in the carb and compare the two carburetors.

    First off, the Keihin. I put the carburetor settings mostly back to "ideal" for the engine, based on my earlier testing and gave it a run. The results weren't too bad. The throttle response was decent and WOT was spot-on with a #160 main jet. I moved the jet needle clip to the top setting, same as the Mikuni, and the mid-range performance picked up.

    My impressions of the Keihin mostly matched the general consensus of a 35mm vs 39mm carb on an engine. Since both carburetors are flat-slide models, the throttle response was good. The Keihin mostly matched my earlier runs with the Mikuni. However, at WOT, the Keihin definitely had more gumption. A Mikuni TMX will flatten out at 3/4 throttle and basically run exactly the same at WOT. The Keihin was much smoother and accelerated nicely all the way out to WOT and showed slightly more spirit when trying to climb the steeper dunes.

    The performance of the Keihin was good enough that I really debated about taking it back off and using the Mikuni. However, I wanted the testing to be complete, especially with the new jet needle on the Mikuni, so I swapped it out.

    I'm glad I did. The new jet needle definitely made a difference on the mid-range. Much snappier performance and the AFR gauge showed the air/fuel ratio hitting consistently in the upper-11 lower-12 range. A consistent mid-range also helped with the transition to WOT but, as you would expect, it didn't really change WOT performance.

    I decided to keep the Mikuni on the buggy. The new jet needle gave the Mikuni the advantage in mid-range throttle response and the AFR readings at mid-throttle were more consistent with the Mikuni. The performance of the Keihin at WOT was good, but it wasn't outstanding. I made the same run up a steep dune with both carbs and the Keihin only got me about 5-6 feet further up the dune. However, I would love to compare a Keihin PWK 35 with the TMX 35.

    So here are the final carburetor settings:

    Altitude 4,000+ feet
    Temperature 68 degrees


    Mikuni TMX35

    Main Jet 280
    Idle Jet 12.5
    Jet Needle 6EN11-55
    Needle Clip #1 (Leanest)
    Slide Cutaway 6.0


    Keihin PWK 39

    Main Jet 160
    Idle Jet 32
    Jet Needle DGH
    Needle Clip #1 (Leanest)
    Slide Cutaway 7.0

    Now that the drama with the carburetor is over, it's time to pivot back to . . . more horsepower. Performance 670 will mill the heads .040 and perform a mild port job for $225.00. That will give the engine another 4-5 horsepower, which would be nice. I don't really need it out on the trails, but the extra horsepower would help when I'm riding out on the dunes. Winter is coming, so that would be a good time to pull the heads and get the machine work done.

    Also, no video. I made the trip to the dunes by myself, so nobody to hold the camera.
    Last edited by darwinpayne2000; 10-31-2020 at 01:58 PM.
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    Re: Re-engine Buggy with a (modified) Predator 670
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    I rule it suspicious, do you really drive it? Or are you just doing dyno pulls? lol
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    Re: Re-engine Buggy with a (modified) Predator 670
    Senior Member darwinpayne2000's Avatar
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    Quote Originally Posted by LIDUNO View Post
    I rule it suspicious, do you really drive it? Or are you just doing dyno pulls? lol
    No, man, I rode the buggy hard yesterday and also two weeks ago and I have shoes full of sand and also a sore neck to prove it.
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    Re: Re-engine Buggy with a (modified) Predator 670
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    Quote Originally Posted by darwinpayne2000 View Post
    No, man, I rode the buggy hard yesterday and also two weeks ago and I have shoes full of sand and also a sore neck to prove it.

    Alright I believe you, next time lean your phone up against a tree or something..lol
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    Re: Re-engine Buggy with a (modified) Predator 670
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    Quote Originally Posted by darwinpayne2000 View Post
    No, man, I rode the buggy hard yesterday and also two weeks ago and I have shoes full of sand and also a sore neck to prove it.
    As they say.....pictures or it didn’t happen! ��
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    Re: Re-engine Buggy with a (modified) Predator 670
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    Tuff crowd!
    All dressed up and waiting for the beer to arrive.
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    Re: Re-engine Buggy with a (modified) Predator 670
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    Quote Originally Posted by jimmyg View Post
    Tuff crowd!
    Not really, we're just emotionally invested in his buggy story..lol
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