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    Re: Re-engine Buggy with a (modified) Predator 670
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    In the Mid-West (WI). I have noticed that they post the ethanol ratings on the fuel, 92 octane, which is only what I run in all my ATV related items shows ZERO ethanol. The label also shows it is for high performance and ATV's (Kwik Trip) for example. I used to run 92 with a splash of Trick racing fuel back in the days....
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    Re: Re-engine Buggy with a (modified) Predator 670
    #92
    Senior Member darwinpayne2000's Avatar
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    The weather never seems to cooperate. The temperatures during the mid-week will crawl up into the low 60's, then plunge down on the weekends. No fun.

    However, this weekend was somewhat decent. We went out camping north of Little Sahara sand dunes (since they're closed due to Coronavirus) and I was able to take the buggy out for a few good runs.

    Mid-range seemed good. I did the carb test, where you floor it, then ease off the accelerator to about 3/4 - 1/2 throttle and check the response. Easing off the throttle tends to richen the fuel mixture, so if you get a power boost on deceleration, that suggests that you're running a little lean on the main jet. That's exactly what happened, so I went looking in my jet kit for a 250 main. As (bad) luck would have it, that's the only jet I didn't have, so I put in a 260.

    It ran fine on the 260, but the mid-range seemed a little boggy. I dropped the jet needle down one clip and that seemed to fix it. Yay!!

    With the VM34 carburetor running in a (hopefully) optimized configuration, I was finally able to feel the increased torque from the new camshaft. When I tackled the hills, it seemed to have a fair amount of grunt in it. The sand dunes would have been the ultimate test, but alas, that was not to be.

    Another change I made was to the Duster clutch. I wanted to try adding three lighter pucks to the clutch, to raise the engagement rpm a tad, but the existing pucks have been in the clutch for a long time. The new (unworn) pucks rode too high. A fresh set of pucks was the solution. Since opportunity was knocking, I also ordered the ribbed clutch cover and a complete set of pucks compatible with the ribbed cover. I don't know if I really need it, but if the clutch is slipping, the ribbed cover will fix it. Also, if I kick this up with more horsepower, the ribbed clutch cover is recommended.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #93
    Senior Member darwinpayne2000's Avatar
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    Some additional thoughts.

    I was looking at the Performance670 website a few days ago and he's now offering turn-key engines with various mods. One of the engines, the Ready-to-Run for $2450 is basically what I'm building. I already have the 507 cam and the stiffer springs installed. I'm using the VM34 instead of the TMX35 carb, but I have the TMX35 sitting on the shelf. I bought it for my Polaris 400, but I've decided to leave it stock and use the carb on the buggy.

    The final step will be the cylinder head work. Mill each head .040 and clean up the ports to boost it another 4-5 hp. Testing the TMX35 carb is the next step. Milling the heads is down the road. I don't want to tear the engine apart right now during prime riding weather.

    According to the website, after I'm finished with all of the mods, it should be good for 43 horsepower. Not bad for an engine that started out with 22hp.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #94
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    Ya! I'd say doubling the HP is pretty good..lol
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    Re: Re-engine Buggy with a (modified) Predator 670
    #95
    Senior Member darwinpayne2000's Avatar
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    Since I won't be having the cylinder head work done for awhile, maybe now is a good time to assess how much I have invested in this project and how much money someone might want to spend to get "more power" out of this engine. Keep in mind that a stock Honda GX690 engine is 21 horsepower and costs about $1329, give or take a few bucks. I picked up the Predator 670 engine on sale for $700. That's a pretty good deal for a 22 horsepower engine.

    The first mods are to remove the governor and shim the valve springs. Removing the governor is kind of obvious, but shimming the valve springs helps get the rpms up and adds some free horsepower. "Valve shims" are 1/16" copper washers that you can get at your local Ace Hardware and cost maybe a couple of bucks. Those two changes are the biggest bang for the buck that you'll find when working on an industrial engine.

    In my case, I spent a little more and ordered the stiffer valve springs and the steel pushrods. Total cost is $80.

    The next upgrade is the Mikuni carburetor. The "carb kit" with the intake manifold is $350 from Performance 670. I think it is well worth the cost because the Mikuni is a much better carburetor than the stock carb. Better throttle response and undoubtedly more horsepower. I made my own intake manifold and ordered a Mikuni TMX35 and the 1.5 valve seat (needed for fuel pump systems) from Ebay for $170.

    Total cost for the engine, upgraded springs/pushrods and "carb kit" is $1130. My cost is $960. I think most people could stop right there and have a pretty good trail buggy.

    Since I'm one of those guys that's never satisfied, I pushed ahead, partly to get more horsepower and also to review and assess how much bang for the buck I could get. A new camshaft and the Gasket Elimination Kit adds another $320 to the cost. I haven't tested this setup with the TMX35 carburetor yet, but with the VM34, it definitely adds some grunt and pulling power to the engine.

    My guesstimate is that I have $1300 invested so far. Not a trivial amount and I know some guys would look at that and think about picking up an older, used 440 snowmobile for about the same money and get the clutches thrown in for free. Also not a bad idea, but I wanted to stick with an industrial engine for this buggy. It just seems to be a better fit for the frame.
    Last edited by darwinpayne2000; 04-10-2020 at 05:39 PM.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #96
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    I was one of those 440 snowmobile people and ended up with quite a headache packaging the engine and clutches so far. the good thing about your method is that there seems to be plenty of parts available for the engine, whereas I am having troubles finding some parts. Thanks for providing all the costs to compare with though!
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    Re: Re-engine Buggy with a (modified) Predator 670
    #97
    Senior Member darwinpayne2000's Avatar
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    My buggy has grown in size over the years. Right now, I can load four ATVs onto my trailer from the back or load my buggy and two ATV's from the side. When I load the buggy from the side, I only have a couple of inches to spare when I close the side gate. Making it longer isn't really an option.

    I have a liquid-cooled Polaris 500 snowmobile engine that I tried in the buggy before I went down the Predator 670 rabbit hole. I could fit the engine into the frame, but adding the big 2-stroke exhaust, the larger clutches and a radiator was never going to work without making the rear much larger. However, I would have loved to have that engine in the buggy. Vroom, vroom!!!
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    Re: Re-engine Buggy with a (modified) Predator 670
    #98
    Senior Member darwinpayne2000's Avatar
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    I went out camping again this weekend to put the buggy through the paces. I now have the Mikuni TMX35 installed and I started with a 260 main jet.

    I took it for a few runs to dial-in the carburetor. The buggy seemed to perform well, but the plug check showed that it was running a little lean. I swapped in a 270 main jet and fiddled with the jet needle and it still was running lean. I didn't have a 280 or 290 main jet (story of my life), so I swapped in a 300. My impression was that the 300 was a little rich and a plug check confirmed it. It was black.

    Time to perform a thorough check of my Mikuni main jets and confirm that I have at least one of every jet size that I could conceivably need. I assumed that I wouldn't need anything larger than a 260-270, since the VM34 ran well with a 240, but the TMX35 is a different beast.

    Speaking of beast, the new camshaft/carburetor setup has really helped with the engine torque. Back when I first installed the engine and I was running the original carb/camshaft setup, I tried to tackle a moderately steep hill and quickly ran into trouble. Not enough torque to get me up the hill. I ran into a similar hill when I was out trail riding and the buggy went up the hill without any problem. Yay!!! More Power!!!

    As an aside, I'm having some issues with the clutches. A few weeks ago, when I took the buggy out with the new ribbed cover, the pucks got jammed-up on the edge of the new cover. A couple of the pucks also fell out. I tapped on the jammed pucks and the clutch cover slammed shut. I hot-footed it back to camp and the pucks again jammed up on the edge of the cover. I put in a ring inside the clutch to keep the clutch cover from opening as wide and I assumed that fixed the problem, but I again had the pucks jam up after riding for almost two days without any problems. The pucks couldn't fall out anymore, but I also noticed that the driven clutch was not closing either. Too much dirt in the driven clutch? I'm sure it's contributing to the problem, so I need to pull off both clutches. Use some dry lube on the driven clutch and make sure that the pucks can't get hung up on the clutch cover when running full-out on the trails.
    Last edited by darwinpayne2000; 04-22-2020 at 09:57 AM.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #99
    Senior Member jimmyg's Avatar
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    Other than the 280 jet problem it sounds like things are better than expected. We all tend to start down these rabbit holes not knowing how deep it goes but when you get a day and night example as seeing the top of a hill or not. Priceless. Doing good work.
    All dressed up and waiting for the beer to arrive.
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    Re: Re-engine Buggy with a (modified) Predator 670
    Senior Member darwinpayne2000's Avatar
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    I did some reading on the Duster clutch with the ribbed cover and the issues with the pucks can happen when the driven clutch gets stuck and doesn't close after you let off the gas. Mystery solved.

    I pulled off both clutches and performed some service. The ribbed clutch cover is just a piece of stamped steel and the edge of the cover is fairly sharp. I can see how it's been digging into the pucks and making it stick open. I used a small file along the edge of the rib folds and beveled the edge. I was careful to stay on the edge and not go too deep up into the folds. It is now much smoother and less likely to bite into the pucks.

    The driven clutch was apparently jammed up with belt dust. I opened up the clutch and flushed it out with some brake cleaner. I also lubricated the shaft with some Comet dry lubricant. I was a little surprised to have issues with the driven clutch because it's fairly new and I ran the old driven clutch for years without any issues. The belt is fairly old and starting to crack, so I ordered a replacement.
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