6hp Briggs Chopper

Discussion in 'Stretch Cruiser & Chopper Motorized Bicycles' started by s1rvr15, Jul 2, 2017.

  1. s1rvr15

    s1rvr15 Member

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    Hello all!

    This build is very much a work in progress, but it is currently in a very much rideable state. I started with a Briggs & Stratton 120000 series, 206cc, 6hp, OHV, single cylinder, 4 stroke engine out of an old roto-tiller; I removed the governor (it won't hit high enough RPMs to cause damage, valve float and power will limit engine RPM), gas tank, hand throttle, replaced the spark plug, cleaned the carb (which still has a bad float, if I leave the petcock fully in the on position it overflows and floods), jury rigged a cable throttle linkage by using a spring from the hardware store and the lever which the hand throttle connected to on the carb (still need to get longer housing, not enough tension to bring it to WOT). The transmission is a Comet TAV2 CVT/torque converter, and even only being able to do half throttle it hits probably close to 30, don't have a speedometer yet to confirm. Wheels are from QBP (a bicycle parts wholesaler, buy from them through my work) and are DT-swiss spokes on DT-swiss 466d 26" rims on Shimano Deore hubs (I used two front wheels and swapped to bolt on axles for both, I don't trust a QR skewer for this). Front brake is some kind of hydraulic brake from what looks like a dirt bike, bought it from Lynn at www.mbrebel.com (you should check her out, really nice lady with good parts and good prices; I also purchased my fork, mounting plate, sprocket, sprocket adapter, throttle and grips from her). Tires are Continental Touring Plus 26x1.75 (I plan to swap to Conti Top Contact II 26x2 tires when these ones wear out). Rear brake is either going to be a Hayes MX5 on a 203mm rotor, a Sturmey Archer XL-FD 90mm drum brake, or a Worksman drum brake: not quite sure yet. Kill switch is just a toggle switch hooked up to a grounding wire from the magneto/coil, and kills the engine real fast. If y'all have any questions, let me know, I'll update this thread as I keep adding on to this bad boy.
     

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  2. Dan

    Dan Staff
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    Lookin' awesome, S1! Has a beast, swept sorta look.

    Looking forward to your updates.
     
  3. xseler

    xseler Well-Known Member

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    Looks like a lot of fun!!
     
  4. s1rvr15

    s1rvr15 Member

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    Dan, thank you! In an area that is particularly Harley heavy, I wanted something that goes for that classic cruiser styling but still stands out.

    Xseler, it is an absolute boatload of fun! The amount of torque it has is absolutely ridiculous, I wouldn't be surprised if the front end would wanna lift up if I used a larger sprocket (currently a 40T).

    My next step is to swap over to a Predator or a Lifan with estart and charging system (availability of parts and fixes, mainly; I really want a slide carb instead of a butterfly), get a speedometer on it, some lights (gonna go with the Very Bright Bike Lights kit from Will K), and repaint the bars.
     
  5. Dan

    Dan Staff
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    purty cool, A1.

    An option to a speedometer is a smart phone app. Gives ya more options like GPS and other stuff. Xseler and I have talked about possibilities such as a solar recharger. Just a thought and not as good looking as a dedicated speedo.

    Also, I have found GPS's will report ya doing 1 MPH when your standing in your garage and holding it in your hand. Not real important but worries me when trying to get exact data on speeds for some reason.

    Just ramblings.
     
  6. s1rvr15

    s1rvr15 Member

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    Sorry for not posting anything for awhile, but I haven't had much to post.

    Dan, I think I may do what I did on a previous build, and use a Vapor gauge from Trail Tech. Thing was dead on accurate compared to a police LIDAR gun and I don't wanna take chances with GPS inaccuracy on this thing, I don't think I could say it's 50cc's with a straight face. Pretty pricey for what it is ($120-$140 depending on model) considering a decent cyclometer that works pretty well is about $50, but it gives speed (to within .1mph), clock, trip time, trip & total running time, engine RPM, air and engine temperature, and has two warning lights to be programmed at certain temperature or RPM points and runs entirely off a CR2032 battery (though it can take a 12V connection to help run the backlight and save the battery life).

    On a general note, I did end up swapping out for a Predator 212, which took all of an hour, and changed out my twist grip for a long pull brake lever (return spring too strong, I'll use the throttle grip again once I get a mikuni on this bad boy). I got rid of the stock muffler and welded up a simple straight pipe using part of the original muffler and some exhaust pipe from the auto store then wrapping the ever living **** out of it with (in order): repair tape to protect the welds, heat wrap, fiberglass insulation, and then a double wrap of heat wrap all to keep my leg unburnt. Exhaust is actually pretty quiet, especially compared to many other bikes in the area (Harley country), and the only issue is the occasional loud bang from an afterfire. I used left over wrap and some foil HVAC tape (probably will swap to EB green for looks and strength) on the "front" of the transmission cover and recoil cover to keep my calves cool, and it seems to work well. Was able to adjust the angle of the front brake caliper a little to get the pads to bite the rotor better, and for the rear brake I'm going to lace up a moped drum hub from Lynn at http://www.mbrebel.com into my current rims with 10g spokes from J&B; hub comes with a 54t sprocket which I am not even going to bother with (front wheel needs to stay grounded), I'm going to pick up a 36, 38, or 40 tooth sprocket for it from a site I found that has the right sprocket with the right bolt pattern. However, I'm sticking to an MX5 rear disc for now, getting lights is more of a priority for me than a drum brake.

    As far as speed goes, this thing does move, and it moves fast. I haven't been able to get it on a stretch of road to take it wide open, but cruising at anywhere from 25-40 is effortless (motor isn't screaming like my China girl electric start bike at 40) and pretty smooth (idle is fairly vibey, but not so much at speed).

    I'm also toying with using a 420cc for the virtue of an electric start, I could do it on the 212 but I *really* don't feel comfortable taking the engine apart and swapping internals on it (4 stroke engines are not in my repertoire, plus working on internals is something I've never done before). From the display models at HF, without fuel tank and muffler (my engine sits far enough to the right that the airbox is no issue for height) they are about just as tall, and I do have the room for the extra length. I could buy a GX200 with the estart, but I don't really feel like throwing $600 at less power and slightly more torque.

    In this rambling book of a post, I'm considering getting an EFI kit from Ecotrons if I decide to go for the 420 (pricey though, $360 for the motor and $800 for the EFI). It would be a major PITA to set up initially and tune (though it does claim to have some self-tuning ability), but I feel like it would be really cool to have after that point.
     
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