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Kimjon

Kimjon's not as cool or epic as Muncie's off-road goped Bigfoot scooter thingy

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Hard act to follow @Muncie with a fucking V-twin on a goped!!!, but if imitation is the sincerest form of flattery...then this is my lame arse  attempt.

So, ever since I was a kid I've wanted one of these

IMG_20180106_074112.JPG.835e7ddf2c8f3b6a6bdc9356e46dbaeb.JPG

It was called the "Bigfoot" and to a little boy growing up on a bush block with no concrete within about 5km, it appealed to me as something I could rip around the gravel driveway on.

However the excessive price tag ment it stayed a dream, as I never got one (rightfully so, these things were something like $1500 to buy in NZ during the 1980's).

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Fast forward about 40 years and unfortunately I still can't justify/afford to rock up to a shop and buy a brand new one, however this fabulous opportunity presented itself on trademe.

IMG_20180105_161912.thumb.jpg.0e3334caacaff59dc13f137875555953.jpg

Now I know what you're thinking, but sadly I had to pay extra for the coffee cup...it wasn't included in the $23.50 I paid for it.

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Anyone with a keen eye will notice a few parts are missing, but for $23.50 what do you expect? However I see this as an opportunity to improve a few things that the original design didn't quite get right.

1) The original was only 22.5cc, it still did 20mph...but there's room for improvement.

2) The original had a tension cable that moved the motor directly onto the rear wheel, where a knurled friction drive would make contact with the rear tyre to drive it. This system wears out tyres, and slips in the wet. I'm going to look at a chain drive alternative.

Those are the main improvements I'll be looking to address, other stuff is just for fun.

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So onto the build:

Engine will be a pocket bike 49cc motor. I have a few of these now, parts are cheap and easy to get and they're pretty good motors for the money.

IMG_20180105_162441.thumb.jpg.9e0a14db37cb3fccab5d9cbdf9309d68.jpg

I started by cutting up the pivot mount, just visible behind the wheel.

IMG_20180105_163322.thumb.jpg.0eb2ea00d4a976a0e9db9f176be2f5ea.jpg

Then I cut the engine mount out of the donor pocket bike also purchased from trademe for $30. I brought the pocket bike for the motor, but the extra bits like this also come in handy and can save a lot of work.

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Welded up the engine mount:

IMG_20180105_172745.thumb.jpg.70c5487645234683ef36c7b3fefbf2a1.jpg

Then fitted this to the frame

IMG_20180105_175846.thumb.jpg.29d763b3748ba19c9b0eb4dd7b15a46c.jpg

And finally popped the motor on for and overall first impression.

IMG_20180105_180639.thumb.jpg.a9ff0b9f3f6c854858a59e85ea2d52d2.jpg

So far, so good. 

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Haha I've only finished one thing and peaked you seem to turn out awesome shit on a weekly basis...... I'm sure there's room for a second engine on this? 2wd??

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Playing around with the proportions. I want to pay homage to the original, by keeping the look it had. 

IMG_20180106_102612.thumb.jpg.e5bc1ec5965a4493e4950f9ab28cc8b8.jpg

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I've seen some homemade variants of these using gravity fed fuel tanks stuck on top in the past that just kinda miss the mark style wise. It's a fine line getting something proportionately correct...fingers crossed it will look the part when finished?

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On to the exhaust expansion chamber (yes that rather rusty one in the above photos).

There's an entire science dedicated to these...and I've used none of it "designing" mine.

IMG_20180106_111729.thumb.jpg.4b3480c6ac997b10b9806573f573f5d4.jpg

IMG_20180106_113447.thumb.jpg.2fe27b2a21e586e3c6faf454d789e504.jpg

What I have is a reasonable past history with 2-strokes, so I'm simply going by what feels right. At the end of this project I'll soon know if I did the right thing or not?

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Struggling to get the shape I want, but nothing a hacksaw, welder and some more thinking time can't solve.

IMG_20180106_131007.thumb.jpg.e1191a2d29cc461adcf2328b3d48c8e9.jpg

IMG_20180106_121939.thumb.jpg.243314ee7e35b754f3687d27d1d2a1bd.jpg

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I feel like I'm winning on this one now, as the expansion chamber starts to take shape around the rear end.

 

Cut, shape and tack:

IMG_20180106_150537.thumb.jpg.57478652b213c5c671faff8130afe5a6.jpg

IMG_20180106_151058.thumb.jpg.a2192997da7898a87df49a8fbfb390b9.jpg

 

And then welded:

IMG_20180106_152113.thumb.jpg.f480bc6485da9f16ff26322cbabbcbfe.jpg

 

I need to pick up a large bend to tie it to the other cone, but I have a plan (mates scrap bin)  :-)

 

 

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So, some rules of thumb.

The longer the header, cone/s and barrel length are the broader the power band will be over the useable rpm range, but less intense.

Inversely: a shorter header, cone/s and barrel length gives a much sharper and more aggressive power band, but this only happens at a higher rpm.

For this project running a centrifugal clutch, I'm keen to have a broad softer starting power band with a wide midrange. Well that's the theory...reality check to come.

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Going for a centrebleed pipe, so marked out location of bleed port.

IMG_20180106_185305.thumb.jpg.3498c71b0afc4249a5274f9f33b6ab67.jpg

String line gives a centerline, just mark each side of the string.

IMG_20180106_185528.thumb.jpg.17e64c2e90ad5535b8b6c39817903966.jpg

then find the tangent and mark that.

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Then I fitted the muffler.

IMG_20180106_191332.thumb.jpg.c976e1fdc424264cee925b2ab0011fe9.jpg

I cut this off another pocket bike, welded an extension that was approximately 60% the size of the header pipe diameter to restrict exhaust flow.

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I cut a port in the main pipe with a step drill to match, and welded it in place.

IMG_20180106_193512.thumb.jpg.48ca4a9232d0edfb37ad832f2ab06656.jpg

Once again using a string line to centre it.

Then I closed of the tip of the cone where the old muffler was, as the exhaust will no longer exit there.

IMG_20180106_171858.thumb.jpg.6b18bd8ea62959ee778c1cef8f1ec974.jpg

I'm going to curve it around and point it down towards the ground...but I couldn't help taping it on just to get a feel for how its going to look.

IMG_20180106_195023.thumb.jpg.a4f614c1fe9e3e2ce25242b312cc407d.jpg

I'll give it more time, as this look is growing on me. I may just weld it up like this?

 

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A couple more pics.

IMG_20180106_194941.thumb.jpg.fe2ebb63848708d5bde0f3712e438469.jpgIMG_20180106_194933.thumb.jpg.a39311a7337d63e68c39bc109ef51c1e.jpg

the cardboard is a mockup of a rear fender I'll make/add. And the yogurt container is there to help me visualise a gas tank.

Next up: I'm going to port the motor and add a larger carburetor with a diaphragm pump, so I don't have to mount the tank higher than the motor, then tidy it all up.

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Waiting around isn't one of my strong points, so to move this project forwards, I welded it straight this morning.

IMG_20180107_113506.thumb.jpg.a36acc2e50d72aca20d4cdbdf624c677.jpg

I think it looks the part

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These chambers vibrate like hell, and eventually this will fatigue the metal.

I added a support bracket, and a little tab to the muffler as well.

IMG_20180107_142822.thumb.jpg.4571c5bffd67ecf91ad83fd344be393f.jpg

Here's how I made the support bracket. 

IMG_20180107_190502.thumb.jpg.3590f6bd1d2cf0b44b1c069a9e1ad033.jpg

All welded, and the muffler tab added too. This metal is super thin and a challenge to mig weld. You'll be going good like a welding God, then it blows a huge hole...but that's the game we play.

 

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On to the front end.

This gem was left outside for many years. I know, hard to tell...but you'll have to take my word for it :-)

IMG_20180107_183502.thumb.jpg.bdb4d6af0260713d23e42d35d4a0588a.jpg

I'm sure it'll buff out, no seriously...fuck it, let's give it a go and see?

IMG_20180107_184917.thumb.jpg.57031d83882247d44d1a6ecbe94114df.jpg

Boom!!! Not to bad.

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I might need to build one of these..... looks a heap less lethal than my one is,

bet it will be just as fun to ride.

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