My MiniMax project

So...the Vmax spoiled me into requiring everything be fast. Among my other toys are a 1988 Suzuki LT230 QuadRunner, a 2007 Baja WR65 minibike, and a 2005 Yamaha RX-Warrior snowmobile. The sled is already stupid fast(essentially a R1 motor with a reduction gear in the case to make it clutchable) so that was good. I'm lucky in the little thumper 230 quad starts, and it's by any definition a "beater" quad.

So the minibike was up for the "Max" treatment. I picked it up totally stock off craigslist about a year ago for $250, virtually new, totally stock. Still had the 12mph governor. Originally it had a Chinese clone of a Honda GX200 motor...they are so close that many parts for a Honda will fit on it's Chinese counterpart. It ran great, despite the abuse it has taken(hydrolocked dozens of times from WOT runs into way-too-deep puddles, it's been downed/crashed dozens of times, ect). Always started on the first pull and ran like a top. It was a 196cc motor with a claimed 6.5hp, going through a total of a 10:1 gear reduction between the crank and rear wheel, plain ole centrifugal clutch. With the governor adjusted(not totally bypassed), I got about 30mph out of it reliably. However, some bigger hills or soggy/sandy terrain bogged it down and it just didn't quite have the nuts to power through it....you'd need a good running start, and sometimes even that wasn't enough. I started browsing craigslist for old engines from snowblowers, generators, ect.

Then the deal of the century popped up. A brand new Briggs and Stratton 1450 INTEK(super heavy duty 11hp) series with electric start and regulated DC output came up. $120. That's an $800 motor new. The ad specified that the drastic price cut was due to "some shipping damage". I called, and he said it had been dropped in shipping and had a crack in the oil pan, otherwise it was still NIB. I went to look, it was easily fixed, so I bought it. A little JB Weld over the crack and good to go, doesn't leak a drop. Of couse, it runs great, it had never even had gas in it before.

So I went to work tearing apart the bike. Out went the old motor, the drive system, and the back wheel. The new motor physically fit into the frame, but just barely(this motor is 305cc, the old was 196). Had to extend the engine mounting plate forward (a piece of 1" angle iron worked great) a bit since the front mounting holes hung over the edge between the downtubes.

Once the new motor was mounted in the frame, I had to go about making the jackshaft plate fit(it drove from a 10T clutch to a 20T to 10T jackshaft, to a 50T rear sprocket, for a total 10:1. The jackshaft was on a rectangular plate that bolted to the motor. Oops, the yellow oil fill cap was in the way of the plate mounting properly. Had to lose the cap that protruded from the casing about an inch, and just use some of that cookie-dough epoxy crap to seal it(can still add oil in the long dipstick tube). Got the plate mounted up, and had to mount the new $150 1" bore clutch inboard to make it line up.
Except the motor sat a bit farther left than it used to(even though it was slid over as far as the frame would allow), so the rear sprocket no longer lined up with the output of the jackshaft. Popped 3 washers between the sprocket spokes and the actual sprocket to move it over about 1/2"....perfect. Some half-links extended the chain a bit to fit.

The motor wouldn't fit in the frame with the gas tank and muffler where they were, so now I had to find somewhere for the gas tank. More angle iron made a little "luggage rack" for it, bolted to the crossbar that supports the seat. I garbage-picked a muffler off an old snowblower which happened to work out perfectly, orienting the exhaust more out, rather than up.

A midget battery(I believe it was for a 110cc kids quad) is nestled under the engine cylinder, powering the electric start and lights.

It's currently now at about a 7:1 total reduction, since the only clutch I could find came only in a 14T variety. Adjusting the governor spring to it's fastest setting, I get about 36mph out of it, and it gets there fast. And on one wheel if you want it to---it wheelies great. And it's only brake is a drum on the back, but it still works good.....it'll lock the wheel up on pavement no problem.

So far it's outrun a 110cc pit bike with transmission/clutch, a 90cc 2 stroke kids quad(hopped up for performance), and my 230 quad(handlily).

Does pretty good on gas also...from what I've measured so far it's about 55mpg(there's a bicycle speedometer on it, JB welded a magnet to the rim).





It's not just a minibike any more....it's the Vmax of minibikes! You can see the battery peeking out there in the last one. Of course I'm way too cheap to buy a battery cable, so I made one out of two 10ga wires. Cranks and starts great. One revolution every time.

Another note...in the second picture the rear wheel chain adjuster used to be an eyebolt. The axle bolt came loose, I hit the gas, and the torque pulled the eyebolt out a ways. 8^O It was 3/8" stainless.

In case you're wondering, those sweet custom pegs are from a steel canoe paddle. The original pegs snapped off when I landed a jump while standing on the pegs. These still break it it's downed at high speed, but there's one screw that holds them in place over the old nub, so if they snap off I just cut a new piece of tubing and slip it on.

That looks like fun!!!!!

I have an engine and drive out of a go-kart.....

Anybody got a mini-bike frame?????

That'll hold 260 pounds?????:rofl_200:

minimalist frame, small diameter front fork ... yeah not far from the max :rofl_200:
makes me thinking when i do kart even not crazy fast it's a lot of fun.

I dunno, I weigh about 180 and this frame has been more than durable, even frequently towing a trailer weighing about 200 pounds(with rider). It's been jumped, stuffed, and beat on mercilessly all summer and the frame hasn't cracked or broken anywhere. I seem to remember seeing it was rated for up to 250lbs or something so I bet you'd be fine. They sell these Baja minibikes at some Tractor Supply stores, I think they go for $500 brand new. Within 5 minutes you can make it go from 12mph to 30+ mph. Stock they have good power for just cruising around, but like I said in loose terrain or steep hills they don't quite cut it.

It would look awesome if you hung some scoops off a real max on it!!:clapping:

That is hilarious. Nice work. I followed along up until the clutch bit. That's beyond me. Very cool Frankenstein bike though.

Looks good!

I have this one... It's a 50cc bored out to 87 with a flat piston. Also has a MUCH larger intake and carb setup. I've seen 55 with it. I had to gear it way up because it was STUPID for doing wheelies. It was going to kill me. The TB pipe sounds great. Like a mini Harley. lol

Cheers

Was that a custom job, or did you buy that somewhere? Looks pretty sweet.

I didn't know TB make pipes for 50cc motors! Mine has the snowblower special edition exhaust!:rofl_200:

Honestly I expected mine to wheelie better than it does---as in like touch the gas and up it goes. It wheelies alright, but requires full power and a good lean back. Since it's a centrifugal clutch, it works better if you're going like 10mph, then dump the gas and lean back since the clutch is already hooked up.

I'd like to put a torque converter on it for better speed, but I already spent way more on this thing than I expected--around $300 before it was all said and done.

The Mini Maxes look good, fellows!

But now if your looking a good power boost, I think this little item should do you just fine.


http://www.chinese-parts-canada.com/turbocharger_fuel_injection.html

Now that is a cool looking little turbo!

Also, some nice fuel injection stuff too.

Mike

A turbo minibike....now that would be just about the sweetest thing ever.

Torque converters are pretty hard to find it would seem...just about the only place is to order them factory direct from Comet, and pay their outrageous shipping fees($40 for super snail mail, like $70 for UPS Ground). Otherwise the kit with drive/driven clutches is like $220.

The nice thing about those is it starts at a 2.7:1 ratio, and ends up at .9:1 ratio, making the final ratio for me variable between 13.5:1 and 4.5:1. I'd be doing like 55 and popping wheelies like nothing!

Its been around as long as the VMax. And to ride one is to love one. Fast? Nope. But the bike is timeless like the VMax. The TW200 is the VMax's true little sister....

Looks like a fun little bike. Never really got into dirt bikes/enduro. I've always had street bikes, well, for the street, and a quad for off-road use. My quad is an old Suzuki 230 auto-clutch- it's not very fast(tops out at about 45 or so) but it will go up any hill in first, and spin the big 12" wide spider-trak rear tires in any slop in second. Gets the job done, and I paid $200 for it.

Anyway, I found out that Comet officially went out of business a couple weeks ago, and they had stopped shipping new products well over a month ago(explaining the big supply shortage).

Strange, because tons of things use Comet drives. Nearly every gas-powered golf cart, those John Deere Gators, older/entry level snowmobiles, and electric clutches for equipment(riding lawn mowers. And nobody else makes a similar product...I've more than looked around.

Supposedly a line of Chinese-made clones are on their way, and get this...will be priced at $70, and the original American-made Comet's sold for around $250.

Kinda sad that another American company bit the dust. Tecumseh engines also just recently went out of business, though the general consensus was that they were pretty much the worst small engine manufacturer.

Thats the bike I did my motorcycle test on here in Utah back in the day. Perfect for the tight little obstacle course I had to go through. There was a guy with a big ass sport bike that put his foot down 3 times in the first 30 seconds and got disqualified and had to retest a week later.:biglaugh:

DenniSM said:

Its been around as long as the VMax. And to ride one is to love one. Fast? Nope. But the bike is timeless like the VMax. The TW200 is the VMax's true little sister....

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So it's update time....I finally managed to track down a Comet "Torq-a-Verter" through lots of ebay searching and classifieds hunting. Since Comet went out of business a couple months ago, not surprisingly their products are getting increasingly hard to find. This works just like the clutches on a snowmobile...a primary that closes with speed, forcing the belt outward, and a secondary that opens with speed, letting the belt fall in. I found the mounting plate/jackshaft/secondary as one assembly on ebay, never used. It was missing the primary and belt. The belts are still available(and now a "belts 'n hoses" company is making a reproduction so that's good), so I just bought one off an ebay store.

The primary was tough. They were made in 3/4" bore and 1" bore versions, however the 1" bore was never very popular, since virtually every go-kart/minibike uses a chinese 6.5, and they have 3/4" shafts. Nothing on ebay for several weeks. I find a forum for minibike restoration, and decide to check their "buy/sell" forum. BINGO! Right there at the top of the page was a "F/S- Comet 1" driver". Signed up so I could send the guy a PM and that went smooth as could be. Said he had been trying to sell it for months but nobody wanted a 1" version. We finally agreed on $90(retailed for $130 new) shipped.

The complete kit originally ran for about $230. I ended up winning the ebay auction for the secondary/mounting plate for $150, including shipping. The primary driver cost $90, and a belt was $21 shipped. So I rounded everything up for only slightly more than what it originally cost...not bad considering the tremendous demand and minimal supply. The complete TAV kits are going for well over $300 on ebay now. Price gouging at it's finest.

So...goodbye fixed ratio centrifugal clutch. That primary reduction between the clutch and jackshaft is going bye-bye, and this torq-a-verter is going in it's place. Still a chain final drive at a 5:1 ratio. However, the Comet drive can vary from a 2.7:1 low range to a .9:1 overdrive at top end. Meaning my total ratio can vary from about 13.5:1 all the way down to 4.5:1.

My top speed should be a tad over 62mph now with the clutches in overdrive. w00t! I might need to investigate rigging up a front brake...currently there's a 4" diameter drum in the back. Not quite adequate for highway speeds.

And with a 13.5:1 initial ratio, this thing will be a wheelie ANIMAL. It wheelies pretty good now with a 7.1:1 ratio at 11hp, and climbs significantly better than the 6.5hp engine did with a 10:1 ratio. So 11hp with a 13.5:1 ratio....I can't wait to see how it does.

I really am almost giddy with excitement waiting for the final part to arrive(the ebay auction for the secondary/plate just ended Friday). I'll post pics and probably a video once I get it all wrapped up.

Well, I got all the parts to the Torq-A-Verter and got it installed. I had to grind a chunk of the cooling fins off the head so the bearing housing would fit, but that was no big deal, and the fins stick a good 3 inches out from the actual cylinder so there's no danger of accidentally going into the actual wall. Otherwise, it was a very straightforward install. Bolted right up to the motor, hooked up the chain and done.

After a bit of tinkering with exhaust clearance(had to cut a small section of the muffler off for secondary clearance), and the secondary's spring tension, this thing HAULS. Will easily wheelie over backward from a standstill if you just dump the gas. Will wheeie "on demand" up to about 25mph. And the top speed....62mph on a GPS unit. This belt drive totally exceeded my expectations...I never thought you could get this performance from only 11hp. These Comet drives are worth their weight in gold. And from what I've heard, they last absolutely forever.

Finally...torque is not a problem on this bike anymore. No more running starts, or "pedaling" at the top of hills to keep it going. It will go up absolutely any hill. It will spin the back wheel, or flip the bike over backwards before it stops. Found a nice large sandy hill that this bike never made it up before with the stock motor and clutch....it would bog down not even half way up. Now I just rolled into it, leaned forward, and nailed the gas. The back wheel instantly broke loose, it threw a gigantic rooster tail, and it just boogied all the way up the hill. I actually had to let off WOT because it was accelerating up the hill and it's a very bad idea to catch air off the top of this hill(trees).

So far it's been reliable, I did about 50 miles with it on streets and didn't have any issues at all. At WOT(say 55mph average), it's doing about 70 miles to the gallon. Can't beat that, espically with it's off road performance.

Once I'm home again for x-max I'll make a couple videos of it.

Cool project! Got one of those converters on my mini.

Check this out... Mini Turbo I gotta have one sooner or later.

That's a pretty sweet mini-chopper. That looks like the Mag 44 series converter...bit heavier duty than the 30 series I'm running.

What motor is in there? Looks about the size of a 13hp clone? Bet that boogies right along with one of those torque converters.

Where's that tank from, or did you make it? Looks really sharp.

RaWarrior said:

That's a pretty sweet mini-chopper. That looks like the Mag 44 series converter...bit heavier duty than the 30 series I'm running.

What motor is in there? Looks about the size of a 13hp clone? Bet that boogies right along with one of those torque converters.

Where's that tank from, or did you make it? Looks really sharp.

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Thank You! That's a pretty cool ride your working on! Right now it's only an 8HP Briggs. It scoots right along with that and does wicked wheelies. The reason I went with the 44 is I plan to replace the engine with a Vanguard V Briggs. Probably 16 - 20 HP... waiting for a deal on one to pop up... their very expensive new. The frames made out of 4130 tubing so it's very light. The tank is just a standard Sportster tank. The front wheel is from a sand dragster.

Kewl. I've heard that the 90's Sportster tanks will fit on the frame of my Baja, but just barely and you have to modify the seat mount a bit. I found one from a parts bike on Craigslist, but the guy still wanted like $100 for it. I've already spent way too much money on this conversion....between the engine, torque converter, and miscellaneous parts/hardware I'm in probably $500. Considering I only paid $250 for the stock bike initially....

Thinking about doing an "8 ball" bobber-look paint job. Rattle-can of course, nothing fancy but just to dress it up a bit. Remove the fenders, and spray those and the faux-tank with a white, lay down two stripes of tape and re-spray with a flat black. Remove the tape, and BAM! instant racing stripes.

Going to cut down that long-ass dipstick tube, and move the control panel to the handlebars to clear the space for the faux tank again. I got a better speedometer for it(rated for up to 100mph rather than 40), a Tiny-Tach for the motor(grab one of these now if you want one---they went out of business but there's still a bunch floating around on ebay). They're nice for small engines since it detects spark just by wrapping a sensor wire around the motor's plug wire. They work great and are accurate to 10 RPM.
Grabbed one of those dipstick-style gas gauges also for the tank. It only holds about 3 quarts of gas, but will go about 50-55 miles.

As for the Vanguard, I've heard that it's not that hard to convert a vertical shaft v-twin to a horizontal, and vertical's are much more common. You can pick up an old riding mower for a couple hundred with a v-twin. Just have to swap the rods to ones that have the "dippers" and make a little elbow so the carb sits straight again. Google turned up a few discussions about it.

Hell, for the price of one of those Vanguard v-twins new you could buy a brand new V-star 250 and steal it's motor! I thought about pulling the motor out of my beat-to-shit Zooky 230 quad and putting that in the minibike, but the mounting looked to be kinda difficult and the motor is getting tired anyway.