My Hari Kari Cycle

[Lon]

Started with an Auto Bike that my dad was going to yard sale. I already had a perfectly good bicycle what do I need 2 for? I also have a 2HP Briggs & Stratton engine, source unknown.

Put the bike up on my table, leveled side to side and front to back. This isnt rocket surgery so I held the engine up the frame, and eye balled where the tube needed to be cut. At the time I thought I needed a jack shaft to go from the left to the right side.

Another round of wrenching and I have a motor plate. The bottom plate is a left over from putting a Chevy V8 into a 53 Ford. It was too low, the tank hit the tire. I used a piece of square tube and another plate to raise the engine. So far everything is tacked together. Somehow the plate isnt quite square.

My plan is to use a left side sprocket, the auto bike has a plate on that side I might be able use. I also want to use a twist throttle, and bend the pedal arms out so they clear the engine.

On to pics. This will a sporadic build, but I promise to take lot's of pics.

 

[Lon]

Short vid of it running. It's more shaky than I thought, I may try to rubber mount the engine.

http://www.youtube.com/watch?v=X9givzU_lBI

 

[wheelbender6]

Looks good. With the seat tube removed, you may be need to make the engine a stressed member of the frame. For example, create a bracket that allows the engine to help support the seat tube and rider weight.

 

[Lon]

I'm thinking of a tube in front of the engine, and a couple on either side of the back tire behind the engine. Also going to plate and reinforce the area where the down tube used to be, under the seat. The tubes behind the engine are going to be hard to work around with a chain on both sides.

 

[maniac57]

You definitely need to provide structural support for the missing seat tubing.
It WILL NOT last like it is now, I guarantee the frame will break at the head tube and bottom bracket in short order with that motor.
Either make a new tube that clears the motor, or make a plate to bolt the engine as a stressed member. You could get seriously messed up if it fails at any speed. Breakage like that makes for truly ugly wrecks!

 

[Lon]

After playing with the chain routing, and engine placement, I may not use this engine. Everything is in the air, without a left side sprocket and clutch on the engine. I plan on using a go cart or mini bike type centrifugal clutch. I'm going to get the engine my dad rescued off of a pressure washer. It's a generic OHV 5 HP, I think the shape will fit this frame a little better. There will be reinforcement of the missing down tube.

 

[Lon]

Shifted the engine to the right. It is right side heavy, but not bad. Wont know until I ride it.

Offsetting solved a lot of problems. I can access the choke, room for an air filter, and the down tube will be easier to route.

 

[wheelbender6]

If you remove the fuel tank and mount it elsewhere, you may be able to rig a bicycle fork to connect the 2 ends of the seat tube and still clear the carb,

 

[Lon]

I'm researching different carbs for this engine. I know on JR dragsters they use a carb and manifold, looking for something like that but cheap.

 

[maniac57]

I'm researching different carbs for this engine. I know on JR dragsters they use a carb and manifold, looking for something like that but cheap.

There is no such animal as a "cheap" jr dragster part.
I'd suggest making your own if you have access to a welder and a drill, it is fairly easy to make flanges to weld on a chunk of tubing.

 

[Lon]

Yeah a piece of exhaust tube or something like and a carb would work. I know nothing about these little engines as far as parts and what I can rob parts off of. Making these small flanges wouldnt be a problem, and I've got a welder.

 

[MEASURE TWICE]

Briggs Engines are what I grew up with.

The slant cylinder engines do fit better I have seen on many bike that are DIY non-kit, but either way you can do it.

I opted on my bike to use just a slight tilt backward to the engine mount plate to get my 3hp Briggs to barely fit. I also used a 90 degree elbow manifold to get a different gravity feed carb mounted and avoid hitting the tube near it. The gas tank I mounted up on top bar.

Anyway I am intrigued about that Auto Bike or whatever that infomercial a decade or score ago was trying to brain wash me. Your going to have what I think equates to a not quite a continuously variable transmission like a torque converter, but the derailleur is automatic shifting. Question, a jack shaft you will be adding can take the power from the engine and drive through the derailleur and you can also pedal also and they don't interfere with one another?

MT

http://motorbicycling.com/showthread.php?t=29678&page=13 Oh don't look for the pedal crank it is gone and only foot pegs, it is for Trail Riding Off Road Only Permit

 

[Lon]

No I cant have both on the same side, somewhere the chains would hit. I'm going to have the engine chain on the left and pedal on the right.


Dad took the bait , and bought two. One for him and one for mom. I still have the ladies bike in rideable condition. They both work , because they were never ridden. Aside from a little rust they are both new bikes.

I'm worried about over carburation. I've looked at Honda and Robin gravity feed carbs. The engine doesnt know what is feeding it, but I dont want too much fuel or air.

 

[MEASURE TWICE]

On the compatibility issue for changing to a different carb, what I did was call up the manufacturer and get answers directly from them. Briggs tech spent some time helping even though the engine was from the 70's as I was buying a carb made today by them.

Only thing is I could have spent maybe $70 on a carb that had a mixture screw for at least idle, but the $32 carb I finally figured what was making it slow to go back to idle.

It strangely was actually one of the 3 belts that was slipping. My bike when it quickly comes to a stop tries to stop the engine through the engaged clutch, but before the engine stalls the clutch frees up. That is normal. When one belt slipped the mass of one of the two jack shafts and a large pulley for super low ratio kept the bell spinning fast for a while before the clutch would release. It was quite like the toy cars you run with you hand over the ground and get a weight spinning though lots of gear ratio, then you set it down an it runs for a while. I tightened the belt more and used belt dressing. A more bendable cogged belt over this small 2 inch pulley or switching to gear an chain just for this one belt may help further when going up steep hills.

MT

 

[Lon]

Fixed the frame. Remounted engine. For the frame I had some round stock laying around, and used that. I used another slightly bigger piece of round tube, split it and plated the joint. That piece runs up from the bottom about 10". Getting the engine to fit was a slight challenge. I will have to get flush oil drain plugs, and make a new engine mount plate. In these pics the engine is clamped in place with welding clamps.

 

[curtisfox]

Maybe get a snowblower type carb off a tecumesh engine. They have the low&high speed jet and new for about $60 if you can't find a used. They work great and kits are cheep made by wallbero i think.
Got the right size big washers for flanges thick and heavy already have the right size hole.Just gring them and drill bolt holes............Curt

 

[maniac57]

Briggs flatheads respond very well to carb swaps using a homemade manifold to fit a honda xr50 or xr75 carb. These are easy and cheap to to find and really wake the briggs up with much better throttle response and metering. I rarely had to even drop the bowl. Bolt-on and go!

 

[Lon]

Are those Mikuni slide carbs? I've got several suggestions of where and what kind of carb to use. I need to find some handle bars to cut up for an intake.Right now, I want to concentrate on what I can do for free. My other project is an 84 GMC truck. I need a few more parts to finish it, when it's driveable, I'll start buying parts for the bike project.

 

[maniac57]

Mikuni I think. (it's been awhile!) You can find these carbs used on many japanese bikes of various sizes and brands available at decent prices. Figure anything over 21mm is too big and you should really like how it makes the flattie feel. Stock small engine carbs are designed to run at a steady rpm and don't meter very well hooked to a twist grip. Throttle response is never going to be what it could until you swap to a cycle style carb which also makes it very easy to tune for your particular engine.
I find motorcycle or ATV salvage yards are the easiest way to get one for less than retail, but they are all over fleabay too.

 

[Lon]

Something like this?


http://www.discountstarterandaltern...?cagpspn=pla&gclid=CLz_gZvCmbgCFedZ7AodqD4AqA


Honestly I thought they'd be a lot more expensive. This is the first carb I came across on a Google search.