Hot Rod HS40-Powered Full Suspension Cat 250

#22
Needed a chain tensioner because that modified hub isn't perfect and the way in which I mounted the swing arm and fabricated the JS plates just made the chain routing too close to the swing arm. I didn't like any of the commercial mini bike offerings, with a silly little spring and a skate board wheel. It might be fine for some applications, but not mine with this much weight, and a tire shredding four horsepower Tecumseh with a cam and a carb and a high rise intake manifold and headers.

So knowing this is not brain surgery, or curing cancer, I spent about two weeks thinking about it and writing stuff down, and looking at motorcycle tensioners out there for $100 and made this thing. If you want to know more about it, or lessons learned or parts used, PM me, although (see brain surgery comment) I will have forgotten already.

Parts I made and used. Torsion spring is 19 LBS.


Assembled. Can you find the Tecumseh alignment dowel?


Upside Down. Honda XR Brake Anchor Arm shown.


Shitty Welds, but they hold.


Right Side Up


From the Side
 
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#23
Looks great going to really enjoy this build! What top speed are you gearing for? Should get some good power out of that motor setup


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#24
Wow, what a "roll your own" build Dave. Wish I had the fab & welding skills you have. Looking to be a very cool build. Will be following thread to see the end results.
 
#25
Looks great going to really enjoy this build! What top speed are you gearing for? Should get some good power out of that motor setup
Bryan, good to see you back posting again. I don't know how fast it will go. Gearing is dependent on which sprocket lifts the chain high enough to clear the swingarm. I lost track of which sprockets I ended up with. I think I am around 5.8:1. Also surprisingly heavy with that swing arm.

Wow, what a "roll your own" build Dave. Wish I had the fab & welding skills you have. Looking to be a very cool build. Will be following thread to see the end results.
Thanks, I'm a hobbiest with a few tools, and nothing but time with which to come up with bad ideas, and grind welds. This entire project has not gone anywhere near where I thought it was going at the outset.
 
#29
I'm loving the chain tensioner design Dave ! :hack::hammer: Home made the way you want it , should work great I think . As for your :weld: there looking good to ….. and I know its not the :grind: that's doing it ...lol
 
#31
mrpat has once again came to my rescue by reaching out with an offer to bend me up some decent bars. :thumbsup:

I sent him this:


And he bent some bars to spec, long enough to reach the moon, and programed a plasma cutter and made a much thicker version of the bar base plate. Exactly what I wanted for this bike! THANK YOU PAT!



 
#32
That's awesome. Great job Mr. Pat.:thumbsup: It is so nice to see some people with special skills. I'm going to send him some Taco forks to fix when I get my butt in gear.
 
#33
Looks great going to really enjoy this build! What top speed are you gearing for? Should get some good power out of that motor setup
Follow up to this question as I'm looking at the clutch. I ended up with a beat up Max Torq SS (Six Shoe) clutch that I'm refurbishing. Bronze bushing on order. I will stick with the 12t clutch sprocket for now, but may go a tooth or two smaller after I test everything.

For now, it's 12-18-20-72 teeth. Those numbers are pretty much what it takes for the chain to clear stuff. This gives me a ratio of 5.4:1 which is fairly tall. I'll see if it'll pull the weight like that. Theoretical top speed for that engine at my self imposed redline of 6K is 41 MPH. But I've never built a mini bike for theoretical top speeds. Besides, I wouldn't want to go that fast on anything I welded, wearing nothing but flip flops and shorts.
 
#34
Follow up to this question as I'm looking at the clutch. I ended up with a beat up Max Torq SS (Six Shoe) clutch that I'm refurbishing. Bronze bushing on order. I will stick with the 12t clutch sprocket for now, but may go a tooth or two smaller after I test everything.

For now, it's 12-18-20-72 teeth. Those numbers are pretty much what it takes for the chain to clear stuff. This gives me a ratio of 5.4:1 which is fairly tall. I'll see if it'll pull the weight like that. Theoretical top speed for that engine at my self imposed redline of 6K is 41 MPH. But I've never built a mini bike for theoretical top speeds. Besides, I wouldn't want to go that fast on anything I welded, wearing nothing but flip flops and shorts.
:laugh::scooter:
 
#35
Follow up to this question as I'm looking at the clutch. I ended up with a beat up Max Torq SS (Six Shoe) clutch that I'm refurbishing. Bronze bushing on order. I will stick with the 12t clutch sprocket for now, but may go a tooth or two smaller after I test everything.

For now, it's 12-18-20-72 teeth. Those numbers are pretty much what it takes for the chain to clear stuff. This gives me a ratio of 5.4:1 which is fairly tall. I'll see if it'll pull the weight like that. Theoretical top speed for that engine at my self imposed redline of 6K is 41 MPH. But I've never built a mini bike for theoretical top speeds. Besides, I wouldn't want to go that fast on anything I welded, wearing nothing but flip flops and shorts.
That should work well I have a bonanza that’s geared about the same with a ohh 55. Mine pulls my butt around and can lift the front tire. Tops out around 35 but it’s governed to about 4000
 
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delray

Well-Known Member
#37



whats going on here dave? that oil looks like it's been run.:rolleyes:




I think I can put you real close to your jetting and pilot . the only thing that might change or dictate your jetting from my numbers would be porting/bowls,timing,intake,exhaust. but either way you will need a 125 main jet start(that may go + or - little) and start with 17.5 pilot.

purchase a outerwear cover for that foam air cleaner. they work good. keep the dirt and dust off the foam. it's a lot easyer to clean off too...….:thumbsup:
photo example:
 
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delray

Well-Known Member
#38
nice dave,that bike will make a good test bed for the hs40

what was the plain for transmission. looks like your going with a clutch setup?
looks like it will be a clutch? you will need a 3100 stall spring,maybe more. that 245 cam doesn't come on until your way above 3000 rpm's.....:thumbsup:
 
#39
I painted it black. I've had this 1974 HS shroud for several years, never could sell it to anyone which is all good, since I was able to use it on this engine. Trying to impress everyone with my painting skills, but I see errors and dust. This is a black enamel in acrylic. Bulging pull start handle is due to massive compression-beating yacht braid rope crammed in there. :laugh:



Here is the pump and fittings I am using. I did some tests on moving a stock tank up and down within the frame, to see if I could get decent gravity flow to the Mikuni. It just wasn't worth taking the chance on. I was going to take a photo of my nice welding of that bung in the OND-supplied intake manifold. Unfortunately my camera does not work when taking photos of extremely ugly welding. I did get it to stop air leaks though, all the way around. It's tight.



One of the old engines I got came with a very used Max Torque six shoe clutch. That is the "SS" version. I took it apart, and using the video Jim Donovan (Max Torque) does, disassembled it. It sat a bit loose, and the bronze bushing is worn slightly. While it's apart, might as well change that, so here is a bushing driver I made specifically for inserting a bushing into a 3/4 PTO sized Max Torque. It is made out of old Stellar and Taco 22 tubing that I've replaced over the years, and retained as scrap. It comes in handy. Welded an old axle bolt head to the thing for hammer-smackability.



This is how it looks with the bushing locked and loaded and ready to fire into the sprocket bore.

 

delray

Well-Known Member
#40
hey dave , just in case you have a problem with that pump? I have purchase a walbro pump in the pass for a china/mikuni carb and work good. some of the aftermarket fuel pumps are to much for the carbs. I believe it's the needle and set can not handle this.
either way here is the part number for the carb wms-fps. I purchase it through turk bros inc. sure you can find it anywhere.:thumbsup:
 
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