Mario Kart Update (aka DuroPower)

[snowjob]

My son and I built a kart from an old Chinese two-stroke kart for the build off in 2019 "Build Thread". It was lots of fun, but complaining neighbors relegated it to Grandma's house and we have not done much with it in the last year. Since that time he has grown nearly a foot and I notice the frame is bending under his weight and exuberant riding. We've decided to do one last round of updates in order to get it ready to sell as his interests have moved onto water sports. We could just freshen it up with some paint, tighten some bolts and call it good......but what fun is that? Instead it is getting race wheels/tires, billet hubs, new sprocket, aluminum racing seat and subframe connectors! Naturally, there is no hope we will recoup this added cost in the sale, but that's ok. Here are the teaser photos as we have breakdown complete and are getting ready for fabrication. The bulk of the fabrication will be changing the front spindle size, mounting the seat and adding the frame reinforcements. Wish us luck.

 

[snowjob]

Oh, I forgot, we also never got to the custom 4-tip under cart exhaust my son wanted either. Now that we no longer care about appeasing the neighbors, we plan to build it without a muffler. It will greatly simplify the fabrication. We found a good testing spot far away so we should get a few miles in before selling it on.

 

[snowjob]

Better late than never. Our projects always seem to go this way. The frame rails are done.

 

[Budget GoKart]

welcome back snow job havent seen you in forever! sounds like its gonna be a good build i always keep a kart around for days you cant do anything else!

 

[madprofessor]

Now there's something you don't see everyday, no pedals. Pretty neat setup there with the hand controls. If it had an electric starter it'd be a fantastic fun toy for paraplegic or otherwise disabled persons' use.
Just curious, that looks like a stock airbox on the motor, but you say no muffler. Does it have any power mods besides free exhaust?

 

[snowjob]

These are later pics of the hopped-up engine with the beginnings of the custom exhaust. I don't recall everything we did to it, but I do remember it was a Stage 2 kit and we removed the governor. It was an absolute fire breathing monster that could go a lot faster than was safe. We estimated 60mph, but none of us was willing to test it much past 40.

.....correction, it was NR Racing stage 3: Kit, along with billet flywheel and stiffer springs.

 

[madprofessor]

Still being surprised here. Very cool exhaust, forward instead of side or backward, and pointed to the ground. Won't make it any quieter at the tip, but the location and the direction would make the db level around it and in the neighbor's yard as quiet as it can get without any restriction added. Guessing that's no accidental bonus, just smart planning.
Further surprise at that final drive shaft, never saw one coming out of that side of a TC driven pulley before. A bonus on that is the ease of working on the chain, when chain on a tiny sprocket behind the backplate is hard to get to. At least it has been for me, has aggravated me repeatedly.
Question: Looks like a rigid live axle through a tube. There's 2 manual calipers on brake discs to brake it. Considering a manual for my next build, have never tested one before. Are there 2 calipers because a manual isn't strong enough to lock it up? If that's the case, then a manual's not going to be a good choice for me.

 

[snowjob]

The exhaust will go down, under and out the back, splitting to 4-tips. It was going to have a muffler in the space in front of the engine, but that is no longer necessary. I only have the first couple of turns mocked up in the picture.

The cart originally had the rear wheels spinning separately, one freewheel and one driven wheel. So dual brakes helped, I guess. The stopping power they provided was horrible initially. I replaced the calipers, built custom spacers and spent time getting them adjusted perfectly. Now it stops nearly adequately. If I hadn't started by trying to build it cheap using most of the original parts, I would have swapped them for hydraulic units long ago. A lower speed cart with a lighter rider could still use the mechanical calipers without too much issue.

 

[snowjob]

Ignore the mess in the background and you can see the new racing wheels/slicks is gonna make this bad-***! The frame mods are done and a fresh coat of paint is on. We (really he/my son) is mocking everything up and we will need some spacers on the back axle and to modify the spindles with a larger axle. I am really impressed how he is taking initiative on this considering I did most of the build in 2019 and he only advised. Now it is completely reversed.

 

[snowjob]

So we are down to the final fabrication tasks of spindles and exhaust and I now understand that my son wants the Mario Kart Wii exhaust (4 megaphone tips). Any suggestions on how to go about this?

 

[Denny]

Take pieces of 18 gauge or thinner sheet steel and roll them into a cone.

 

[snowjob]

Thanks Denny. I have a brake press, but not a slip roll. If you have a suggestion on an inexpensive bench or vise mount one, especially if it can also do beads, that would be great. I also found a site that sells exhaust components in the smaller diameters we would be looking for. The header is 1-1/4" and I had planned for the individual pipes to be 1". The site is https://www.coneeng.com/. Looks like similar tips would be in the $15 range which wouldn't be too bad. They also sell tubing which will help with the intermediate pipe I need to fab. I sure hope he doesn't want the smaller diameters in the middle of the cones.....that will be a ton more work.

 

[madprofessor]

18 gauge sheet metal is pretty stiff stuff, double-adjust roller would definitely be needed for me if rolling cones myself.
"Back in the day" 4-cylinder street bikes (Honda, Yamaha, etc.) were very common, some with 2/1 exhaust collectors, some with 4/1's.
If you had one of those, turned around backwards, you could add tips and have the 4-tip megaphone. If a chrome collector, then some cheap chrome tips from auto parts vanity aisle would make a shiny package.

 

[madprofessor]

Here's a great fake............
Muffler parts aisle in auto parts store. A section of exhaust pipe extension (I bought 3" chrome on last build). A reducer (I bought 4" long ones) of largest possible size that goes down to extension's size. 4 tips bunched and slid into reducer. That's the total dimensions.
Use VHT flat black header paint to completely coat the inside of the reducer before assembly (did this myself). Also paint the 4 tips, or mask off the parts that will be sticking out, paint the other parts.
Nobody will ever be able to see that on the inside of the reducer the header pipe doesn't connect to anything, just blows into the reducer.
You can see how that VHT hides the inside on my youtube video about the minibike being (type this in the search bar) "quiet but unrestricted".

 

[snowjob]

He likes the idea of 4 simple cones. No reducing band in the middle, no baffle, no cap, just pure megaphone. Previously we were going for quiet, but now it seems we are shooting for as loud as possible. He claims it will make it easier to sell. I tasked him with mocking it up with cardboard cones so we can work backwards and route the exhaust. Hopefully he will have it mocked up today and we can place the order this weekend.

 

[Denny]

Make your cones out of poster board to use as a template. Transfer your template to sheetmetal and cut out. Work your cut out into a cone shape and weld together. Wear leather work gloves while doing this. It will be easier to do than it sounds but will be some work. Put a legnth of pipe in a vice to work the sheet metal into a cone shape.

 

[snowjob]

Thanks again Denny. I had watched some Covell fabrication videos in the past and saw a similar technique. Since I don't have enough sheet stock lying around for all 4 cones and they are readily available from Cone Engineering, along with needing some extra tubing and bends, I am going to place the order on Monday when they open.

Separately, he is nearly done with assembly. We had a scare when the cart fell off the sawhorses (it is painfully rear heavy), but no real damage. He hopes to button it up and do a test run with the stock muffler today. I am not sure that is wise in our neighborhood, but at least running circles in the yard around our own house is completely legal. We'll see how it goes....and I'll get some more pics.

 

[snowjob]

Seat attached.

 

[madprofessor]

That is one beautiful piece of (aluminum?) welding for the butt. Lots of seam welding in that thing.
Would your knees be naturally bent up far enough to keep that front lip from bearing on the backs of the thighs? Skinny people like me really feel that kind of thing.
Regardless, it's perfect for holding in the flat cushion I'd have sitting in there for my bony backside.

 

[snowjob]

Speedway Aluminum Bomber Seat

Seat

We'll see if the front lip poses any issue. Without foot controls, you can pretty much straighten or bend your legs while driving as needed.