Motorcycle Powered Kart Question

If installing a motorcycle engine ('79 CB650 to be exact) on an offroad kart with a swing arm rear suspension, do you think harm would come to the engine or would it not run well by being mounted on the swing arm? IOW, the engine would move with the arm and the tires, not be suspended. It would be mounted far forward on the swing arm near the pivot, but it would still see a lot more movement and shock loading than it did on the motorcycle.

It would probably work for a little while, until it would shake itself apart. But it would increase the unsprung weight of that suspension so much, that it would render it useless. Might as well go solid at the rear and try to get some balloon tires.

Any pictures of the kart in question?

In reply to fanfoy:

The engine that came on it from the factory was installed on the swing arm also. It's been fine for many years, and the suspension works fine also. The bike engine is heavier than the scooter engine that came in it, but not by much.

Take a look at "slingshots" http://www.speedwayentertainment.com/ Slingshot By Tobias: They use a 20hp twin B&S motor on the swing arm, they work. The problem you'll run in to with your old Honda motor will be fuel foaming the B&S uses a no float bowl carb and a diaphragm fuel pump. you may have to extend the bowl area and use foam inside. This was common in late 70-80 dirt bikes.

In reply to 44Dwarf:

Slingshots? I got the page, but where on the page are you referring me to?
The carbs were what I was most concerned about. Is that fix you mention what was actually used on dirt bikes to solve the problem? IOW, is it a known cure or just an idea?
I can mount the engine to the frame rigidly, but it obviously complicates getting the power to the wheels, which will be suspended. I'm wondering if chain drive to the rear axle with a tensioner on the slack side would work. The other down side to doing it this way is that it would necessarily lengthen the wheelbase.

If you mount the engine to the frame and keep the output shaft as close as possible to the rear suspension pivot, it would minimize problems with the chain. Then you may be able to get away with just a guide, rather than a tensioner.

I suspect that the biggest problem with this thing will be having a go kart powered by a 650cc motorcycle engine...

Woody wrote: If you mount the engine to the frame and keep the output shaft as close as possible to the rear suspension pivot, it would minimize problems with the chain. Then you may be able to get away with just a guide, rather than a tensioner. I suspect that the biggest problem with this thing will be having a go kart powered by a 650cc motorcycle engine...

Yeah, I know what you are saying, but there's no way for me to get the engine output shaft on the same arc as the rear axle, so there will be some change in distance between the output shaft and the rear axle as it articulates. I was originally going to do an IRS, but we've been contemplating this for a few years and I want to get it done, so simple is the plan for now.
Right now the kart will fit in the back of my pickup. I don't really want to lengthen the wheelbase for that reason and also because it will make it hard to run it on some ATV trails if it gets too long. Plus, I have to make an entirely new swing arm, so mounting the engine to it is the easiest way to get the job done. I just don't want to have problems with the engine because of it. It would take quite a beating, although the Honda scooter clone engine that's on it now is mounted that way.
I have no idea what you mean about the problem with the engine on the kart.

bravenrace wrote: In reply to fanfoy: The engine that came on it from the factory was installed on the swing arm also. It's been fine for many years, and the suspension works fine also. The bike engine is heavier than the scooter engine that came in it, but not by much.

I know a few karts use that design, but it's a poor design to begin with, so problems are exaggerated. You say, "The bike engine is heavier than the scooter engine that came in it, but not by much.", but how much heavier is it? Also, I'm pretty sure the center of gravity of the engine would move away from the pivot point because the bike engine is externally larger. So you end up with more mass further away from the pivot point...not good.

But the only ways to know is to run the calculations, or try it.

You can always decide to try it and if the rear suspension is overwhelmed by the extra weight, remove the problem from the equation and go suspension-less is the rear.

bravenrace wrote: In reply to 44Dwarf: Slingshots? I got the page, but where on the page are you referring me to? The carbs were what I was most concerned about. Is that fix you mention what was actually used on dirt bikes to solve the problem? IOW, is it a known cure or just an idea? I can mount the engine to the frame rigidly, but it obviously complicates getting the power to the wheels, which will be suspended. I'm wondering if chain drive to the rear axle with a tensioner on the slack side would work. The other down side to doing it this way is that it would necessarily lengthen the wheelbase.

the picture is so small and grainy you realy can't see anything on there site but poke around you might find someone with good picture on the web forums.

Yes the carb fix works but doubt you find ones that bolt to your carbs. you'll have to copy the design. http://www.oemcycle.com/Item/product/900012331/?utm_source=NXT&utm_medium=cpc&utm_term=900012331&utm_campaign=NXT

In reply to fanfoy:

Its getting a new suspension that is appropriate for the weight. This is a kart just for fun, not competition. I don't think the weight is an issue for us, as we've already accounted for it.

In reply to 44Dwarf:

So it's basically a larger bowl with foam in it? I assume the whole purpose is to counter-act sloshing from the shock loading?

In reply to bravenrace: yes larger volume and round edges to curl any slosh back toward the center. foam will help too some have plastic rings in the center with slots or multi holes to allow a well of fuel around the main jet area.

Thanks for the help!