Mountain Weedy

Hi all this is my first build and first post. So here we go. It all started out when I found this old engine from a 1974 weed wacker. The engine is a Tecumseh 85cc 3 hp. It also has a scary looking weed zombie on it which is pretty cool.

Sorry the image is upside down.

So I got the bike all built up with a back rack, chain tensioner and hand made clam shell adapter.






I have a 42 tooth gear on the bottom and an 11 tooth gear on the engine. I was so happy and ready to go. But it was not meant to be. I fired it up and i wont move, the engine runs good with the chain disconnected but as soon as a load is put on it it just does not move. If i lift the tire up it will spin it really fast and i lost a chain that way and destroyed it.

In the early stages of this build I was an idiot and started the engine with the bell housing off the clutch pads. You can imagine what happed clutch pads and springs went flying. I found the pads but the springs were shot. I went to ACE hardware and purchased some music wire, which is spring steel. I bent my own springs and put everything back together. The output shaft does move a little more at idle that it did before the mishap but the bike will still not move.

I am at a loss. Is it a clutch problem or is the engine really that week? Should I ditch the clutch and just direct drive it, i would have to kill the engine at stop lights then. Or should I get a different engine. I am confused, please help anyone.

 

[daddyfredregill]

I still don't think my clutch is going to work. If I change the ratio it will be worse than it already is. The engine never produces full rpm the way it is.

 

[keatonx]

What are you using for a belt? Looks like a rope
The drive pulley being too big would cause it to not rev up enough (clutch constantly slipping). If it revs up with the wheel lifted but bogs down and doesn't pull hard on the ground, your drive pulley is too big.
The weed eater clutch will be fine, I made a few weed eater bikes and the clutches bit pretty hard. On one i replaced the weed eater clutch with a pocket bike clutch and it SUCKED (slips too much, wears fast)

 

[daddyfredregill]

The belt is just for testing it is called link belt or something. You can make what ever size belt you want by adding or taking out links. Pretty cool stuff. I honestly think it would work for a permanent solution. I will try a smaller drive pully. Thanks

 

[keatonx]

One of my bikes, which has a 4hp lawnmower engine, has a 8.8:1 ratio in first gear. And it IDLES at around 15kmh, or fast jogging speed. And at around 4000rpm in 1st it will go maybe 45-50kmh. Since it looks like your pulley is maybe 1:6.5th of your wheel diameter, you have a 6.5:1 ratio. To put this in perspective, my 5th gear (top gear) has just under 5:1, and at 4000rpm the bike will be at around 110-120kmh! Plus, you will need a higher ratio for the centifugal Clutch, because it won't bite that hard compared to the manual clutch on my bike, which I can just drop and get infinite grip.
At your ratio, you'd be going 76kmh (almost 50mph!) at 4000 rpm, assuming you have a 26" wheel. There's no way you can get to that speed from a dead stop without killing your clutch from the friction.
I'd suggest maybe an 8:1 ratio.
This will give you 62kmh (almost 40mph) at 4000rpm, on a 26" wheel.

Go to this site for figuring out ur gear ratios-
http://www.csgnetwork.com/kartpotentialspeedmcalc.html
Just have the amount of your engine pullies that fit into ur rear wheel diameter in the "teeth on axle" section, and put 1 into the "teeth on clutch".

Make your top speed a bit lower, not higher than what you think is reasonable, because with a cent. Clutch you have to have a higher gear ratio (slightly less speed).

Your belt isn't slipping, right? I wouldn't be suprized, since it doesn't look like rubber (more like rope lol)

 

[professor]

Those Techumseh engines are a quality item. But, being a 2 stroke, have very little torque at low rpm.
You need a much smaller engine pulley.
Also, more than likely, there is a governor on the engine. This is not a bad thing, but it can be adjusted for more rpm, motors with governors usually do not blow up from over reving.

If you can't get the clutch to fit a smaller pulley- you can delete it and use a fixed small pulley, with an idler/ type engager (a pivoting lever with a pulley to push against the belt). And a china kit clutch lever to control it (what I use).
When you get the belt size correct, then you can go to a regular v-belt which I think will grab better (being made with rubber).

 

[keatonx]

Those Techumseh engines are a quality item. But, being a 2 stroke, have very little torque at low rpm.

my lawnmower bike has a tecumseh 140cc 2 stroke, ungoverned, and it will pull wheelies from idle. It starts making torque right at the rpm where it's Just fast enough
To not stall (like 800rpm). But this is a smaller displacement, probably piston ported engine (mine had reeds).

 

[keatonx]

Wait never mind, it's a reed valve