New and Confused!

fullerg86

Member
Oct 17, 2019
24
37
13
35
Hi all, I am definitely a rookie with entry level knowledge on mechanics however, I have a basic understanding and enough skills so that I have built, welded, fabricated and pieced together my own motorized bike. I am running a 79cc predator (with a torque converter) engine with a v-belt that is about 70" which is running to a 16" pulley on a 26" rear rim. I also have a belt tensioner in between the drive pulley and the rear pulley to cut some slack out of the belt. With this set up I just cannot seem to get enough torque/speed out of the bike. The bike does have enough torque to get the bike to pull but as far as actually riding, it goes less than 5mph. Like I said I am new to this so any feedback would be helpful. I did recently fabricate my muffler that I took from a 150cc KLX dirtbike... would that have anything to due with inhibiting the power? Even without the muffler it still has a lack of any power to it. Any feedback here is much appreciated. Some of my 'guesses' on why there is no torque/speed...
-Exhaust too restricted?
-Torque converter not engaging correctly?
- perhaps belt/tensioner is too little or too tight?
- All the above? haha
Any positive feedback is VERY much appreciated.
 
Last edited:

curtisfox

Well-Known Member
Dec 29, 2008
5,138
1,559
113
minesota
Sounds like it is geared to high, maybe. Does it work OK with the wheel off the ground?

The tension-er is on the top witch is the power side, should by rights on the slack side down below. No belt slipping ? ........Curt
 

fullerg86

Member
Oct 17, 2019
24
37
13
35
Sounds like it is geared to high, maybe. Does it work OK with the wheel off the ground?

The tension-er is on the top witch is the power side, should by rights on the slack side down below. No belt slipping ? ........Curt
Thanks for the reply Curt! To be totally honest, I am left in the dark when it come to 'common knowledge' of these sort of things. I did not consider the tensioner could cause an issue being on the top part of the belt.

To your question with the tire off the ground, it does. Spins fine and picks up speed seemingly well to the eye. Does not appear to be a struggle to turn. I have also not noticed any belt slippage either. Just seems to have a real struggle to move the bike along. I also weight about 180 lbs so I dont think weight is too much of a considerable problem... I would hope not anyhow ;) Thanks again.
 

curtisfox

Well-Known Member
Dec 29, 2008
5,138
1,559
113
minesota
Tensioner should of still worked, with that big a pulley, just that they bite better on slack side.
You may half to go with a bigger rear pulley, like a 24” bike rim........Curt
 
  • Like
Reactions: fullerg86

fullerg86

Member
Oct 17, 2019
24
37
13
35
Tensioner should of still worked, with that big a pulley, just that they bite better on slack side.
You may half to go with a bigger rear pulley, like a 24” bike rim........Curt
I may end up trying just that... Thanks again!
 

fullerg86

Member
Oct 17, 2019
24
37
13
35
I may end up trying just that... Thanks again!
Tensioner should of still worked, with that big a pulley, just that they bite better on slack side.
You may half to go with a bigger rear pulley, like a 24” bike rim........Curt
One other question regarding the tensioner and a thought I had... when it comes to tension on the belt, what is the proper tension rate? How should one know what is too tight or not tight enough?
 

fullerg86

Member
Oct 17, 2019
24
37
13
35
Best would be a spring, like screen door spring, let float.........Curt
So after work today I replaced the tensioner and guess what...the bike now rides and cruises very well!! I’m guessing it’s riding at about 20-25 mph. I need to work on some other things but I very much appreciate your help curt! It’s amazing the difference!! :D
 
  • Like
Reactions: Greg58