Is a 79cc Predator too small to move a grown adult or is there another issue?

#1
I recently finished this mini bike (more has been done since the picture). It was found in the garbage all rusted in 1993, and we grabbed it. It sat in another storage unit for years until we discovered this year that it was still there. I forgot all about it. We cleaned it up and painted it, put some new hardware and a 79cc Predator engine on it. Don't mind the bolts through the front forks, as one of the shocks broke and I just wanted to get it done and ride it. I thought the 79cc would be enough to get us around, but keep the kids from killing themselves, as opposed to the 212cc.

It is fairly heavy, but it seems like I am either having a gear ratio or clutch issue to the extent that it won't even take off with me or my 15 year old son on it. With my 9 year old, it does okay. I am wondering if it just isn't getting enough RPM to engage the clutch, or what the deal is. Going down hills is a lot of fun, but the fun ends as soon as you hit flat ground.

Is it that the 79cc Predator is just plain not powerful enough, or do I have another issue? Governor, etc.?

I'll take any advice I can get. I am really close to just buying the larger engine, but don't want to if I don't really need to.

Thanks for your advice.


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#2
what is your gear ratio. Front sprocket and rear tooth count. If you had a larger rear sprocket it would help and depending on the clutch tooth count you could go down on the front sprocket, If it will not move and you keep trying you will fry the clutch. If it is geared correctly it should move you but not real fast.
 
#3
what is your gear ratio. Front sprocket and rear tooth count. If you had a larger rear sprocket it would help and depending on the clutch tooth count you could go down on the front sprocket, If it will not move and you keep trying you will fry the clutch. If it is geared correctly it should move you but not real fast.
I'll have to count them both when I get home. I can say that it used to have a shaft with sprockets in the middle where that hole is just in front of the back tire, but it was all so rusted and destroyed I tried to do without it.
 

Addicted 2 Minis

Well-Known Member
#5
Find the biggest rear sprocket you can get for your wheels/tires and the smallest clutch sprocket, these things are wimpy!. It's a fine line for sure finding what's strong enough for an adult but mild enough not to kill the kids. You can always go the 212 route and adjust the throttle stop but it will still take off fast until the governor kicks in. If your looking for a good in-between power plant, the Honda GX120 or GX160 is perfect but three times the price. I had a GX160 on one of my bikes and it was well worth the extra $$$.
 

joshua. c.

Well-Known Member
#6
a 79cc with the correct gearing it should take off even with an adult but it wont go fast at all. also the PMR jackshaft that used to be sold for doodlebug mini bikes was made to solve this exact gearing issue so maybe you should look into getting one. the 79cc is weak but a 212 is to big for a child so something in between like an old 5hp flathead or the gx160 Addicted to Minis just mentioned would be better. save the 212 till he gets older.
 

Addicted 2 Minis

Well-Known Member
#8
a 79cc with the correct gearing it should take off even with an adult but it wont go fast at all. also the PMR jackshaft that used to be sold for doodlebug mini bikes was made to solve this exact gearing issue so maybe you should look into getting one. the 79cc is weak but a 212 is to big for a child so something in between like an old 5hp flathead or the gx160 Addicted to Minis just mentioned would be better. save the 212 till he gets older.
I wish Honda would give me a cut every time I recommend the GX160. It has been hands down one of, if not the best engine I have ever owned... period!. Not that I recommend just leaving an engines sit with old nasty gas but there have been times where I forgot to drain it and it has sat for years and it just fires right up after draining and adding fresh gas, didn't even have to take the carb apart. I still have it to this day, hell, I might just be buried with this thing!, Hahahaha. Now the GX200 that came on my power washer is a different story, I don't know what it is about that engine but it hates me!. I don't know why, I specifically purchased the power washer because it had a genuine Honda and that decision was based off my GX160 and that's the thanks I get, must have been made on a Friday!.
 
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#10
I finally got a minute to take a look at my gear ratio. The front sprocket on the clutch is 12, and the back sprocket on the wheel is 60. Looks like 5 to 1. I think I probably need a jackshaft. What do you all think?
 
#12
Here's what I am looking at doing. If anyone has a similar setup let me know. I don't think I can do a bigger rear sprocket because of the bolt pattern of the rear wheel being kind of odd. I already have the holes for the jackshaft.
 

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#14
That jackshaft should get me to 6.92 to 1 and also I can move the engine over a little. Also should get me 17 mph. I have a goof cart that runs 14 mph, so we can ride together. That's all I am looking for. If I need more speed I will remove the governor. I am sure at some point I will end up getting a larger engine, but for now I just want it to go.
 
#16
There's a happy ending to this one. I got that jackshaft kit and installed it. I did have to slightly knotch the rear control arm to have clearance for the jackshaft sprocket. At first, it was a little better. I realized that it didn't roll very smoothly, so I loosened the brake up a bit more. The combination of those things made it really zip along. I have a great video of me driving it, but can't get it to post. Thanks for the advice all.
 

Addicted 2 Minis

Well-Known Member
#17
There's a happy ending to this one. I got that jackshaft kit and installed it. I did have to slightly knotch the rear control arm to have clearance for the jackshaft sprocket. At first, it was a little better. I realized that it didn't roll very smoothly, so I loosened the brake up a bit more. The combination of those things made it really zip along. I have a great video of me driving it, but can't get it to post. Thanks for the advice all.
Cool beans, gearing or governor removal is key to these engines, although I don't fully recommend removing the governor. I'm glad you were able to get'r going without too many problems.
 
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