1971 arctic cat prowler mini bike with Sachs 50 has no power

[Lorentzs]

I have a 1971 arctic cat prowler mini bike with a sachs 50 motor in it. It will start and idle fine but if you give it some throttle it barley has enough power to turn the tire if it’s off the ground. We have tried a new carb and spark plug with the same results starting to wonder if it is possibly has bad crank seals any ideas what might be causing the lose of power would be appreciated thank you

 

[ole4]

You can pressure test to check crank seals. Leaking seals can cause low power and motor will flatten out and not rev has timing been checked.

 

[Lorentzs]

I have a buddy working on it. Not sure if timing has been checked. I know compression was good in the top side. How would you go about pressurizing it to check crank seals

 

[ole4]

You block off intake and exhaust ports. Then remove spark plug and screw in adapter. I have a squeeze bulb like a blood pressure tester has and a tee fitting with a pressure gauge. I pump it up to 8 to 10 psi and see if it holds pressure. if it bleeds down use soapy water to check seals. You can use a mity vac as well but you can’t tell where it’s leaking with vacuum. I can post a picture of tester tomorrow if you want to see it.

 

[Lorentzs]

Thanks for the response I understand what you are talking about buddy that owns a repair shop really feels it’s crank seals. not Sure how hard it is to split the Sachs motor but will do the pressure check and if the seals leak we will look into splitting it and putting crank seals in

 

[ole4]

Can’t you remove the seals without splitting the crankcase?

 

[Lorentzs]

not Sure I have not taken it apart yet to look. They seemed like they really needed to split it

 

[ole4]

Pics of small 80cc Yamaha seals accessable from the outside. I have had a lot of 2 smokes all had seals pressed in from the outside. No guarantee yours is like that but a high probably. also a pic of pressure tester.

 

[smudvapor]

Check the reed valve that is between the intake manifold and the jug. If it is bad you can have that type of problem.

 

[gotee193]

Remove the exhaust pipe and try it. I have had pipes plugged more than once.

 

[Lorentzs]

Thanks I will try those things. I have tried the reed valve with no luck but have not tried removing the exhaust.

 

[Rapidrob]

Great info here, don't forget to check the reed valves as stated, I bet their very tired. I'd replace them.
Symptoms are low compression and smoking like a forest fire, idles OK and give it the gas and it poops out.