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loss of power

Posted by Steve Paliobeis 
loss of power
August 24, 2005 01:03AM
I know these little cars don't have that much power anyway but mine seams to ave lost a little. Does anybody have a specific 2 stroke oil to recommend, maybe that's part of the problem?

Also, what is the compression psi supposed to be?
Re: loss of power
December 07, 2005 07:00PM
The compression ratio is 6.4:1 so max pressure is 6.4 time 14.7 psi (at sea level) or 94 psi. If you get 90+ percent of that, you're rings/valves are probably OK. Be sure throttle and choke are open when you crank. Try a wet test if pressure seems low, should be only slightly higher than dry if rings are OK. Cylinders should be within 10% or each other. You could check bleed down rate but I'm not sure what acceptable rate is. Dynamic test would check for intake/exhaust blockage. I suspect Vespa mufflers can get plugged. As for oil, I use Yamalube 2-S which is a semi-synthetic 2 cycle oil though I think any good quality 2-cycle oil will do. I'm no expert, so if others have better info, please chime in.
Re: loss of power
January 07, 2006 10:16PM
Probably you have crankcase/crankshaft seals that are leaking. This is the most frequent cause of low power and hard starting in older two strokes. Good crankcase pressure is absolutely a must for acceptable performance, and if the seas are bad - good luck!! Unfortunately to install the seals it takes complete teardown, so it's best to replace the rings + at that time.
Finding appropiate seals is not easy.
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