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 Low Compression (50PSI) on 2005 Zuma 70cc - new rings? 
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Scooterologist

Joined: Sun Oct 11, 2015 8:51 pm
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Post Low Compression (50PSI) on 2005 Zuma 70cc - new rings?
Ive been blowing out a lot of white smoke recently and not running the best. My cheap compression tester tells me I only have 50PSI compression, and although it is cheap, it has proven pretty spot on side by side with a Snap on. If I understand correctly I just need new rings?


Tue Jul 10, 2018 8:08 pm
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Post Re: Low Compression (50PSI) on 2005 Zuma 70cc - new rings?
More often then not you will need a new pistion to go with the rings as they are a soft al. Put a little motor oil down the bore and then retest the compression and see if it goes up. If it does that’s positive for needing at least rings if not pistion too.

But you have to look at the costs some times it’s almost as much for rings and pistion cir clips wrist pin and bearing

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Thu Jul 12, 2018 7:37 pm
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Scooterologist

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Post Re: Low Compression (50PSI) on 2005 Zuma 70cc - new rings?
Got it thank you. I had to take it apart to even figure out what is in it. Piston head is all black and covered in carbon build up, or whatever it is. Looks like at least part (header) of it is Stage 6 and currently ASSUMING it is all Stage 6, and if I believe what the guy told me who sold it, and the norm, it's 70 cc. Trying to match a serial/part number up now. Looks like Rocket 4 crankshaft which I guess is stock?


Thu Jul 12, 2018 8:14 pm
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Scooterologist

Joined: Sun Oct 11, 2015 8:51 pm
Posts: 37
Post Re: Low Compression (50PSI) on 2005 Zuma 70cc - new rings?
Yeah, looks exactly like this one: viewtopic.php?f=3&t=13024

So guessing it is a Stage6 Racing 70cc AC Cylinder Kit. Not exactly great news as appears to be limited sellers. :-/


Thu Jul 12, 2018 8:24 pm
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Scooterologist

Joined: Sun Oct 11, 2015 8:51 pm
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Post Re: Low Compression (50PSI) on 2005 Zuma 70cc - new rings?
Just to follow up, looks like new rings did very little, but the carbon fiber reeds were shot. By shot, definitely to big of a gap and frayed at the ends. I replaced with an ebayed stock cage/reeds and ordered a new set of carbon fiber reeds. Right off the bat I have another 10PSI. That's the good news, but the bad being compression is still just a little over 60, so guess there is more work to do on this 70cc . Just not sure yet if it is only Piston, or needs new cylinder as well at this point.


Thu Aug 23, 2018 9:28 pm
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Scooterologist

Joined: Sun Oct 11, 2015 8:51 pm
Posts: 37
Post Re: Low Compression (50PSI) on 2005 Zuma 70cc - new rings?
I did a follow up piston ring install, with motor oil down the bore (and a little spray fogging oil, to make sure everything got around) and then retested the compression and still got 50-60PSI? If I know I just fixed the reeds problem, where else do I have to go? Maybe even though new ring, my piston is that screwed up?

Note I also did an shrouded/fan cover, cold engine start, and sprayed carb cleaner around as I heard I would hear sudden acceleration if a vaccum leak anywhere. Let it go 15 seconds and turned her off, with no results. :(

Or would an exhaust leak (gasket) do this?


Mon Aug 27, 2018 10:39 am
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