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1970 90CC Yamaha

  • The Bo
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1970 90CC Yamaha was created by The Bo

This bike runs great up to about 10 mph then engine starts to skip, now using 90 octane ethanol free gas.  Feels like a carburetor problem but have cleaned every inch of carburetor and adjusted the air screw.  Appreciate any help.
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16 Sep 2021 13:27 #1

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Replied by RT325 on topic 1970 90CC Yamaha

Pull the baffle & try it. Will be noisy. Could pull the air filter unless ya sure its good & not falling apart. My HT1 pulled 55mph on a racetrack all day long. Depends what you mean by skipping though. If the mag is a bit weak & points a bit dirty plus plug gap too wide then yes you'll get an electrical misfire which could be described as skipping i guess. Misfiring it instant missing where blocked exhaust is more restricting performance to a limit but a gradual limit rather than a cutoff limit. Hope that makes sense.
ps, gap alters timing but i'm thinking if its out past recommended max of 15 then timing is likely a bit early anyway & wide gap will cause misfiring, not the early timing exactly. Conversely  if the points are barely opening from fiber heal wear then it'll be way late on timing & kill the performance but probably not misfire, just flat power.
Last edit: 16 Sep 2021 15:26 by RT325.
16 Sep 2021 15:20 #2

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