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Loss Of Power Over 5k RPM

Discussion in 'The Garage' started by Joe S, May 3, 2019.

  1. Joe S

    Joe S XS400 Member

    She was misfiring this morning so I gapped the plugs to 42 thousandths and reset the idle throttle position so it would idle at 1.7k with the choke wide open, now she's got no power over 5k rpm and refuses to accelerate. Before this morning it screamed over 6k and accelerated like it hated the past but I'm worried its floating valves. Anyone with more experience got advice for things to check? I suspect AFR is off due to open choke but after messing with the choke I saw neglegible to no change
     
  2. xschris

    xschris a lifestyle not a trend Top Contributor

    What year/model bike? Plugs for sohc bikes should be .028-.032 in. A good running bike can run to 9k rpm's which is red line. Not that you need to do it. Could be many things. I would check all the basics first. Post some pics of the bike so we can see what your working with.
     
    Joe S likes this.
  3. Joe S

    Joe S XS400 Member

    '82 Maxim. Little scuffed up, picked it up last August. Using 20w50 oil, changed before and after each season so far. Had to swap the gauges a couple times now and I still don't have a speedometer but as I understand it has roughly 12k miles. I've taken care of it like my own child since I got it but she's been a bit of a handful this season and I really just want it running well again. I need to switch to NGK plugs anyway so I'll probably get those and gap them to .032 but 32 thousandths was too short for these cheap copper bastards
     
  4. Joe S

    Joe S XS400 Member

    This is the picture of her
     

    Attached Files:

    buztabuzt likes this.
  5. xschris

    xschris a lifestyle not a trend Top Contributor

    Look up specs for dohc bikes as they will be different than the sohc ones.
     
  6. Joe S

    Joe S XS400 Member

    I plan on doing a cold dry compression test later today. I doubt it has anything to do with rings or head but it doesn't hurt to check. I'd love to adjust afr but yamaha didnt make the adjustment screw on the carbs very easy to get to...
     
  7. xschris

    xschris a lifestyle not a trend Top Contributor

    You may just need a carb cleaning. Or it could be a tci box failing. Hope it's not that.
     
  8. Oleschool

    Oleschool XS400 Enthusiast

    I've got a similar problem.5500 and up it falls on its face. Carbs cleaned, tried larger jets and even replaced the tci with another used one but same thing.
     

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