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XS360: Oil on right cylinder spark plug

Discussion in 'The Garage' started by blaketots, Oct 12, 2020.

  1. blaketots

    blaketots XS400 Member

    Hey y'all! I have an all-stock 1977 XS360 that is having power issues on the right cylinder that is causing idle issues when coming down from speed (dying at stop lights if I don't keep revved up, but easy kick to start back up; erratic idle when warm).

    The right cylinder runs way colder than the left (which is running great!) and I think it's because the spark plug is only firing sometimes since its getting covered with very small amounts of oil and eventually fouling.

    MY question is, what is the most likely culprit you think before I begin taking my top end apart:

    a) blow by due to bad piston rings/scored cylinder
    b) improperly sealed valve cover (I recently took this off and put it back on with Yamabond4)
    c) bad oil control gaskets

    The bike is definitely not overfilled on oil. This spark plug oil problem only started recently, the bike was running fine (hard to start) until maybe a month ago until the spark plug boots decided to not conduct anymore and I replaced those. Points were on the way out so I replaced those as well, but not before assembling my advance column 180 degrees out which had me scratching my head for two weeks (you live and learn).

    I'm new at wrenching and am loving learning by working but wanted to get some input in case there was something I could be missing. Figured this bike is done for the season so I have all the time in the world to work on it this winter.

    Thanks for any time in advance, I've been a lurker of this forum all summer and it has helped me IMMENSELY with this bike.
     
  2. BBS360

    BBS360 XS400 Guru Top Contributor

    Do a compression test, dry, record results, then drop an oz of oil in the cylinders through spark plug hole, repeat the test.
    The results, and possible differences between them, will shed some light on cylinder and valve condition.

    Did the same. Might have taken longer to figure out.
     
    blaketots likes this.
  3. blaketots

    blaketots XS400 Member

    Dry compression on both sides is same as wet. No change. 155 on both aides.

    Also, I think the thread where you resolved the advance cam is what lead me to figuring mine out, so thanks for that!
     
    Last edited: Oct 15, 2020
  4. blaketots

    blaketots XS400 Member

    My valves don't look perpendicular to the springs. Don't have a way to compress the springs right now, but is that normal? Bent valves?
     

    Attached Files:

  5. xschris

    xschris a lifestyle not a trend Top Contributor

    If you get 155 lbs of compression your valves are fine. That's how they look.
     
  6. blaketots

    blaketots XS400 Member

    Any idea as to why I'm getting oil on a plug then? Not overfilled, oil was on the low end actually.
     
  7. blaketots

    blaketots XS400 Member

    Plug and plug hole. Plug had oil on threads before I wiped it off earlier.
     

    Attached Files:

  8. xschris

    xschris a lifestyle not a trend Top Contributor

    Is it oil or fuel? The bike will smoke blue if it's oil. If it's fuel I would make sure the carbs are setup correctly and have been synced with a manometer. If you haven't done so already make sure the points are set and clean as well as timing. All things that can cause a cylinder not to fire. Make sure you re-set your valves after you have removed the rocker box.
     
  9. blaketots

    blaketots XS400 Member

    It's oil. New points, dead on (static) timing (I'm fairly certain). Carbs were bench synced and cleaned very recently, plan on getting or making a manometer when I can if I get the bike running again. But yeah no smoke tho which I thought was weird, right side cylinder ran way colder and would seemingly misfire (left side was consistent, while right would putter).

    But you think since the compression was this good, it shouldn't be valve seals?
     
    Last edited: Oct 15, 2020
  10. blaketots

    blaketots XS400 Member

    Also, thank you for entertaining this. Time ain't free and I appreciate the replies.
     
  11. amc49

    amc49 XS400 Addict

    Could be valve seal leaking oil. If the ignition is strong enough you get no real smoke until the oil amount finally overwhelms the ignition enough it cannot burn it completely.

    Timing can be dead on yet dwell off (gap) and coil then fires very weak. Plug then loads up like that. Hard to really tell the difference in whether it's oil or fuel as fuel will reduce by the VOCs burning first in a lackluster burn to leave residual oils behind. The occasional firing or misfiring a bad cylinder can do.

    '...oil was on the low end actually...'

    Could be proof of the valve seal thing. How many miles on this engine?

    I'd be looking close at plug wire and cap on that side. Swap the coils to see if the problem switches sides, bad coil.
     
    Last edited: Oct 15, 2020
  12. blaketots

    blaketots XS400 Member

    Thats what i'm figuring, amc. Ordered some new ones since they're fairly cheap and I'm gonna wait to take off the springs till they come in since i don't want to take the head off and replacing those without seems like it might be more hassle than 13 bucks lost.

    Thanks everyone for the help, I really appreciate it!! I'll report back next week.
     
  13. xschris

    xschris a lifestyle not a trend Top Contributor

    Post some pics of the bike. Looks like the mufflers are not stock but some aftermarket ones. You may have some other "mods" that can cause your issue/issues.
     
  14. amc49

    amc49 XS400 Addict

    MILEAGE? Question is to verify the rather high compression numbers, they may be fake. Cheap crap gauges do it all the time.
     
  15. blaketots

    blaketots XS400 Member

    The bikes mileage is around 23000. Sat for 2 years after being getting worked on by someone who is well known in my area for wrenching. Bike started right up with a new battery when it was bought.

    The exhaust was painted by a previous owner, the pic in my profile is old. I‘ve since removed the paint and the pipes are chrome.
     
  16. xschris

    xschris a lifestyle not a trend Top Contributor

    I was referring to the mufflers.
     
  17. blaketots

    blaketots XS400 Member

    They're Yamaha branded mufflers, though?
     
  18. xschris

    xschris a lifestyle not a trend Top Contributor

    Hard to tell from the tiny pic.
     
  19. amc49

    amc49 XS400 Addict

    I suspect the high compression at that mileage. Not impossible but not that usual either. Certainly not both being the same. The same numbers wet and dry say it too. They should be different. Says a gauge that is not quite accurate in needle action.

    Just me though.
     
  20. blaketots

    blaketots XS400 Member

    Sorry, I was mistaken, they are aftermarket/non-OEM mufflers. I though I had seen a Yamaha branding on them but I had not.

    Anyway, replaced valve-stem seals and then flung a valve cotter across the garage. New ones came in, got everything together, and boom! Bikes running again! Woo!

    Ran the baby for 45 minutes, seems oil fouling is no longer an issue, but the idle is still erratic and dies when coming down from high RPMs. Buddy suggested that its a carb sync issue, so I'm borrowing a manometer from another buddy to get them tuned up and will report back when that's all done.
     
    xschris likes this.

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