Harleys are notorious for valve noise or clicking from exhaust, so when my 2011 Ultra with 110 Screamin' Eagle started clattering a bit more than usual I didn't worry too much, but then a few miles later it reacted very loudly when I tried to accelerate hard so I gently coasted for a while.

After stopping, it then wouldn't start. Symptoms include backfiring, loads of smoke from the right exhaust, and some from behind the air intake when pressing the starter, and immediate stall when the starter is released.

The recovery guy made a guess that it could be a failed spark plug (which I hope is all it is) but he didn't have any tools to check (Imperial sizes in a metric country :-( ) so that was a guess.

Any thoughts?

  • And of course this happened 300 miles from home, so we spent the rest of the day getting relayed home with the bike on the back of 5 different recovery trucks!
    – Rory Alsop
    Commented Jun 11, 2019 at 11:44
  • 1
    How old was the fuel, was it the right octane for that engine?
    – Moab
    Commented Jun 11, 2019 at 23:53
  • 1
    The tank was filled that morning with the correct fuel.
    – Rory Alsop
    Commented Jun 12, 2019 at 15:11

2 Answers 2


With a no-run scenario, think FASTEC:

  • Fuel
  • Air
  • Spark
  • Timing
  • Exhaust
  • Compression

As there's smoke on one side only, I'd be focusing on testing for spark, timing and compression.

If I had to hazard a guess, the smoke near the intake tells me that the intake valve is not seating properly.


FASTEC is exactly the right process to analyse this, as @Zaid said. It turns out it was contaminated fuel! That doesn't really explain why smoke just from the aft cylinder, and why there was smoke coming out from near the air intake... My guess is the misfire was powerful enough or off-time enough to get through an intake valve.

The downside: required full flush and clean out The upside: no damage, so even though I need to pay for labour costs, it's not too bad.

Our assumption: the area we were in that weekend had suffered extreme rainfall and flooding so perhaps runoff had washed contamination into the garage's fuel storage.

  • 3
    Not sure what your costs were or if this would be relevant or not, but the one experience I've had with contaminated fuel resulted in the service station's insurance paying out to cover repair costs (for myself and many others who filled there on that day).
    – dwizum
    Commented Jun 12, 2019 at 17:44
  • 1
    I am chasing that, yes :-)
    – Rory Alsop
    Commented Jun 12, 2019 at 19:52

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