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I've got a Honda 919 for a couple of years now. It is 2006, under 20K miles, always maintained and garage kept. I put around 2K miles per year. This season I've put a fresh gas on it and started it, but noticed, that when cold it has lower idle RPM than when it is warm. It idles around 900 RPM when cold and around 1200 RPM when warm. If I rise the idle during cold to be 1200 RPM, then it gets too high when it is warm. That was not the case in previous seasons. It drives perfectly fine, no power loss at all. I wonder if fuel pressure regulator is the reason. Any ideas?

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  • Well, before this "issue" i could start motorcycle cold and it was idling 1200 RPM and was keeping idle level at 1200 RPM when it got fully warmed, so there is a "problem".
    – oryades
    Mar 22, 2017 at 14:55
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    When was it last serviced? Oil/filter changed? When did you last check valve clerances?
    – Sir Swears-a-lot
    Mar 23, 2017 at 9:19
  • @Peter it is regularly serviced, 3000 miles or 6 months, all the fluids and filters have been changed one month ago. I haven't checked valve clearances, but they never shown any sign of needing an adjustment. These engines call for 16K miles valve adjustment intervals, but there are a lot of people reporting on forums, that even at 40K all valves are in spec.
    – oryades
    Mar 23, 2017 at 13:05
  • @oryades A lot of people can see that, but I wouldn't assume that is the case with yours. How many kms? If it's been over 16k since they were last done, it's very possible some are out of spec.
    – raydowe
    Mar 23, 2017 at 16:17
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    How are you adjusting the idle? You mention a fuel pressure regulator, and the 919 is fuel injected, but then how are you adjusting the idle?
    – Hari
    Mar 24, 2017 at 23:53

1 Answer 1

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Do you get any FI light when you start the bike? Can you check for codes? https://www.youtube.com/watch?v=CyffdHvF4X8

I would suspect a faulty sensor. There are a number of sensors on the bike like coolant temperature and airflow that allow the bike to adjust it's fuelling. If the bike doesn't "know" it's cold, it might not be adjusting properly for this.

Even with no codes, a sensor could be reading incorrectly. Grab a copy of the service manual. It will show you which sensors your bike uses, where they are located, how they are wired, and how to test them for accurate values.

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  • I had never get any FI lights at all. I understood your idea of checking sensors. I guess the only sensor for diiferenting cold and warm engine is coolant sensor, but it behaves as usual on dashboard, no sign of incorrect readings.
    – oryades
    Mar 25, 2017 at 4:02
  • + 1. I agree. I'd be suspicious of what sensors are telling you. For example an oxygen sensor in exhaust? I'm not sure how smart the bike is, but an exhaust gas sensor may be more susceptible to changes in heat between cold and hot. It might be smart enough to try and alter mixture.
    – Sir Swears-a-lot
    Mar 27, 2017 at 0:27
  • Fortunately this bike does not have o2 sensor in exhaust. Though it does have cat converter.
    – oryades
    Mar 27, 2017 at 6:33

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