Honda VFR 400 not all plugs firing They are sparking but not great, only one can is heating what's the problem. What size spark plugs do I need? @

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02 Dec, 2017

  • 80%
    Solved this issue
  • 100min
    Time to fix
  • 65%
    Recommend to DIY
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Hi, Andria you need "FIVE" things in order for a cylinder to run properly:
1. FUEL: in order to validate your not getting fuel spray some starting fluid into the air cleaner and hit the starter button, if it fires up and runs for a few seconds then you know you have a fuel delivery issue. Multi carb banks should be bench "SYNC"
2. SPARK: remove the spark plug and with it connected to the spark plug cable ground the threads to something metal you should see a bluish white spark if not you have a faulty spark plug, spark plug cable, ignition coil, condenser, CKP, ECM, sensor or the wiring in between.
3. COMPRESSION: you must have at least 80-100 PSI for most bikes, multi-cylinder engines should be within 10-15% of each other if not perform a leak down test you may have a burnt or bent valve or hole in the piston or broken rings.
4. CAM TIMING: confirm your timing marks are aligned to see if the cam chain or adjuster are worn out and the chain has skipped a couple teeth.
5. IGNITION TIMING: on older bikes check to see if your points have not closed up, timing plate has not become loose and confirm with a timing light for proper retard and advance functions, on newer bikes where timing is controlled by an ECM and is nonadjustable check you CKP, TPS, MAP, O2, sensor or its counterpart for integrity.
For more information about your issue and valuable "FREE" downloads that you will need for viewing or printing please click on the blue links below. Good luck and have a wonderful day.
No Spark to plugs problem
400GreyBike View topic NC30 Only running on 3 cylinders
Honda VFR400R Service Manual
https://www.partsfish.com/page/oem-parts-for-honda
http://mybikemanuals.com/honda
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