My bike died on me the other day. It had been running fine prior but on the day it died the acceleration was acting funny, slowing down intermittently. I was able to get it running by swapping out all of the spark-plugs and jumping the battery. Some of the old plugs were fouled:

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From there I was able to ride it about a mile home without any problems. Left it sitting for a few hours and hopped back on, instantly the same problem again, jumpy acceleration, followed by the bike shutting down entirely. Parked it and checked all the spark plugs. No fouling, although some of them had the very slightest trace of yellow/orange residue.

Not sure why swapping the spark plugs completely fixed the problem for a few minutes. Not sure what to check next. Air filter is new, gas tank and carbs were recently cleaned, fuel lines are new.

  • Welcome to Motor Vehicle Maintenance & Repair! What is the year/make/model/engine of the bike in question? Aug 29, 2021 at 0:45
  • @Paulster2 1987 Honda Interceptor. VFR700
    – Griffin
    Aug 29, 2021 at 17:55

1 Answer 1


Spark plugs are one ignition component in a chain of variables to deliver fuel combustion. I have read nothing in your description that even narrows the list to ignition diagnostics. The plugs, although carboned up, are not beyond functional, IMO. In fact, just pulling the tank and wiggling fuel hoses and ignition wires could have been what temporarily relived the sputtering.

So, there are three basic systems that keep your bike running. Mechanical, fuel, and ignition. We’re going to rule out mechanical atm. We need to make sure fuel is being metered and a high enough energy spark to ignite the fuel in the roughly ten atmospheres of pressure in the combustion chamber. Pull a spark plug boot off the spark plug, leave it connected to the coil and wire put the cleaner of the two old plugs in the boot so it clicks in. Then lay the plug on the valve cover so it’s getting a decent connection to ground.(bike in nuetral on stand) Turn the engine over with the start button. Look for a big blue spark. If it’s yellow, or non existent start inspecting components. If it has resister caps pay close attention to wire and cap ohm values. But if both cylinder wires throw good blue, visible in daylight, spark. Then we look for fuel delivery issues. I’d start at the vacuum petcock

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