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I've looked everywhere for an answer, but without success.

My problem is this:

When my v-twin, twin-exhaust motorcycle is at idle, there is a significant difference in the pressure experienced by a hand placed at the end of one pipe, compared with the other one.

Each of the two cylinders has TWO spark plugs, presumably to aid combustion.

What are the possible causes of the pressure difference?

Is there perhaps only one cause - that one cylinder isn't firing at all?

Please help!

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  • Putting your hand over the exhausts isn't exactly a scientific method, are you sure that the pressure are discernibly different? Have you asked a couple of other guys if they can feel a difference, without biasing them by directly asking if they can feel a difference in pressure?
    – James T
    Jan 19, 2017 at 9:48
  • Can you share the make/model/year of your bike along with if you have a OEM headers and exhaust or an OEM/stock exhaust. Thanks, cheers and welcome to the site!!!
    – DucatiKiller
    Jan 19, 2017 at 20:57
  • if only one cylinder is firing it wont be anywhere near as hot as the other, CAREFULLY place your hand near each cylinder when the engine is running to see which is hotter, or use an infrared/laser thermometer.
    – Mauro
    Jan 20, 2017 at 8:59
  • @James Trotter, There is a difference in pressure so great that you don't need to ask a friend, honestly. One cylinder pushes you hand away like a gale while the other one doesn't move your hand. Does this help you to give me an answer, please?
    – Tapster
    Jan 20, 2017 at 11:01
  • @Tapster That's fair enough, that's what i was asking. Sometimes it easy to get an idea stuck in your head, and it helps to take a step back and look at it again - at least from my experience. Thanks for clarifying.
    – James T
    Jan 20, 2017 at 11:04

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Check that there isn't a crossover pipe in the exhaust system, if one pipe is slightly more restricted than the other this may cause that issue. Is the bike running ok?

If you are concerned something is wrong and the bike is perhaps not running as it should firstly do a compression test on the cylinders just to make sure everything is ok there.

If cylinder pressures are ok remove exhausts and check for any restrictions in the baffle sections, or if you have any sort of flow valves in the exhaust system check that they're working as they should.

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