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My name is Joel from Sydney and I'm trying to diagnose a strange problem on my bike. Apologies if this is the wrong forum to be asking this question I'm new to this forum.

Bike: GSXR K5 1000 Mods: Air-horn, Scorpio i900 Alarm, Akrapovic Carbon Slip-on, K&N Air Filter, Gilles Rear-Set, Aftermarket screen

Symptoms: If you have been riding the bike for most of the day, on a hot day (say 30C), the bike will sometimes turn off meaning that the engine stops the taco drops but all dashboard lights remain and no FI codes. Sometimes you get a few semi-stops before it does this where the power momemtarily drops out. It has been happening on and off for a while now (probably two years) but was previously so rare I didn't investigate it further. It can now be triggered relatively consistently. When it turns off the temperature of the engine will be around 100-105C (in the normal range) generally, sometimes even lower. If you attempt to start it straight away the starter motor will just click and then if you turn it off and then on after some minutes it will fire up again. The problem generally re-occurs if you try and keep riding after it has happened once unless you leave it.

What we have tried to fix: Performed a full service, checked valve clearances, replaced air filter, tightened all screws and checked everything around airflow and general bike cleanup. Also recently replaced the clutch cable. As far as I can tell the airflow is flowing perfectly well and the bike cools rapidly when accelerating, and the fan is coming on at around 104 as it should. Also checked the kickstand and ended up modding it slightly so there is a higher lean angle and so it doesn't bounce around and gave it a good clean. My mate who is far more knowledgeable than me gave it a really thorough clean.

What I suspect it is:

  • Air Intake Temperature sensor might be faulty and when the air is very hot inside the airbox it is sending an incorrect amount of fuel
  • Air Pressure Sensor likewise
  • I considered killswitch sensor but I'm not sure the symptoms match
  • I saw some people have had ECU issues but it seems weird an ECU problem would be so heat related
  • With custom wiring possibly either the alarm or air-horn is shorting something when they get hot but this also doesn't seem to match the symptoms

Any advice of what to check? I'm a super-noob at these things. I tried checking the forums and while some people have had similar symptoms I didn't see anything that matched what I have.

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  • This sounds almost like it's vapor locking. Fuel system is getting too hot and then the fuel vaporizes somewhere in there. Just throwing it out there.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Nov 9, 2014 at 18:57
  • If you are able to start immediately after the bike dies, it probably isn't a vapor lock since that usually requires waiting for the lock to clear or clearing it by opening the gas tank.
    – Paul
    Nov 12, 2014 at 5:03
  • @Paul Vapor locking predominantly (IMO) refers to gasoline in the fuel lines vaporizing, and causing the injectors to starve of fuel, as opposed to referring to a vacuum being created in the gas tank due to a blocked tank air vent.
    – Shamtam
    Jan 29, 2015 at 19:06

3 Answers 3

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I have switched out the fuel pump with another I bought on ebay for $40 and ridden the bike on hot days. I found the fuel filter was heavily clogged which possibly contributed. I think as some of you have suggested it was an electrical fault when the bike was hot due to higher resistance.

Thanks for all your answers! I'll update if the problem re-occurs but I think its fixed.

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From your description I'd suspect an electrical fault. Maybe a fine crack in a circuit or a broken soldered joint. With enough heat the gap opens enough to break the circuit. You could try swapping components from another bike to help isolate the problem in a process of elimination.

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  • I agree with @peter. Try swapping those sensors you think are bad with another bike.
    – gh0st
    Nov 20, 2014 at 9:58
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This really sounds like an Ignition Switch problem.

Go over the symptoms carefully. The engine just stops (as if the ignition was turned off). The starter just clicks (does not turn the engine around).

There are many contacts in the ignition switch, so the indicator lights stay on. One or two of them are out of spec, and when it gets hot, the connection fails.

When it has failed, check to see if there is voltage to the ignition system (you could even set up an LED to verify this voltage 100% of the time, like I did with the fuel pump in my Honda). If there is no voltage there, you have found the problem. A slightly different type of failure is also possible, there could be voltage, but not enough current (due to a bad contact), so be wary of that also.

That may also be one of the cheaper things to try testing/replacing.

Good luck!

--Dave

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