Author Topic: Loss of power on Motorway  (Read 447 times)

Offline StrandedSam

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Loss of power on Motorway
« on: August 15, 2019, 08:23:15 AM »
Hi guys,

Just bought an '07 GS500F and have had it for 2 weeks - love the bike, but have had an issue riding back on the motorway.

Finished work, started the bike with the choke, no problems there, let it warm up and turned it off like usual. As I joined onto the slip road I began speeding up to 70mph, hit 50mph before losing acceleration and not being able to speed up any further. I pulled the clutch in and banged it up a gear but was still getting nothing. Pulled onto the hard shoulder and tried to get the bike to start up by moving the petcock to reserve and could hear the engine cranking over but no actual ignition. After leaving the bike for 10 minutes and opening the fuel cap to make sure I wasn't out of fuel the bike managed to start with the choke fully on, and I rode away with no problems.

On getting home, I switched the petcock back to the on position and started the bike and it had no issues starting right up, and as of yet have been unable to reproduce the problem so am not sure what's going on  :icon_lol:

As far as I can tell from looking at other posts it looks like it could be a petcock issue, as I didn't notice any wooshing noises coming out of the tank when I opened it (to be fair it was on the side of a loud motorway), any ideas on what else it could be? Luckily the bike is currently under warranty, but I need an idea of what the issue is first.

- Thanks guys, Sam.

Offline Watcher

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Re: Loss of power on Motorway
« Reply #1 on: August 15, 2019, 09:56:28 AM »
I've noticed a tendency to "outrun" the fuel supply at higher speeds if the fuel flow is bottlenecked.  If you have an accessory in-line fuel filter get rid of that.

Beyond that, a petcock issue can be diagnosed with the PRI position, as that bypasses vacuum.

If PRI doesn't help, might be a carb issue.  Potentially float or float valve related.
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Offline StrandedSam

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Re: Loss of power on Motorway
« Reply #2 on: August 15, 2019, 01:08:45 PM »
Thanks for getting back to me!

As far as I can tell the fuel lines haven't been modified, but will have a more thorough look tomorrow.

I've done as much research as possible and as you say it looks like fuel starvation is likely the cause of my issue which can be solved by switching the petcock to the prime position.

As far as I can tell this was a particular issue with petcocks on the older models, but not so much the newer ones; is there anything I could do to try and rectify the issue?

The plan is to take the bike out for a good stretch and see if I can reproduce the issue and then fix it by moving the petcock to prime so I'll keep this thread updated with how it goes!

Thank you very much for your suggestions! :)

- Sam


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