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Hey everyone - I'm hoping you folks can help me diagnose the problem that's been plaguing my 2009 250 GTS super ie for the last few months now. My suspicion is that the fuel pump is failing, but it doesn't really fit the exact profile. Originally noticed the issue at freeway speed after about 10 mins where the RPMs dropped off suddenly and the scooter started to hesitate and lurch. Letting off the throttle to keep it rolling at about 50-60 km/h worked, but it would not power back up until the bike was shut down and had cooled off. That happened a few times, but never had any issues if I kept it at or under 90 km/h around town and stayed off the freeway. My local Vespa dealer couldn't diagnose the problem. A couple of days ago I decided to take a quick check on the freeway to see if it was still happening and it bogged down almost immediately upon hitting highway speeds, and now, it's happening full-time and at much lower speeds. If I'm on level roads and don't accelerate hard, it works fine - try to accelerate quickly or climb a hill and it bogs down and nearly dies. It's not stalling, just won't allow me to twist the throttle beyond maybe halfway or it starts to lurch.

Sound like a fuel pump issue or any other ideas? Air filters have been changed and like I said, a qualified Vespa mechanic seems stumped. The fuel pump was replaced years ago in the recall. Any suggestions greatly appreciated.
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Hi Valley and welcome to Modern Vespa!

Below is a reply I made to cdwise in Another stalling GTS. Might apply to you, too.
Quote:
Sorry to hear about your troubles. I've had a similar issue I've been chasing on a 2006 GTS. In my case, the latest round of stalling occurs only when the engine is warmed up / hot. The current diagnosis is a failing stator.

Also replaced in the prior year or two was a faulty kill switch, a loose spark plug cap and boot, voltage regulator and ECU.

Hope you get it sorted soon!
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Thanks for the link to the other thread - sounds like my mechanic has had a lot of the same guesses, though I'm not sure about the stator - that seems like it could be a possible cause. Do you not think the fuel pump could be the culprit? I'd certainly rather it not be that as it's a pretty big and costly job to replace, but seems like it could be it.
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It might be your fuel pump. Fuel pump problems were very common. One thing that may help you diagnose - turn the key and listen. Do not press the starter, just listen for whirring sound the fuel pump usually makes. If you don't hear it and you have to wait for the engine to cool down significantly before it starts again, the fuel pump probably is the culprit.
This thread has some good info GTS Fuel Pump Failure. There's lots of other threads, too.
Hope you and your mechanic are able to sort it out!
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The fuel pump whine is there and at last check my mechanic said the fuel pressure was good. That's while it's on the bench, of course, but wonder if the high RPM riding conditions might be producing a different result. I'm wondering if it could be possible that the battery (or electrical system in general) might be failing and not be able to keep up with the demand for spark at higher RPMs.
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Make sure the cursory stuff is checked first. It could be a fuel pump, but it’s much easier to make sure the throttle body is fully seated, clamps are tight, no other vacuum leaks, etc.
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Fuel filter plugged? Miguel
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Valley wrote:
I'm wondering if it could be possible that the battery (or electrical system in general) might be failing and not be able to keep up with the demand for spark at higher RPMs.
If this were the problem, it would likely be caused by the stator, ignition coil, or ECU, not the battery.
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Miguel wrote:
Fuel filter plugged? Miguel
My mechanic says that the fuel filter on this bike is not an inline filter, but basically a mesh bag with tons of surface area so very unlikely to be clogged. I had the same thought but he shot that one down very quickly.
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Dooglas wrote:
If this were the problem, it would likely be caused by the stator, ignition coil, or ECU, not the battery.
Right, makes sense.
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In case anyone reading this is curious - after trying many, many options, my mechanic did a valve adjustment and it seems to have (so far) resolved the issue. Fingers crossed that it's in the past! Thanks for the suggestions.
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Valley wrote:
In case anyone reading this is curious - after trying many, many options, my mechanic did a valve adjustment and it seems to have (so far) resolved the issue. Fingers crossed that it's in the past! Thanks for the suggestions.
I'm glad it got worked out! I don't think you mentioned how many miles are on the bike, and how many miles since last valve check?
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berto wrote:
I'm glad it got worked out! I don't think you mentioned how many miles are on the bike, and how many miles since last valve check?
The bike has about 22000 km on it, but I’ve only owned it for the last couple of years so, unsure of when the last valve adjustment happened.
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