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Thread: GTS cuts out at speed, and won't start until cool!

  1. #1
    apriliaforum Member Mike Holland's Avatar
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    GTS cuts out at speed, and won't start until cool!

    My GTS250 has always been extremely reliable, but now has a fault that I can't resolve.

    Last Wednesday, coming home on the freeway at about 120 kph, the engine hiccupped and then stalled. It would not restart. After a few minutes of cooling, it would start, but stalled again as soon as I opened the throttle. I eventually established that after a bit of cooling, it would idle and rev slightly, but cut out again at 3000 rpm. I was able to crawl home at little above idling revs. I checked the fuel level and the spark plug lead and cap, and they were all fine.

    Fiddling the wiring loops around the engine, I found that jiggling one of the Malossi Force-Master wires cause the engine to cut out. So I removed the Force-Master from the equation by un-installing it (destalling?). No change. My ignition and ECU are all bog-standard now.

    The next day the engine started perfectly, and seemed fine. So I went for a ride. As soon as I got out of the 50 kph suburbs I opened the throttle wide, and the engine stalled. Same symptoms again.

    This sounds a bit like the famous fuel pump problem, but my scooter is the wrong vintage (2007). The fuel pump problem involves the engine not restarting after a run, until it has cooled down. But my engine fails at speed, and then will only restart to idling, until it has cooled down properly.

    I have a spare fuel pump, but am reluctant to go to all the hassle of fitting it until I am sure that is where the problem is. Spoke to a car mechanic friend last night, and he insists my symptoms indicate ignition coil problems. Anyone had these symptoms before?

    Mike

  2. #2
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    If it was a Chinese bike I would say that the ignition trigger coil might be failing when it got warm. On the Vespa it is a reluctant variation (pick-up)/revolution timing sensor.

  3. #3
    apriliaforum Member Mike Holland's Avatar
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    Been following that up, and it looks like I would have to replace the complete rotor. Could it be the connections between the rotor and the ECU? I will check them out and make sure they are clean and healthy.
    Thanks, Mike

  4. #4
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    These types of gremlins can be hard to trace. Do you have access to a Piaggio Navigator for diagnostics or the Service Station Manual for your bike? On my 2009 Sport City it does list some checks you can make with a Volt Ohm Meter which should be similar but...

    I had a Chinese 150 that would do pretty much what you desribed but once I took the seat bucket/covers off it would cool down and no longer be faulting. Then running with the covers off the sensor would not get hot enough to fault. It was not until it failed completely that I was finally able to hook up a meter and see where the problem was.

    It would get hot and hesitate like there was a fuel delivery problem dying like there was a vapor lock or a plugged fuel tank vent then after 15 minutes or so would run like nothing had happend which almost had me to the point of replacing the pump and looking all through the fuel system for issues but it was the silly coil on the stator which thankfully on that bike was available from one supplier as a seperate part for less than $20. This started at the end of Summer on my evening commute home from work and the bike would be fine afterwards as the sun was setting and the evening cooled or during the morning commute when the heat of the day was not upon you however Fall arrived and I had foolishly thought that replacing a few vacuume and fuel lines had resolved it until the first warm day leading into Summer hit us and then it was the same story again. Thankfully the pickup failed shortly after that and the problem then became obvious.
    Last edited by Rockynv; 06-02-2014 at 12:52 AM.

  5. #5
    apriliaforum Member Mike Holland's Avatar
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    Well I might try a local scooter wreckers for a replacement coil. Bloody problem is a nuisance to test. - I will have to take along a sandwich and book!
    Mike

  6. #6
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    Quote Originally Posted by Mike Holland View Post
    Well I might try a local scooter wreckers for a replacement coil. Bloody problem is a nuisance to test. - I will have to take along a sandwich and book!
    Mike
    Yes the more sophisticated the systems get the harder they can be to troubleshoot. Makes one at times consider stepping back 30/40 years technologically to that simpler time.

  7. #7
    Honest always, feared often Micah / AF1 Racing's Avatar
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    Mike, you need to check fuel pressure, on yours you can add a gauge, on the return side to get accurate numbers since regulator is in tank. I'm betting the fuel pump both the behavior is similar between a pick up coil and pump. You either are not getting spark or fuel...this is what you have to test for when it fails.
    Diminished expectations is the key to happiness in life.

    Micah Shoemaker
    AF1 Racing
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  8. #8
    apriliaforum Member Mike Holland's Avatar
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    Rocky, you are so right about the technology. With my old two-stroke Vespas, almost anything could go wrong and I could do a roadside fiddle to get home. Have ridden home stuck in 3rd gear, no clutch, full bore when the throttle cable bust, etc. Now I just have to pull out the mobile phone and wait for help!

    Micah, a neighbour has lent me a fuel gauge, and now I just have to figure out how to connect the hoses. Booked up today but will try it tomorrow. The problem has got worse - the engine now fails to get beyond idling even when cold. So I don't need a ride to warm it up first.

    Mike

  9. #9
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    Hopefully that will make it easier to trouble shoot. 22,000 miles on my 2009 250 and its been so much more reliable than the others that I can't complain too much however the days whey you could get going again with just a Swiss Knife some bailing wire and/or a scrap of shoe leather are gone.

  10. #10
    apriliaforum Member Mike Holland's Avatar
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    Connected up the fuel pressure gauge, and all looks fine with the pump. Switch on the engine, and the pump primes it up to 1 bar. Then start the engine and it climbs up to 2.5 bar. All as it should be. Open the throttle slightly and the engine cuts out and it slowly drops down from 2.5.

    So I'm taking the fuel pump o of the equation.

    Mike

  11. #11
    Honest always, feared often Micah / AF1 Racing's Avatar
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    Leave gauge connected until failure occurs, ride with it...that's what I do but on the dyno. Pick up coil does behave very similar when cracked...spark or not, easy enough there.
    Diminished expectations is the key to happiness in life.

    Micah Shoemaker
    AF1 Racing
    699 W. San Antonio
    New Braunfels, TX 78130
    830-626-3966
    micah@af1racing.com

  12. #12
    apriliaforum Member Mike Holland's Avatar
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    The problem has already got worse. Now the engine cuts out when I open the throttle even when it is cold. So I was able to test it easily with the gauge connected, and the fuel pressure is fine - primes up to 1 bar, then rises to 2.5 when I start the engine, and only drops slowly after the engine has cut out.

    I looked at the workshop manual for removing and fitting the magneto flywheel, and the lining up when fitting looked rather delicate, so I have passed the job on to a repair shop. Hope to have the answer tomorrow.

    Mike

  13. #13
    apriliaforum Member Mike Holland's Avatar
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    So it turned out to be a faulty spark plug. I hadn't replaced the plug because firstly I couldn't get the bloody cap off, and secondly because the symptoms didn't match anything I've experienced with faulty pugs over the past 50 years. No backfiring, and scooter started an idled perfectly!

    Mike

  14. #14
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    Quote Originally Posted by Mike Holland View Post
    So it turned out to be a faulty spark plug. I hadn't replaced the plug because firstly I couldn't get the bloody cap off, and secondly because the symptoms didn't match anything I've experienced with faulty pugs over the past 50 years. No backfiring, and scooter started an idled perfectly!

    Mike
    Either end of the ignition circuit can behave like a fuel problem. It happens and all of us were looking for the more complicated problem and overlooked the simple one so your not alone.

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