Modern Vespa

Today, at 109F temp indicated, Salima's GTS 250 changed from one second to the other: very reduced top speed to around 30, no strong acceleration, hesitant and sputtering when accelerating (not when coasting). She said giving it very little gas is better than full throttle. I drove it too and had a hard time riding up the very lightly sloping driveway because I couldn't get the RPMs up high enough for the clutch to grab.

It starts up every time but idles hiccupy, occasionally dies again after start without throttle. Revving it up on the center stand is more successful than when riding it.

I checked:
HT lead at the plug: OK
Plug: replaced, no change.
Battery: normal (12.6V @ no load, around 14V at ?3000 RPM, all plates under water, both poles firmly attached).
Injector control cable seat: OK

After the spark plug change and on the center stand in the backyard, with the rear wheel somewhat touching the grass/ground, I got it to rev up to 6K but not beyond that. Have yet to try that with the wheel in the clear to see if that lets it get higher. Also want to see if cooler temp and a cold motor will change anything, so will try that Sunday morning.

From all I know, I feel the problem is with the fuel delivery. It feels like it does not get enough fuel with open throttle, so there is too much air and not enough gas.

Tank is at two bars, and I think the pump should either work or not, but not a little, or am I wrong?

When I take out the injector, will I be able to tell whether it is clogged? How do I check that?

The GTS has 13K miles on it and ran perfectly until one second before this happened. What is wrong with it?

Thank you for helping us out.

Sounds like a fuel problem, dumb question - but have you checked the fuel is ok? I am sure somebody far more knowledgeable will be along shortly...

Have the rollers ever been changed out?

Good to see you back Arno.

Love Bill and Genie.

X

Air filter checked?

Went on a group ride a fe weeks ago and a rider's Honda Helix started bogging with similar symptoms. Turned out that a mouse/rat decided to build a nest in the air box.

Thank you for the responses so far!

At 08:30 this morning, at "only" 84F, it almost felt like all was back to normal. Well, it felt like that because the problem yesterday was so crass that anything better would feel like bliss. Turns out that it is not back to normal just yet.

I was able to reach about 50mph(i), then I ran out of road. Riding at 30 and then accelerating didn't give me the snap in the back that I get on my GTS. Idle is still a bit shaky (but it didn't die). Then I added a gallon to the tank but that did not change anything.

I wanted to reiterate a point that may have been missed by the suggestions I received so far: the change from normal to dismal happened within one second while riding. Not gradually. So gas quality and filter state should not really be able to cause this very sudden change.

FTR, filter was cleaned 2000 miles ago, new rollers 1800 miles ago.

I remember from others' experience that defective fuel pumps went out in hot situations and came back normal when cooled down. Since in our case, we are not back to normal when cooled, could this still be the fuel pump? And if so, where can we get a new one that is for sure the improved version?

Keep cool,
Arno

What year is Salimas Vespa (wrt the fuel pump)?

Fuel pump is easy to rule out, especially if you are worried about power. Disconnect the fuel hose from the injector (it just unclips) and cycle the ignition on and off holding hose over a container. If it is working propely you should get a steady strong stream of fuel for a few seconds, then the flow will stop. You can repeat this as often as you want.

2007

Good idea, Doug, thank you.

From previous reports on failing fuel pumps, I learned that they either work or not at all. Ours, if somehow defective, works badly with hot weather, but it still works, and the engine starts every time, with air and engine being hot, hot, hot.
Next morning, with everything cooler, it just works better than when hot, but still not as good as it should. Again, this is under the hypotheses that the pump is somehow defective at all and nothing else is wrong.

Looking at the injector, could that behave like that with hot/cool temperatures? And would it likely be clogged (fixable) or defective and needs to be replaced? I could (could!) swap out the injector with mine. But it is hot in the garage and outside, even in the shade, so I don't really want to do that if there isn't a good reason to. Please advise.

Thanks,
Arno

I gotta ask, who goes out to ride or mess with their scooter when it is 109 degrees ?

.

You must be from Indiana. Everyone who rides in the South West. 112 in S Nevada yesterday.

You know, Salima is one of those wonderful women for whom life never stops ... not even at 109 F

Evap system. High time to disconnect the thing.

That was prior to the period of defective pumps affected by the Piaggio "upgrade"/recall. Not that one could not fail, of course, but they weren't in the defective series. The described symptoms don't seem to fit. Malfunction of the evap system/tank venting is very easy to diagnose. Loosen the filler cap and the problem goes away. (to belabor the obvious - if the evap system isn't malfunctioning, removing it won't fix anything )

The symptoms don't fit but that's no reason not to disconnect the evap system.

Hey, Arno. I don't have much to add, but it seems you are on the right track with the fuel pump. Maybe its a heat expansion issue, a small pinhole letting in air when heated up, after cooling, the contraction closing off the hole? I had an air leak in my pool water return, and although it was tiny, it kept the pump from running. hope you get it sorted soon, stay cool.

So, to sum it up, it looks like it could be a defective fuel pump or a clogged injector. Does it? Could either of these two systems cause the sudden change, always start up the engine again, still keep the scooter going (if slow), and improve some with cooler temperature, but not back to normal?

If these symptoms fit both, I'd be swapping the injector first, before I have the pump replaced.

Can you confirm that both systems could cause these exact symptoms?

Sounds very much like fuel pump issue, before you replace it, find someone with a set of pressure gauges who will easily be able to test it in seconds...

With the ignition turned on, and after its primed you should get about 2.5 bar and it should hold about 3.0bar when running... From the symptoms ill bet its 1/2 that.

The GTS doesn't use anything special in its fuel line connections so the gauges are very universal and plenty of garages should have a set... Let me know the outcome.

Have you adjusted the valves?

I don't know about water-cooled engines, but from my air-cooled perspective this was my first thought when I read this yesterday. The symptoms given are identical to a tight exhaust valve.

Interesting, I did not know that.

Could the exhaust valves change from perfect to tight within one second, and then stay there?

Thanks for that tip. We will have that done.

I conclude from it that, yes, fuel pumps can go weak but still keep going.

So I got a pressure gauge and am ready to check the pump's pressure.
Which of the two hoses is IN and which is RETURN?

PS: I found out. So, for future reference, it is B.

Verdict: weak fuel pump. Delivers 1.1 bar when it should deliver 2.5.
Cheekythomas wins, and I am hunting for a post-recall fuel pump now.

I guess you saw the 1.1 bar measurement.

The new pump is in, and after reading through your excellent thread on how to install it, I am ready to do this myself. Only question I have is the gasket: will the old one be reusable (then I can finish it this weekend), or should I wait till a new one gets in on Monday?

PS: in your sequence, why would you bother getting the piece of wood under the center stand, when instead you could remove the steel plate of your lift and make room for the wheel to drop?

Salima says, her GTS is now as perky as it was one year after she got it.

The fuel pump replacement was not as bad as I feared, and cheekythomas's tutorial was a great help. I will be adding some points to it that I learned along the way and missed in the tutorial. I ended up reusing the gasket after I cleaned it.

While the engine was dropped, I also checked the valves, they were right on target.

cheekythomas, no need to answer my PS. I figured it out why

Maybe if you said why, it might help the next guy.