Modern Vespa

Just lately my GT125 occasionally almost cuts out when accelerating from a standing start and take off seems to be poor now. Then when at top speed it almost feels like a brake has been put on, this happens at about 67mph and I don't think it is the rev limiter as until this week she would happily take me to 75mph. This bit is intermittent aswell, sometimes she is normal.

I do high mileage, 10,000k since April, my scooter is fully serviced but is now due to change lots of things such as rollers, belt, filters, plug etc...This stuff is on order already.

I am just wondering if anyone has suffered similiar so that if it is not an item I've got on order I can get it and do all the servicing at once.

Advice much appreciated!!

I don't think this applies to Euro-spec Vespas, but it's worth checking: after you've been riding at high speed and notice the cutout, pull over and open the gas filler. If air rushes in, then the tank isn't venting correctly, and has formed a vacuum. This is something that afflicts GTS250s in the US, but it is because of the evaporative emissions recovery system, which I don't think you guys have over there. In the US, it causes cutouts at high speed that feel similar to the rev limiter kicking in, but at speeds where you wouldn't expect the rev limiter to kick in.

The other possibility is that it really is the rev limiter, and it really is kicking in at a lower speed. Some possible reasons for this could be a flat spot on a roller or a groove worn into the variator pulley.

Thanks for the response Jess, I think the fuel supply is Ok, at least I never noticed air rushing in and generally I go everywhere flat out!
I will inspect al the other stuff at the weekend when I do the strip down, should be Ok so long as it is not an electrical fault...I don't understand stuff I can't see!

Hi, I had many of the same issues on my GT125 as well. Will soon turn 34K km on mine.

Jess, I don't think we have the venting issue since the fuel tank set up is somewhat different on the Euro version.

OTOH, I think the loss of "umph" will be fixed once you get the maintenance parts installed.

However, the stalling is most probably due to a worn spark plug. I also had an intermittent stalling issue that was caused by the spark plug wire socket not making good enough contact.

New spark plug wire socket and all is well.

I think your problem is that you aren't riding your T5 enough. I'd give you Jess's left nut for one of those.
I'm not the GTS expert though, so good luck.

Thanks for the advice, unfortunately the T5 is no more.......

Anyways I am just changing the plug and I notice that the sight bubbles on the air filter are black, last week only the rear one had a slight amount of oil in it as normal. I have took the air filter out and there was quite a lot of black oil in there....think this could be my problem! I have not got the new parts yet so I am afraid the filter is going to have to go in the washer and will do until the weekend!
Now my question is why has oil suddenly started leaking into the filter housing? Checked last month and it was dry, been dry for about 7000k.

The front filter on the variator inlet was also clogged with wasps and bees so I have obviously sorted that, could that have done it?

Thanks as ever.

So now I have a clean filter and new plug but it is just the same......actually take off might have improved and I'll put that down to the plug but its still not good at top end. Any more ideas?

When was the last time you changed your rollers?

The rollers have never been changed Spock, hence the planned maintenance this weekend. I hope it is just that.

change your belt and rollers and then report back.

i'd guess that's your problem.

also, don't listen to spock.... he's got T5 lust...
(but he still knows what's up)

best,
-greasy

Hey Greasy, your T5 and I had a quiet moment while your back was turned the last time I was at your place.

Thanks for your help, I think that the new rollers (my stuff arrived 10 mins ago) and belt will probably fix the performance issues, we will see in about an hour but what is causing all the oil to fill the air filter. I know the crankcase has a breather to the air filter so assume that is the route but why?
I noticed the engine oil was low last night so topped up and after 30 miles my sight bubbles are full of engine oil!

So now I have replaced belt, rollers, oil + air filters, plug, fresh oil and it still feels like something is holding it back at top end. Dunno what to do next, main dealer I guess but I know the guy is a dummy and they are very expensive so I am loathe to do that!

Don't know yet if I still have the engine oil spurting into the air filter problem, I have not been far enough yet.

I am not familiar with this scoot, but always have something to say, even though I have no idea of what I am talking about. Does this motor have a pcv Positive Crankcase Ventilation valve? If so, and if it is stuck open, there is your oil in the air filter, and the loss of power through a bad vacuum leak. Check it out. I am occasionally right, if not often.

I agree about the PCV valve being a likely candidate for the excess oil accumulation (although it's not uncommon for some oil to make its way out of the crankcase via that valve). However, I'm not sure that would cause a vacuum leak -- the PCV valve vents blow-by gases from the crank case, but vacuum is (AFAIK) the sole domain of the intake side.

The problem seems to be getting worse so I spoke to a mechanic who says that the piston rings must be worn to allow the crankcase to get that much pressure (or the head gasket is leaking into the crankcase).
So I am off to the shop in the morning to pick up a Malossi 210 kit.....maybe a PM exhaust also.....

If I still have problems after that I will set her on fire and claim insurance.....no can't do that, love her too much!

I almost set fire to a certain super beetle I once owned. I feel your pain.

Thanks all,

Now I am totally stuck....got a Malossi kit on though!!

Still got oil coming throught rocker cover breather pipe into air filter.

I am wondering what happens if the by-pass piston gets jammed shut (GT200 workshop manual page 153), would that increase the oil pressure so much so that it is coming out of the top of the rocker cover?
What is it for anyway?

Thanks to anyone who can help as usual!!

PS, with stock filter & exhaust do I need to rejet the carb? Thanks

Everyone I've talked to that's rejetted their 4-stroke hasn't seen any difference in performance. Leave it alone.