Modern Vespa

It's a carbed 2009 LX150. Even on the center stand, giving it full throttle it only accelerates slowly. The valve clearances are spot on, new spark plug, recent coil and spark plug cap, clean air filter, recent fuel pump. The gas is fresh, it's ridden daily year round with 43K miles on it now. It starts easy and still does 60 mph on a long flat road but struggles up the big hills much more than it used to. Seems this problem has crept in slowly over the past two months and now it's become irritating to wick the throttle and have slow response.

So I'm wondering if I should tweak the mixture screw on the carb? (I have to make a D shaped tool first). Or should I look elsewhere?

Any suggestions welcome.

Bill

Dirty carburetor and / or membrane to be replaced...

The mixture screw is only for idle so that shouldn't be the issue. You didn't mention anything being done to the CVT like new belt, rollers or clutch service.

I put a Malossi variator in my ET4 and that make a lot of difference for climbing hills with me on it. with that many miles on it, most of the aluminum in the variator could be worn and not pushing the belt as high as it did. Also the carburetor might be worn out too. There are aluminum and steel parts that rub together, and wear out over time.
When you let off the throttle, does the engine speed sort of float for a while before dropping down to an idle?

Slowly lowering the throttle involves the cable and relative knob, then the up and down valve in the carburetor body. But there is also another possible cause ... between carburetor and cylinder there is a gasket that could be slow and suck in air (if there is a sleeve check it too)

Hi Attila and Pink-

Thanks for the ideas. I was thinking the mixture screw was controlling the rpm between the idle jet and the main jet, both those jets seem to be working good.

I could have some dirt in the carb I suppose, and the carb membrane might be worn. But the carb seems to work good at idle and full speed.
This carb has never been apart so i may need to tear it down for inspection.

I replaced the belt and rollers about 1000 miles ago and always use OEM parts. I do the regular maintenance intervals but I could inspect the drive components again. The driven pulley was replaced a year ago when the seals started to leak. It's the original variator though. There are no notable grooves on the faces of the variator halves but the ramp side shows some slight "polish" wear where the rollers bear. Maybe it's time to replace it.

Bill

Yes, I sprayed the rubber intake manifold with carb cleaner, finding no obvious vacuum leaks. The vacuum lines are not leaking and the charcoal canister hose was removed long ago.

It may be just the accelerator pump is gummed up - does it stutter slightly as it gradually speeds up when you twist the throttle open? Easily checked by removing the air intake from the carb, and looking inside with a mirror as you push down on the accelerator pump - no need even to remove the carb to check this.

Hi Tortoise, thanks for the video, that might be the ticket, seems really similar to my issue. Well worth me having a look at these parts.

Bill

Thanks JimC, I will have a look at that. The mirror trick is a good tip.

Thanks all for the helpful feedback. I will check these carb items out and report back.

Bill

And the winner is... Attila!

So I removed the cover from the carb and pulled out the slide and needle assembly for inspection. I found 2 tears in the diaphragm. The slide was slightly scuffed and the needle looked good. So I'm off to get parts and see if this solves my issue.

Great job folks!

Bill