Modern Vespa

I bought a used 2006 Piaggio Fly 150 with 7600 miles on it around 2 months ago and aside from a few minor issues it has been running great. Got it up to 66mph on the highway, GPS speed, new tires, battery is strong, new spark plug, fresh brake fluid and oil, etc.

I recently had a problem where fuel wasn't traveling from the tank to the carb even with the engine running. I looked at the fuel tap and there was some grunge built up on the bottom of the vacuum tap and in the vacuum tube. I thought the tap was just worn down and was sticking shut, or was requiring more vacuum to operate than was being provided by the airflow. I ordered a new part and fresh tubes, but in the meantime I was manually pulling a vacuum when I wanted to ride using a small syringe and a clamp to keep the vacuum to the fuel tap on.

It worked, with a few bad rides where vacuum was lost to the fuel tap and I had to pull over and pull it manually again to get gas in the carb, but it still drove perfectly at highway speed.

When the part came I replaced it, and while I had the body trim off I decided to pull the Evap canister off as well (the evap tube running to the carb had already been removed/crumbled to dust when I bought it, only the line going to the engine side manifold was left)

I replaced the fuel tap, put fresh fuel and vacuum lines on, and capped off the manifold nipple for the evap line, rerouting the evap line to vent onto the street in case of an overflow.

After putting everything back together, the fuel tap is working perfectly again... except now my scooter has a top speed of 35 mph at full throttle open, and very poor acceleration to get there.

I was completely confused and dismayed. I tried reversing what I had done, putting the Evap system back exactly as it had been but that didnt fix it. I hadn't changed anything about the carb yet, so I took the carb apart and cleaned it, making sure all the parts were working as intended.

That didn't help either.

I'm completely at a loss right now. It ran perfectly fine the day before when I went to work, full power, got to its usual highway speeds. I changed the fuel tap and removed the evap canister, capping off the useless nipple, and suddenly it doesn't want to go fast anymore, even if I reverse what I did.

The engine SOUNDS perfectly fine, no knocks or stuttering that I can tell, idles just fine, it's just that opening the throttle all the way only gets it to 35mph now, and slowly at that. Like the engine just decided 35mph was it's new top speed.

I've been racking my brain trying to figure it out. Like maybe the engine is losing compression now. But it sounds the same aside from not reaching high revs, and it didn't make sense to me that it would just fail suddenly overnight.

I DID also remove the battery when I removed the body work so I was also wondering if maybe something electrical changed? Like the immobilizer or virgin circuit?

I honestly need help, I have a limited budget and it's my main transportation to and from work right now. I can get there going 35 if I have to, but I just want it to run correctly.

sounds like you've got a vacuum leak somewhere.

lets see some pics and see if we can sort this out.

I thought only fuel injection bikes are supposed to be capped at the evap hose fitting and carburetors are supposed to have a make shift air filter at the evap hose fitting?

Can do. This morning I did a little vacuum test on all the parts accessible from under the seat by spraying some carb cleaner around and across air connections and listening for changes in the engine.

I did Airbox->Carb air tube, around the Automatic Choke/Starter on the carb, the Carb->Manifold rubber connector (I had an air leak there in the past, but I already replaced the gasket there a while back and it doesn't have an engine reaction anymore), the vacuum line from manifold back to the 'T' junction, the vacuum 'T' junction back to the vacuum ports on both the fuel tap and the SAS valve. None of them produced any engine response.

While doing my check I noticed the air intake tube coming from the airbox has a tear in it at one end, but I doubt that is the ultimate problem, as it would just be sucking some air from atmosphere rather than through the relatively small air filter. (I ordered a replacement that comes on Wed, so we'll see if that actually helps at all)

My next course of action is to take a look at the CVT, but I doubt that is the ultimate problem either. I replaced the 2006 OEM belt on it soon after i bought it, and cleaned the variator plates/discs and installed new rollers, as well as giving the pulley spacers and splines a wipe down of any built up residue, and it was running fine for more than a month since then.

My final idea is to rent a compression testing tool from a local auto parts store and hook it onto the spark plug hole to test engine compression (the factory manual states a 10.5:1 ratio = 154 psi)

My thought is that with only 9000 miles on it as of now, and having always been properly oiled, the metal engine parts should all be in perfectly working order still. BUT I had the thought that, if I had to replace the gasket on the air intake manifold due to age, the rubber sealing components in the engine might also be failing quietly due to degradation over time.

Thoughts?

There are 2 places the evap hose connected to, one is a nipple on the rubber air manifold connection just after the carb, and one is on the carb breather that goes to the float bowl. I DO need to make a makeshif filter for the float bowl port, but it already came like that when I bought it and drove fine for months since so it was a low priority I kept putting off. That port is left open to air to let float bowl breath, I only capped off the manifold connection, as it was recommended to do so during the procedure.

EDIT: As an additional note, I HAVE already tried leaving both ports vented to atmosphere, reinstalling the Evap system entirely, and leaving off one port but not the other and each time the engine still had low power (though the sound and power were less stable when vented to atmosphere)

Is it possible that there is a vacuum leak going to the SAS? Maybe just Cap that hose off at T connection and try again.

slap a piece of duct tape over that crack in the intake and see what happens.

that tear is probably what's causing you grief. with a CV carb, the intake tract is tuned so any changes, even slight, can result in poor running issues.

I highly doubt you've got a compression issue seeing as that it ran just fine before the work. unless it ingested something, that is.

Tried wrapping duct tape around the split, and even secured it down with 3 zipties to make sure it was snug and wouldn't peel off.

No change at all, sadly, but I do have a replacement for that coming in the next day or two.

I have the net 2 days off work so imma take more time to check more stuff.

double back and check the work that you've done. I'm sure it's something simple that you're overlooking.

because it runs, but only up to 30 it sounds like the vacuum diaphragm on the carb is compromised or not working properly. i'd start there, or giving a real hairy eyeball to the intake tract from the air filter, air filter box seal, inlet and breather all the way to the valves with a stop over in carburetor town.

good luck and keep us posted!

B I G S U C C E S S

It was (at least mostly) the vacuum diaphragm in the carb. When I cleaned it the first time I thought for certain I'd gotten it seated properly. When I realized the power loss and originally re-opened the carb, not only did I not notice that it hadn't been properly seated the first time, I didn't seat it right a second time and air was escaping past on one side.

THIS time I (think) i really, actually, truly got it on right. I immediately noticed more power from a cold start.

I took it up and down the block and it seemed much better. I put a gallon of gas in it and took it up and down the access roads to give it a test. It's about 45f today with a 15mph wind from north to south, I took it a mile up and down, both ways, twice so it had time to warm up.

Now, it does mostly work, but it still seems a little under-powered: Going against the wind it didn't want to go over 45mph, and with the wind 50-52mph. That is still a far cry from how it was before, but it is a huge step forward.

The diaphragm doesn't look torn anywhere, but I'm wondering if it still isn't sealing 100%. Either that or maybe it's just an air/fuel ratio problem from here on out?

I was considering taking some general-purpose waterproof grease and applying a very small film just on the lip of it to keep it stuck down in the little groove when I put the case back on it and help seal up any remaining marginal air passage.

Thoughts?

So that carb has a CV top like a Buddy 125 carb? If so, that rubber "seal" kicked my butt the first time we met! Hopefully that was your problem and it sorted now. Congrats on figuring it out!

No problem with a little dab of grease on the lip to keep it in place.

Double check the needle is fully seated and secure in the slide and not hung up or bound.

Also check the needle guide is the right way around!

You're close to getting it wrapped up!

And look for any pinholes or tears in the rubber part. I had a small pinhole on the Buddy carb.

Took it apart (again) yesterday for one final look over. No pinholes in the diaphragm, and the 3 little plastic feet on the needle guide/holder were correctly aligned with the little divots cut out for them on the inside of the venturi. I sealed it all back up, this time applying just a little bit of multipurpose grease to the groove the diaphragm sits in and the lip of the lid that clamps it down, put it all together carefully, and it was perfect.

Throttle response is great again, and today I took it to work at full speed, 60mph true speed (70 on the needle) against a 7mph headwind, pretty good for a carburated 150cc scooter from 2006.

Thanks all for the advice and responses, so glad this wasn't a fix requiring some multi-hundred dollar work/part.

Now if only I could check the Air-Fuel Ratio in a convenient way... I'm sure its tuned well enough from the factory, but it would be nice to know for sure...

Anyway, this problem is considered by me to be FIXED, but I'll keep a careful eye on it, thanks again!

To adjust the idle mix ratio without measuring CO levels:

Reduce the idle speed as much as you can while the engine is still just idling smoothly. Now tweak the mixture screw out a quarter of a turn. If the engine splutters or stalls, move it back and try the other way. If the engine speed increases, reduce the idle speed again - rinse and repeat until the idle speed adjuster is at a minimum. Then you'll have the correct idle mixture for the engine.

I recently removed my EVAP system mainly because I ruined a perfectly good air filter by overfilling my gas tank. That won't happen again, and if it does, it won't matter.

I didn't like the idea of leaving that bowl vent port open, nor did I like the looks of the improvised piece of hose with foam wrapped around it. So, in my past I worked with some lavalier mics that have very small foam windscreens. I bought a 5 pack of them from Amazon for around 5 bucks.

It fits (once I bushed out the port opening
: I used a vacuum cap with the end cut off as a bushing). I WORKS! And it is VERY inconspicuous. Want one? Send me a pm and I'll mail it to you. No biggie. [img]/Users/rick/Desktop/Screen Shot 2023-02-19 at 2.28.14 PM.jpg
[/img][img][/img]

The technical name for those windscreens is "spoffle".

Little known fact.

Thanks for posting your success. I just took my carb apart for cleaning and now having same issue (new to me 2007 fly 150, sitting for 2 years) I'm sure it's the diaphram as you have found. good work, saved me lots of troubleshooting.