Hey all - I joined this forum a couple years ago but never posted. We had a 2006 LX150 that was a joy to ride, sold it to buy a Moto Guzzi V7, but now we're back on a Vespa, this time a 2007 LX150. Our last one was a strong little runner - so I know what they should feel like. This new scoot is having a problem that is leaving me quite perplexed...
This LX150 has 2,200 miles on it, and was last registered 5 years ago, so it's been sitting a while. When we checked it out it cranked right up and idled perfect. When I test rode it I noticed it would bog when wide open. The seller was selling for a friend, who he said mainly used this bike for bicycling events as a pace vehicle. He thought it was just old gas - and I suspected a simple carb clean would get it back up to snuff, boy was I wrong! Anyway, I haggled on the price a bit and rode it home - doing about 40-45mph indicated as long as I stayed under about 3/4 throttle it was running ok.
Ok, so I get home and I start to tackle the problem. I'm just going to list off what I've done so far over the past month or so:
1. Cleaned carburetor - as suspected the main jet and emulsion tube were partially obstructed. Tested the auto-choke. Ran slightly better but the problem persisted...
2. Replaced fuel tap/petcock
3. Replaced fuel line
4. Replaced vacuum line to petcock and SAS valve
5. Capped off EVAP vacuum line
6. Replaced Intake boot gasket
6.1 GAVE UP AND BOUGHT BRAND NEW CARB
7. Cleaned and inspected airbox - old filter was clean - replaced anyway
8. Checked intake tube from airbox to carb for leaks
9. Sprayed carb clean and map gas all around to try to find a leak - no change in rpm
10. Replaced Spark Plug (NGK CR8EKB - gapped to 0.8mm)
11. Replaced intake boot anyway (thought maybe it had a hairline crack that would only draw air at full throttle)
12. Checked compression (~160psi w/ throttle closed)
13. Checked valve clearances - all good
14. Replaced coil w/ Racing Coil from Scooter Parts Co (829671R)
15. Replaced spark plug AGAIN - Denso U24ESRN this time
16. Ran without Exhaust (wow that's LOUD )
17. Ran without Fuel Cap
Still doing the same thing...
I'll try my best to describe exactly the symtoms, as I know it's really hard to diagnose something like this over the internet. The bike starts up and idles perfect. At partial throttle openings, it revs up and acts like a perfectly healthy engine. At between 1/2 to 3/4 throttle you can get up to 40-45ish mph and everything seems fine.
At greater than 3/4 throttle, the engine bogs and loses power, surges a bit, and continues to accelerate but slowly - getting little spurts of power. Once you get up over about 30mph things start to smooth out and it starts running better. It will eventually get up to about 50mph and, while still surging a bit - is running quite a bit better. One other note - when you wack the throttle open you get a little spurt of what feels like nearly full power.
This behavior REALLY makes me feel like it's running lean or starving for fuel - either the carb isn't getting the fuel it needs, the needle isn't raising up like it should, or I have an air leak. However, the carb is BRAND NEW - the fuel tap and clear fuel line are band new, the vacuum lines are brand new, etc etc (see list above).
About the only thing left is the CDI. Unforutnately there's no way to test that and it's expensive. There's also a pickup at the stator but I would imagine that would be more of an all or nothing spark situation.
Mainly posting to vent about the situation but I'm all ears if someone has any other suggestions. I have not checked the CVT yet but judging by the engine sound an how it's directly related to the thottle opening, I'm hesitant to think I have a problem there...
It's a good looking little scoot - help me get it running like it should be!