Modern Vespa

In 2017, I felt like undertaking a project and decided to rebuild my 2006 Vespa LX 150 with only 2,000 miles on it. Yes, it was running fine. Yes, I now realize how dumb this was.

I got it all apart, cleaned everything, scraped off any remnants of old gaskets, installed all new gaskets, torqued everything down to the torque specs, and rebuilt my carb while I had it apart. When I got it all back together and it started, hurray! But my joy was short lived since now it runs worse than before the rebuild.

Symptoms:
When at a stop (stop sign or pulling out of a driveway), and I give full throttle, it does not go. It hesitates for ~4-5 seconds, then slowly moves forward. Once it's going about 5-10mph, it will accelerate like normal.

Troubleshooting:

-I've done a valve adjustment, didn't help.
-New spark plug with correct gap set
-New air filter
-I took it in to a shop thinking it was just a carb air mixture adjustment, and they charged me $175 to tell me they couldn't adjust it to fix it and recommended a $300 full car rebuild and ultrasonic clean. Well a new carb is $300, so I took it off and had my friend clean it in his ultrasonic cleaner. AFter reassembling, it still didn't fix the issue.

Possible problems:

-Could it be something in the fuel line? Do I need a new fuel tap?
-Even though the carb is clean, should I replace with a new carb to officially rule that out?
-Do I just suck at adjusting the carb? I've followed several online guides, and I have a tachometer so it shouldn't be that hard.
-Will checking the compression give me any additional information?

I'm pretty much at a loss of what my next steps are. I'm ready to sell the bike, but I'd really like to fix it first since as is I probably can't get very much for it.

hey there... i dont have your specific bike so it could be something specific to that model..i know some had issues with fuel taps

however for basic troubleshooting, it sounds like it could be the carb

questions:

how many miles on the rebuild and did you get new rings or just a gakset set?

does it idle ok? what rpm does it idle at?

how many turns out is the mix screw?..the standard is typically 1.5 turns out

are you using the stock airbox and filter and can you confirm its on there snug?

what happens if you slowly ease on the throttle, does it seem to work better than if you whack the throttle wide open? if you have a choke, if you have the choke on and then whack the throttle does it seem to behave better?

questions:

how many miles on the rebuild and did you get new rings or just a gakset set?
Got a new gasket set. I have about 200 miles on this rebuild, mostly just trying to troubleshoot or riding it when my car is in the shop. I did not install new rings.

does it idle ok? what rpm does it idle at?

It idle's fine. It idles anywhere from 1400-1800rpm depending on how i set the idle screw.

how many turns out is the mix screw?..the standard is typically 1.5 turns out
I've tested it at all the way in, 2 turns out, and further out after attempting to adjust it, probably somewhere around 3 turns seemed to be where the rpm's maxed out.

are you using the stock airbox and filter and can you confirm its on there snug?

Yes, using the stock airbox, I'll check it tonight.

what happens if you slowly ease on the throttle, does it seem to work better than if you whack the throttle wide open? if you have a choke, if you have the choke on and then whack the throttle does it seem to behave better?

Yes, seems to have a magic spot ~1/4 or 1/3 into the throttle twist where it will inch forward. That's the only way it's rideable. It has an electric choke, so I don't think I can test it with the choke on or off other than letting it warm up. But I've tried both and it still boggs down. Also when I adjusted the carb it was warm.

Is the diaphragm seated correctly?

at first glance i might say that your needle is too rich....do you know which notch the clip is on?

on the other hand if you didnt change anything other than swap gaskets and clean it, and it was running good before...that makes me wonder if its not related to the carb....

do you know if you have good compression from the cylinder?..i wonder if you are experiencing a leak somewhere...maybe at the reed cage

@ Nightwing: Yup, I've double and tripple checked the diaphragm and o-ring in the carb.

jixaw: I'm not sure, I'll open up the carb and post a photo. I also cleaned the carb when i was rebuilding the engine, so I could have changed something in advertently.

I have not checked compression yet, I guess that would be a useful datapoint to have.

A couple of things to check..... and they may have already been mentioned...

- Did you remove and clean the airfilter? - is it seated back on the carb correctly?

- Did you change any of the settings on the carb, the "low rev" mixture is controlled by the air/fuel mixture screw - check the setting of this by carefully screwing it all the way in until it stops (soft stop) whilst counting the number of turns so that it can be reset if required. Then compare that number of turns to the factory setting which is probably somewhere about 1.5 - 2.5 turns out.

- Is the Autochoke working correctly and seated into the carb fully?



Hope this helps.........

A couple of things to check.....

- Did you remove and clean the airfilter? - is it seated back on the carb correctly?
I've been dealing with this for over a year, so I've taken it on and off the carb many times. I'm sure it's attached correctly, and the intake is attached correctly. Honestly I cleaned and checked the air filter a year ago when this first started happening, but I haven't checked it recently, good idea.

- Did you change any of the settings on the carb, the "low rev" mixture is controlled by the air/fuel mixture screw - check the setting of this by carefully screwing it all the way in until it stops (soft stop) whilst counting the number of turns so that it can be reset if required. Then compare that number of turns to the factory setting which is probably somewhere about 2.5 turns out.
Yeah, i've done this and set it at 2 turns out. and tried tuning it further out to maximize the revs, but both settings did not effect the bog down.


- Is the Autochoke working correctly and seated into the carb fully?
I've checked that it's seated fully, but how do I verify if it's working correctly?

The autochoke on these models can be temperamental.

They either "go wrong" in one of three ways....

1 - check the electrical connection is snug and clean

2 - check that the autochoke is seated into the body of the carb fully - a bit of white grease around the seal helps Ive found

3 - most common is that the autochoke doesnt extend enough or too little, its a wax unit that when gets warm it extends to block a choke gallery inside the carb. sometimes they dont extend when getting old so that the carb is "stuck on" other times they work so that it is always "stuck off". If it starts from cold ok then it signals that it may be stuck in the on position but doesnt extend to block the gallery hole so it runs too rich at idle hence giving you a "bogging" problem until the carb opens up to clear it at higher revs.

Remove the choke from the carb and turn the ignition on and measure the distance that the autochoke need sticks out initially when cold and then say ten minutes later


Like this............. https://www.sip-scootershop.com/upload/files/modelle/00001152_015.pdf

fabio,

Awesome, I'll give this a try, thanks so much.

I think it is the same carb as an lx50 so no needle clip.
I fixed the same issue on mine with the diaphragm. It took me probably 6 tries to get the diaphragm to seat and slide correctly. I always thought that it looked good put the cap on and same no middle throttle, I posted details a while back

Clean the diaphragm with dish soap. Make sure that the plastic needle seat part is not covering any holes. Install it convex instead of concave, when the seal locks in you will know it. Test by blowing small amounts of compressed air into the slot at top of intake with carb off. It should slide easy.

@lasm01: Thanks, I'll give that a try as well.