Modern Vespa

Man can't get her to run smooth. Idles well, but rolling on the throttle slow it stumbles bad. Giving it full throttle off idle it stumbles bad. 3/4 throttle it does ok ish. Ive gone through the carb 3 times now i'm sure I have the diaphragm and everything right. I've tried playing with the mixture screw but its not helping the stumble. Only other things I can really think of are maybe rejetting? I went up to a 38 pilot but that had the same results, maybe I need a new/different main?


https://www.youtube.com/watch?v=41igLr5ymrc

When you first start it and it's on the enricher circuit do you have the problem? If it only happens when warm then I would think its the Pilot jet and idle circuit. If it happens at full throttle as well then something is dirty in your carb.

Do you have a 190 on it?
No? Then you do not need to upjet.

Pull the evap line off, you don't need that anyway. run thru the carb again. Make sure the accelerator pump works. Check the choke well clean and auto choke for proper operation. Pull the a/f mix screw and clean that as well. Air should blow freely thru the idle circuit.

If it's running like ass before 1/2 throttle it's not the main. You're looking at idle, choke or a dirty carb, maybe fuel delivery.

Circle back and check.

Also, run back around and check your intake tract. Air filter is good, not wasted or overly saturated. Box and tube aren't compromised, intake manifold isn't cracked and leaking, no vacuum leaks on the lines.

Good luck!

-g

Found out its missing this silver needle sleeve. Anyone know where I can pickup another without having to buy a whole carb? I tried scooterwest but its not even shown in their carb diagram.

2006 LX150 stock Keihin carb.

So I have been touching a lot of carbs these days and I've found that no matter how good of a job I "think" I do I have had to go back in to EVERY SINGLE ONE to re-do my work to get it right. So that entails using a can of compressed air (duster) to blow through the ports. Wear safety glasses if you aren't sure where the air is supposed to come out! I also always re-check the jets! leave the float bowl full of some gas but do press the accelerator pump plunger in a safe area to observe the "gas squirt-gun" is functioning properly.

I am replying to you because the last scooter I went through kinda acted like yours and when I went through it I found some deposits on the black end of the thing to the right of what you circled above. It's the float valve plunger with the black tip. Very simple to get to once you remove the float bowl and set it aside (WITH GAS IN IT FOR A QUICKER RESTART LATER!)

Pro Tip: just loosen the screw that holds the pivot bar and remove the couple of parts.

I am not sure if the deposit was where this had stuck semi closed or not but I used my fingernails to remove it all and make it look nice and presto-change-o all good!

For some reason, a lot of people think changing the jets will fix a bike that was running right for years and thousands of miles, but suddenly doesn't run well, They will sometimes work around a problem and give you a lot of what you don't have, but this isn't fixing the problem.
If it sat for a long time, and you've messed with it over and over again, it's time to buy a carburetor.

Time to start looking around the shop floor (n.b. it is stainless, so a magnet isn't gonna help ya on this one).

There's no work around here. You need the correct piece- so if you don't find it, you'll need to buy a busted carb for parts or buy a replacement.

I'm 90% sure it was never there. I've taken apart a lot of carbs and i'm generally pretty good at not losing pieces. It runs without it, just poorly. Which is how its always run... ive given a good look through the garage and no luck. So i'm leaning on it was never there. (this is a used scooter of course, and there were signs the carb has been taken apart before, so previous owner could have lost it)

I emailed scooterwest with some pictures, hopefully they have a spare laying around.

Well shit. lol whos the idiot now!? Just went through my garage garbage can and guess what I found? Honestly can't believe I managed to do that. Oh well. Onward!

I always find the small missing parts when I'm working on another scooter. It then takes time to remember which one it came off of.