Modern Vespa

Hi I am new to the modern vespa family with an 06 lx150. i am needing some advice and have tried everything i have been able to research out of the million posts about my problem. I am getting a super rough idle, hard start, backfire on decel, and some smoke. the scoot only has a couple hundred miles on it and had been sitting. to try to fix the problem this is what i have done.
New Battery
Took the carb apart and cleaned jets
fresh gas and seafoam
detached EVAP unit following a thread on this site
adjusted the mixture screw-theading it all the way in and backing it out 1 turn and then a half turn to try to find a desired spot and no changes
New twin tip ngk plug
checked all lines
checked exhaust bolts.

just cant find anything wrong here? runs great with the gas on but on decel it pops and sputs al over the place and idles like crap.
thanks in advance

Welcome to the forum SILVER6!

I will try to help but more information is needed.

When you took the carb apart and cleaned the jets did you remove the jets and clean the passages? Did you remove the float, needle and seat and clean those passages? Was the float bowl tarnished or was there residue? Did you soak the carb or just spray cleaner through the jets?

Did you siphon out the old fuel before refilling? How much seafoam did you use?

Have you inspected the airbox, cleaned and re-oiled the airfilter?

Thanks for the reply,
when i pulled the carb i cleaned the 2 jets that i was able to take out with a flat head. i shot carb cleaner through both of them and the holes were visible with light through them if that helps, I didn't remove the float. i did remove the mixture screw to spray cleaner through that too. no tarnish or residue, everything looked new to me.
I did not siphon the little gas that was in it, i just added about 3oz with a gallon that i put in to play with it. i have since filled the tank with fuel and have burned through almost half a tank of that.

on a side note- is the hose that comes from the SAS to the manifold supposed to be sending air? when i start the scoot that hose does nothing when i had it off?

SILVER6, it sounds like a fueling issue. In my experience most carb cleaners that come in a spray can don't cut very well. I recommend Yamaha carb cleaner for soaking carbs and jets. I would remove the float and needle(aka-fuel inlet needle) that is hooked to the float tang and clean the passage where the float needle rests. I would also consider soaking the whole carb after disassembly. All it takes is a small amount of gunk in one of the passages to cause irregular performance. I would also soak the jets(especially the low speed jet).

Did you check the spark plug?. If not, pull it and check the color.
If the plug is white, you're running lean, too much air, not enough fuel.
If it's black, with grime it's running rich,.too much fuel, not enough.air.
If it's a grey or chocolate brown, it's getting a good mixture.

Checking the plug is like taking a temperature, it's a must for early checks.

By your description I'm guessing it might be lean. Lean problems usually present themselves under acceleration usually a hesitation or cough when you hit the throttle. Also, running lean tends to run hot too. It can present itself with a rough idle as it might be struggling to stay running. It's also common for the backfiring problem as well.

Once you figure out if this is the case it'll give you a better idea of how to troubleshoot.

Keep us posted.

Thanks- ON IT! My buddy works for an airline so i may send i to work with him and have him give it a real bath.

out of curiosity do you know what the function of that hose that comes from the SAS to the manifold in front of the carb is? there is nothing coming out while running and i couldn't suck any air through it either(don't ask)

That sounds like a good idea! I hope you get it sorted out. Be sure and report back and let us know.

new plug, smoke sometimes black, and a dark plug that i pulled out- seems super rich but no matter how much i change the mixture there is no change

Set your air screw back to factory spec(after the carb is thoroughly cleaned) and check that air filter.

The mixture screw is there for fine tuning, definately wont help with as bad as your issue is. I'm leaning toward either a vacuum leak or a vacuum hose or diaphragm being plugged, those are tricky lil' issues to find. The air filter is also a possibility, but to be this bad it's gotta be disgusting. Do check the filter first, i agree with that.

well i just got the scoot and it had 170 miles on it when i got it if that says anything. i pulled the filter cover off and the filter looks brand new and still has a little oil on it so i didn't screw with it.
Lets talk about this vacuum business? i just cleaned the hell out of the carb and the jets and anything i could take apart and everything looks brand new, took it out for a spin and again rough idle, backfire, little smokey, and drinkin fuel. at idle it chugs rough like a harley.
can someone explain to me the vacuum system and i can run through that?

Well, the vacuum has a number of purposes, but with you're issue, it's being used to help provide a consistent fuel and air pressure (mostly air). If you have a vacuum leak, it usually allows for either too much air causing lean issues, or if on the return side, loosing air sort of funking up the pressures.

It's not as common for a vacuum leak to cause rich issues, but it can happen. Especially if you're scooter is using a vacuum Diaphragm to deliver the fuel instead of gravity. If one of the lines is clogged, or one of the many diaphragm's aren't working properly it can cause very similar issues. Basically air not able to get where it needs.

Looking for leaks is tricky, but a stethoscope can help. As far as cloggs a little harder. Again, I'm not saying this is the issue what you're dealing with, a possibility.

Thanks for the tips. I am going to open up the air box tonight and see if something lies within that. I really feel like it is starving for air by the behavior. I would really like to ditch and plug the evap and SAS holes in the manifold to eliminate that crap from my equasion, i am pretty sure doing that won't effect anything, arent they both there for emission reasons?

Gotta love CARB..... Ya, they're just for emissions. There's a write up on how to ditch them in the FAQ section.

Spark Plug Cap

Got a new plug, NGK twin tip. cleaned carb all up. cleaned filters. I am just getting a gross amount of back pressure on decel and idle, it's drivin me nuts what could i be missing here?

So after reading about different ideas here on the forum, i blocked off the SAS exhaust pipe and now NO MORE BACKFIRE!!! hopefully there is no long term effect here but it runs like a champ. i still have the rough idle and sorting that out but the backfire was great to eliminate from the equation.