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Hello
I'm new to this forum. I'm in need of help. My PX loses power after idling at a traffic light for a while. The PX will want to die and stall out. It gets going after twisting the throttle wide open till the mix is back. It usually happens when I ride around 10 miles or so. Any suggestions on my carburator tuning? This is what it looks like at the moment.

20/20 Carb
a/c: 160
BE3
110 main jet

idle jet 155/160

Polini venturi air filter

SIP Road II muffler

I'm at sea level. Any help will be appreciated.
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Veni, Vidi, Posti
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What does your plug look like?
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I will check tonight when get home. I just installed a new Br7hs over the weekend. The old one was brown and dirty looking.
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Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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110 main jet sounds rather high for a 150. Cat exhaust would've been a 98, de-catted with a Sito+ would've been around a 102. SIP Road maybe a little higher, but 100 sounds rich to me.
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I went from 102 to 110. SIP suggested to go 5-8 points up when installing the Polini foam air filter with funnel intake. I should have a 105 lying around. I'll try that.
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Molto Verboso
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You didn't mention the air filter change.
What's the plug look like?
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What's your mixture screw set at? Throttle response should be a crisp rev up and fade down
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I gotta pull the plug when I get the chance. It's dark now I don't have a garage unfortunately. I'm not sure how to adjust the mixture screw. I know it's in the back of the carburetor enclosement, but cannot seem to get a screwdriver in place because what I believe is the CDI. Would I have to remove CDI?
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Its tight quarters back there and it may help to unbolt the CDI so you can get access to the mixture screw. Once you can get access back there the screw is covered by a black rubber plug. Pry that out and then with a long screwdriver you can adjust the screw.

If your scooter normally revs up crisp I wouldnt focus on the mixture screw, but if its a 1-2 second bog and then clean rev up it wouldnt hurt to try and clean that up.

Whats your new plug look like?
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Molto Verboso
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If it's an 05 it'll have the later style airbox and carb with the long hex head mix screw sticking out the back - could be a 6mm or a 7mm, I've seen both. That one's even worse to get to. A torch bent wrench with an extended handle works best.
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Thank You all. I've yet to set the mix. I will do so. For the moment I have went from a 110 jet to a 108. When I have a long ride again, I'll test to see if it loses power after a long light. I did check the spark plug. It is new. It has seen less than 75 miles. It looks like it's been fowled. I'm not sure, please advise. Here is a pic of the plug.
Forum member supplied image with no explanatory text
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Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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That's a fouled plug that sooner or later will short out the spark = loss of power.

Was that after you adjusted things?
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PDXJIM, thank you. That was two days ago with a 110 main jet. Was I running too rich?
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Molto Verboso
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Looks like it. Should be mostly dry, chocolately brown.
Have you made sure the choke isn't sticking open?
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The choke is not out. About 2 months ago, I drained the oil and mixed 2% at fill ups. My sight glass was cracked and leaking oil. I decided to just not deal with oil spots in my parking spot.
Anyway, let's see what happens. I do like the added power of the polini air foam intake and Venturi funnel, but if the bog and power loss continues I'll revert back to the bellow intake and piaggio air filter. And or play with the mix screw.
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Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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Unless it's backed nearly all the way out, the mix screw will mostly affect it only at idle.
The main jet will affect the top 2/3 throttle.
The slow-running jet will affect all, but mostly the lower 1/3 throttle.
The mix screw is only to fine tune the slow running jet when explicitly at idle in order to obtain a steady tickover. It becomes irrelevant as soon as the throttle is opened past the idle position.

I think you mean your slow running jet is a 55/160, don't you?

You need to do some serious plug chop runs to get that filter and venturi dialed in. It looks too rich now, but which circuit is too rich? Slow? Main? One could be right on and the other off.
You don't want to wind up with white plugs and a seize.
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It is all starting to make a bit more sense. Thank you. Yes you are correct, I'm running a 55/160. What would you suggest?
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Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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That's probably about right, given the air filter, etc, but I can't suggest. You need to do range specific plug chops.
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