2005 PX150 carb air mix screw
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Member
Vespa PX 150
Joined: 06 Jul 2007
Posts: 19
Location: Nazareth, PA
Tue Aug 22, 2017 11:25 am quote
I just rebuilt my carb and it is running better, but it keeps bogging down at certain points. What size is the head on the bolt for the air mixture on the carburetor? I have looked online and everyone seems to have a bladed screw whereas mine is a hex. It's really tough to get into the spot and a socket won't fit. Any ideas?
Member
2016 Vespa GTS 300 super.1979 Vespa px125/177Polini,2005 Vespa p150x Seri America
Joined: 28 Oct 2013
Posts: 30
Location: Indianapolis Indiana USA
Tue Aug 22, 2017 12:05 pm quote
It's a 6 mm hex.After you pull the plastic cap off the hex.I modified a 6mm box end wrench in a 90% angle to access it.A little tight with the starter motor in the way but can be done.Have a little patience with that.
Molto Verboso
2005 PX150 In a Love-Hate Relationship with a 2-Stroke Vespa Since 2007
Joined: 01 Sep 2007
Posts: 1813

Tue Aug 22, 2017 4:23 pm quote
There are 2 sizes, 6mm and 7mm. The 6mm ones have slightly rounded edges around the top of the hex head. The 7mm ones are sharp edged. Hard to describe. The long shaft that's hidden under the black cone-shaped grommet is also different shaped but you can't really see that without pulling the carb out.

6mm one
https://www.dellorto.co.uk/shop/dellorto-motorcycle-carburettors-parts/carburettor-parts/si-parts/si-mixture-screw-2/

7mm one
https://www.dellorto.co.uk/shop/dellorto-motorcycle-carburettors-parts/carburettor-parts/si-parts/si-mixture-screw-3/
Molto Verboso
2005 PX150 In a Love-Hate Relationship with a 2-Stroke Vespa Since 2007
Joined: 01 Sep 2007
Posts: 1813

Tue Aug 22, 2017 4:44 pm quote
Here's what I made to adjust it, which sounds similar to what FunSensei came up with.

A box wrench bent 90 deg with a torch, the other end cut off and ground to a taper, then hammered into a piece of copper tubing to make a nice long handle.

Mix screw tool.JPG

Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1657
Location: London UK
Tue Aug 22, 2017 7:42 pm quote
Ingenious but does that spanner fit in the glove-box?

Another way is to cut about 5mm off the end of the mixture screw, then saw a thin screwdriver slot into the top of whats left.
Molto Verboso
2005 PX150 In a Love-Hate Relationship with a 2-Stroke Vespa Since 2007
Joined: 01 Sep 2007
Posts: 1813

Tue Aug 22, 2017 8:32 pm quote
Why cut the end off?

I tried the slot idea and the starter motor is in the way.
Hooked
2005 Vespa PX 150
Joined: 23 Feb 2010
Posts: 248
Location: Houston, Texas USA
Tue Aug 22, 2017 8:46 pm quote
Here's mine, inspired by pdxjim's.
Works like a champ!
I did break the wrench on the first bending attempt.
Heated it with a torch for the second one.
Then some glue, some hammering on the copper tube, and a valve stem cap for the final touch.

idle mix screw wrench.jpg

Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1657
Location: London UK
Tue Aug 22, 2017 9:00 pm quote
pdxjim wrote:
Why cut the end off?

I tried the slot idea and the starter motor is in the way.
Ah, that's because if you cut the slot before shortening it, the starter motor is in the way
Member
Vespa PX 150
Joined: 06 Jul 2007
Posts: 19
Location: Nazareth, PA
Wed Aug 23, 2017 2:18 am quote
Thank you! I think my wrench sets only go to 7mm so I'll have to go shopping and get a couple and see what kind of fun I can have with bending the wrench and see how it goes! Thanks again!
Molto Verboso
2005 PX150 In a Love-Hate Relationship with a 2-Stroke Vespa Since 2007
Joined: 01 Sep 2007
Posts: 1813

Wed Aug 23, 2017 7:23 am quote
Don't try bending the wrench without torching it or as Aiosi says, it'll break.
Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 297
Location: Central Ohio
Thu Aug 24, 2017 8:28 am quote
I have had the same issues when trying to adjust my idle mixture screw on my 2005 PX150. I removed the small plastic cap that covered the screw using 12 inch forceps. Then, I turned the screw 1/4 turn counterclockwise using the same forceps. Later, I purchased a 6 mm flexible ratchet that had the 5 degree increments for use in tight places. I then put a small mark on the ratchet part using a gray Sharpie pen. I set the ratchet initially and after an adjustment, I look at the mark and know exactly how far I moved the screw.

My new 2005 PX150 is now running great with no off idle bog. It pulls strong from zero to top speed and is a real pleasure to ride. For reference, here are the adjustments made to my 2005 PX150:

Main jet stack: 102/BE3/160
Slow idle jet: 55/160
Drilled air cleaner
Slow idle screw: 1/4 turn CCW beyond the stock setting of 1 3/4 turns.
SIP Road 2 muffler
NGK BR7HS spark plug

DSC05756.JPG
2005 PX150

DSC05966.JPG
Idle mixture screw 6 mm on back of air box protruding through rubber grommet. .

DSC06047e.JPG
Flexible 6 mm ratchet with gray mark for orientation.

Veni, Vidi, Posti
T5s
Joined: 19 Feb 2009
Posts: 17006
Location: The West Of Yorkshire ... Gods Country
Thu Aug 24, 2017 10:10 am quote
Bell ends
Don't fuck about ..... shove a socket on one of these ..... Some people just wanna make life hard

If the sockets too deep put a nut inside first

61BYGrriFDL._SX355_.jpg

Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: 06 May 2016
Posts: 297
Location: Central Ohio
Thu Aug 24, 2017 11:29 am quote
Re: Bell ends
T5bitza69 wrote:
Don't fuck about ..... shove a socket on one of these ..... Some people just wanna make life hard

If the sockets too deep put a nut inside first
You obviously do not have a PX with electric start and want to adjust your idle mixture screw.
Addicted
74 Rally 200. 79 P-whatever
Joined: 07 Jul 2008
Posts: 570
Location: Austin, TX
Thu Aug 24, 2017 11:34 am quote
starter motor makes things more difficult than they need to be haha.i always used a swivel socket with smaller ratchet set, works fine.
Veni, Vidi, Posti
T5s
Joined: 19 Feb 2009
Posts: 17006
Location: The West Of Yorkshire ... Gods Country
Thu Aug 24, 2017 12:15 pm quote
pfffftin
electric start .... do i look lazy
Addicted
74 Rally 200. 79 P-whatever
Joined: 07 Jul 2008
Posts: 570
Location: Austin, TX
Thu Aug 24, 2017 12:53 pm quote
Re: pfffftin
T5bitza69 wrote:
electric start .... do i look lazy
......
Member
PX 125/Polini 177
Joined: 07 Jun 2019
Posts: 22
Location: Gloucester UK
Wed Jun 12, 2019 9:12 pm quote
Mixture screw etc
All good suggestions here, I have a 7mm ratchet spanner on order.
I have not found an answer to another example of cunning Italian engineering. On top of the air box is a rubber grommet, remove it and there is a screw. Itís simply described as a screw in the Haynes manual. But it has a pointed bottom end, it appears to hold the filter in place, but does it actually have a function. I canít find it mentioned in the sip guides, or anywhere else. Huh?j
Molto Verboso
2005 PX150 In a Love-Hate Relationship with a 2-Stroke Vespa Since 2007
Joined: 01 Sep 2007
Posts: 1813

Wed Jun 12, 2019 9:32 pm quote
This has been discussed in other threads. Itís the ďwinterizingĒ plug. Some call it the ďsummer plugĒ, donít ask me why. Itís meant to be a way to squirt oil into the carb without having to remove the airbox cover or air filter.
Member
PX 125/Polini 177
Joined: 07 Jun 2019
Posts: 22
Location: Gloucester UK
Wed Jun 12, 2019 10:48 pm quote
Winter plug
Thanks for the answer. It may have been discussed before, but as someone new to the forum, and not knowing what the thing was called it would have been difficult to find former threads...
Hooked
1978 MotoVespa 160GT, 2009 LML Star 150 2T (Stella), 1961 Lambretta S2, 1962 Lambretta S3, 1964 Lambretta J100
Joined: 02 May 2009
Posts: 279
Location: Belgium
Thu Jun 13, 2019 2:21 am quote
pdxjim wrote:
This has been discussed in other threads. Itís the ďwinterizingĒ plug. Some call it the ďsummer plugĒ, donít ask me why. Itís meant to be a way to squirt oil into the carb without having to remove the airbox cover or air filter.
I've also wondered about that special screw. Maybe I'm missing something, but why would you want to squirt oil into the carb?
Member
PX 125/Polini 177
Joined: 07 Jun 2019
Posts: 22
Location: Gloucester UK
Thu Jun 13, 2019 3:04 am quote
Reply to norm
Iím guessing, if youíre laying the scoot up for winter, to inject some oil into the cylinder..
Hooked
1978 MotoVespa 160GT, 2009 LML Star 150 2T (Stella), 1961 Lambretta S2, 1962 Lambretta S3, 1964 Lambretta J100
Joined: 02 May 2009
Posts: 279
Location: Belgium
Thu Jun 13, 2019 3:09 am quote
Could be, but I would have thought a squirt down the spark plug hole would be more direct though.
Hooked
Joined: 14 Jun 2016
Posts: 100
Location: Macedonia
Thu Jun 13, 2019 3:10 am quote
norman wrote:
pdxjim wrote:
This has been discussed in other threads. Itís the ďwinterizingĒ plug. Some call it the ďsummer plugĒ, donít ask me why. Itís meant to be a way to squirt oil into the carb without having to remove the airbox cover or air filter.
I've also wondered about that special screw. Maybe I'm missing something, but why would you want to squirt oil into the carb?
For winter conservation.

Your meant to add oil in the engine and do a few turns on the kick-start so there is oil inside.

I usually did this by removing the spark plug, but some Italian engineer figured it out without removing anything, other then the winter plug.
Molto Verboso
2005 PX150 In a Love-Hate Relationship with a 2-Stroke Vespa Since 2007
Joined: 01 Sep 2007
Posts: 1813

Thu Jun 13, 2019 10:24 am quote
The plug and the screw. Iím not sure thereís really much of a user advantage, but I could see there being one during manufacture and distribution, especially if the product is expected to potentially sit in extended storage before sale. This way, torqued factory assemblies only need to be minimally disturbed.
Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 89
Location: Bellingham, WA
Tue Jun 18, 2019 8:29 am quote
I used my Dremel with a grinding blade to cut and shorten the hex head on the stock mixture screw and again to cut a slot in the head of the shortened screw. Now I easily access the mixture screw with a long skinny flat head screw driver no problem.
Member
PX 125/Polini 177
Joined: 07 Jun 2019
Posts: 22
Location: Gloucester UK
Wed Jun 19, 2019 8:56 am quote
Mixture screw spanner
This works a treat

BBCE6904-7899-4C63-8392-E1CE55F1E275.jpeg

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