Replacing LX150 Idle Jet
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2006 LX150 "Amadora"
Joined: 01 Feb 2006
Posts: 7129

Thu Aug 07, 2008 12:06 pm quote
I set out to replace the idle jet on my LX150 today. For those who don't know, the N.American version has a smaller idle jet which can contribute to the hesitancy when starting off of the line. I wanted to swap out that one and replace it with the 38 jet offered by Motorsport Scooters here


I took some photos of the process, and posted them on Flickr. Unfortunately, I cannot figure out how to properly embed them into this thread. Instead, you can access the photos here. There are four, but only a couple are needed for this discussion, and I'll reference them below.

The tools needed are simple: a small flat head screwdriver, small Phillips head screw driver, and a rag. Of course, you need the 38 idle jet. You may also want to purchase the carb air/fuel mixture adjustment tool in case you need to reset the carb. I have one, but haven't yet used it. That will be in another step.

The first thing you'll notice when you look down at the carb is that it is held by two large hoses/connectors. You need to remove these by undoing the hose clamps and gently twisting them off. I found the hose towards the front of the scooter to be much easier to remove. The one in the rear took a lot more effort. Be careful that you don't pull so hard that you inadvertently stretch or break a line.

(Picture 2 in the photoseries shows the first hose off]

Once you have both hoses off, place the rag over the top of the carb. This will be needed to catch any gas that flows out once you turn the carb over. Then gently turn the carb over. Make sure that you do not catch any other lines in the process. You'll soon see that the carb can only be turned in one direction easily. For me, I was standing on the left side (as you straddle the scooter) and twisted the bottom towards my side and the top away from me.

When it is turned over, you'll appreciate having used the rags! On the bottom of the carb is a cover that is held on by four small Phillips screws on the corners. Remove these. Once off, the cover can be removed. I found that I could just move it out of the way, rather than take it off all together.

(Picture 3 in the photoseries shows the cover off of the carb)

With the cover off, you'll see the idle jet sitting in the recessed middle receptacle. Use the small flat head screw driver to remove it. Carefully thread in and tighten the 38 idle jet.

Replace the carb cover and tighten the four Phillips screws. Carefully turn the carb back to its original orienation, making sure that you are not catching any other parts or lines. Then replace the two main hoses/connections. Once tightened, the carb is secured.

You should then be able to start it right up! I found that unlike the original idle jet, I didn't need to give the scooter any twist of the throttle to start it. Rather, it just fired up!

I also noticed that my idle is a little high, so will be adjusting the air/fuel mixture when I have a spare moment.

Hope that you have luck in making a similar change. And if anyone knows how to embed a Flickr photo into this thread, let me know.


Last edited by michael_h on Wed Jul 29, 2009 10:54 am; edited 1 time in total
Hooked
LX 150 - "Ginevra"
Joined: 06 Jul 2008
Posts: 367
Location: Sacramento, CA
Thu Aug 07, 2008 1:15 pm quote
I just ordered the jet and this thread was exactly what i was looking for.

Thanks!
Moderator
2006 LX150 "Amadora"
Joined: 01 Feb 2006
Posts: 7129

Thu Aug 07, 2008 4:14 pm quote
Now that I've taken the scooter out for a spin, I can definitely see the change. Gone is the short "please don't hit me from behind" pause when accelerating from a stop. I can't speak to what changes will occur with my fuel efficiency, but expect a hit there. I did have to adjust the idle down a wee bit.

I am pleased with the result so far!
Enthusiast
Vespa 150s
Joined: 30 May 2008
Posts: 92
Location: Sierra Madre
Wed Sep 10, 2008 5:45 pm quote
Thanks Michael,

This helped me greatly. I just got done with this project (30 mins). I found the front hose came off easier as well. Your walk through helped so much I was surprised and thought; there has to be more to it. But lo, I was done!

I gave each of the four screws a slight tap before removing. I then loosened each screw as if they were lugs in order to prevent any binding.

I can tell the difference in pep already.

Thanks for the step by step.
Moderator
2006 LX150 "Amadora"
Joined: 01 Feb 2006
Posts: 7129

Wed Sep 10, 2008 6:10 pm quote
You should be aware that there is a small hose coming from the bottom side of the carb towards the left (as you straddle the scoot) side. I didn't notice that this was disconnected, and did not reattach it at first. If you notice a smell of gas, check to see that the hose is connected.
Enthusiast
Vespa 150s
Joined: 30 May 2008
Posts: 92
Location: Sierra Madre
Wed Sep 10, 2008 10:54 pm quote
Why do you suppose they used the 35 if the 38 seems to work better? Is there something we're missing? Like we need to adjust exhaust exiting to account for more gases being generated. Reduced engine life due to increased combustion? Guess I'll peak at the plug in a weEk or two.
Molto Verboso
GTS 250ie
Joined: 21 Jun 2008
Posts: 1995
Location: Rhode Island
Thu Sep 11, 2008 2:08 am quote
Probably related to emissions testing.

Slightly (slightly) richer idle won't hurt anything.

P.
Addicted
1978 P200E, 1963 GS 160
Joined: 31 Aug 2006
Posts: 663
Location: Decatur, GA
Thu Sep 11, 2008 9:01 am quote
My LX has been hesitating and stalling like a mofo and Seafoam hasn't helped. Thanks for the pics. Ordered the new jet today.
Enthusiast
Vespa 150s
Joined: 30 May 2008
Posts: 92
Location: Sierra Madre
Thu Sep 11, 2008 9:40 am quote
Gaseous_Clay wrote:
My LX has been hesitating and stalling like a mofo and Seafoam hasn't helped. Thanks for the pics. Ordered the new jet today.
http://www.modernvespa.com/forum/topic26968?highlight=stalling

Michael, I think it was Michael, had a post about this too, and I can't find it.
Veni, Vidi, Posti
946
Joined: 18 Jun 2007
Posts: 5792
Location: Acworth, GA
Thu Sep 11, 2008 10:45 am quote
Michael,

Thanks for your write-up on this! It made my 38 idle jet install as smooth as silk. I did one thing differently than you, however, and I wanted to post it here in the even that it might help someone in the future.

With regard to the removal of the 2 hoses, I took the front one off first (easy peasey), and then started in on the second. It was just NOT wanting to come off. I suppose I could've really pulled and pried for another 10-15 minutes, and maybe it would've come off, but maybe not! Instead of removing that hose at the carburetor, I loosened the clamp on the other end of the hose where it comes off the back of the airbox.

This made for a much quicker and easier removal of the hose. The carb was able to be inverted without problem with that hose still attached. It's a minor point, but one that I felt was worth mentioning. Thanks again!

PS - another good thing to do, IMO, is to make sure the screw heads on the band clamps are tightened in such a manner that they can be easily accessed in the future. From the factory, the screws on my clamps were pointing straight sideways (i.e., at the cowls). Fortunately, I had a "stubby" flathead screwdriver and was able to proceed without issue. In a side-of-the-road situation, however, one might not be so lucky - even if carrying a tool kit. I just like to make things as accessible as possible to alleviate any possibility of getting hung up on some minor detail like having the correct tool for the job, but not being able to get it into position to work.

Cheers...
Addicted
1978 P200E, 1963 GS 160
Joined: 31 Aug 2006
Posts: 663
Location: Decatur, GA
Thu Sep 11, 2008 11:11 am quote
VinciGPR wrote:
Gaseous_Clay wrote:
My LX has been hesitating and stalling like a mofo and Seafoam hasn't helped. Thanks for the pics. Ordered the new jet today.
http://www.modernvespa.com/forum/topic26968?highlight=stalling

Michael, I think it was Michael, had a post about this too, and I can't find it.
Been there, done that. Thanks though.
Lurker
2008 Piaggio Fly 150
Joined: 11 Sep 2008
Posts: 2
Location: Nashville, TN
Sun Sep 14, 2008 10:32 pm quote
Idle Jet MPG effect?
Michael,
Thanks for the info on the idle jet replacemtent. Priceless to have a forum with such great advice!
Tell us, did you find out if the new idle jet made any noticable difference in mpg? I'm sure the performance off the line is great! I'm having a little trouble and considering the switch.
Thanks!
--NV
Moderator
2006 LX150 "Amadora"
Joined: 01 Feb 2006
Posts: 7129

Mon Sep 15, 2008 9:33 am quote
Re: Idle Jet MPG effect?
Nashvegas wrote:
Michael,
Thanks for the info on the idle jet replacemtent. Priceless to have a forum with such great advice!
Tell us, did you find out if the new idle jet made any noticable difference in mpg? I'm sure the performance off the line is great! I'm having a little trouble and considering the switch.
Thanks!
--NV
I lost some of the mileage that I was previously having. I don't notice it too much on the highway, but more in the city. That should make sense, since the idle jet is used more when you start from a stop - a lot!

I like no longer having the momentary hesitation when the light changes, and I apply the throttle. It gets a little scary when the car behind you starts to accelerate, and you haven't begun moving yet.
Member
Piaggio Fly 150
Joined: 16 Sep 2008
Posts: 39
Location: Charlotte, NC
Tue Sep 16, 2008 9:56 am quote
michael_h wrote:
You should be aware that there is a small hose coming from the bottom side of the carb towards the left (as you straddle the scoot) side. I didn't notice that this was disconnected, and did not reattach it at first. If you notice a smell of gas, check to see that the hose is connected.
I'm curious about this. I have a hose that didn't appear to be connected to anything when I took off the cover. It looks about the size and thickness of a fuel hose. Could this be that hose? It is coming from somewhere behind the carburetor area on the left side. So there is a connection under the carburetor this goes to? My scooter seems to be running fine.
Moderator
2006 LX150 "Amadora"
Joined: 01 Feb 2006
Posts: 7129

Tue Sep 16, 2008 11:38 am quote
ScooterScum wrote:
michael_h wrote:
You should be aware that there is a small hose coming from the bottom side of the carb towards the left (as you straddle the scoot) side. I didn't notice that this was disconnected, and did not reattach it at first. If you notice a smell of gas, check to see that the hose is connected.
I'm curious about this. I have a hose that didn't appear to be connected to anything when I took off the cover. It looks about the size and thickness of a fuel hose. Could this be that hose? It is coming from somewhere behind the carburetor area on the left side. So there is a connection under the carburetor this goes to? My scooter seems to be running fine.
A photo would help. I'm having a tough time visualizing where that hose might be.
Member
Piaggio Fly 150
Joined: 16 Sep 2008
Posts: 39
Location: Charlotte, NC
Tue Sep 16, 2008 3:00 pm quote
Here you go.





Enthusiast
Vespa 150s
Joined: 30 May 2008
Posts: 92
Location: Sierra Madre
Tue Sep 16, 2008 7:01 pm quote
Looks like a Breather tube for the gas. Expansion, etc.
Moderator
2006 LX150 "Amadora"
Joined: 01 Feb 2006
Posts: 7129

Wed Sep 17, 2008 6:17 am quote
From the pictures, I would have thought that it was the evap hose. I don't see one connected to your carb, and many members remove them anyways (I did as well). However, it looks more like fuel line hose material than the shiny black that my evap hose is.

Check out the photos on this thread and see if it may be the same hose, but using a different hose material. If it is the evap hose, don't worry about it since it is perfectly fine to leave it off. If it isn't the evap hose, then I'll poke around my LX after work to see if I can locate the same one.

ET/GT/LX: Hard Starting, Rough Idle, or Stalling
Molto Verboso
GTS 300
Joined: 02 Nov 2005
Posts: 1499
Location: Belgium
Wed Sep 17, 2008 6:53 am quote
Just looked @ the Motorsportsite and the explanation says :

"...For USA only scooters..."

Why is this? I've a European LX 125 with Keihin carb.
I presume this is the same carb as on the US models.

The idle jet of 35 is the same.

Can I use this Pilot jet 38???
Member
Piaggio Fly 150
Joined: 16 Sep 2008
Posts: 39
Location: Charlotte, NC
Wed Sep 17, 2008 6:56 am quote
Michael,
It does appear that might be that Evap hose. That is what I suspected when I saw it and I saw that port on the carb, but I wanted to make sure.

One thing I noticed on your pictures was that your hose had a short clear portion at the end. an adapter possibly to allow that hose to connect to that fitting? Perhaps that is why my hose is different, as it doesn't need the adapter.

This is on a 2009 Piaggio Fly 150 BTW.
Addicted
'06 LX150
Joined: 08 Aug 2006
Posts: 798
Location: San Francisco, CA
Wed Sep 17, 2008 7:26 am quote
I'd like to install this mod, but I don't really have the confidence to do it myself. Any Bay Area folks want to help?
Moderator
2006 LX150 "Amadora"
Joined: 01 Feb 2006
Posts: 7129

Wed Sep 17, 2008 11:23 am quote
ScooterScum wrote:
Michael,
It does appear that might be that Evap hose. That is what I suspected when I saw it and I saw that port on the carb, but I wanted to make sure.

One thing I noticed on your pictures was that your hose had a short clear portion at the end. an adapter possibly to allow that hose to connect to that fitting? Perhaps that is why my hose is different, as it doesn't need the adapter.

This is on a 2009 Piaggio Fly 150 BTW.
If you mean the photos that I linked to from the Technical Library, those were from a GT (I believe). My evap hose did not have a short clear portion.
Moderator
2006 LX150 "Amadora"
Joined: 01 Feb 2006
Posts: 7129

Wed Sep 17, 2008 11:25 am quote
LX125 wrote:
Just looked @ the Motorsportsite and the explanation says :

"...For USA only scooters..."

Why is this? I've a European LX 125 with Keihin carb.
I presume this is the same carb as on the US models.

The idle jet of 35 is the same.

Can I use this Pilot jet 38???
I am sorry, no. Only N. Americans can use this.

Actually, I thought that the reason for the N. American selection was because the idle jet installed on our scooters was smaller than the one used in Europe to meet the more strict California emission control standards. Guess I was wrong if your idle jet is the same size.
Enthusiast
Vespa 150s
Joined: 30 May 2008
Posts: 92
Location: Sierra Madre
Thu Sep 18, 2008 5:01 pm quote
cynner wrote:
I'd like to install this mod, but I don't really have the confidence to do it myself. Any Bay Area folks want to help?
Honest, if your somewhat proficient with a screwdriver you can do it.

Just make sure you don't strip the screws on the bottom of the carb. Tighten the 4 carb screws like you would the lugnuts on your car wheels, a little at a time, and opposite each other-so they don't bind.

After you're done with it you'll feel empowered, and so will your scoot
Addicted
1978 P200E, 1963 GS 160
Joined: 31 Aug 2006
Posts: 663
Location: Decatur, GA
Tue Sep 23, 2008 5:29 am quote
VinciGPR wrote:
Just make sure you don't strip the screws on the bottom of the carb.
+1

They were really tight on mine and I came close to having to replace one. Also the stock jet was tight enough that I had to use pliers around a screwdriver handle to break it loose.

Other than that not too hard a job.
Lurker
Joined: 19 Sep 2008
Posts: 4

Sat Oct 11, 2008 10:49 am quote
I did the swap, but started to get stalling issues, any thoughts?
Moderator
2006 LX150 "Amadora"
Joined: 01 Feb 2006
Posts: 7129

Tue Oct 14, 2008 11:49 am quote
Gibson wrote:
I did the swap, but started to get stalling issues, any thoughts?
Is your idle set correctly?
Enthusiast
Vespa 150s
Joined: 30 May 2008
Posts: 92
Location: Sierra Madre
Tue Oct 14, 2008 9:23 pm quote
That's strange, I had stalling before the swap-and the stalling has completely disappeared now. I did however have to adjust the idle.
Addicted
2012 LX 150ie
Joined: 14 Aug 2008
Posts: 538
Location: Oklahoma City Oklahoma
Sun Oct 19, 2008 8:34 am quote
Thanks for the information, Michael.
I ordered the jet as well as the Sito Plus exhaust and will post performance gains in a week or so.

Bill
Veni, Vidi, Posti
946
Joined: 18 Jun 2007
Posts: 5792
Location: Acworth, GA
Sun Oct 19, 2008 11:08 am quote
michael_h wrote:
Gibson wrote:
I did the swap, but started to get stalling issues, any thoughts?
Is your idle set correctly?
If I were a bettin' man, my money would be on "not."
Member
MP3 250
Joined: 27 Sep 2008
Posts: 18
Location: Easton,MD
Tue Oct 21, 2008 8:21 pm quote
I found the pictures!!!!!!!!!
http://www.flickr.com/photos/29354074@N06/
Enthusiast
2013 BV350 Black
Joined: 12 Jun 2011
Posts: 63
Location: Knoxville, TN
Sun Jun 12, 2011 12:12 pm quote
so what if you stripped the heads on the four screws on the carb? POS soft screws. guess i'm not changing my jet anytime soon.
Lurker
lx 150
Joined: 21 Feb 2012
Posts: 2
Location: lake wylie south carolina
Thu Mar 01, 2012 4:38 pm quote
bestbuyguy21 wrote:
so what if you stripped the heads on the four screws on the carb? POS soft screws. guess i'm not changing my jet anytime soon.
Exactly what is the purpose of your negative comment ??? WHo benefits. Thanks, Dave.
Member
Vespa LX 150
Joined: 13 Jun 2012
Posts: 30
Location: Philippines
Thu Aug 09, 2012 2:28 am quote
After replacing the idle jet with a size 38, I guess its best to close the fuel supply screw a little. From 2 turns out to 1 and 3/4 turns out.
How about yours? Did anyone reduce or add to the fuel supply screw setting?
Thanks in advance.
Ossessionato
09 190s taormina
Joined: 08 Apr 2010
Posts: 2045
Location: Googleville
Thu Aug 09, 2012 7:33 am quote
Yes. Will need to adjust idle mixture.

From fully closed as you turn screw out idle revs will increase up to a point then will drop. Correct setting is ~1/4 turn back from "drop." Should be highest rpm.

May need to repeat several times as need to set idle speed at same time. Best with a tach, but can get close enough by ear.
Member
Vespa LX 150
Joined: 13 Jun 2012
Posts: 30
Location: Philippines
Sat Aug 11, 2012 4:08 am quote
bluecloud wrote:
Yes. Will need to adjust idle mixture.

From fully closed as you turn screw out idle revs will increase up to a point then will drop. Correct setting is ~1/4 turn back from "drop." Should be highest rpm.

May need to repeat several times as need to set idle speed at same time. Best with a tach, but can get close enough by ear.
Great ! This is the perfect procedure. Thanks a lot , my LX runs very good now!
Member
Vespa S150
Joined: 02 Jul 2013
Posts: 10
Location: DC
Fri May 30, 2014 1:33 pm quote
S150 won't start after jet replacement
Folks,

I have an S150 that ran pretty well, up until trying this jet replacement this afternoon. Everything went pretty smoothly with the replacement, and I was expecting it to start right up... but nothing after several attempts.

I then set to messing with the idle screw, and fear that I've turned it completely out of whack. So my questions now...

1) Is there way to set the idle screw back to a "base position" of some sort that gives me the best chance of ruling out the screw as the starting issue?

2) Any ideas what I might have done mess up this jet replacement and how to solve?

Thanks for your time.
Member
Vespa S150
Joined: 02 Jul 2013
Posts: 10
Location: DC
Fri May 30, 2014 3:02 pm quote
Re: S150 won't start after jet replacement
Tigidal wrote:
Folks,

I have an S150 that ran pretty well, up until trying this jet replacement this afternoon. Everything went pretty smoothly with the replacement, and I was expecting it to start right up... but nothing after several attempts.

I then set to messing with the idle screw, and fear that I've turned it completely out of whack. So my questions now...

1) Is there way to set the idle screw back to a "base position" of some sort that gives me the best chance of ruling out the screw as the starting issue?

2) Any ideas what I might have done mess up this jet replacement and how to solve?

Thanks for your time.
Cancel that folks... Isn't it the most fulfilling when you can answer your own question?...

I never really knew how the idle screw worked, so I took it out completely and saw it just pressed in the throttle to make incremental adjustments. I then just turned it just until it touched the throttle plate and tried starting... nothing. Kept doing a 1/2 turn and trying to start it, and after maybe 5 tries it started up.

Tweaked it a bit more, went for a ride, and was definitely pleased with the performance enhancement over the stock jet. Monologue complete.
Hooked
Joined: 06 Sep 2018
Posts: 125

Thu Nov 15, 2018 5:47 am quote
bestbuyguy21 wrote:
so what if you stripped the heads on the four screws on the carb? POS soft screws. guess i'm not changing my jet anytime soon.
Following up on this for posterity: if you strip the heads while trying to remove them, you should be able to get them loosened with a needlenose Vise-Grip pliers...which are one of the most useful tools in a scooter toolkit anyway.

The original carb bowl fasteners have a Japanese variant of the Phillips head that is quite prone to stripping with non-Japanese driver bits. Press down very hard on them when loosening, to minimize this risk, so the driver won't skip out of the fastener. Those bolts are size M4 0.7 14mm, and non-Japanese substitutes are readily available at hardware stores that carry metric fasteners.

The best solution, though, is to replace them with Allen (hex) head bolts, which are inherently less prone to stripping than Phillips heads. You may not find these at your local hardware store, but they are easily available on Amazon or McMaster.com in very high quality steel (12.9 grade).

Ensure that all O-rings and gaskets are properly placed before you tighten down those fasteners. I was careless with this on the other side of my carb, where the diaphragm and spring are (it is NOT necessary to mess with this side of the carb to rejet, but I was curious), and I introduced an air leak that made the scoot run terribly. This was trivial to fix, once diagnosed, but one still runs the risk of crushing/tearing/cutting the O-ring or gasket so that it will have to be replaced.

The 38 pilot jet is a nice, cheap, easy upgrade.
Hooked
2006 LX150 (carbed) | 2007 GT200
Joined: 29 Jun 2016
Posts: 477
Location: Toronto
Thu Nov 15, 2018 5:56 am quote
tenders wrote:
The best solution, though, is to replace them with Allen (hex) head bolts, which are inherently less prone to stripping than Phillips heads. You may not find these at your local hardware store, but they are easily available on Amazon or McMaster.com in very high quality steel (12.9 grade).
If it's easier to just add to a parts order, they are also available through scooterpartsco:
https://scooterpartsco.com/lx-150/lx-150-air-and-fuel/m4-0-70-x-12-bolts-with-washers-set-of-4
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