Modern Vespa

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 11:54 am; edited 1 time in total

I just ordered the jet and this thread was exactly what i was looking for.

Thanks!

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!

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.

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.

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.

Probably related to emissions testing.

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

P.

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.

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...

Been there, done that. Thanks though.

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.

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.

Here you go.

Looks like a Breather tube for the gas. Expansion, etc.

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

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???

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.

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?

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.

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.

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

+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.

I did the swap, but started to get stalling issues, any thoughts?

Is your idle set correctly?

That's strange, I had stalling before the swap-and the stalling has completely disappeared now. I did however have to adjust the idle.

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

If I were a bettin' man, my money would be on "not."

I found the pictures!!!!!!!!!
http://www.flickr.com/photos/29354074@N06/