Scooterotica

Since I fitted an iron 175 kit on my Series 3 Li, I've struggled to get the carburation right. I have a similar set up on my chop, and with a PWK copy, it runs pretty nicely. But it runs open mouthed.

The Li I wanted to run through the airbox so I had a Sh1/20 carb. Never could get it to run clean, it always seems too rich up to about 1/4 throttle no matter what slide or atomiser combo I was using. Fine on long runs, but around town it wasn't pleasant.

I was starting to consider another PWK, with a air hose and manifold to fit. Then I found a newish Jetex SH2/22 I was running on the chop and ordered a GP manifold and put that on. A bit of chopping and changing (and discovering a dodgy plug) and wow, does it run nicely! I don't think its run this nicely since I took the original 150 top end off.

Jetex has it's critics, but I'm loving this one. It didn't run well on the chop open mouthed - random gusts of wind would upset the carburation. Running it through the airbox though, and it's fine. I like it - there are so few options, I just set it up as GP200 and off it went. Might still be a bit rich as I'm running a 122 main, but it pulls away smooth and clean.

Doe anyone one know if the SH1 and SH2 series of carbs were designed specifically for Lambrettas?

I've been restoring lambrettas for twenty years. Over and over I have heard the refrain 'Jetex are rubbish'
The reality is, jetting a carb. is not simple, it requires some time and thought. When it becomes difficult it's easy to blame the Jetex and discard it in a fit of pique.
Still, let them keep doing it and I'll keep picking up 22mm Jetex Carbs. on eBay for a song.

Daggs wrote: ↑Tue Jun 09, 2020 8:22 am I've been restoring lambrettas for twenty years. Over and over I have heard the refrain 'Jetex are rubbish'
The reality is, jetting a carb. is not simple, it requires some time and thought. When it becomes difficult it's easy to blame the Jetex and discard it in a fit of pique.
Still, let them keep doing it and I'll keep picking up 22mm Jetex Carbs. on eBay for a song.

I think the same is true of many carburettor's & there are debates about the PWK's going on.

The facts are that ANY carb should be stripped & rebuilt & (to use a word that I often use ) 'blueprinted' to ensure that all of the components function & interact with each other.

Unfortunately, there is a 'herd' mentality prevalent in our hobby

Were the SH's specifically designed for Lambretta? Does anyone know?

I seem to vaguely remember something about them being used on other Italian bikes, but I couldn't tell you which ones.

Glad you got it sorted. The Jetex is much maligned. But it doesn't really take a lot to get them running well. When I've run them in the past I've found that they don't really let enough fuel through and the engine felt like it was being held back. It's a simple fix to drill out the needle valve. And when they are fitted with Dell'orto jets they are as good as you'll get. I've got one fitted to a scooter of mine. It was only meant to be a temporary thing, but it goes so well that I've never changed it.

I use a jetex on a series 1.I've used it for over a year without any problem.

I've used Jetex, many dellorto and Miikuni. I'd say it comes down to the quality of the specific production run. They all have part suppliers and quality standards can vary by who is running a machine on any given day. Or who things are outsourced to.

A company I worked for outsourced manufacturing. We found out later the QA samples were hand made and perfect. They bore little resemblance to what came off the production line.



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I have no idea about carbs, but I have a Series 2 with a SH1/2 carb that had a Stage 4 175 conversion from 150. I was advised to change the main jet to a 110 for the running in and hen go back to the original 107.

The plug looked as if it was running a bit lean with the 107, so I switched back to the 110. Everything else in the carb is as it was before the conversion and the scoot runs fine.