Koso 34mm Carb Revving Issue

[plantphoto]

I have just purchased a TS1 with 700 odd miles on the clock.
It has a Koso 34mm Carb and JL 3 Exhaust.
When I rev the engine the revs sometime dont drop completely with closing of the throttle.
I've checked cable etc and it all seems fine but I've noticed the carb slide looks like it rattles as it slides back down and hence fails to shut smoothly and quickly.
It also spits a lot of fuel everywhere !
I'm not 100% happy with set up so probably going to change for a 30mm Dellorto and get it on a rolling road but wondered what others here think?
Simon

[rossclark]

Some of the slides in the Keihn copies can wear badly, very soft metal, but also worth checking the body isn't worn.

[plantphoto]

Many Thanks

[Warkton Tornado No.1]

There are a lot of Chinese copies. It sounds as though you have a mismatch of slide to body.

Have a look @ this link:

http://www.mid-atlantictrials.com/Sales.html

If genuine, there are still some modifications that should be carried out, which is why I’ve done a bit of research, as I have an OKO Ø30 mm, which I bought on a whim.

I’ve not tried it but, from what I’ve read & can see, having dismantled the carburettor, I think they have great potential.

While the majority of two stroke manufacturers of MX bikes tended toward flat slide Keihins or Mikunis, you would have thought we would tend to do the same. In racing, flat slide carburettors probably dominate as far as Lambrettas are concerned, mostly Dell’Orto, but the round slide version finds favour with most road Lambretta tuner/riders.

I’m not sure why.

[MickYork]

Quote; "I’m not sure why. "

Cost ? flat slides seem to be dearer for some reason.......

[St George]

I run a 30 mm OKO, much better than my old 30 mm Delly.

[plantphoto]

Yeah good old 30mm Dellorto I'm sure will be fine once set up for my purposes.
I'm just intrigued why this one is causing the issues it is.
Cheers guys.
Simon

[drivera]

The throttle spring inside the OKO carbs is very weak , try a genuine keihin one it should help , Splat Shop sell them

[rossclark]

Yeah good old 30mm Dellorto ....

I think this is most likely why most are still on round slides... familiarity - we tend to stick with what we know.

Dellortos took over from Amal in the eighties because they offered more flexible tuning and were relatively cheap.

Now there's a shed load of information to help people set them up based on 30 years of use.

It's far more difficult to find ballpark settings for PWK or TM / TMX types.

[corrado]

When I rev the engine the revs sometime dont drop completely with closing of the throttle.

I'd be looking for an air leak with those symptoms. See SLUK for air leak testing. Also covered in new scootrin mag.

[CHRIS in MARGATE]

Great carbs and easy to dial in. Try throttle slide spring first and if that don't fix it then start looking for an air leak.

[plantphoto]

Thanks guys getting it dyno'd snd checked over next week.
Simon