Jetex 22 - restore my sanity, please

[dansuper]

Having failed to find happiness on a Casa 185 with a PWK 24 clone and a Mikuni TM 24, I'm down to a Jetex 22.

So:

1) Please explain the max. 3/4 turns out airscrew label? If rich is out on these carbs, wouldn't there be a minimum out setting instead? Or is it about emissions?

2) What is the standard (unmarked) atomiser meant to be the equivalent of on a GP200 spec Jetex? The 2 Dellorto atomiser?

I'm running a 50 choke, 50 pilot and 128 main through a standard 125 S3 air box and filter and am getting lean chops at 3/4 and WOT?!?!

I have the 5899-1 atomiser from the original SH 1 carb and am going to try it to see if it helps with the chops.

Any assistance would be appreciated.

Cheers,

Dan

[nelson pk]

You probably need to drill the jetex atomiser.
This is from the LCGB site:

One tip on tuned machines, it is sometime prefferable to drill the bottom of the atomniser (more so on Jetex atomisers) if you need a richer mid range. Start by drilling to 2.00mm, if you still need more fuel, 2.5mm

regarding the airscrew...the 3/4 thing i'm not really sure about but i would set airscrews as i normally do.......set the tickover higher or hold the throttle at just before 1/8 opening and set the airscrew at the point of fastest revs. If the revs keep going up as you turn the airscrew in you'll need a smaller pilot. If the revs keep going up as you turn it out more and more you'll need a richer pilot.

[nelson pk]

Also another tip on air screws/mixture screws.......
If the screw adjustment sits after the slide on a carb it is called a mixture screw (standard lammy carbs, Vespa carbs and delly PHBH). Turn the screw in to weaken and out to richen.
If the screw adjustment sits before the slide, it is an airscrew (Keihin PWK, Mikuni TMX). Turn the screw in to richen the mixture out to weaken.

So remember, when you are reading info on how to jet from a motorcycle forum/motorcycle web page they will generally say in to richen/out to weaken because most two stroke bikes use Keihin/Mikuni carbs. Apply the same theory but remember if you have a mixture screw its opposite to an air screw.

[Donnie]

You are definitely using a 200cc type Jetex I assume? ie. the 200 slide??

Atomiser wise the 1's too small Id say you need the standard 2 (again standard for the 200cc carb)

Plenty of mugello 186s on that setup with no problems so cant see why the casa kit shouldn't work on it either.

I know some advocate the drilling of atomisers but I've never seen a scooter that's needed it to be fair, but your milage may vary.

P

[dansuper]

Thanks for the replies.

Donnie, re. the atomiser - I read somewhere that the number sequence doesn't follow an order of leaness to richness and that the 1 is actually richer than the 2? I can't validate this, of course. As for my carb, yep, the slide is not scooped and I bought it new and it was packaged as a 200.

Cheers,

Dan.

[Doom Patrol]

It does, but in reverse order. With number 1 being richest with 4 the leanest.

[Donnie]

I'm getting old I tell thee. Mind you been ages since I've had to tinker with a carb! Think I'd have to dust down me sticky manual for the details lol. Definitely sound that you have the right carb there then but again, I'd think that should jet up ok?

[dansuper]

I put the 5899-1 in and it now seems even leaner - it's very crisp every where.

To modify the atomiser for richness, do the two bottom holes need to be enlarged?

[Special X]

You need to be using the 200cc atomiser and slide (slide is flat on the engine side - the 150 has an indentation). Drilling the atomiser is b@11@x and got started with clowns using a 150 atomiser when they should have used a 200. This also resulted in the use of 135 main jets and other such silliness.

Use a 200cc atomiser/slide and fit a 123 main for safety. The airscrew adjustment can be more than 3/4 turns out but if it needs more than 2.5 turns you should fit a slightly bigger pilot jet.

[dansuper]

You need to be using the 200cc atomiser and slide (slide is flat on the engine side - the 150 has an indentation). Drilling the atomiser is b@11@x and got started with clowns using a 150 atomiser when they should have used a 200. This also resulted in the use of 135 main jets and other such silliness.

Use a 200cc atomiser/slide and fit a 123 main for safety. The airscrew adjustment can be more than 3/4 turns out but if it needs more than 2.5 turns you should fit a slightly bigger pilot jet.

Lol, thanks Special X.

A friend has tracked down a genuine 2 atomiser (200) so I hope to try this in a couple of days. If the standard Jetex atomiser is the same, then I'm in trouble as it was already lean looking running that. Another friend suggested an air leak, and although this makes sense I can't see where it would be coming from. Everything seems nice and tight, and the revs aren't hanging on when I roll of the throttle.

The slide is definitely a 200 as it is flat on the engine side.

Cheers.