JL Curly on a standard Li150

[TheSeeker]

Hi Folks

In anticipation of receiving a JL curly pipe to fit to my Li150 Series 2 I have been thinking about carbs and jetting. Engine is a standard Li 150.

Everything I read about the JL curly says "get more fuel in or it's running too lean".

With that in mind I've thought about fitting an SH1/20 carb which I have spare from a previous engine rebuild. It seems much easier to get components for this carb than for the original MA18 currently fitted.

The SH1/20 is from an SX150 and is jetted as follows :-



Main 105
Choke 50
Atomiser F899-5
Pilot 45

A couple of questions :-

1. I understand the atomiser is supplying all the petrol from 3/4 throttle on up. Is the F899-5 big enough? Is see there is even a F899-6 available at Cam Lam.

2. Do you think the main is big enough?

3. Will I get it right with simple trial and error?

Best regards

Ben

[soulsurfer]

From what I know About this pipe (which ain't much) this is a very bad comination of pipe to cylinder and carb. Isn't this a revvy pipe requiring a tuned cylinder and much larger carb? I stand to be corrected but I would think this pipe would be strangled by your proposed combo and only lead to a knackered top end. You'd be better off with a standard 42mm AF Clubman pipe IMO

[ArKaTxU]

Is a JL3 or JL4 Curly?

[TheSeeker]

Is a JL3 or JL4 Curly?

It's a JL3 Road Curly. Sorry forgot to specify.

Ben

[J1MS]

Not really much help to you with this one as I have never ran a JL on a 150 cylinder on a 20mm Carb. But to try to help you to understand the Emulsion tube (Atomizer) and how it works, so you can better understand how the holes in the side of the Atomizer work...
The holes in the atomizer are all covered by fuel at idle or low revs. As air pressure reduces in the carb and air speed increases the first set of holes are revealed drawing petrol and air in from the holes in an emulsion (mixed) these are then drawn through the center hole of the atomizer into the venturi, as revs and air speed climb the second first & second set of holes are revealed then as air speed increases the lower holes are revealed as well...

So the position & size of the holes through the Atomizer is allowing air in at different mixes for higher or lower revs, the holes in the side of the Atomizer tube nearest where the main jet sits, these effects the higher revs more, the holes in the middle the mid revs the holes at the top the lower revs... The size of the hole through the center of the Atomizer should let more fuel through at all revs if it is enlarged slightly (Possibly more at lower to mid throttle settings as the main jet will limit the maximum fuel flow at or near full throttle when the engine is at high or maximum revs...
I thought If you understood the basics of the way these carbs draw on the Atomizer it might help with any choices or modifications you might make... If you compare a -2 Atomizer with a -4 Atomizer, one fitted to a 200 GP the other fitted to a 150 GP, they both run on the same size main jet. Then you can see how more air and less fuel is drawn on the 150 with a -4, because of the side holes. The jetting is leaned off by these holes in the atomizer more on the 150 compared to the 200 by their position and size... Don't use Indian Atomizers as they do seem to have quality issues.

If you cant jet it with standard Atomizers, then maybe modify one to make it richer by filling the original holes (solder & remove any surplus) and then drilling slightly smaller holes at 90 degrees to the original... Or weaken it by making the original side holes slightly larger.

The Atomizer will govern the fuel flow from fairly low revs to about 2/3 throttle then the main jet choice will have a major effect but there will still be an influence from the Atomizer choice, this owing to how the fuel comming through is mixed with air through the emulsion tube (atomizer)...

[soulsurfer]

Hi J1MS, that's very informative. I assume the atomiser acts in a slightly different manner as the SH has no needle, could you explain this for say, a VH flatslide? I'm trying to learn more about carbs these days but hadn't found out much about atomisers. Cheers

[TheSeeker]

Many thanks J1MS!! That's an excellent description. I was wondering how it worked without a needle.