Jetting Relations

OK,

New here. Wish I would have found this place ages ago!

In America, please dont hold that against me! Been riding some form of scooter or motorcylce for over 14 years. Done some moderate tuning in the past.

Of the crop of scoots I have, my '03 Stella (LML) is my daily beater.
My wife owns a '59 VBA

The Stella has just turned over 36,000 miles. I ride her everyday here in Chicago, including winter. 150 eng, P2 primary gear, 24/24E carb. Stock barrel with exhaust and transfers opened up. Zirri pipe.
Slapped on a friends JL and saw a HUGE increase in power. Jetting is currently at:

55/160
160
BE5
125

Runs tits!

I have a question. I would like to find a definative source that can explain in great detail what each jet does AND how they affect each other on the Delorto SI carbs.

Thanks everyone,
Duane

Duane, have you tried a BE3?

Hi Duane this is 24/24s as I know them. Most of this will be me teaching you to suck eggs im sure! Ok mixture screw contols weakness and richness on tickover and crucially when the throttle is shut off at high revs. Slow running jet controls the amount of fuel flowing at tickover plus when the throttle is shut. The mixer tube controls the midrange-BE3 is richest BE5 is weakest. The Air corrector controls the volume drawn through the jets. The bigger the jet the less pull-imagine the difference between suckin through a straw compared to a toilet roll. Finally the main jet controls the last 1/4 of the throttle opening.
Bear in mind that the air corrector has an influence on all of the jets so if you change it adjust eveything else accordingly.
Hope this is of some help Duane.

No smaller aircorrector pulls more through. Imagine a drinkin straw and a much larger tube-which one has the stronger pull. Air correcter controls the strength of the pull the jets the volume. If your weak with BE3 on your set up my gut feeling is there is something else wrong.
Sorry don’t know what WOT means.
I think BE1 and 2 are richer.

I know the guys a genius. You never know what he’s gona come up with next!

Original von diablo: No smaller aircorrector pulls more through. Imagine a drinkin straw and a much larger tube-which one has the stronger pull. Air correcter controls the strength of the pull the jets the volume. If your weak with BE3 on your set up my gut feeling is there is something else wrong. Sorry don't know what WOT means. I think BE1 and 2 are richer.

WOT means „wide open throttle“

Something else wrong like an air leak?

Duane

Thanks Curare, I hope its not an air leak!
It is an LML with reed induction.

Duane

Duane you will find very few people will be able to explain exactly how these carbs work even in the trade! Are you still using it because you want to keep the autolube? No disrespect but when you say the exhaust and transfers have been opened up how fer have you gone? Its possible this could be the cause of your problems. Is your exhaust port is to big you will get poor sacavenging and it will be difficult to set up. There is an excellent book by Alexander Graham Bell called Two stroke Tuning which gives great advice on maximum sizes for ports and their shape etc.

Ok, this helps a great deal. Thanks.

So right now I am having a lean condition mid throttle, especially After WOT and I roll back off of the throttle to cruise.
So, if the BE3 is richer than the BE5, I have a BE2 and BE1, they would be even richer? And if I also understand correctly, the air corrector controls the volume, so a bigger air corrector may help pull more mixture through.

Duane

RTMOP,

Last nite I replaced the mixer with a BE4, upped the main to a 135. Still lean at WOT in 4th. Even third a little. 1st & 2nd wind out fine.
I still want to learn what each jet in the Dellorto SI does, and HOW they work with each other.

My eng specs:
LML 150 factory reed
Cylinder transfers and exhaust matched to Pinasco 177, case not opened up as wrk was done with eng in the bike.
JL pipe
P 200 primary
stock timing

I have even gone as far as writing Dellorto for a breakdown and specs on the carb. No reply yet!

Thank You,
Duane

Replaced the air corrector with a 185, even better. God I wish I had a dyno!

Does anyone know if a manual or PDF file exist regarding the operation of the Dellorto Si?

Something to show the relation each jet has to each other.

Duane

Sorry, air corrector, on top of the mixer.

Duane

… I don’t spend words on jet relation since I can’t do a better job then the one Diablo did on this subject.

Diablo wrote
‚‚There is an excellent book by Alexander Graham Bell called Two stroke Tuning which gives great advice on maximum sizes for ports and their shape etc.‘‘
Didn’t Alexander Graham Bell invent the telephone??? I’m surprised he had time to tune 2 stroke engines as well. The guy really gets my respect.

Grimesy

Hi which jet is the 160?

hello vesparex,

yes I think something is not going the way it shopuld in your engine.
Main jet 125 also seams too large for your set up that is, if I understood correctly, a standard 150 with altered ports.
This kind of main jet size you generally use with Polini 208 or Malossi 210 with the 24/24. (Of course with no major work on the engine)

And iddle jet of 55?!
it should go well with a 48.

An engine like the one you have should be Ok with a main jet of 116 or 118 if you are using exhaust of the SIP, JL kind.

But what I am saying concern engine with rotative admission!
You have a reed LML so… it could be.

Make some checking about having an air leak.
If you cant put your engine through a pressure test, at least check the clutch oil seal. Just open the srew to refikl the oil in the engine. If with this screw out the engine rev higher then you know your cluch seal is good for replacement.
Check the flywheel side oil seal or directly change it since is not that great deal doing it. 8 times on 10 when you have an air leak is on this side.

But at the end, if everything is OK, and your engine is running fine, enjoy it.