• Welcome to RCTalk! 🚀

    Join the #1 RC community where hobbyists connect, share, and get expert advice on RC cars, trucks, boats, drones, and more!

    • ✓ Friendly & passionate RC enthusiasts
    • ✓ RC tips & troubleshooting
    • ✓ Buy, sell & trade RC gear
    • ✓ Share builds & upgrades

Sirio .21 mid range needle

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.
HumboldtBlazer

HumboldtBlazer

RCTalk VIP
Messages
6,620
Reaction score
16
Points
708
RC Driving Style
Ok all the slide carb engines I have owned to date only have an idle, low speed needle, and a high speed needle. Well my Sirio has a mid range needle also. It says not to adjust you mid range needle until you are an advanced tuner, so what does the mid range needle effect? Well it increase my performance or should I leave well enough alone? It was kinda a challenge that the manual said not to touch it...it makes me want to adjust it. Can major damage be done by the mid range needle being off just a little? I'm a little confused.:loser:
 
humboldt - i have a MSN on my rossi - dont touch it! lol

the midrange is set at the factory for optimal performace. To adjust the MSN, u have to do it at the same time as the LSN, with two seperate screwdrivers. they are very close to each other, and u can damage the LSN by moving the MSN. i wouldnt recommmend adjusting it, unless u have a professional tuner there with u, explaining how it is done.
 
:opps:

I just moved it an 1/8 richer and put it back after a lap or 2. You think I screwed it up?
 
i dunno. its possible, but i would worry, unless u see signs of an air leak. then it means u have damaged your LSN. But i doubt u caused any problems.
 
Imagine the mid range needle more like a pipe that the spray bar slides in and out of when you open and close the carb. Look down the venturi and you will see this action. when you close the mid needle, you cover the spray bar more when at WOT. When you open the mid, you expose the whole spray bar earlier.

What this does is controls when you want to get the max amout of fuel to be distributed. It controls more of the power band than the power itself.
 
I cannot recommend enough that everyone READ ALL OF THIS:

http://www.parisracing.com/engine_tuning_with_coversheet.htm

From the man himself, Ron Paris:

5. The mid range needle [regulates fuel to engine after idle and before full fuel position.

Notice as you open and close the carb the tapered needle [mentioned above in item 4.] enters into a small tube this is called the spray bar/jet.

This spray bar is were ALL the fuel enters the airflow stream regulated by the high speed, mid range and idle/minimum adjustments!

Normally somewhere between ½ and ¾ throttle open position the needle is completely out of the spray bar, This is what is called full fuel position or FFP [at this point 100% of the mixture is controlled by the high speed needle.

On many carbs the low speed and midrange are not independently adjustable so the mid rage is a factor of the needle taper and is engineered by the factory.

On some SLIDE carbs there is both independent spray bar and mid range needle adjustments. CAUTION: be very careful with these type carbs!!!
Click to expand...

The LSN sits inside the spray bar and makes a nice little mist of air / fuel mixuture when you're sitting at idle. If you pull on the throttle the LSN pulls out of the spray bar and fuel starts dumping into the engine as fast as the HSN will allow.

The mid range needle moves the spray bar in and out.

Hence, it's kind of like adjusting the LSN in some aspects. A 1/8th turn clock-wise on the mid range needle is like a 1/8th turn clockwise on the LSN, but you have changed at what position on the throttle the the LSN leaves the spray bar.

You can turn the lsn and the mid range needle at the same time. You give a 1/8 clockwise turn on the mid range needle and a 1/8 counter clockwise turn on the LSN. You keep the LSN setting the same but you again change at what position on the throttle the the LSN leaves the spray bar.

I've heard many many many people say just don't mess with the mid range needle. If you're careful, however, I don't see how playing with it could hurt. You just have to remember where "home" is so you can reset it.

Doh, I also forgot to mention the mid range needle adjusts where the fuel enters the airflow stream. Hence, it will change your top end as well as your transition to it.

-Rob
 
Last edited:
Its not really like the LSN where the LSN adjusts the amout of fuel coming into the engine. The Mid adjusts when the FFP happens. If you close the mid, the FFP happens more towards WOT. If you open it, FFP happens before WOT. When you adjust the mid, you are not adjusting the amout of fuel, but when that fuel comes out or is distributed.
 
I was refering to the case where someone adjusts the mid range needle and leaves the LSN alone. Doing that will effect your LSN setting because you've moved the spray bar in realtion to the LSN.

Another great, MUST READ source of info on the topic:

http://www.rcnitro.com/rn/articles/carburetor.asp
 
You are very correct. if you bring the mid in too much, you are essentially leaning out the LSN because you are not allowing the needle to get to FFP.
 

RC Builds

Back
Top