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Midrange needle (msn) discussion:

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2revo1maxx

2revo1maxx

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I've been thinking, why is it that people say to never touch the midrange needle? They always say to set it at the factory setting and leave it there, but what good is it if it can't be tuned by an average tuner? How hard can it be?

I started this thread to educate myself and others on how to tune the msn, your input is welcome.
 
I have often thought about giving it a bit of a fiddle on my 18tm but I guess if they no touch I better leave it
Still curious as what it would do with an adjustment, does it direct the a/f mix differently? ?
 
Just write down your MSN settings a mess with it if you feel confident in your tuning skills. Worse case scenario you have to reset everything to factory settings a retune.
 
i guess my question is what does it do,does it affect a/f mixture or the direction its injected into the motor??
 
All I know is that it affects the mid range, that's kind of why I started this thread. I have experimented with my 18tm just a little, but I'm unclear on what to look for when I do adjust it.
 
2revo1maxx said:
I've been thinking, why is it that people say to never touch the midrange needle? They always say to set it at the factory setting and leave it there, but what good is it if it can't be tuned by an average tuner? How hard can it be?

I started this thread to educate myself and others on how to tune the msn, your input is welcome.
Click to expand...

What this "mid range needle" is is actually a jet and changing it will reposition the jet in the air flow that goes through the carburetor. The low speed mixture NEEDLE is actually sliding into this mid range jet.

When you reposition this jet it will impact how much air blows across it causing a vacuum that sucks fuel into the engine. This mid range does not have to be moved much to get the jet out of the most favorable airflow and that will dramatically impact how the engine runs.

Years ago Picco released an engine that came with 2 different needles and 2 different jets (mid range needle) so that you could tune your engine for smooth power delivery or an abrupt hard hit. I experimented with the position of the jet on this engine and found that it worked best in about a 1/2 turn range. When I got it out of the working range it was almost impossible to tune the engine. The best setting was with this jet flush with the carburetor body.

One last thing - this jet has O rings on it and these rings wear out pretty quickly when you continue to adjust this jet because they are sealing against the aluminum carburetor body which is not as smooth and is more abrasive than a steel surface.

I hope I did not confuse everyone.

Lee
 

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