Motorized Bike Forum
Welcome to!

Feel free to log in, register, or just browse around and see what we're all about here at MxB Forum.

If you got help here, REGISTER and help the next guy!

If that's not enough motivation, the ads will go away when you are logged in!

If that doesn't do it for you - registering will allow you to search the forum!

Ride safe and have fun!


Adjustable Main Jet

Go down

Adjustable Main Jet

Post by Fabian on Sun Jul 29 2012, 08:47

For those wishing to pursue the goal of an adjustable main jet, either fixed to the carburettor or adjustable on the fly by installation on the hand bars, this group of products may be of interest.

Three versions are available; each having their advantages:

Thunder PowerJet



The "Thunder Powerjet is the simplest system, also being the cheapest, only adding raw fuel to the airflow and controlled by a knurled needle valve.

The Dial-A-Jet is a more complex system in that it delivers an emulsion of both fuel and air through the delivery nozzle, via a 5 position valve body, allowing graduated amounts of air to be added to the fuel stream.

The Intelaject uses the same design as the Dial-A-Jet but takes the sophistication a step further with a control valve and rotary adjustment knob which can be remote mounted onto the handle bars to allow mixture adjustment on the fly.

* How it works *
The system works as a supplementary fuel supply, requiring the main jet to be set artificially lean, enabling the additional fuel to optimize air/fuel mixture.
Just as in a carburettor, fuel is drawn into the air stream by a drop in pressure over the fuel delivery nozzle.
At idle and low throttle positions, there isn't enough airflow to significantly impact idle quality, but as air speed increases over the nozzle outlet, extra fuel is drawn into the air stream.
This product would be very useful to those living with the standard carburettor (or any conventional carburettor) and wishing for an easy method of tuning the air/fuel ratio without having to spend hours disassembling and reinstalling the carburettor, then test running the engine to find an optimal jet size, only to find jetting requirements change when air pressure, air temperature and humidity fluctuates.

With the standard configuration aside, another option that makes this system so special is the ability to combine "two" kits, enabling multi-fuel delivery.
For those who are racing on a closed (off-road) circuit, this concept gives rise to supplying ordinary fuel to one nozzle and supplying a different fuel to the secondary nozzle, like methanol or nitro-ethane (nito-methane doesn't mix with petrol) allowing a great leap into a new world of engine tuning.
By positioning the nozzles at different heights above the carburettor bore centre line, the extra fuel supply can be sequenced to the throttle slide opening position i.e. methanol or nitro-ethane could be supplied above 80% throttle, yet still maintaining a correct air/fuel ratio so the engine doesn't burn up.

This is another method of an adjustable main jet:

or the Khein version with an external remote adjuster:

MxBF Power User

Posts : 338
Reputation : 3
Birthday : 1970-09-03
Join date : 2011-06-08
Age : 47

Back to top Go down

Back to top

Permissions in this forum:
You cannot reply to topics in this forum