Howdy all , Ive had a basic edit of the Grizz version here. This is the version we are putting out so there is no confusion between long and short needle carbs as we only deal with long needle carbs.
FYI no matter what carb you have Either the older Short needle or the more Modern Long needle you MUST ALWAYS TUNE LSN AND IDLE GAP FIRST ! tuning the HSN first will not optimise your carburation.
GO GX & MG66 series tuning guide;
The carburettors on the GO GX Series and MG66 engines are fitted with a long taper Low Speed Needle (LSN).
The long tapered needle gives a very smooth power band and great economy, which is why GO and Massive Mods use it in their carburettors.
Be aware that the High Speed Needle (HSN) settings on these carburettors will be different from other common brands of motor on the market. They are more sensitive.
Here is a simple step by step tuning guide for the older GO Gen 4 and 5 Pro Series motors, and the newer GX Series and MG66 motors fitted with the long taper low speed needles.
We would like to acknowledge the help of Massive Mods Australia in the preparation of this tuning guide.
Required steps to properly tune your motor for racing
1. Return needles to factory settings:
This step is normally only required if you have completely "lost" the tune, and are starting again from scratch.
HSN (High Speed Needle) – Flush
LSN (Low Speed Needle) – Flush
2. Set the idle air gap and the initial LSN setting using the " MassiveMods 7 second Pinch Test"
The first and most important step is to ensure the idle gap is set correctly.
Because the LSN is directly connected to the throttle slide, getting the idle air gap set properly, so the throttle slide and LSN are correctly positioned before you start tuning is paramount.
Fill the fuel tank and start the motor. Let it warm up for 30 seconds on the starter box - no more.
If the motor will not idle pinch the fuel line to listen where the idle gap is set to, lean the low speed needle 1/8 of a turn at a time until the motor idles without stalling.
Now, fully pinch off the fuel line 1 to 2 cm back from the fuel nipple.
What you are looking for is a slow and steady rise in revs (only 500 rpm or so), which will indicate the idle air gap is correct.
If the revs rise high or "chirp up" quite high, this indicates the idle air gap is too wide.
Decrease the idle air gap a little at a time until you get the slow steady rise previously mentioned.
2a. Initial setting of the Low Speed Needle
Now that the Idle Gap is correctly positioned you can adjust the low speed needle so the motor will die from fuel starvation after 7 seconds when you pinch off the fuel line.
The length of time it takes the motor to die reveals how rich or lean the bottom end is.
If the motor dies at say 4 seconds that means its too lean , you need to richen the bottom end. If it takes 10 seconds for the motor to die, you must lean the bottom end.
7 seconds is the time we want to achieve for a basic tune on the motor.
NB: The idle air gap and 7 second pinch test procedures outlined above need to be carried out before the motor gets too warm - otherwise higher crankcase temperatures will not allow the correct results to be achieved. You need to be able to conclude this procedure in about 2 to 3 minutes. Once you get the hang of it you can do it in less than a minute.
Now we have the idle air gap set correctly, and the low speed needle close to where we want it, run a full tank of fuel through to warm the motor and saturate the chassis with engine heat. Depending on the chassis this can take up to 3 consecutive tanks.
You must always fine tune a motor when it is hot - this is very important.
If the motor chokes up and will not run cleanly unless you keep blipping the throttle to clear it out, lean the LSN a little more at a time until it runs cleanly - DO NOT ADJUST THE IDLE TO COMPENSATE FOR A RICH BOTTOM END.
3. Setting of High Speed Needle
Refill the fuel tank and go for some high speed runs.
Adjust the high speed needle so you achieve a nice clear exhaust note with good exhaust smoke evident right through the rev range. This will depend on the fuel you run , some smoke more than others so bear that in mind. Good high performance fuels dont smoke as much as RTR fuels. Indeed watching the top drivers you will notice barely any smoke out the pipe.
NB: The HSN is very sensitive and only requires very small adjustments. 1/12 th of a turn WILL make a considerable difference to performance.
It is best practice to adjust the HSN in terms of "Hours" (ie hours of the clock face).
Going on our experiences, you shouldn't need to lean the HSN any more than 2 - 3 hours from the factory setting of flush for peak performance (although differing fuel, plug and pipe choice may dictate otherwise).
4. Re-visit Low Speed Needle
Because the HSN setting has a direct bearing on the fuel flow to the LSN, after adjusting the HSN it is necessary to re-check the LSN again.
Adjust the LSN as required for a crisp clean take off from a standing start after letting the buggy sit for 5 - 7 seconds.
If the motor coughs and falters with excessive exhaust smoke, lean the LSN 1 hour at a time until a clean take of is achieved.
If the motor hesitates with little or no exhaust smoke before pulling away, richen the HSN 1 hour at a time until a clean take off is achieved.
Once you have both HSN and LSN set correctly, fill the tank again and run this entire tank through at race pace.
5. Check for Lean-Bog
While running this tank of fuel through the motor, the power should remain constant all the way to the bottom of the tank - if at any time during this tank of fuel (particularly below half a tank) you get lean bog off the mark, or out of corners, this is what you need to do -
Richen the High Speed Needle 1 hour at a time until the lean bog is cured.
YES THE HIGH SPEED NEEDLE ! NOT THE LOW SPEED
Here is a quote from the Massive Mods web site to explain what is happening:
"As the tank pressure gets lower as a result of the fuel being used, the pipe has to pressurise a larger space. When you accelerate off the mark, that’s when the engine has the least amount of pressure in the tank. So for a split second the engine appears to have lean bog, because there is a lesser amount of pressure to push the fuel through the line.
The only needle regulating this is the HSN, because it is the first needle in the fuel system to offer resisitance to the fuel flow of a low pressure tank. If you richen the HSN at this stage, you will allow fuel flow to the engine with the lower tank lower pressure. Then when you go to accelerate, the lower pressure can force fuel through the HSN to the LSN and you won’t get lean bog.
If your motor performs well from full, right down to the bottom of the tank - you now have a basic tune.
Realise that this tune will be good for this particular surface and ambient temperature.
If the surface or tyre choice changes the tune will change.
If the ambient temperature changes more than 5 deg C, the tune will change.
If you change plugs or pipes the tune will change. "
OK Peeps i hope this is informative. The full version is on the LRRCC site for those who want to read the whole shebang.
Cheers MassiveMods Australia