The tuning bible at the top of this thread has a copy, may need to go back a few pages to find it thou.

Here's the one I posted on the LRRCC forum;

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 long needle carburettors will be different from other common brands of motor on the market.



Here is a simple step by step tuning guide for the older GO 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 correct.
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 SCREW.

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.

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

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.



Some tuning tips:

Remember that changing the HSN settings will have a direct effect on the LSN settings.
If you lean or richen the HSN to any extent, you will lean or richen the LSN too.
This is because the HSN (along with setting the amount of fuel delivered for top end running), also directly determines how much fuel the LSN receives overall.
Think of your engines carburettor as a garden hose. The HSN is the tap, and the LSN is the nozzle on the end of the hose. The tap (HSN) controls how much water gets through the hose to the nozzle (LSN).

Changing the idle Gap also changes the LSN settings, because the LSN is part of the throttle slide assembly. If you increase the idle Gap, you are also richening the LSN. Conversly if you lower the idle speed, you are also leaning the LSN. This appies to all slide carburettors.

If you get lost with the tuning – just return everything to the factory settings (including the idle gap) and follow the above tuning procedure. Remember, once you have the idle gap and basic LSN settings done, always run at least one tank through to ensure the motor is close to normal operating temperature. Always tune your motor when it is hot - this is very important.

Once you have your motor tuned and running sweetly it should not change it's tune dramatically.
If your motor suddenly looses performance or appears to start running lean or rich - don't automatically start tweaking the needles. If the motor is in good condition, the tune will not change that much, so start looking for external faults -

Check the glow plug. Make sure it is in good condition and done up tight.
Check the fuel lines for bad connections or pin hole air leaks.
Also Check the pipe and header seals aren't damaged.
Check the fuel tank lid to ensure the lid spring is shutting the lid tightly, and that the O ring in the lid is in good condition and not leaking.
Fuel tanks can also develop cracks around the seams.
Check that the head bolts and pinch bolt screw are nipped up tight.
Check for a broken clutch spring causing early engagement (can feel like lean bog).
Check the carb needles to see if they are loose or the O rings are worn.
Also check that you haven’t left your fuel in the sun. Try to keep your fuel at an even temp by storing it in a shady and well ventilated area.




MAINTENANCE

Nitro powered Micro Engines, because of the harsh environments they operate in and the extreme stresses and strains placed on them by constant loading and high revs, require very good care and maintenance.
Any single cylinder engine this size, producing nearly 3 hp and revving at close to 40,000 rpm will eventually fail if not regularly serviced, with high wear components being replaced as required.

AFTER RUN OIL
We strongly recommend the use of after run oil every time you have run your motor. It only takes a few minutes to carry out this procedure, and it can add litres onto the life of your motor.
When you have finished running your motor for the day, run it out of fuel.
Disconnect the fuel line from the motor. Apply the glow starter to the motor and turn it over on the starter box until it will not fire anymore. This burns most of the fuel out of the crankcase.

Now remove the air cleaner, open the throttle fully and place 3 to 5 drops of MRI after run oil down the carburettor throat.
Spin the motor over on the starter box for two bursts of 4 seconds to atomise and disperse the after run oil throughout the entire crankcase and bearings etc.
Make sure motor is at BDC, then replace air cleaner and glow plug.
The after run oil gives a protective coating to all the internals to help prevent rust forming internally, plus it also stops your motor getting a "dry start" next time you use it.
Rust will form inside the engine because of traces of fuel left on the internal components, even after we have run the motor out of fuel. The methanol fuel is hygroscopic, meaning that it attracts moisture. The moisture it attracts reacts with the methanol and nitromethane to form surface rust, which can penetrate bearings etc and cause premature engine wear and ultimately engine failure.

BEARING REPLACEMENT
Everyone has differing views on bearing life and when your engines bearings should be replaced.
Obviously, if you are checking your motor and find any sloppyness, stiffness or notchy rotation, the bearings should be replaced immediatly. However, the best policy in our opinion is to replace major components like bearings etc before this happens, as stress and strain on other components resulting from the faulty bearings has most likely already happened by this stage.

As a guide we recommend changing front and rear bearings every 13.5 litres (3 gal) of fuel through the motor. This equates to approx 105 tanks of fuel in a buggy, and 90 tanks of fuel in a truggy. Some will say this is over-kill, but we think it's better to be safe rather than sorry.
105 tanks of fuel in a buggy equates to 15 club meetings of racing, which is a lot of wear and tear on a motor, especially in summer with the dusty conditions.
The cost of front and rear bearings for your GO motor is $52, so it's not a massive outlay once or twice a year depending on how much you use your motor to keep it in good condition.

CON ROD REPLACEMENT
Once again, everyone has differing views on con rod wear and replacement.
Of all the components in your motor, the con rod does the most work. As you may have read in the run in section, most manufacturers suggest replacing the con rod at around 9 litres (2 gal) after the initial break-in period and some racing. This alleviates any possibity of rod failure due to the rod being strained because of the initial tightness of the motor. A spare rod is supplied with all new GO motors just for this purpose.
Once you have replaced the initial con rod at 9 litres, it is just a matter of inspecting the con rod at regular intervals and replacing it if you suspect any undue wear. Most con rod wear is found in the big end bushing, where the con rod attaches to the crank pin. Remove the back plate from your motor and rotate the motor to TDC where the piston locks at the top of the stroke. Now see if you can wiggle the flywheel and notice any slop in the bushing around the crank pin. If there is noticeable movement, you should replace the con rod. Remember - this motor is spinning at up to 40,000 rpm, so any slop can result in excess wear and possible component failure.
In older or well used motors, this slop can sometimes be caused by a worn crank pin. This requires the crank to be replaced as well as the con rod.
Also, if you have an over-rev situation, caused by faulty radio gear etc, it is a good idea to replace the con rod (due to possible stretching of the rod) and give the rest of the motor a thourough check over.

I found this on the GO NZ web site re edited by MassiveMods , for all you guys that run GO or MG66's.

Cheers Flanno

Yo