This is a common thing with the new MGT's, This is the setting I found was best for running in the MGT .46........
I changed my Plug for an OS #8 and used 20% fuel.
HIGHSPEED NEEDLE: 3.25 turns open (close needle down to a soft seat, open up two and three quarter turns)
LOWSPEED NEEDLE : 6.25 turns open (clse needle down to a soft seat, open six and a quarter turns)
IDLE: 1mm open (make sure to set the idle speed so that the carb does not close any more when you use the brakes).
Run for a minute or two with the Glow ignitor on, to warm the engine up a bit.
Start your break-in procedure from here.
If you are still having problems getting the motor to keep running, change the plug for a slightly hotter one. Make sure that you get the engine up to running temperature as soon as possible. Run at operating temps for 2-3 minutes and then allow the engine to cool for 5 mins with the piston at BDC.
Do the above for 5-6 cycles. Contrary to popular belief, you can run the motor in, whilst driving the truck.
After heat cycling the motor (as above), lean the HIGHSPEED needle about 1/8 turn (clockwise). Run the truck with varying throttle settings for a whole tank of fuel. Check periodically for engine temps (spit on the glowplug, if it boils off straightaway, then the motor is too hot, if it sizzles and evaporates in 5-10 seconds, then your still ok), ideally use a temp gun( they aren't expensive). Allow motor to cool with piston at BDC (always get into the habit of doing this).
Dont be tempted to touch the LOWSPEED NEEDLE yet (you need the top end dialled in first before adjusting the bottom end).
Run another tank through at the above settings, using short bursts of full throttle (about 5 second bursts are fine), with most of the running done at half throttle. (just make sure you dont keep the throttle set at one setting all the time). Take note of the amount of smoke produced at full throttle runs, lots of smoke is good at this stage.
DO the above again for another complete tank. Remember, keep an eye on those temperatures.
On the next tank, do full throttle runs on the longest straight you can. Do a pass and take note of the amount of smoke and the motor sound. Turn the HSN in (clockwise) 1/16 turn and do another high speed pass, you should notice that the truck reaches a higher top speed/ engine note, with slightly less smoke. Keep doing this until you can notice no difference in top speed or engine note, or the truck start to faulter or bog down at full throttle. When this happens, turn the HSN out (anti-clockwise) 1/8 to 3/16 turn, to richen the mixture. This will give you a safe HSN setting.
Now we can start on the LOWSPEED needle.......
Run the truck up to operating temp (at least half a tank of normal driving).
Bring it to a standstill and let it idle for 5 seconds or slightly longer. Now hit full throttle. If the truck quits instantly with very little or no smoke, turn the LSN anti-clockwise 1/8 turn. DO another full speed pass to clear the engine and then repeat the 'idle, wait, full throttle.
If the Motor bogs down, hesitates before accelerating (with lots of smoke), then turn the LSN clockwise 1/8 turn.
What you are looking for is a smooth, instant transition from idle to a hard acceleration, with medium smoke and no hesitation.
Once you think you have the LSN set, try this test:
With the engine at operating temp, do a full speed pass and then come to a halt and idle for 5-10 secs. Pinch the fuel tube hard, about 1/4 inch from the carb nipple. If the revs rise very slightly and the motor quits in about 2-3 secs, you've got it just about perfect!
If the motor revs rise a lot before quitting, lean the LSN (clockwise) about 1/16turn. (it means you were way too rich).
If the motor quits almost instantly without any rise in revs, you're way too lean (turn the LSN anti-clockwise about 1/16 turn and retry.)
: Keep an eye onthe temperature of the motor at all times. Also, don't let the typical know-it-all mate tune your engine so that it screams, runs too lean and then self destructs. We all know someone like that...... dont we??