Originally Posted by grizz1 (Post 7187611)

Remember - if you lean the top end needle you are also effectivly leaning the bottom end needle at the same time.
You say you set the bottom end right, then went and leaned the top end some. If you don't go back and richen the bottom end again to compensate, you will end up with a lean bottom end and lean bog.
Also - just very small adjustments at a time. No more than 1/8 of a turn at a time, or you could miss the tuning sweet spot and be chasing your tail all day for a tune.

What your describing also sounds like a rich bottom end disguising a wide idle gap - resulting in a way too lean top end. This will cause the motor to run OK, but it will run cool, then start lean bogging at around half a tank, then run really lean as the tank runs out. It's a classic mistake, made by pretty much every RC gas racer at some time during their learning curve. It's hard to pick because the motor will actually run not too bad, but nowhere near it's full potential.
Check that idle gap by pinching the fuel tubing off about 1" back from the fuel nipple when the motor has just started, before it gets too warm. If the idle comes up quite high, your idle gap is too big. Reduce it and pinch test again until the revs only rise up very slightly. This indicates a correct idle gap for your motor. If the engine won't idle for long at this setting, lean the botton end - DO NOT ADJUST THE IDLE GAP. Now tune bottom end, then top end, then re visit the bottom end if you made big adjustments to the top end needle. You should now have a ballpark tune. Fine tune from here.

Originally Posted by MAGPIE-121 (Post 7191633)

If you have the red, silver or orange head .21 yes
i have the mg66 internals in my old red head 3 port & it rocks

Originally Posted by chevydc44 (Post 7191974)

Ok cool thank you yeah I have the silver head where did you get the mg66 internals

Originally Posted by MAGPIE-121 (Post 7192051)

from the engine designer, mark, of massivemods : http://www.massivemods.com.au/index....ath=24&&page=2

you have the 5 port

Originally Posted by chevydc44 (Post 7192111)

Yeah I have 5 port silver head im gonna change the carb also

Originally Posted by Jesussaves (Post 7191310)

Grizz1, when I had the engine behaving the way it should, not lean bogging, bottom set correctly, I had no top end. I was getting humiliated down the straight. To get some top end I leaned the top end then the lean bogging starts.

Ideal gap is 0.5-0.7, to me that sufficient? Isn't it?

I’ll go and try out now. Richer on top and lean out the bottom end.

Does the pinch have anything do with the behaviour of this engine? That's why I asked the question if it would be ok to but heat gun get it really hot to get some pinch out?

Thanks for your help. Get ready for NZ 7’s team to beaten tomorrow in Hong Kong. :nod:

Originally Posted by MAGPIE-121 (Post 7192168)

lol good one u won't be disapionted with the gx or mg internals or the carbs

Originally Posted by chevydc44 (Post 7192207)

Do you know what are the stock settings are on the old carb

Originally Posted by Jesussaves (Post 7191249)

Bigmatt, thanks for the feedback :). I don't think I have a air leak, as this is happening with all 4 carbs I have tried, 2 Go Carbs (Gen 4 and 5), 1 Nova Carb ( 2 needle on road), 1 OS carb.

Engine is shimmed as per factory spec for using 25% nitro. Head bolts are tight, very tight.

Originally Posted by grizz1 (Post 7192277)

It will vary depending on the type of low speed needle fitted.
Gen 5.5 and more recent (GX, MG66) with the long needle carb, the factory settings are flush on both needles.