Gas engine tuning for newbies....

[alec taylor]

if moter tuned to fly at 400 ft. asl then you fly at sea level , do you have to alter the high end needle. if so which way. 3w170 ? alex

[Tired Old Man]

A 400' change in elevation will not have an appreciable affect on carb tuning. If so we would forever be chasing the needle tuning for the constant altitude changes our planes fly through. The diaphragm carbs we use are generally self compensating for altitude changes of well over 2,000'. If you have the carb well tuned for your local field altitude there's really no need to fuss with it when flying at a field that's 1,500' either way of the home field. Any gains will be negligible.

There have been planes that have flown with starting density altitudes of below sea level and ended up flying above 18,000' asl without any carb adjustments. Many others frequently fly at altitudes over 12,000' that have carbs originally tuned for a base altitude of 500' or less. However, they do start out in an excellent state of tune. No further adjustments are ever made.

The trick is being accurate with the original needle settings.

[alec taylor]

thanks for that

[Slam]

Hi All

I've got a new DL50 that i'm running in at the minute, i've been following the tuning methods described, but it has a misfire at WOT every 5 seconds or so, do i need to lean it out a bit more?

cheers

Duncan

[mfuess]

Try adjusting BOTH ways to eliminate the misfire.

[Nathan King]

	Quote: Originally Posted by alec taylor
	if moter tuned to fly at 400 ft. asl then you fly at sea level , do you have to alter the high end needle. if so which way. 3w170 ? alex

FYI: Like previously mentioned, 400 feet won't matter. BUT...Generally speaking, lower air density (hot, humid, high altitude) will require a leaning in the mixture and higher density (cool, dry, low altitude) will require richening.

It makes sense when you think about it. You are trying to maintain a ratio of fuel to air. If you get less air molecules, you need to introduce less 'molecules' of fuel to maintain the ratio. It's all about density altitude.

[Slam]

With the 2 stroke engines i race with in karts it's the opposite to that, in high temp air we richen the mixture and in cool dense air we lean the mixture. Can't think of any reason it would be different in a planes engine???? It's more to do with keeping the temp of the engine the same than air particles, when fuel is cold the density increases so you can lean the carb to get the same amount of fuel, the opposite is true when the temp of the fuel increases

Duncan

[rcmergler]

Slam is correct, with alot of motor at there you would lean for hot days, however in anytype of two-stroke motor that runs on premix oil, like we run, the hottier it is the richer the mixture must be, that is due to the oil being premixed in with the gas

[rcign]

A G62 that is tuned for Phoenix at 1000 ASL needs to be leaned to run well in Williams, 6800 ASL..It loses about 400 rpm in the process....

[KAMELLO]

Hy i have a DA 50cc whit 2 gallons on it, i gonna try the MFUESS tuning method but i have one question...

My needles are in the original position, its very rich at this time, i should set the lowend & highend needles to about 1 3/4 to 2 turns each, or i can do the tuning method where my needles are at this time?

i fly at 1500meters above sea level

What you recomend guys this is my firts gas engine and my firts tuning

[mfuess]

Start from where you are at.

[KAMELLO]

	Quote: Originally Posted by mfuess
	Start from where you are at.

Ok i gonna try it next weekend hope this things works really nice, i dont want a dead-stick lol

MFUESS i have another question

I have a brand new DA 100cc (the new version) If the engine if to rich can i close a little the highend and lowend just for safety whiout affecting the break-in? or what you recomend personally to do when you have a new engine running rich in the break in process??

When DA send the motors down here the factory settings dont works really good and the engine always runs rich and i feel so scared because of it

Thank U