Mixture Control Screw

[button head]

Is it harmful to have the mixture control screw closed (turned completely to the right)?

[srhadden]

I think definately because you'll overheat your engine. It should be set for the stock setting or slightly lean (to the right).

[button head]

Ok, thanks a lot. I remembered having trouble getting the engine to idle & it would only idle with the screw completely leaned. This was back in the colder months.

[TheBum]

Remember that the mixture control screw controls the mix over the entire throttle range of the engine, not just the idle. If you look closely at the carb, you'll see that the nozzle in the air intake is lined up with the mixture control and that the high-end needle is a little off to the side (it feeds the mixture control).

[srhadden]

Originally Posted by button head

Ok, thanks a lot. I remembered having trouble getting the engine to idle & it would only idle with the screw completely leaned. This was back in the colder months.

If you are having trouble getting the engine to idle, if this is a NEW problem from when you first got it, give everything a look over. So far in my experience, changes in the way my engine performed which made me lean the mixture screw was once bad rear bearings, and the other time I didn't locktite the throttle servo horn and it came loose, but i caught it before I took off!

[button head]

I'll set the screw back to center & bring the needle to 1.5 turns out to start over. Does it matter which is adjusted first?

[srhadden]

Are you able to idle? Also it is normal for an os 50 to have a rough spot reving up to hover speed. Just pulse thw throttle to get past it.

[MaSt0RaS]

i have mine to 0.45 in order to achieve 90-95C is this right? i use OS 8....

isnt it too lean?

Also somethin else in idle its not ok but alwasys was not ok do i have to change the other screw? to close 0.15 or what?

[srhadden]

95C is ok on the head soon as you land. When you are at low stick is the carb slightly open? Looking at the line on the carb control that is attached to your servo horn

I have had a lot of success with enya 4 plugs too.

[button head]

Originally Posted by srhadden

Are you able to idle? Also it is normal for an os 50 to have a rough spot reving up to hover speed. Just pulse thw throttle to get past it.

I have been able to idle (with the mix screw leaned all the way out). I flew about 1/2 a gallon like this. I was going over the heli & noticed the position of the screw when I thought to myself, this can't be right (even though the heli was idling & flying fine).

When I initially leaned the screw completely, I think I was just content with the engine idling & forgot to think about what might be happening to the engine.

[button head]

So today with the mix screw at 50% of its range & needle 1.5 turns out, I began playing with the engine. At one point I was hovering & the engine failed to respond to more throttle & began to fall. I checked the engine & it was HOT...& smoking slightly (I forget where my needle & screw were positioned at this time). After letting things cool, I positioned the needle one turn out & the screw a touch on the lean side. After a few minutes of hovering & forward flight I could hold my finger on the back plate for about 5 sec. The head was hotter than the back plate, is this normal?

Also, with the needle one turn out & screw a touch lean, I could only get the engine to idle with my low throttle curve point set to 15% & throttle trim a few clicks above the 1/2 way mark. Is this OK?

[MaSt0RaS]

of course the head must be more warm than the backplate..!

[TheBum]

Originally Posted by MaSt0RaS

of course the head must be more warm than the backplate..!

And that's because all the combustion is happening in the head and the oil in the crankcase will tend to keep the crank area relatively cool.

[srhadden]

Leave the screw alone. Just a slight 1/8 turn fom stock is good. Too lean on the screw will cause overheating too. Just start rich on the needle and adjust only a click or two at a time. Stop when engine power is good.

[button head]

Originally Posted by srhadden

Leave the screw alone. Just a slight 1/8 turn fom stock is good. Too lean on the screw will cause overheating too. Just start rich on the needle and adjust only a click or two at a time. Stop when engine power is good.

Will do!

Let me stray off topic for a moment. I've been running a linear curve in normal with the low point set at 10% & the high at 100%. I'm also using an ATG setup as per the Finless vid. Is 100% too high? Is it necessary to turn the governor off when making any adjustments to the engine?

[Sonic_BOOMER_SOONER]

It's best to achieve a hover near mid-stick on throttle so you have a smooth transition to idle up, so you'll want to adjust your curve appropriately. On DX7se I have normal throttle curve 0:0, 1:42.5, 2:60, 3:INH, 4:100 and normal pitch curve 0:44, 1:INH, 2:50, 3:INH, 4:100.

Note that I'm running an AR7100R & Rev-limiter so my throttle will never get to 100. Also I'm using Gear switch as a throttle cut and a side effect of that I have a lot throttle trim at idle, so the bottom of my throttle curve, while set a zero, is effectively about 14.5 with the trim. Depending on your setup and tuning you'll need to tweak your curves accordingly, but this will give you a starting point.

Also note the DX7 has throttle and pitch rockers (button style switches) that will allow you to modify your throttle and pitch curves on the fly in normal mode, which can be really handy for achieving a hover at mid-stick!

Cheers.

[button head]

With my mixture screw at its 1/2 way mark & the needle a few clicks past one turn, I was able to obtain a good idle (backplate not too hot after a minute of idling).

My question now is...in order to obtain this idle I had to bring my low throttle curve point up to 25, is this ok or signs of a problem?

I set the throttle hold to 25.5 which prevented the throttle link from moving when switching throttle hold on & off, however. If I hit throttle hold & bring the collective all the way down, the engine would quit when turning throttle hold off (unless I bring the collective up a little before disengaging throttle hold). Should I raise it higher than 25.5?