Rotax 914 mixture setting

[cavalon48]

Rotax says 1.5turns out on mixture screw from fully in, but cylinder 3 and 4 always seem to be running rich (plugs have black soot 3 and 4). Has anyone tried 1 x turn out on mixture screw from fully in. Also engine temp does not go into green stays just below, but in summer some times gets into the lower end of the green area on rotax engine temp gauge.

 

Oil temp always stays in the green, so no issue there.

 

 

[Downunder]

I run my 912 uls at 1 turn as do a few people in my area.

 

Black plugs are pretty normal after idling the engine. The only sure way to read the plugs is to immediately shut it down after a high rev run.( which I've not done)

 

I was concerned like you are with the plugs but was told it's normal as long as it runs fine in flight and sensors read normal.

 

They are tuned to run at 5000 to 5500.....and love doing so.....

 

 

[cavalon48]

I run my 912 uls at 1 turn as do a few people in my area.Black plugs are pretty normal after idling the engine. The only sure way to read the plugs is to immediately shut it down after a high rev run.( which I've not done)

I was concerned like you are with the plugs but was told it's normal as long as it runs fine in flight and sensors read normal.

 

They are tuned to run at 5000 to 5500.....and love doing so.....

Thanks for that have now set mixture to 1 x turn, lets see what happens this weekend

 

 

[crashley]

What are you looking for after you lean the mixture IE what is the problem with the setting at the moment

 

As has been mentioned in the earlier posts the only way to check mixture by looking at the plugs is to shut both mags off after a sustained high speed run which is not possible

 

even taxing for a few minutes will cause black plugs on two cylinders

 

and if two cylinders are running rich and you back the mixture off the other two cylinders will run lean

 

 

[cavalon48]

What are you looking for after you lean the mixture IE what is the problem with the setting at the momentAs has been mentioned in the earlier posts the only way to check mixture by looking at the plugs is to shut both mags off after a sustained high speed run which is not possible

even taxing for a few minutes will cause black plugs on two cylinders

 

and if two cylinders are running rich and you back the mixture off the other two cylinders will run lean

Engine is running cold on CHT, 3-4 cyl showing black soot. Cyl 1-2 just ok but still too dark grey for my liking.

 

 

[alf jessup]

Standard is 1.5 turns out, running unleaded is the reason for the black soot, if we were running avgas or leaded fuel they would be grey, nothing to panic about just the norm, sooty more so on the lower plugs.

 

I have over 1000hrs in Rotax 4 strokes and that has been normal for all that time.

 

I'd be more concerned if the oil temp was not reaching 90 deg when running at cruise power.

 

Alf

 

 

[crashley]

If you lean your mixture till you get no soot you will be running way to lean when at normal cruising power you cant judge mixture by cht or by plug appearance

 

try swapping the plugs around and see how quickly they get soot on them during idle runs

 

 

[rick morawski]

The mixture screw as it is commonly called is actually the idle air mixture screw and it controls the amount of air (not fuel) in the idle circuit, so screwing it in for less air richens the mix, screw it out for more air an leaner mix.

 

This only affects the idle circuit. When the butterfly opens up a bit there is not enough vacuum through the idle circuit an the job is taken over by the midrange circuit, the needle jet and jet needle, then once the jet needle is withdrawn enough the full throttle mixture is controlled by the main jet.

 

So moving the idle mixture screw will affect your idling but not your cruise speed.

 

I think just covering a portion of your radiator with some duct tape will raise the temps a bit and easy to go back or you could try a fitting a coolant thermostat, see John Gilpins Stolspeed site for an in depth investigation into fitting a thermostat.

 

Hope this in someway helps.

 

Cheers

 

Rick

 

 

[cavalon48]

The mixture screw as it is commonly called is actually the idle air mixture screw and it controls the amount of air (not fuel) in the idle circuit, so screwing it in for less air richens the mix, screw it out for more air an leaner mix.This only affects the idle circuit. When the butterfly opens up a bit there is not enough vacuum through the idle circuit an the job is taken over by the midrange circuit, the needle jet and jet needle, then once the jet needle is withdrawn enough the full throttle mixture is controlled by the main jet.

So moving the idle mixture screw will affect your idling but not your cruise speed.

 

I think just covering a portion of your radiator with some duct tape will raise the temps a bit and easy to go back or you could try a fitting a coolant thermostat, see John Gilpins Stolspeed site for an in depth investigation into fitting a thermostat.

 

Hope this in someway helps.

 

Cheers

 

Rick

Thanks Rick, you are correct it is the air mixture screw turning in has to effect the idle cutting the air mixture, hence turning out must lean same as the bing carbies on the 582.

 

 

[alf jessup]

Rick,

 

Just off topic

 

Just putting some info out there regarding increasing coolant temp without covering the radiator as this is my experience I have had.

 

When I bought my Tecnam it had a 50/50 glycol mix in it at the time of purchase and I couldn't get much more than 60 / 65 deg out of the cylinder head temps in cruise, as per a Rotax instruction when I had my 4 stroke trike they advised to use the Evans waterless coolant instead of the glycol mix as some engines had boiled over time with the water evaporating out, when I changed to Evans on the trike it gave me about a 10 deg increase in coolant temps.

 

When I changed my Tecnam glycol out for the Evans I got a 30 deg increase in temp in cruise to 90 / 95 deg.

 

I have flown my Tecnam at almost max gross weight out of Yarawonga on a 37 deg day climbing full song all the way to 8500 to cross the ranges without the temps going out of the green so I am sold on the Evans.

 

I am guessing the Tecnam got a bit more of an increase because the engine is inside a cowl where as the trike was out in the open air.

 

Cheers

 

Alf

 

 

[facthunter]

Running hotter with Evans is consistently reported, and considered normal. It contains NO water and doesn't form steam pockets when running hotter. It doesn't cool as efficiently as water plus a salt (not common salt). Glycol is not as efficient as water plus salt either even though it raises BP and lowers freezing point.. (Don't mix you own brine, for heavens sake). I'm talking principles only. Nev

 

 

[alf jessup]

Nev,

 

Glycol wouldn't get the temp up to anywhere near what Rotax advises to run at, with the hotter/normal running temps now 90/95 deg it also gave me about a 10 deg increase with oil temp also, mind you I still have to partially cover the oil cooler in winter to get it to run at 90 deg.

 

Lot of my mates with Rotax's gloat about how cool there oil is and think its fantastic, I have forewarned them that 90 is what it should be running at and running cooler oil temps like 60 & 70 deg is not doing them any favors.

 

Alf

 

 

[facthunter]

Evans gives you a chance to run the motor at a temperature closer to desired than water glycol mixes. glycol degrades over time too. Many Rotax 912's run too cold. Oil may go cloudy due water if run too cool. I consider 85 degrees about a minimum for a desired oil temp.

 

I have tried to regulate the water temps with foam near the radiator with mixed success. A thermostat is something else to go wrong so I personally would prefer an inflight adjustable cowl gill or louvers. Better for descents too. Nev