over rich mixture

by John Roberts in General Tech Discussion 10 years ago

Hi all, Checked the plugs & found they have a soft black sooty deposit. I am sure this is over rich, I find oil burn is near zero ie no top up required in 40 hours. I cruise at 5000 rpm & performance & fuel burn is excellent. Temps are all good. I have the correct grade of plugs. If this was a motorcycle I would just go one grade of hotter plug & check after 5 hours. I am not confident in doing that, any one any suggestions.
We have had a run of hot weather in Perth, all days since xmas have been plus 30 celcious & some days + 35. Could this make a difference?
John Reay

Re: over rich mixture

by Roger Lee » 10 years ago

Roger Lee

125 5.12k 4.53k

Hi John,

Don't change the heat range. Having a black dry soot can be normal after idling. It may not even be the same plug all the time. Hot weather will add to this. You don't have the dry soot running up at regular cruise rpms, only after idle or a long taxi. Just a note, make sure the mixture screw on the bottom of the carb is turned out 1.5 turns from all the way in. Run the engine up at 4000 rpm for a couple minutes to get rid of the soot then immediately take it to idle and turn it off. The plugs will look normal.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: YEN NIEN YU

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Re: over rich mixture

by John Roberts » 10 years ago

John Roberts

2 5 3

Thanks Roger , that makes sense, now I remember about the need to do a "plug chop"when tuning high performance engines. Taxi is also sometimes near 1Km. I am near the annual & will do a check when I do the high speed carb balance. Please say hello to Hal for me.
Best regards
John

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Re: over rich mixture

by Roger Lee » 10 years ago

Roger Lee

125 5.12k 4.53k

Hi John,

I was wondering if that was you, it's been a while. Hope things are going well. Weather here lately has been 75F-85F and it's supposed to be winter. Works for me.
If you have any issues you can call any time.

Take care.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: over rich mixture

by Rhett Mitchell » 10 years ago

Rhett Mitchell

8 99 0

Hello John,
I'm in Bunbury.
I posted this last year..
http://www.rotax-owner.com/rotax-forum/3-4-stroke-technical-questions/4452-912-slightly-rich#5938
It seems our engines have similar traits, especially in summer.
This summer I've dropped the needle one notch (now second from top) and is running fine.
I will need to monitor it carefully moving into winter as it may get too lean.
(Colder temps meaning denser air, so more oxygen leaning out the A/F ratio)
If it turns out better to run a different winter and summer needle settings then I'll do that.
I can see the factory erring on the side of caution and setting it rich as they have no idea of the conditions it will be run under.

Thank you said by: John Roberts

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Re: over rich mixture

by John Roberts » 10 years ago

John Roberts

2 5 3

thnx Rhett, I should try that this hot weather. now 82 days without rain & most days 32Cel plus.
I may get to the fly in!

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over rich mixture

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