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Old 07-06-2004, 10:24 AM   #1
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Default The spit test.

Im new to nitro r/c and I don't have a temp gun yet but will be buying one soon. I was wondering how the spit test works on it. Thanks.
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Old 07-06-2004, 11:35 AM   #2
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When you put some spittle on the cylinder head it will either simmer slowly away or evaporate on impact.

If it simmers slowly you engine is fine but if it evaporates on impact you are running the engine way too lean (need to turn the needles out).
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Old 07-06-2004, 08:57 PM   #3
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Spit and water boil at 212F. So if your spit is boiling off slowly chances are you in the 212F range give or take if it sizzles off your likely in the 240Fplus range..

Again its not going to be precise but you will at least know for sure if your below 212F if it dont boil off.

There is no majic temp either. Old skool thinking was not to go hotter then 220... But in some cases 270F is good and in others 240F is good. We had a race once summer where the outdoor temp was so hot we where running at 270F and running out of fuel in less then a 5minute qualifier. It was a very tuff day to manage temp and run time
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Old 07-08-2004, 10:02 AM   #4
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Quote:
Originally posted by Joel Lagace
Spit and water boil at 212F. So if your spit is boiling off slowly chances are you in the 212F range give or take if it sizzles off your likely in the 240Fplus range..

Again its not going to be precise but you will at least know for sure if your below 212F if it dont boil off.

There is no majic temp either. Old skool thinking was not to go hotter then 220... But in some cases 270F is good and in others 240F is good. We had a race once summer where the outdoor temp was so hot we where running at 270F and running out of fuel in less then a 5minute qualifier. It was a very tuff day to manage temp and run time
usually the hotter the temperature is outside you would run the car leaner ,the colder the outside temperature is run it richer.
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Old 07-09-2004, 10:10 AM   #5
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Quote:
Originally posted by Marcos.S710
usually the hotter the temperature is outside you would run the car leaner ,the colder the outside temperature is run it richer.
Sorry to jump in,.. but isn't it the other way around?
I usually richen it when ambient temp is hot to cool it down. and lean it when temp is cold to build more heat and reach "optimum" working temp...
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Old 07-09-2004, 11:32 AM   #6
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Quote:
Originally posted by orangbaligila
Sorry to jump in,.. but isn't it the other way around?
I usually richen it when ambient temp is hot to cool it down. and lean it when temp is cold to build more heat and reach "optimum" working temp...
Its all about mixture. If your mixture is already correct to begin with then in theory, warm ambient temperature means that there is less oxygen. To bring your mixture back to the right ratio of oxygen-fuel then you need to lean the engine.

When ambient temperature is cooler, you tend to have "heavy" air and more oxygen which is why you need to richen your engine to bring your mixture back to the correct ratio.

Now that I have moved from Asia to the UK (i.e. warm, tropical climate to a cooler climate) I am a firm convert of this theory. All my engines which were running great in Asia now needed to be re-tuned. Otherwise, as soon I start them up they are running so lean and overheating like mad!
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Old 07-09-2004, 11:32 AM   #7
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Default Old question...

No, Marco has it correct.

Cold=more air molecules per unit volume, thus it requires more fuel. Richer

Hot =less air molecules per unit volume, thus it requires less fuel. Leaner

This applies to optimum mixture for performance. Other factors, such as air flow over the head, head size and delta temp between the head and air flow may determine where you actually run.
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Old 07-10-2004, 10:42 AM   #8
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Default Re: Old question...

Quote:
Originally posted by ZipZap
No, Marco has it correct.

Cold=more air molecules per unit volume, thus it requires more fuel. Richer

Hot =less air molecules per unit volume, thus it requires less fuel. Leaner

This applies to optimum mixture for performance. Other factors, such as air flow over the head, head size and delta temp between the head and air flow may determine where you actually run.
thanks ZipZap
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Old 07-12-2004, 05:46 PM   #9
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if tour spit dissolves in 5 or more seconds your motor will probably be over heating
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