Engine Trouble How's this plug look?

four cu

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Plug chop. No leaks whatsoever
 
This is what your spark plug should look like with the engine running at wide open throttle for long enough that the cylinder head temperature has had time to stabilise.

The photo represents prolonged periods of wide open throttle between 3,500 and 3,800 rpm, using Australian (lower eastern states) 98 octane fuel and 25:1 oil/fuel ratio and a CR Machine Manufacturing low compression straight plug billet cylinder head and a Jaguar CDI using jumper settings selected for the most advanced ignition curve.
I am running a No 77 jet in the NT carburettor with atmospheric conditions at the time being an 18 degree (65 degrees Fahrenheit) day with 59% humidity and approx 120 meters elevation above sea level.
The cylinder head temperature was 140 degrees Celsius (266 degrees Fahrenheit) and the exhaust gas temperature (read from an onboard KOSO EGT sensor and gauge) was 370 degrees Celsius (700 degrees Fahrenheit).


20140515.jpg
 
This is what your spark plug should look like with the engine running at wide open throttle for long enough that the cylinder head temperature has had time to stabilise.

The photo represents prolonged periods of wide open throttle between 3,500 and 3,800 rpm, using Australian (lower eastern states) 98 octane fuel and 25:1 oil/fuel ratio and a CR Machine Manufacturing low compression straight plug billet cylinder head and a Jaguar CDI using jumper settings selected for the most advanced ignition curve.
I am running a No 77 jet in the NT carburettor with atmospheric conditions at the time being an 18 degree (65 degrees Fahrenheit) day with 59% humidity and approx 120 meters elevation above sea level.
The cylinder head temperature was 140 degrees Celsius (266 degrees Fahrenheit) and the exhaust gas temperature (read from an onboard KOSO EGT sensor and gauge) was 370 degrees Celsius (700 degrees Fahrenheit).


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fabian, you covered EVERY detail, bar one...

what plug are you using?

the heat range of a plug denotes how clean or dirty it will be. ngk 4 will be white, while ngk 13 will just be a hideous black mess, on the same settings...

try it out one day ;) get the lowest and the highest b*hs you can find.

and the difference in head temperatures will astound you :eek:
 
I use an NGK BP8HS

In an air cooled application, it pays to use a reasonably cold plug to cover yourself against extremes of cylinder head temperature, especially when using the standard cylinder head which can make it's way past 300C* (572 Fahrenheit) on a hot day, particularly when climbing a steep gradient, with low air speed passing over the cylinder head.
 
Nothing wrong with a No 6 heat range spark plug, though my experience with NGK has shown that you can get away with a No 8 heat range, thereby covering yourself for a wider range of cylinder head temperatures, minimising the chance of pre-ignition from an excessively hot electrode when cylinder head temps start to go stratospheric.
 
I agree. didnt i post a thread that said something about if you do something silly like use a number as HOT as a 2? :)

and as jaguar once tested... the hotter spark plugs also raise head temperatures, not by a few degrees...but by a LOT!
 
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