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Old 09-03-2021, 03:30 PM
Join Date: Jan 2011
Location: , HI
Posts: 54
Received 5 Likes on 5 Posts

Originally Posted by thailazer View Post
Fellow flyer has a fairly new Magnum XL 180 and it idles great, but will die suddenly when advancing the throttle often. When it does get up to full power, it seems to have plenty of power and is not lean or too rich. Fuel is 15% nitro content which I am thinking may be the issue, as my Webra 120 needed a short plug and extra glow plug washer to be able to run 15% nitro. Does high nitro fuel affect detonation timing at mid-range that could kill the engine suddenly? There is no sputtering as it just plain stops. All advice appreciate.
First of all try and adjust the idle needle assuming there is one. Idles great is very subjective. When the idle circuit is either too lean or too rich the carburetor will not be able to adapter to the sudden fuel/air mixture change when opening the barrel and the engine just dies. You can have an engine idling very nicely with a combination of idle needle adjustment and carburetor barrel opening. To test it as mentioned in other posts you need to do a fuel line pinch test while the engine is idling. The engine needs to increase in RPM for a short time and dies. If it dies right away without increasing RPM your idle mixture is too lean. If it increases RPM for a long time before dying you are too rich.

No you won't have detonation issue at mid throttle. Detonation will occur when the engine is running full bore. You will hear a "fry egg" sound as per Clarence Lee. If you need to continue to run 15% fuel and think that the engine is detonating all you have to do is to put another head gasket on the engine.