procharger Posted March 25, 2023 Report Share Posted March 25, 2023 Can anybody explain why this happens off the same carb. same side? Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted March 25, 2023 Report Share Posted March 25, 2023 If you mean dirtier plugs on the front cylinder vs. the rear cylinder, rear cylinders get less air flow, so they run hotter and leaner typically. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted March 25, 2023 Report Share Posted March 25, 2023 5 hours ago, FlyingMonkey said: If you mean dirtier plugs on the front cylinder vs. the rear cylinder, rear cylinders get less air flow, so they run hotter and leaner typically. I'm going to assume you meant more air. Less air creates a rich mixture causing unburned fuel on the plugs, at least for a piston engine. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted March 25, 2023 Report Share Posted March 25, 2023 48 minutes ago, Madhatter said: I'm going to assume you meant more air. Less air creates a rich mixture causing unburned fuel on the plugs, at least for a piston engine. At that point it is less fuel/air mixture. Because of the design of the intake manifolds and the flow of the fuel/air mixture, it has a hard time making the tight turn to the rear cylinder. This packs more fuel/air mixture to the front cylinder. At least that is my uneducated thoughts on what is happening. It is a common thing for the from plugs to be darker in color than the rear plugs. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted March 25, 2023 Report Share Posted March 25, 2023 49 minutes ago, Tom Baker said: At that point it is less fuel/air mixture. Because of the design of the intake manifolds and the flow of the fuel/air mixture, it has a hard time making the tight turn to the rear cylinder. This packs more fuel/air mixture to the front cylinder. At least that is my uneducated thoughts on what is happening. It is a common thing for the from plugs to be darker in color than the rear plugs. The only one to know for sure is Rotax with cylinder induction fuel/air flow data. As long as the engine keeps running I'm happy. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted March 25, 2023 Report Share Posted March 25, 2023 10 minutes ago, Madhatter said: The only one to know for sure is Rotax with cylinder induction fuel/air flow data. As long as the engine keeps running I'm happy. Exactly Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted March 26, 2023 Report Share Posted March 26, 2023 There is a normal air / fuel imbalance on all 900 series Rotax engines between front and back cylinders plus the bottom plugs are not as efficient as the top plugs in the firing / burning. This is normal and nothing to worry about. The dry black sooted plugs happen at idle rpms and not higher flight rpms. No need to worry. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted March 27, 2023 Report Share Posted March 27, 2023 On 3/25/2023 at 3:15 PM, Tom Baker said: At that point it is less fuel/air mixture. Because of the design of the intake manifolds and the flow of the fuel/air mixture, it has a hard time making the tight turn to the rear cylinder. This packs more fuel/air mixture to the front cylinder. At least that is my uneducated thoughts on what is happening. It is a common thing for the from plugs to be darker in color than the rear plugs. That was my thinking...less fuel/air to the rear causing the cylinders to be starved vs the front ones and leaving some fuel unburned. Quote Link to comment Share on other sites More sharing options...
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