Newowner Posted October 10, 2019 Report Share Posted October 10, 2019 Engine runs good at all power settings with no backfire and no stumbles during all flight and ground ops. My concern is that I don’t have rpm rise while leaning on the ground. If keep leaning it’ll get rough and shuts down due to fuel starvation. Any thoughts? Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
corn_flake Posted October 10, 2019 Report Share Posted October 10, 2019 My does the same. Except my also occasionally back fire on extended ground ops. My AP advises to leave it alone since lean running engine on the ground will keep the plugs clean. Quote Link to comment Share on other sites More sharing options...
Guest Posted October 10, 2019 Report Share Posted October 10, 2019 Traditionally the idle mixture setting was adjusted to give a slight rise in RPM(25-30) while pulling the mixture control to ICO. Both carburetors and fuel injection systems have this adjustment. Clarence Quote Link to comment Share on other sites More sharing options...
David Lloyd Posted October 10, 2019 Report Share Posted October 10, 2019 The reason for adjusting the mixture to give a slight rise is to make it easy to identify the idle mixture as being not too rich, not too lean. If yours happens to be adjusted for no rise and you don't get any rough running of backfiring at sea level, you are good to go. Quote Link to comment Share on other sites More sharing options...
PT20J Posted October 10, 2019 Report Share Posted October 10, 2019 If there's no rise, the idle mixture is too lean. With too lean a mixture, you can get poor acceleration when you move the throttle somewhat rapidly open from idle. There's a procedure in the service manual for setting it correctly, so why not just do what the manual says? Every engine since the radials of WW II calls for a rise in rpm just before it quits. If you change the mixture, you'll find you need to adjust the idle speed, afterwards as there's an interaction. You might have to go back and forth a couple of times. 1 Quote Link to comment Share on other sites More sharing options...
brndiar Posted October 22, 2019 Report Share Posted October 22, 2019 Hi. Where exactly in manual find I procedure for idle mixture setting for Marvel Carb? (1977 M20C)? By Idle (cca800 rpm) when i move mixture control toward ICO just before ICO (ca 1 cm before) I observe rise cca 25-50 rpm before engine quits. Thank, m. Quote Link to comment Share on other sites More sharing options...
Andy95W Posted October 22, 2019 Report Share Posted October 22, 2019 From your description, it sounds like your carburetor is set correctly. Quote Link to comment Share on other sites More sharing options...
Skates97 Posted October 22, 2019 Report Share Posted October 22, 2019 53 minutes ago, brndiar said: Hi. Where exactly in manual find I procedure for idle mixture setting for Marvel Carb? (1977 M20C)? By Idle (cca800 rpm) when i move mixture control toward ICO just before ICO (ca 1 cm before) I observe rise cca 25-50 rpm before engine quits. Thank, m. Page 1-5 Turning the idle adjustment counter clockwise will enrichen the idle mixture, clockwise will lean it. Turning the throttle stop screw counter clockwise will lower your idle rpm and clockwise will increase it. (It only takes very small adjustments to make a difference) If your idle is set at 800 rpm then it is too high and will lead to longer landings. MA-4 Carb Manual.pdf 1 Quote Link to comment Share on other sites More sharing options...
Hank Posted October 22, 2019 Report Share Posted October 22, 2019 3 hours ago, brndiar said: Hi. Where exactly in manual find I procedure for idle mixture setting for Marvel Carb? (1977 M20C)? By Idle (cca800 rpm) when i move mixture control toward ICO just before ICO (ca 1 cm before) I observe rise cca 25-50 rpm before engine quits. Thank, m. That is how it is supposed to be set. 25-50 RPM rise just as the engine quits is perfect! Quote Link to comment Share on other sites More sharing options...
brndiar Posted October 22, 2019 Report Share Posted October 22, 2019 Idle RPM? Quote Link to comment Share on other sites More sharing options...
Hank Posted October 22, 2019 Report Share Posted October 22, 2019 11 minutes ago, brndiar said: Idle RPM? I think my C hovers just below 800, but it's only there on short final and rollout, when I don't really look at it. Otherwise, I taxi at 1000, climb at 2700 and cruise 2300-2500 depending on altitude. In the pattern, I watch airspeed not MP or RPM--90mph on downwind and base; wings level on final at 85mph; slowing to 70-75mph by short final depending on weight; idle when I have the runway made and touch down as the stall buzzer chirps. Quote Link to comment Share on other sites More sharing options...
Skates97 Posted October 22, 2019 Report Share Posted October 22, 2019 48 minutes ago, brndiar said: Idle RPM? Go fly, after flying and before shut down pull the throttle all the way out, and see where it is running. It should be somewhere between 500-700 rpm. 1 Quote Link to comment Share on other sites More sharing options...
Guest Posted October 22, 2019 Report Share Posted October 22, 2019 4 hours ago, brndiar said: Idle RPM? Lower idle RPM results in shorter landing distances and less brake wear. I would set it low enough that it won’t quit on roll out, 500-550 RPM. Clarence Quote Link to comment Share on other sites More sharing options...
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