Carb Tuned Now Too Rich
Greetings Jab support,
As in my recent posts, the engine was running too lean by evidence of higher EGT’s and light tan color of the spark plugs. Carburetor tuning appeared to be in order.
I removed the original jets;
main jet 255
needle jet 2.76
idle is 35.
I stayed in the pattern for initial flight testing but have yet to fly in cruise settings. The following is what I observed. It idles at a much lower RPM 700 - 1000 RPM. Before anything under 1000RPM would cut off engine. The spark plugs are sooty which is a clear indicator of too rich mixture. The needle is the original equipped with the 2200A Bing CV94 carb so i assume it’s not the compound apexed that you made for the economy kit. I’m not certain if the soot is from too rich a mixture from idling or from flying in the pattern. Perhaps flying it in cruise configuration to stabilize the engine would be better to asses the mixture by closely monitoring the EGT’s. And suggestions would be very appreciated. Thanks in advance!
Without one of our current carburettor needles it will be hard to get the mixture right everywhere. You should be able to get it closer with a bit of trial and error.
For cruise and full power we use EGT's to tune the mixture. Up to 720C in the cruise and below 690 at full power is the general guide. Remember that the carb richens as you go higher, so the worst case scenario for EGT's and leanest mixtures is at sea level.
For example if you are hitting 720 on a cylinder at 3000ft it will be too lean at sea level. Also remember that egt sensor indications take a while to catch up to the actual temperatures so for proper readings at least a minute at each point is needed.
What I would do first up is change the idle jet back to the 35 and see if that helps with the sooty plugs.