Rough running engine at idle/low power
I've been having an ongoing issue with the Lycoming IO-320 engine on my RV-9A running rough at idle/low power settings. I purchased the engine new from Lycoming through Van's with the Silver Hawk fuel injection system. In talking with others and reading the troubleshooting guide from Precision Airmotive (P/A) it was suggested that air might be getting introduced somewhere in the fuel system. I followed the recommendation of installing clear tubing in the fuel line just upstream of the servo and also between the servo and the flow divider. Once this process was complete I ran the engine at low power with the following results; clear fuel, no visible air between the fuel servo inlet and upstream; large bubbles of air visible between the servo and the flow divider. In discussing this with P/A they asked me to do some additional testing which included another low power engine check with a "stone cold engine", checking for air with just engine driven pump, then adding fuel boost pump to see if there's any change, and finally conduct what they call a "baby bottle check" where the fuel nozzles are removed from each cylinder, reconnected to their respective lines, each inserted into a bottle of the same size then with fuel boost on, mixture rich and throttle open allowing an amount of fuel to flow into the bottles and visually noting any significant difference in volume. Not sure what this last check has to do with resolving air between servo and flow divider. Would really appreciate any thoughts anyone might have in this area particularly if you've had a similar experience. Thanks
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