My Skywagon has a broken primer line to the #6 cylinder. No big deal. Easy repair, cheap. My question is this: Prior to discovering the broken primer line the plane was 5-6 knots slower than normal. This prompted me to open the cowl upon landing to look for anomalies. Would a broken primer line result in less engine power?

you are sucking a tiny amount of air through that broken line which would affect the mixture distribution. But that is already so crappy in an O-470, that I can't imagine such a small addition would ne noticed.

would be an interesting experiment though - fix the primer and see if it speeds up, then loosen a different primer line and see if it slows down again

James

#5 & 6 have the leanest mixtures in the O-470, 1 & 2 tend to be the richest as a result of the rather poor design of the intake system. Do you have an ESI? If so the data from that will answer your question. I would not find it hard to believe that cylinder was sucking enough air through the line to go far too lean. Also would be a less obvious issue at full power.

As an aside, those lines are ungodly expensive, they are not just brass tubing. A few years ago during a cylinder change we had one break at the connection. Just plugged the cylinder port and engine starts fine on 5 cylinders getting primed.

RAS

The last time I had a 5 or 6 knot reduction in cruise speed in my 182, I fixed it myself; I closed the cowl flaps.

Like the others, I doubt a cracked primer line would lean a cylinder enough for that kind of airspeed reduction. and you sure would have seen it on your EGT gauge, if you have an engine monitor. It would probably have to be so lean as to feel some roughness.