New engine runs rough?

Just started up new from overhaul O-320 with ported cylinders and 9.5:1 pistons. One P-Mag, one Slick. Getting 100 RPM drop on either. Seems rough. And never had a drop on the EI before....
Neighbor A&P says it will smooth out as the rings seat and compression comes up. What do you think Mel, Walt, Smoky, RocketBob?
Thanks!
Taking a dinner break then will pull plugs and check timing.

No reason for a new engine to run rough, fix it before you fly it!

What do you mean rough? Unsteady speed, misfires, or more vibration in airframe, or uneven sound in the exhaust?

9.5:1 will give more feedback to the airframe.

BillL said:

What do you mean rough? Unsteady speed, misfires, or more vibration in airframe, or uneven sound in the exhaust?

9.5:1 will give more feedback to the airframe.

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Doesn't seem like any plugs are not firing but it shakes a lot more than the 7:1 did, particularly at idle. Does idle slower. The RPM drop in the EI is not normal from my experience. Usually doesn't drop at all. I'm getting 100+ RPM drop on the EI and the Mag.
Throttle up is stuttering too. New behavior with same carb.

Check your idle mixture.

A high compression engine will generally give a perceived feeling of running rougher than a similar lower-compression engine, but if it's really running rough, one of the first things I'd check on a carbureted Lyc is the intake tube hoses and gaskets for possible vacuum leaks. This seems to be somewhat of an Achilles Heel of Lyclone engines. I recently replaced the rubber intake tube hoses on my O-320 due to one of them getting baked from close proximity to the exhaust pipes and discovered that 3 of the 4 intake flange gaskets had been leaking quite badly. With new gaskets and rubber hose segments, my O-320 has never run smoother in the 150+ hours I've owned it. I also discovered that if you're not absolutely meticulous in your installation of the intake flange gaskets, you can easily screw them up and cause an induction leak and it's pretty easy to damage the gaskets upon installation... this might be something worth checking in a freshly assembled engine.

I was extremely meticulous in installing the intakes. Careful gasketing, gasket cement, special clamps. etc....
Will check anyway.
Also the idle mixture Bob, thanks! Need to look up how to do that next....

When I went from 7:1 to 9.5:1 I noticed my engine was not quite as smooth as before, but I wouldn't call it "rough". It's more noticeable with a light-weight prop.
Once I went to the Catto 3-blade, my smoothness returned.

Thanks Mel. I have a Catto 3 blade so no excuses for this. Guess I have a few things to check. Long Sunday....

rocketbob said:

Check your idle mixture.

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That's all it was, Thanks Bob!