XP-360 Roughness in Midrange & Lower Power Settings

We've recently installed a Superior XP-O-360 in an RV-7A. Runs nicely but have a few minor issues. When reducing power setting to approx. 20" , a slight roughness is noted. Leaning makes it worse. Also, when idling the engine in flight, it backfires severely. When increasing power off idle, it's got a dead spot for a second before RPM comes up, (ie. Landing Approach)

We've checked induction system to make sure clamps are tight, etc.

Any ideas?

Thanks,

Jim

Try adjusting the idle mixture a bit richer to help with the flat spot or hesitation coming out of idle. Also confirm that the accelerator pump discharges when the throttle is pumped when the engine isn't running by observing fuel running out of the air box drains while pumping the throttle. Most O-360's have a little hesitation transitioning through about 12-1400 rpm on the ground but I wouldn't call the hesitation severe. Look for induction leaks; one could cause almost all of your symptoms.
If you have straight exhaust stacks you will sometimes get idle backfire noise or popping out the exhaust. Also if you have any exhaust leaks, near the cylinders, you will get Idle popping in flight.
Try running the carb heat, as you reduce power, to see if the roughness goes away. If it does it might be an indication that the carb had a lean spot and may need some rework or replacement to eliminate the roughness.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."

Could also be a prop issue. c/s or f/p? Most props have a rough range, some worse than others.
Tom
RV3

Roughness

Mr. Jim,
Had a similar experience with a C172 with O320. It had more than one issue, the major one was the caburator. The throttle plate body was so badly worn, the shaft moved nearly 1/16" up and down. The throttle stop apperently had never been set, and the trottle plate actually wore a groove onto the throttle plate body. The plate was worn beyond recognition. The discharge tube was broken off, and fuel from the accelerator pump (when it was working) splattered all over the venturi. The accelerator pump was worn as well as it's linkages. A rebuilt carb was installed with and most of the problems vastly reduced.
It also had tired worn plug cables, worn plugs, magneto points badly pitted, and the "foam" filter spewing foam parts into the intake tract. Lastly his valve lifter bleed down clerances were all out of the ball park. 320/360 Lycs are set at .028 to .080. This engine had every valve beyond maximum limits. .100+ to .180. It was amazing the engine even ran or flew.
This is not to say that you may have the same "problem's as this "beauty", but it's a start to look for your problem.
T88
RV10