Continental A75 power loss, BIG Mystery

[Tasca]

I run in my J3 replica one Continental A75 -9, feed by a Stromberg carburetor and 2 electronic ignition.
With the wood propeller it fly leveled fill open throttle at 2450 rpm, maximum for this version is 2600 rpm. It use to has a great performance compared to the 8 others J3 there is in our airpark.
220 hours after tbo, I notice a power loss and maximum leveled rpm is now 2200. The takeoff roll is bigger, climb rate is poor and maximum ais lower, sound of the engine has changed a lot. I have 4x1 with no muffler exhaust, it is louder than regular J3 muffler, but is different even from the ground, to silent !
On break maximum rpm is 2150 and on takeoff roll drops to 2100 !!
I look every little thing possible; at least what I could image…

• Air induction filter, flown without filter
• Carburetor, checked twice, changed one
• Induction pipes and connections
• Gas feed, gascolator, roses
• Changed avgas
• Changed ignition system, new plugs, cables, coils
• Compression check 80/78 all cylinders
• Open the engine and check camshaft, tappets, push rods, all clearances
• Test 3 different propellers
• Checked ignition time with time light
• Engine run smooth as ever, mag check drop is less than 25 rpm as ever with electronic ignition
• Muffler is clean

However, no results…. Any clue? I appreciate any help
Thanks all

[rwanttaja]

Is it possible the carburetor heat is jammed on? The full-power RPM change is consistent with the carb heat being on all the time.

Do you still get an RPM drop during runup when you test the carb heat control?

Have you run an analysis of the oil to see if the engine is making metal?

Ron Wanttaja

[Tasca]

I swept carburetors and run without heat box, just to check if there was any restriction on the induction, no results …
I remove the rear section and open the engine to inspect camshaft and tappets, the is no metal on screen and oil tank
Boroscoped carburetor to be sure it was wide open … nothing

[rwanttaja]

I just sent you a PM with the email address for the Fly Baby Continental Engine Guru, Harry Fenton.

Ron Wanttaja

[Tasca]

thanks Ron

I'll try !

[Eric Brown]

Would you happen to a Mitchell Instruments brand tachometer installed in your plane? I also have had the odd RPM drop on the take off roll. Try to borrow a shoot thru the prop tachometer to check tach accuracy.

[Tasca]

Hi Eric I've already made that. I check with electronic tachometer and the indication is ok. General performance has droped a lot, takeoff, climb rate, every thing... it is like i did note open full throtle !
last weekend I put new ignition on it, no results. I'm preparing one magneto to install and try.
tks