I have a ztr 428 1992 model dixon riding mower which came with 12 hp single piston briggs. I purchased a used 17 hp twin 2 ic [42a707 type 2653 e1 ]opposed vertical shaft and installed it on the dixon mower ! It ran pretty good for a while but started making a click or a mettalic ping noise while mowing and started to loose power . The engine does not smoke and there are no oil leaks .One of the spark plugs has a wet fouled look so i replaced both plugs but still have loss of power and mettalic clicking or ping noise coming from engine while loosing power under load while mowing ! I'am not sure if its and intake valve not seating or other probs! The engine also makes a poping noise like the exhaust vales are leaking off while running also . If you have any ideas on this subject please feel free to reply with any information . Thanks

May have loose valve seat(s). Would require removing the heads to visually inspect valve operation and valve seats.

That "ping" sound you hear could also be a spark knock. Check your clearances. And your flywheel key.

I installed a new armature magneto solid state ignition module and the engine is running great now ! The wet fouled spark plug made me suspect there was no spark to that plug hence -it might have been lacking spark installed a new ignition module boom bam problem fixed ! You guys have a good day !