1992 Yam 225 2-stroke Intermittent power or cylinder/s dropping
My friend just bought a '92 225HP 2-stroke on a 23'8 Proline. He has been battling a power lost at certain throttle/power settings.
I tested with him today. The engine ran great for a couple min after idling out then you could feel an immediate although slight decrease in power followed about a minute later by another more noticeable drop. My dad has a late '90's Johnson that did very similar and was caused by a faulty power pack. Replaced and ran great so I tried more testing to see if I could gather more evidence.
At about half throttle and 4000 rpm it would step down after about 2 min to about 3800 rpm then down to 3200 after another 2 min or so.
At higher throttle setting and 4500 rpm the exact same step down but after about 1.5 min to 4200 then about 3600.
At about 3/4 throttle and 5000 rpm it happened after about 30 seconds followed by the 2nd step down about 50 sec after that to 4800 and then 4200.
Final test was full throttle and trim up maxed at about 5500rpm and no step down was felt. Not sure if it happened immediately and we just didn't notice it or not. Previous owner said he used to get 5800rpm.
Each time this happened it would never recover unless you reduce power. At about 1500 to 2000 rpm you could feel the 1 or 2 cylinders kicking back in or you can reduce to idle for 30 sec and repeat the above procedure almost identically every time.
I don't believe this is fuel problem due to the repeatability of the problem and the sudden cutout like losing 1 cylinder followed by losing a 2nd cylinder a short time later.
This seems like an electrical problem caused by heat that happens sooner with increased power setting.
I think the model was TPXR or something like that. Hard to read the numbers. Plugs all look good. Does this sound like the coil packs to 2 of the plugs or the micro computer system heating/cooling?
He has a Yamaha tech set up for Thursday but would like to save him some $$ if possible.
I was thinking about buying one coil pack and swapping them leapfrog until one or both "step-downs" stopped unless someone has better idea.