Right/Left swap of plugs created RPM issues // 242x Surfing

[Shady28]

This weekend I swapped the plugs between the two engines, no reason, did it by accident after I retied the tethers.

Here's the weird thing:

• When not surfing:
  • RPM's for both engines were aligned when under load with no ballast and not surfing; 6500
• When Surfing:
  • RPM's for the surf side engine were 6500 with ballast and non-surf side spike and maintained 8000
    • Ballast setup made very little difference in normalizing the RPM's (more/less middle or non-surf side, fully loaded surf side - bag + 500 steal on swim deck)
    • Moving 4 people around in the boat made no difference
    • Non-surf side/high RPM side - even with non-surf full ballast and 4 people on that side didn't impact RPM's (e.g. ensure that side of the boat/engine was deep in the water to prevent cavitation)
• Swapping plugs instantly fixed the issue......and RPM's normalized between the engines at 6500

Plugs are identical, the "proper" non-surf side plug did have a two very small nicks on the lip of the very tip of the plug (which I would think be more likely to cause cavitation, not fix it).

Anyone else ever come across this issue or resolution?

 

[tdonoughue]

My uneducated guess would be... cavitation.

My bet is that you sucked something up which caused cavitation (thus the 8000 rpm). When you stopped and swapped the plug, it dislodged whatever it was and you were back to normal.

 

[sunbyrned]

I’m wondering if over the years the seal conformed to any imperfections that the hole may have and when swapped, the seal was not as tight.(?)

 

[Shady28]

Oddly hadn't thought of either of those two scenarios.

I'll have to test swapping them back again to see if it was an object issue (though it happened two days in a row while surfing, but not at all at lower speeds or WOT tubing the kids either day) or if it may be driven by the seals having conformed to their respective tube/engine. What was really odd was that it only occurred when ballasted and under load, everything was good at all non-ballast speeds and lower ballast speeds.

Thanks for the suggestions.