Incorrect spark plug gap cause loss of RPMs at WOT?

impy03 said:
Been a while since an update, but it has been determined that the harmonic balancer is failing on one engine, which I would assume would cause some timing issues. I have a new one on order and will update again once I get it installed and get the engine timed correctly. I also went ahead and replaced fuel lines and anti-siphon vales just to alleviate any potential issues with the fuel system. Fingers crossed this will resolve my RPM issues.
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I agree with the techs here, you found a bad balancer on one engine. Has nothing to do with 2nd engine. This will not solve the problem.
 
So I got the new harmonic balancer installed and it definitely helped the smoothness of the idle, but no change in RPMs on that motor. Checked the timing and it is in spec according to the spark arrestor cover. I checked the hull and I do have a very thin layer of light slimy marine growth, but nothing over the top as this is a freshwater boat. I do have a few more things I'd like to check, as I believe my port motor is compensating for the lack of RPMs being produced by my starboard motor per my sync gauge. I also now notice that after the starboard engine cranks and runs for about 20-30 minutes, it will sometimes die while in drive and idling. If it dies, it is typically hard to start again even being warm. The other thing I have noticed is that once the throttle is applied to the starboard engine and I get to 3000-3200 RPMs, the engine will sometimes quickly skip or lose RPMs suddenly and then return to normal within a matter of a split second. This symptom is very erratic and only happens from time to time. All fuel lines, filters, and fuel have been checked and/or replaced thoroughly for bad fuel, obstructions, etc.

#1 - Is it possible that my starboard engine's coil wires could be crossed and the engine still crank and run?

#2 - Do the above newer symptoms sound like I should replace the coil and/or distributor sensor on my starboard engine? It is a thunderbolt IV ignition system and I have new spares for both parts that I have yet to install.
 
scoflaw said:
Cap and rotor replaced? Sounds like a loose wire. Check and clean them all.
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Yes and yes. That was replaced last season and I have double-checked all wire connections and the firing order for my starboard engine several times.
 
SCORPIO said:
Do you have zebra muscles in you area? If so, they are worse than barnacles. Grass, muscles etc will all cause issues. Start with a clean bottom and see what you get. The fact both motors are doing the same thing leads me to believe it's something common, like a fouled bottom.
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No muscles in my area that I have seen. The bottom is a bit slimy but it is a very light layer that is easily rubbed off. Seems like my port engine is now running consistently around 3600-3800 RPMs WOT and my starboard engine is staying around 3200-3300 RPM WOT per my tachs. I feel that my port engine is lugging due to the lack of power from my starboard engine.
 
Still gotta clean that bottom. You seem reluctant to do that for that reason? You've gotten advice from knowledgeable people that this could be, at least, part of the problem. I don't mean this in a sarcastic way - just wondering why since that is definitely at least part of the issue.

You may have multiple things going on - but let's see what happens once you've got a really clean bottom and running gear.
 
Lazy Daze said:
Still gotta clean that bottom. You seem reluctant to do that for that reason? You've gotten advice from knowledgeable people that this could be, at least, part of the problem. I don't mean this in a sarcastic way - just wondering why since that is definitely at least part of the issue.

You may have multiple things going on - but let's see what happens once you've got a really clean bottom and running gear.
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My apologies, I did dive and take a stiff brush to the hull which removed the majority of the growth. That is why I say it is just a light layer of slime now as I did that about 3 weeks ago and a small amount has returned.
 
impy03 said:
My apologies, I did dive and take a stiff brush to the hull which removed the majority of the growth. That is why I say it is just a light layer of slime now as I did that about 3 weeks ago and a small amount has returned.
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After you did that first cleaning, did you run the boat right away? Was there any difference? You'd be surprised what just a little growth can do - it creates quite a lot of drag. Whether or not this is the entire problem remains to be seen - but physics is real so this has to be causing some loss of RPM and speed.
 
Lazy Daze said:
After you did that first cleaning, did you run the boat right away? Was there any difference? You'd be surprised what just a little growth can do - it creates quite a lot of drag. Whether or not this is the entire problem remains to be seen - but physics is real so this has to be causing some loss of RPM and speed.
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I did run the boat immediately after cleaning the hull and that was before I was able to replace the harmonic balancer that failed. I had the same or very similar results and I could tell that my port engine still seemed to run a few hundred RPMs faster (mid to upper 3000 RPM range) than my starboard and the starboard still ran as it did before (low 3000 RPM range). I'll also mention I have reduced the weight on the boat for testing purposes by leaving only a 1/2 to 1/4 tank of fuel, no water in the holding tank, and removed as much unnecessary junk/weight from the boat as possible without any noticeable difference in RPMs on either engine.
 
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