i have seen engines run fine one day and develope a problem the next day.these marine engines get worked pretty hard and things happen.i am just thinking out loud.i had a similar problem i chased for a long time,one engine was down 200 rpm.it ended up being an exhaust valve sealing poorly due to a small amount of reversion caused from a cracked weld in the exhaust header.most people would be suprised at how valve seal effects power.

Oh I totally get that, just not sure how it would not show up on dyno that's all.

I think I dribbled a bit of pee out on that one!.

Apples to oranges, but I have built a lot of identicle atv motors. same oem head, jug carb pipe, bore etc everyone of them had their own personality and no 2 ran exactly alike. Close but not exactly the same.

[ATTACH=CONFIG]558193[/ATTACH][ATTACH=CONFIG]558194[/ATTACH]dyno identical.... I think many are missing that..

No.

They just don't have last word on actual performance. The performance on the water, or track,or etc does.

It is an interesting thread.

Any new info ?

I get that, but to see 200 rpm loss in boat is equal to 1 cylinder down, that WOULD show on Dyno..

Something else is causing it, old engines were equal from what I can find in pics, but so much was changed since then I need to eliminate any possible thing, dynoeing was a huge one.

Storming so no info, I am going to swap distributors and coils and test Friday... just in case being in boat with waves make them act up and not on dyno, the mechanics of engines I am very confident are ok, they run great and smooth, just lack rpm in one. I have had a coil do things like this in the past... so I am gonna look at ignition.

What's strange is its not a cylinder that's down though or you'd here it plus you'd be down more than 200. No the whole dyno deal with being nearly spot on makes no since. Once you swap out coils be sure and post the results. I realize your getting a lot of repeat info but at least you have likewise others trying to help. These kind of problems can be a m/fker. Mike tkachs post is where I was leaning last night also however once again rpm loss was prior to dyno sessions that resulted in nearly the same identacle results. So with all grounds good and same voltage to each engine I can only speculate it's gotta be after the engines.

What's strange is engines before though didn't have these issues. Been a lot of post so sorry if repeat but fuel pressure fine on down side? No kinked line anywhere during r & r. Was last dyno session with engines pulled or in boat prop dyno?

Let me start with I REALLY appreciate everyone's input, and help!!

Correct both engines were same before but I would have some intermittent issues in past but can't remember for sure, too many issues between then and now to keep track.

Dyno was done in marine trim with my exhaust, sea pumps, and alternators. Fuel pressure 6-7 psi

I am really looking at things in boat that did not effect on dyno, I am planning to also directly wire ignition right to switch, that bypasses my harness, as the harness may have been ok on old engines but act up after being messed with? I am reaching for straws here anymore lol

Been fighting this issue a log time, I am going to hold videos I have from last summer and now to see all the documentation you can pause and read air fuels and rpm easily