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Glenlivet

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Reply with quote  #1 
E75DPLSOR serial 05098692

Before I had my engine serviced I noticed the exhaust blowing through the joint between the gearcase and mid section. The outer exhaust housing and megaphone were found to have melted and have been replaced, boat back in the water and it's still blowing with little or no exhaust showing from the prop.

I've also had problems with the engine not revving above 4500rpm and I'm now wondering if there is a blockage preventing the exhaust from exiting cleanly through the prop. I've read on here about an exhaust filter but can't find it in the schematics in the workshop manual. I'd like some ideas before going back to the mechanic as I don't want to melt the exhaust components again (VERY expensive!) and I'd like to find the extra revs the engine is so far refusing to give up. Any ideas will be gratefully received!

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olypopper

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Reply with quote  #2 
Melted exhaust components are almost always caused by over propping/over fueling conditions.

The exhaust filter is nothing more than a mesh foam that is housed in the exhaust relief port housing. It's where exhaust comes out when off plane, directly above the tell tale overboard discharge.

Have you changed props to achieve more rpm? Can we assume that your mechanic checked the basics first like spark, compression and fuel pressure? Did he perform a cylinder drop test?

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Glenlivet

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Reply with quote  #3 
I've changed props down to the point where I was getting 8 knots at 4000 rpm, still no go above 4500. The boat with this engine is rated at 23 knots. The current prop gives 15-18 knots@4000rpm which is ideal cruising and should top out at around 23 knots@ 5200ish. He knows the problem and as far as I'm aware has checked everything, I'm waiting for the diag print out but have one from a couple of months ago. No faults showing, either current or historical apart from winterisation. I'm puzzled as to why the exhaust is blowing from the gear housing joint when sat on its berth in the harbour. I've not seen this before with other outboards.

Edited to say the engine doesn't miss or lack power up to 4500rpm, hole shot and acceleration are as expected.

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olypopper

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Reply with quote  #4 
"still no go above 4500"

Have you verified engine rpm with laptop via Evinrude Diagnostics?  Analog tachometers are notoriously inaccurate, especially at higher rpm. 

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Glenlivet

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Reply with quote  #5 
Quote:
Originally Posted by olypopper
"still no go above 4500"

Have you verified engine rpm with laptop via Evinrude Diagnostics?  Analog tachometers are notoriously inaccurate, especially at higher rpm. 

Not yet. We were going to have a run out with the laptop attached but the weather got in the way (been a terrible summer here). Even if it is reading 700rpm under I'm missing at least 6 knots top speed, and it doesn't sound like the engine is revving high. I'll have a better idea when I see the print out as the percentage time run at x revs should tell the story.

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