Mercury 115 Optimax rough idle and surging on idle

JohnPenhall

Recruit
Joined
Aug 14, 2021
Messages
3
My Opti 115 had some water issues after a fill at a remote location.I have drained fuel system , replaced plugs and filters , checked coils and compression. Replaced fuel filter , drained VST - a little bit of water , no debris. It has new dual 12 v batteries that are fine. Fuses are fine.
No error codes on the vessel view system..
Still struggling to start and idle and when it does it sputters and surges up to 100 rpm . I cleaned the TPS as this apparently can be an issue- no change.
It runs fine at WOT - no power loss or surges at all.
I suspect the air pressure regulator and am not keen to be pillaged by mercury for a new rail.
Fuel pressure is good - 120
Pressure differential between fuel and air regulator> 20
I removed the rail and the regulator diaphragms. There is no tracker valve on the 115
They are the purple ones - the air pressure regulator one was caked with gunk , which I carefully removed. I don't see a hole or tear and there is one tiny rough spot on one of the edges , but it appears to seal fine. The fuel pressure regulator diaphragm appears pristine. I'm really worried that I have a reed valve problem as the fuel rail and injectors all appeared fine.
Do I need to buy a new diaphragm?
How can I inspect the reed valves without disassembling the entire system?
I may as well do it as all the cowlings are off , but removal of the oil tank and the myriad of tiny hoses intimidates me.
Help a technically challenged immigrant!
 

schematic

Lieutenant Junior Grade
Joined
Jan 12, 2008
Messages
1,102
not the engine for the inexperienced.
MAKE SURE THE PLUGS ARE THE EXACT NUMBER!!!!
 

JohnPenhall

Recruit
Joined
Aug 14, 2021
Messages
3
not the engine for the inexperienced.
MAKE SURE THE PLUGS ARE THE EXACT NUMBER!!!!
I got them from the dealer but will definitely double check. Im experienced but way out of my depth here. Very complicated motor even with the service manual , which isnt very helpful on troubleshooting.
 

papspontoon

Cadet
Joined
Aug 18, 2021
Messages
22
does your engine have two fuel pumps? mine was doing something similar. my lower pressure mechanical fuel pump has one way valves and needed replaced. small disc valve..
 

JohnPenhall

Recruit
Joined
Aug 14, 2021
Messages
3
Yes it does. I will the vapor separotor and check.
Checked the reed valves today. They were fine.
Thank you
 
Top