Merc 90 four stroke rough idle, stalling

[Rich Stern]

Calling Bob B...2006 Merc. 90 four stroke.



Had my boat out for the first time yesterday. Launch at the ramp and run for the first 10 minutes back to my dock was fine, motor running perfect.



Few hours later, go to start up, idle out and the motor starts to stumble and stall. Won't stay lit at idle. I can get it to start in neutral at about 1500 to 2000 rpm, but it runs rough, with lots of smoke around the lower cowl area. Everything under the cowl looks dry, no leaks or disconnected fittings or wires. When I squeeze the fueld bulb, I see fuel movement in the filter leading to the fuel pump.



I usually use the boat over the winter, but was too busy this year, so the boat sat in my garage with 1/2 tank of gas, probably untreated (can't remember). I added some fresh gas mixed with Seafoam, let the motor high-idle for a few minutes today. Same result. I also had a spare fuel line/bulb assembly, so I swapped that in, just in case it's an air link. Again, same result.



Thinking of changing the fuel filters, and/or draining the gas out.



Any help appreciated.

 

[joseph currier]

try running your motor on a small remote tank with fresh fuel.

may help you ditermine if the fuel in your main tank is bad?

 

[Rich Stern]

try running your motor on a small remote tank with fresh fuel.

may help you ditermine if the fuel in your main tank is bad?

Joe, thanks for the suggestion. Did this just now. It made no difference. Ran the boat from a 3 gallon remote with fresh gas. Tried idling and high idling for about 10 minutes. Same behavior from the motor. Surging at high idle RPMs (1200 to 1800), quits at anything below 1200 rpm.

 

[Bob Bourget2]

Ok, from what it sounds.....there is a bit of debris in the carbs. I would flush the system first. There's a drain at the bottom of each carb. You might have to remove the chaps in order to expose the bottom carb. Remove drains, purge with your fresh fuel and the remote tank. Be sure to double up the recommended Sea-Foam mix. Lots of problems with those carbs....

 

[Rich Stern]

Bob, it's a fuel injected motor. Sorry, I should have stated that in my original post, but I didn't realize there were carburetor fed versions of these motors.

 

[Bob Bourget2]

Rich, I'll need the serial numbers. Want to see exactly which EFI you have. There are TWO...

 

[Rich Stern]

Serial no: 1B393231



Thank you!

 

[Bob Bourget2]

Rich;

You have the new "verado" style Merc. Great motor. First and foremost, you must REMOVE the primer bulb. This series of engines does not need, nor is it recommended that there be one. Whomever rigged that engine on that boat should have known. That engine has a lift pump within the FSM {fuel supply module} that electrically does it for you, based on fuel levels within the FSM. If a primer bulb is used in this application, over-pressurization can cause running idiosynchrasies, {and susbsequent codes / faults} as fuel can enter the FSM vent system. There is a schrader valve on the FSM that you can depress, to allow fuel to drain back into the FSM. This would be the only attempt I'd recommend before "key up" again. If this does not work, a trip to the dealer and a Computer Diagnostic Readout is in order.

 

[Rich Stern]

Bob...advice greatly appreciated!

 

[Bob Bourget2]

No problem...if I can be of further assistance, let me know....

 

[Wes W]

Did you resolve this? If so, how? Same boat, same engine, same problem. Any advice or help is GREATLY appreciated.



Thanks again,



W

 

[Rich Stern]

Wes, no luck yet. I wasn't able to spot the Schrader valve Bob referenced, but I did change out the fuel house to one without a bulb. No difference. Still can't idle low nd per her in gear. Gonna have to tow it over to the ramp and leave it at the Merc service place in town. Might be a couple of weeks before I am able to do that, but I will post a follow up.