Mercury 150 saltwater hard starts and stalls at idle

[Captterra]

I have been having issues with my engine stalling at low rpms and also hard starts when warm or cold. I have replaced water pump, water seperator and fuel filter in motor. My marina is a tight squeeze when docking so stalling at low rpms makes it a bad experience. Also, i have treated fuel with startron. Any help would be greatly appreciated.

 

[Chris1956]

Re: Mercury 150 saltwater hard starts and stalls at idle

Maybe the carbs are dirty? Do you have carbs? What do spark plugs look like? What year motor?

 

[Captterra]

Re: Mercury 150 saltwater hard starts and stalls at idle

Yes it does have carbs. It is a 2004. The carbs were my next step. What is the easiest way to clean them?

 

[Captterra]

Re: Mercury 150 saltwater hard starts and stalls at idle

Oh yeah. Sparkplugs are new.

 

[CharlieB]

Re: Mercury 150 saltwater hard starts and stalls at idle

New plugs are fine, but did you test for at least a hot blue spark of at least 7/16 inch on each cyl cranking? If any fail it will cause low speed problems.

 

[Captterra]

Re: Mercury 150 saltwater hard starts and stalls at idle

I wouldnt even begin to know how to test for that.

 

[CharlieB]

Re: Mercury 150 saltwater hard starts and stalls at idle

Nail to nails partway into a board, bend the heads and turn them so you get a 7/16 inch gap. Rig a ground wire to one and another wire to a spark plug wire. Crank the motor and look for a hot blue arc. Repeat on each plug wire.

You can remove the spark plugs and ground all the rest of the plug wires, that will save a lot of strain on the starter motor and the battery, plus the motor won't start.

You just want to see if you have 'good' spark at cranking (low) speed.

 

[Captterra]

Re: Mercury 150 saltwater hard starts and stalls at idle

What would cause poor spark? And how would I fix it? By the way. Thank you for your rapid responses. I really appreciate it.

 

[CharlieB]

Re: Mercury 150 saltwater hard starts and stalls at idle

IF, and that is a BIG IF, IF you have a weak spark cranking the ignition may not adequately fire the plug cranking or at low engine speeds. Commonly caused by low voltage output of the stator, HOWEVER< there is NO RETURN on electrical parts, and they are not cheap, so it is wise to properly test and PROVE any fault before making any wild assumptions (which are usually wrong).

Test spark while cranking, if it is a nice hot blue arc over a 7/16 inch gap then we proceed to something else.

Spark, then check compression, once they are both proven acceptable then you move onto the fuel system.

One step at a time.

 

[Captterra]

Re: Mercury 150 saltwater hard starts and stalls at idle

Could the low voltage output be caused by a week battery? The reason I ask is because I am having issues keeping my batteries fully charged. Either way i will be down at the yard this weekend testing for good spark. Thanks!

 

[CharlieB]

Re: Mercury 150 saltwater hard starts and stalls at idle

Battery is for cranking, and accessories, EFI models use the battery for fuel supply, otherwise, the ignitions are all stator/alternator driven, with a minimum cranking RPM of 300, slower than that the motor may not spark or start at all, but once started idling 700 or better, each cyl should have a hot blue arc it least 7/16 inch in free air.

Batteries dying often turn out to be the contant drain of the radio/cdplayer, they have a constant 12 V to keep station presets in memory, and a separate switched 12 V line to turn on with the ignition switch.

Disconnect either battery cable, rig a test light between the battery post and the disconnected cable, if the light is on, something is drawing power and will kill the battery. Start pulling fuses, one at a time until the light goes out to isolate where the problem is.

 

[Captterra]

Re: Mercury 150 saltwater hard starts and stalls at idle

Thank you!!!!