Mercury 90HP 2 stroke 0B153965 won't idle - poor running

[Rpiazza6857]

Hello all I have a new to me 90HP Merc that I cannot seem to get running correctly. So far I have rebuilt the carbs with kits and new needles, replaced all fuel lines, replaced enrichener solenoid, gone through the lync and sync procedure, replaced the plugs and wires, removed oil injection, new water pump and gear oil, and various other minor things. Compression is 120 dead even across the board with the engine luke warm and the throttle completely open. There is very good spark to all three cylinders. The issue is the motor will run until the top cylinder loads up at idle, it can be made to run longer by applying more throttle manually at the throttle plates but smokes badly and seems to have a miss. I used new spark plugs when testing and when pulling them the top plug is badly carboned and wet with fuel oil mix even after a short period of time, the middle and lower still look new. I am going with a starting point from the book of 1.5 turns from lightly seated to start with the carb tuning. I have verified the wiring from the switch box to the coils is correct. Wiring looks factory original and motor is very clean for it's age. I have tried adjusting the low speed needles and the low speed timing just to see if it would make a difference and it changes things slightly but engine does not respond to adjustments like I think it should. I'm not sure where to go from here, I plan on rebuilding the fuel pump to rule that out because it's cheap, and possibly swapping coils around to see if the problem follows the coil, could a coil be bad and still fire strongly? Any suggestions would be appreciated, thank you!

 

[flyingscott]

Does Spark jump a 7/16" gap? What is your compression? Fresh gas? What about a link and sync? Do you have a factory manual?

 

[Rpiazza6857]

Does Spark jump a 7/16" gap? What is your compression? Fresh gas? What about a link and sync? Do you have a factory manual?

Yes spark is verified to jump the gap, compression is 120 on all cylinders, testing is being done from a remote tank with brand new non ethanol fuel mixed 50:1 with amsoil synthetic marine rated 2 stroke oil, brand new fuel filter on pressure side of fuel pump, and well as a new inline filter from the remote tank just for safety sake and because I had it lying around, lync and sync procedure has been done step for step except maximum timing advance. I am working with the factory manual for reference.

 

[racerone]

How did this motor run for you last season ?-----Are wires from CDI / switch box going to the correct coils ?-----Checked flywheel key ?-----Why did you replace the enricher valve ?----No need to open throttle for a compression test on this 2 stroke motor.

 

[Rpiazza6857]

How did this motor run for you last season ?-----Are wires from CDI / switch box going to the correct coils ?-----Checked flywheel key ?-----Why did you replace the enricher valve ?----No need to open throttle for a compression test on this 2 stroke motor.

The motor is new to me, I have not run it on a boat yet, yes the wires from the switchbox to the coils have been checked against the diagram and are correct. The enrichener valve was replaced because it was not working, it is currently working and hose routing was double checked. I have not checked the flywheel key.

 

[racerone]

You may have bought a trouble motor.---So check the reed valves behind the carburetors.----Check the flywheel key.-----A sheared key throws timing way out.-----And no , you can not find a sheared key with a timing light.----Possible that cylinder sleeves have rotated as well.-----Inspection for that if all else fails.

 

[Rpiazza6857]

You may have bought a trouble motor.---So check the reed valves behind the carburetors.----Check the flywheel key.-----A sheared key throws timing way out.-----And no , you can not find a sheared key with a timing light.----Possible that cylinder sleeve have rotated as well.-----Inspection for that if all else fails.

Would a sheared key be throwing the timing out on just one cylinder? I did look at the reed valves when the carbs were off and they looked ok but who knows for sure.

 

[racerone]

A sheared key throws timing out on all 3 cylinders !-----Some simple trouble shooting will find out what is wrong.-----Throwing parts at it gets expensive.

 

[Rpiazza6857]

A sheared key throws timing out on all 3 cylinders !-----Some simple trouble shooting will find out what is wrong.-----Throwing parts at it gets expensive.

What simple trouble shooting should be preformed? I am having an issue on one cylinder best I can tell, it didn't make sense that it would be a sheared key to me that is why I asked the question if it could effect only one cylinder. Why would you suggest that? I am asking questions to find out were to go next, I never planned on just throwing parts at it, especially expensive ignition components.

 

[flyingscott]

What is your float level set at? Where did you get the carb kits from? Did you soak the carbs and clean them correctly?

 

[Rpiazza6857]

eared key throws timing out o

What is your float level set at? Where did you get the carb kits from? Did you soak the carbs and clean them correctly?

Float level was set per the manual but without it in front of me if I remember correctly it is just a hair above level with the bowl turned over, I used oem carb kits which I got from a well established online retailer, everything matched up nicely, I have also tried using the old needles to no avail so I switched them back to the new ones. Carbs were not very dirty to start with and they came out almost spotless after soaking for a few hours and being blown out with compressed air.

 

[racerone]

In my opinion the motor was sold because there was something wrong with it.-------Likely something that is elusive.-----Is it the one cylinder that is bad or is it the other 2 that are not firing properly ?----You said those 2 plugs still look like new !!!-----Outboards are just a little different and trouble shooting seems to be a lost art.-----_--Is oil injection in service and oil output tested ?

 

[Rpiazza6857]

In my opinion the motor was sold because there was something wrong with it.-------Likely something that is elusive.-----Is it the one cylinder that is bad or is it the other 2 that are not firing properly ?----You said those 2 plugs still look like new !!!-----Outboards are just a little different and trouble shooting seems to be a lost art.-----_--Is oil injection in service and oil output tested ?

Almost a 100% guarantee the engine was sold because it does not run correctly, but it has good compression so I believe it can be repaired, do you suggest I just give up and buy something else? If you would kindly read what I have already posted you would see the oil injection system has been removed and there is no need to check the oil output. I also mentioned I am using a 50:1 ratio of non ethanol gas and amsoil oil. A brand new set of plugs was installed and the upper one is coming out black and wet with unburnt fuel and oil. The unburnt fuel and oil is also apparent in the exhaust. The upper cylinder does not respond to low speed adjustments. The other two plugs look like they were firing cleanly and have good spark. If the plugs all looked like the one coming out of the upper cylinder I have doubts this motor would even fire.

 

[racerone]

Good luck with your project.

 

[Rpiazza6857]

Thank you to everyone that replied, I had some time to work on the motor last night and problem solved, it ended up being a bad fuel pump flooding the cylinder, I didn't think it was going to be that as it did not respond to pumping the primer at all. I decided to rebuild it because it was cheap and fairly easy to do. One of the diaphragms was brittle and dry rotted. I used OEM p/n 42909A4 which is a superseded number from the original. The kit did not have any rubber check valves like my original, which after some research I found out mercury no longer uses the rubber, they only use plastic ones now. So coming out of the pump was two individual pieces a rubber and plastic valve, going back in was just the plastic as no rubbers are included in the kit and are no longer needed. Also the paper gaskets and rubber diaphragms go together backwards of the manual I have per the instruction sheet included in the updated kit. Just a few things I noticed with the kit I thought I would mention because it took longer to find that information than actually doing the work. I hope that helps someone in the future. After reinstalling the pump the engine fired almost immediately and idled well. Thanks again.

 

[Rpiazza6857]

Another question on timing this engine, manual states to set the max timing @ 28 degrees BTDC while cranking, the motor was set @ 33 degrees when I checked last night, I moved it back to the proper 28 but I have heard of people retarding the timing a touch to compensate for the possibility of bad fuel. If I wanted to error on the side of caution should I set it at lets say 27 degrees or 29 for max timing, I understand the low speed is kind of variable and the 2 degrees is a starting point and final adjustment is idle speed in gear in the water. If you adjust the low speed in the water does the max timing then have to be adjusted as well, or a different way of saying it, does the low speed adjustment effect the high speed since the two arms are linked together.

 

[Faztbullet]

Leave timing where its at and no low does not effect high.

 

[Rpiazza6857]

Just to be clear, your saying leave it at the 28 for factory spec not the 33 i found it at correct?

 

[Faztbullet]

Yep