Mercury 90 inline 6

[bigtrout1949]

Hey out there. Having problems with my 1984 Mercury 90 inline six. Starts easy, runs very smooth at low rpms. When trying to open it up it seems to drop a cylinder for a few seconds, then runs great, then repeats. Any suggestions? Seems fuel related, could be ignition. Is it safe to use berrymans b12 chemtool? Any help would be greatly appreciated. Thank you

 

[sutor623]

Re: Mercury 90 inline 6

How long have you owned this motor? Have the carbs been cleaned recently, fuel pumps, spark plugs, wires? Give some maintenance history so we can give you some ideas. What is the serial number? With the mercs we need serial, not year.

 

[bigtrout1949]

Re: Mercury 90 inline 6

Just got the motor. Plugs are clean. Previous owner says it has recent carburetor job.

 

[sutor623]

Re: Mercury 90 inline 6

Just got the motor. Plugs are clean. Previous owner says it has recent carburetor job.

Serial #. Does this motor have ignition coils or a distributor? I believe it is distributor.

 

[sutor623]

Re: Mercury 90 inline 6

Once you find what serial number it is, you can find the ignition manual here. It will give you a step by step checklist to find your electrical problem (if it is in fact electrical) It may also be fuel pump issues. The motor may be losing speed due to a fuel delivery problem.http://www.cdielectronics.com/downloads/troubleshooting%20guide/

 

[Chris1956]

Re: Mercury 90 inline 6

Hard to tell what is wrong from that description. Berrymans is fine to use to clean carbs, after you have disassembled them. It is useless and maybe dangerous to allow the engine to burn it. Try pumping the primer bulb while running. If this fixes issue, the fuel pump or some fuel line restriction is part of the issue. If not, the carbs may be a bit lean.

Does it "drop a cylinder" once you are on plane? I presume that motor is an ADI ignition with 6 coils?

 

[sutor623]

Re: Mercury 90 inline 6

Does it "drop a cylinder" once you are on plane? I presume that motor is an ADI ignition with 6 coils?

Thats what I was trying to figure out.

 

[bigtrout1949]

Re: Mercury 90 inline 6

Yes. The engine acts like it drops a cylinder for a couple seconds, then hits full throttle, then repeats this scenario. Has 6 coils. how do you test the coils? Thanks

 

[sutor623]

Re: Mercury 90 inline 6

Check the link that I sent you in my reply. That will give you all the info.

 

[jimmbo]

Re: Mercury 90 inline 6

never mind you said it has 6 coils

If it cuts out as you are advancing the throttle, there could be a wire grounding, shorting, or opening as the linlages are moving.
Years ago my friend had an engine doing that. We found a chunk of carbon in the spark plug gap. removing the carbon solve the issue. I doubt that that is affecting your engine, it uses surface gap plugs.

 

[sutor623]

Re: Mercury 90 inline 6

never mind you said it has 6 coils

If it cuts out as you are advancing the throttle, there could be a wire grounding, shorting, or opening as the linlages are moving.
Years ago my friend had an engine doing that. We found a chunk of carbon in the spark plug gap. removing the carbon solve the issue. I doubt that that is affecting your engine, it uses surface gap plugs.

True, and on my '67 merc the trigger wires coming from the distributor would move when the ignition advanced. It eventually caused a short in the wires causing intermittent flow. Definately something to check.

 

[bigtrout1949]

Re: Mercury 90 inline 6

Thanks to everyone for the advise. It gives me a few ideas to start. Appreciate the help