looking for info

Joined
May 30, 2013
Messages
5
I have recently purchased a 1976 challenger mark 2 tri hull boat. It has a mercury 900 straight six outboard motor. I am looking for information on the motor. I have no clue the year or where to find the serial number to get manuals for it. It needs some work that I cannot complete until I get that information. Can anyone tell me more about it? I need spark plugs fuel filter battery and all oils need to be changed. Also is it a two stroke? If so what is the fuel mixture? Thanks in advance for any information.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: looking for info

Almost certain it is 2 cycle. Fuel::eek:il mix is 50::1. Look on the triple clamp, between the transom clamps for the serial number. It will define the year. Post a picture with the cowling off and someone can make a real good guess.
 
Joined
May 30, 2013
Messages
5
Re: looking for info

I will do that when I get off work today. I just couldnt pass up the deal. It was the boat motor and trailer for 300. I am just clueless about boats. I am not afraid to do the work. Irebuilt the eenginein my car. I jist need a manual for the motor to know what im looking at.
 

muskiemike12

Petty Officer 2nd Class
Joined
Apr 7, 2010
Messages
153
Re: looking for info

Those old tower of power's are great motors. You need to check the condition of the internal wiring. I had all my old wiring and hoses replaced last year. Check compression on all 6 cylinders and make sure they are within 10% . My mechanic suggested to run premium gas through it also. Non-oxy if you can find it.
 
Joined
May 30, 2013
Messages
5
Re: looking for info

As I am an electrician replacing all the wiring will not be a problem. I was going to replace all the spark plug wires anyway.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: looking for info

OK, looks like mid 70s or so. Has distributor on other side of motor, right? That makes it pre-1978. Sparkplug wires are solid, stranded stainless steel conductors, with threaded ends. They are avail on the web at vintagemercs or oldmercs. Look for yellow tigertails. Spark plugs are Champ L76V or NGK BUHW, but check application guide to verify. Sometimes merc went down a heat range for different years.

Motor harnesses are avail at surplusunlimited on the web. Change the gear oil. It takes 25oz of marine gear oil for mechnaical shift motors.

Really need a serial number. Does it have a plug on the block with a number?
 
Joined
May 30, 2013
Messages
5
Re: looking for info

I am looking at the motor now. There is a block that says sn but it is written in sharpie it looks like. What I can read is 4243 I think. On the front it says 1978 m-900 timing pick up 4-6 degrees btdc max spark -21 degrees btdc at 5000 rpm. The distributor is on the other side.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: looking for info

OK sounds like a 1978 motor. A serial number starting with 42 is fairly consistant with that age motor. You can look on the maxrules website at the model year guide
 
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