73'/74' Mercury 850 Marathon

[garvamel]

Hi all

Well as the title says I have a Mercury 850 (not sure about which of those years...). It hasn?t run for quite some time.
Tried to fire it up, all sparkplugs working, fuel in the carbs, etc... It just makes some explosions but does not start. I even tried with Starting Fuild and nothing, so I'm not sure what is happening, any ideas?


Thanks in advance.

 

[Laddies]

Re: 73'/74' Mercury 850 Marathon

Stop using stater fluid or it will be junk, it sounds like the engine is either out of time or the dist cap is dirty. Clean the cap with hot water and dish soap drying well after cleaning. DO NOT try to remove the rotor as it and the shaft are one piece and it's a $100 item. next make sure the timing marks are lined up.

 

[Chris1956]

Re: 73'/74' Mercury 850 Marathon

If that motor has 4 ignition coils it is a later model and has the ADI ignition.

Check compression on the four cylinders. They should be 100+PSI and vary no more than 5% from each other. If this checks out, the rest is easily fixable.

 

[garvamel]

Re: 73'/74' Mercury 850 Marathon

Thanks Laddies and Chris

As Chris said, the engine has an ingition coil, not a dist, so maybe it is out of time. If that were the problem, I'm not sure how to adjust it, because I don't own a stroboscope.

And Chris, that pressure check you recommend, is it to see if the valves are stuck? (I don't know if "valves" is the correct word for that part, but my vocabulary in this area isn't that good). I'll have to get a manometer for that, I'll post the results after I do the testing.

Thanks again.

 

[Laddies]

Re: 73'/74' Mercury 850 Marathon

With ADI ign. (4 coils) it is a 1976 or newer engine