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1978 mercury 90hp

M

Mike13wayne

New member
Bought new battery for boat but motor still acts like it doesn't wanna turn over. Could it be seizing up from lack of oil? New help on what I should do to save motor?
 
Pull out all the sparkplugs and try turning the flywheel by hand. If it turns freely it's not seizing.

Why would you think it is lacking oil? You are running premixed gas, 50:1 with 2 stroke oil - correct?

As to sparkplugs - this is an old style Merc ignition. So this one breaks the rule - from factory this ignition came with Champion L76V surface gap plugs (and they continue to be the recommended plug for this model).

NGK's DO cross reference but this particular ignition was not designed to fire NGK's (which require higher coil voltages than Champion plugs).

So, if you are otherwise happy with the performance, leave the NGK's in there for now, but when they are due to be changed I would go back to the champions.

There is no listed spec for a "gapped" plug on your model so can't say if one will "fit" (require space in the top of the head so the piston doesn't crash into the ground electrode) - if you want to "try" a gapped plug (which gives you better performance at idle, lower speeds and is better for cold starts), a Champion L77JC4 (or QL77JC4) IS the gapped equivalent of the L76V/QL76V. Just make sure that it will not interfere with the piston if you opt to give it a try.

Surface gap plugs are "designed" for "sustained" high speed running. My 140 Evinrude (on the back of a 26' walkaround cuddy) is used mostly at cruise speed or "no wake" travelling through canals. I swapped my QL76V's for QL77JC4's and was far more satisfied with the performance...
 
I'll assume 2stroke/cycle.Check all your connections,clean them,especially the battery earth/ground,make sure you have 12v both sides of the solonoid,jump and see if that works,if not,remove the plugs and turn the flywheel by hand,cw,if it turns,your connections/battery/starter may be the problem.If it doesn't turn,drop the lower unit and try again,if it turns,your problem is in the lower unit.
 
The starter motors on these engines can not tolerate long / repeated cranking.----A motor that does not turn fast will have a " no spark " condition.-----If you are interested I can coach on how to check the starter.
 
Ok thanks for the advice on if it was seized up. Its ok turns freely. I was told i could spray some lubricant like WD40 into the plug holes and help the motor turn over better when starting. Is that true?
 
WD40 is highly flammable. Jumping the two large studs on top of the solenoid will tell you if the cable between the battery and solenoid and between the solenoid and the starter are good if the starter cranks normally. The normal cranking would mean the solenoid is suspect. If it still turns slowly then jumper between the solenoid stud to the starter and the starter + stud. Hit the keyswitch...if it cranks normally then that cable is bad. If it is still slow then the starter needs serviced.
 
Next question is my transom is cracking. The previous owner had a small aluminum plate on it. Any recommendation that don't involve taking it in?
 
If it is dry rotted it needs to be replaced. Sound it w/your knuckles. A knock is solid and a thud is rot. If it is solid you can bolt on a larger aluminum plate. If it were mine I would just replace it if there is rot. Removing the old transom is not hard nor is installing a new one and glassing it in place. Leave the outer skin alone and do all the replacement inside. I did a 19' I/O; had to pull the engine. Yours is an OB so it just takes a few hours labor. I have a link to a youtube series of videos where a guy replaced everything in a large Sea Ray I/O. He shows you the step-by-step process. Let me know if you want the link.
 
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