Motor Problem 90hp Mercury
 

Iam stumped ,,I picked up this 1993 mercury 90hp 3-cyl. outboard the motor sat for 3 years ..Its very clean and has good compression the problem is the motor acts like its to tight ,, the starter will only turn it slowlly one reval at a time ,,,, if i pull the plugs the starter spins the motor fine,, put in one plug and the rotation starts to slow ,,2 plugs in slower,, and then 3 plugs it slows to nearlly a stop ...I thought that maybe the starter was weak ,,so i tryed to rope pull it and I could bearlly get it to rotated with a rope,, so again i pulled the plugs and it spins freelly ....it almost like the motor has to much compression...ANY Ideas what may cause this....THANKS Guys

Is this a rebuilt motor...did the PO put the wrong rings back in it?...

No it not a rebuild it all original ,,,,it has a fuel enrichener on it thats what merc used instead of a choke,, the enrichener dumps fuel right in to the cylinders or manifiold for cold start I wonder if the enrichener is malfuncting and dumping to much fuel into the cylinders and loading them up for a hard/high compression start any ideas whould be helpfull

If it were doing a fuel dump, the plugs would be wet, wet. That enrichner circuit is easy to test. Pulling it off by hand, well I think it could be done, I think from about 60hp on up you might drop a nut trying. Do they still give the rope start kits out to the big v-6 motors? The 90 wasn't meant to be started by hand.
If it were me I would check the enrichener valve/solenoid, check my voltage on the batt. , check the cables for resistance. If it rotates freely by hand without the plugs in you have eliminated interference or being overly tight as a problem. I would still be looking at the starter. Does it have good spark?

I can rope start my Merc 150's as long as it is lined up on the backside of the compression stroke. Might be a case of a weak starter or a weak arm or a rusted crank, sticking rings. Take the plugs out spray some pb blaster in each hole and turn the flywheel by hand you should be able to decipher each bump of compression for each hole motr should turn easily. If the motor feels tight and binding doing this ..rut roh. If not I would revisit the weak starter and arm.

B

Try starting it with a little juice behind it on a boost setting on your b attery charger that should rule out weak battery. My 135 does the same thing to me with a fresh charged battery. Im thinking the starter is pooping out on me or like Ridge said it could be bad cables (corrosion inside sheathing createing resistance

Have the heads have been shaved and there's too much compression?

Thanks for all the advice I was only able to spend a little time on it today ,,I still cant rope start it just to much compression.. hooked up the battery inline with the jumpstart on my battery chager and got it to rotate a little faster so i went for more power even though the battery is in good cond. and has been load tested i went and got my truck and hot- shotted the good battery with the battery in the truck with the truck runing and finally got the motor to spin normlly so i am thinking mabe a very week starter,,,, I got it to run for about 5 seconds then she died and wont start again ,,I will check for spark tomorrow ,,,,,gas is good ,,,,, I even tryid starting fluid we will see ,,,,,,,the only other problem i will have if i get it running is how am I going to get my truck out in the middle of the bay to help with a start....:you:

Sounds like a weak battery or corroded cables or connections. Be careful using that starting fluid, it doesn't have any lube oil in it.

Definetely watch the dry starts with ether(starting fluid). A friend of mine had a rough starting 9.9 gamefisher and he always used starting fluid to start it. premature wear on the rings due to dry starts ultimately lead to low compression and he ended up burning the motor up