Need advice on Mercury 75 2stroke problem

[MBay Pete]

My Mercury 75 2stroke has a problem turning over. I tried to start it today after it had sat for 4 weeks and the motor would only crank about half a turn. I had the same problem 4 weeks ago and after several attempts it started and spat out a quantity of oil from the exhaust then ran normally. I decided to see how it starts today and the same problem only would not crank any more than half a turn. I pulled the plugs out, checked inside the cylinders and all looked normal, turned over the motor with no plugs and it spun over without a problem. Put the plugs back in, checked fuel, oil,and spark- looking ok, tried to start and same problem, feels like something is stopping the full revolution at the start. Battery has full charge so all well there. Any suggestions for me before I have to outlay for an outboard mechanic.
Pete

[Aussie123]

Sounds like the battery has dropped a cell or you may just have a dirty battery terminal.
Try another battery and see how it goes then.
The oil is probably just unburnt 2 stroke oil, nothing to worry about.

[Noelm]

Yep first steps are the easy ones, get another known good battery, clean the battery terminals while you have them off, test and get back to us.

[MBay Pete]

Have checked the battery - 13.4 volts. Tried another battery, full charge on test, same result trying to turn motor over. Even connected the batteries in parallel - same result, no go.

[Noelm]

OK, battery appears OK, battery cables are next, do you have a multi meter, and do you know how to use it?

[banshee]

Bad/dirty connection is my guess,start at the terminals and work from there.

[scottar]

Don't guess - do a voltage drop test. Also check whether you can turn the flywheel by hand (ignition off) - just to make sure we are barking up the right tree.

[hweebe]

Have you tested the ignition coils. Could be a coil starting to go giving u intermittent issues? Simple test with a multimeter but u will need a service manual for acceptable ranges across the different pins.

[Noelm]

Probably unlikely to be a coil causing it to turn over slow, but, you need to trouble shoot methodically, the battery is said to be OK, not exactly sure it is, but it's all we have, connections, cables and if the motor turns over free by hand is the next steps with voltage drop test.

[MBay Pete]

checked voltage at starter terminals, same as battery, tried to turn over again - only got half a turn, sounds exactly like a flat battery but it's not. Battery terminals got hot after 3 tries to get it to turn over. Gave the motor a 10 second turn over without plugs and turns over without a problem, put plugs back in and no go. It's like the compression is too much for the pistons to work. Spark at plugs, plenty of fuel, electrics all ok with power where it should be. I can't think of anything else. I will have another go tomorrow and if no go looks like will have to go to the workshop.
Pete.

[Fed]

Take one helper to turn the key, one voltmeter for you to test with and two minutes to find the fault.
To DIY just ask or give 'the man' $100.

[Fed]

checked voltage at starter terminals, same as battery,

That is impossible.

[Fed]

FWIW Pete I had a similar thing with my evinrude.
Battery tested good & voltage drops tested good.
Pulled the starter, cleaned, checked and replaced brushes then refitted & tested...same.

Mine would turn very sluggishly for the first few compression strokes then speed up & crank normally.

It turned out to be a slipping bendix clutch, the nut on top would spin fast but the cog would only turn slowly.

[Dirtyfuzz]

I’d also bridge the starter and see if it will turn over normally, and check the connections at the starter solenoid also


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[bluefin59]

Has it got a pull start rope under the cowling (my 60 hp 2 stroke did) if so try and pull start it a couple of times it should fire without the battery anyway mine did when the battery crapped itself under load . Matt