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

[Noelm]

A lot of jumping here and there and guessing, first up, you need to check the battery voltage while you are turning the key to start, at both the battery end, and the starter end, the battery terminals getting hot indicate bad connections, have you actually removed and cleaned them? or are you just relying on them "looking" OK? don't jump all over the place with half tests.

[Fed]

A lot of jumping here and there and guessing, first up, you need to check the battery voltage while you are turning the key to start, at both the battery end, and the starter end
The above is the very first thing I'd do.
Be aware, test at the battery posts, testing at the battery lugs is not the same as testing at the battery posts.

[MBay Pete]

That is impossible.

Disconnected the cable on the starter and had partner turn the key.

[MBay Pete]

Will try the pull start tomorrow, hadn't thought of that Matt.
Pete

[MBay Pete]

Thanks for all the tips so far, will revisit the problem in the morning and see what happens.
Pete

[Noelm]

No need to actually pull start it, just try turning the flywheel, with the key OFF to see if it's easy to turn, or really tight. If you do attempt to pull start it, be VERY careful, if it's tight, and you give it a good yank, you will end up with very long arms, or very sore shoulders, next, be very sure the rope only goes around the flywheel once, not a few times, because if it starts, the rope will remain on the flywheel and be whipping around like a 75HP whipper snipper, giving you a pretty good whipping, before even trying to pull start, you need key on, primer bulb hard, manual choke on, and hope!

[Noelm]

Disconnected the cable on the starter and had partner turn the key.
Don't understand what this test would achieve.

[scottar]

Need to do it with everything connected Pete. Without the load from the starter the voltage reading means nothing. A bad connection creates a resistance which then creates a voltage drop as amps are drawn - the more amps equals more drop which is why it possibly seemed ok without the plugs in.

[bluefin59]

Will try the pull start tomorrow, hadn't thought of that Matt.
Pete

Pull start rope should be in a bag under the cowling , it shouldn’t be that hard to start with it my 60hp was easy in comparison to a 140 2 Suzuki I used to have . Matt

[Fed]

I don't understand why you would want to pull start it, we know it runs?

[Gon Fishun]

I don't understand why you would want to pull start it, we know it runs?

To eliminate hydraulic lock .

[Fed]

I pulled the plugs out, checked inside the cylinders and all looked normal
I don't think water would be likely but no harm trying I guess.

Don't be surprised if it's hard to pull over I remember struggling with my old 3 cyl 65s when I was young & fit.

[Noelm]

None of them are easy to pull start direct to the flywheel, pull starters had a gear to make it easy, a rope around the flywheel is possible, especially if you are broken down in the dark with a flat battery, it's amazing where that super human strength comes from!

[Steeler]

Just throwing it out there but when you pulled the plugs out to check there condition was there any sign of beading or very very small brownish marks on the plugs to indicate water ingress. Not uncommon for water to enter those Mercs and cause difficult starting but normally early signs are those symptoms i mentioned particularly on the bottom plug.

[Fed]

It sounds like you've been there & done that Steeler, even mentioning the tiny droplets.

[MBay Pete]

Cleaned the battery terminals, gave it a try - no go. Battery shows full charge. Tried Matt's suggestion of the pull start and fired up first pull (So simple, sometimes the simple things are not thought of), motor ran perfectly. Gave it a run to warm it up and then tried the key start - 5 tries and perfect start every time. Now I will check and clean the connections for the solenoid and the starter and see if that makes a difference, if not will get the solenoid and starter checked to make certain they are ok. Thanks to all who offered suggestions and especially Matt for the simple suggestion of the pull start.
Regards to all
Pete :)

[Aussie123]

You may have corrosion inside one of the battery cables so you could connect jumper leads from the battery to the motor and give that a test.

[Steeler]

It sounds like you've been there & done that Steeler, even mentioning the tiny droplets.

Yeh had a few Mercs and Mariners over the years do this. Still wouldn't swap a black one for a white one however LOL.

[bluefin59]

Cleaned the battery terminals, gave it a try - no go. Battery shows full charge. Tried Matt's suggestion of the pull start and fired up first pull (So simple, sometimes the simple things are not thought of), motor ran perfectly. Gave it a run to warm it up and then tried the key start - 5 tries and perfect start every time. Now I will check and clean the connections for the solenoid and the starter and see if that makes a difference, if not will get the solenoid and starter checked to make certain they are ok. Thanks to all who offered suggestions and especially Matt for the simple suggestion of the pull start.
Regards to all
Pete :)

If that’s the case maybe look to see if the starter motor doesn’t need new brushes or something along that line

[Steeler]

If your model utilizes the same style tilt & trim solenoid as the starter solenoid then why not try one of those and see how you go.