Mercruiser 120/140 restarting problems

I have an '84 mercruiser that I have been having some restarting problems with. The engine starts without much difficulty when cold, however if I run it for 20-30min and then shut if off, I many times am unable to get it restarted before my battery gives up. I will be replacing the battery in the next day or so, but was wondering if anyone else has had this problem. Could it be an alternator problem, that the batter would not have the power to crank after running? Gas line/Vapor lock? Any suggestions? I recently overhauled the carburator and I have cured the hesitation/acceleration problem that I had previously noted. I disconnect the battery after every use or I will often find my battery drained and unable to start the engine.

Re: Mercruiser 120/140 restarting problems

I don't think the battery is your problem.

Is your choke operating correctly ?

Have you replaced your fuel filters ?

Tune up ?

Re: Mercruiser 120/140 restarting problems

Tmulder said:

.... I disconnect the battery after every use or I will often find my battery drained and unable to start the engine.

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You have some current leakage somewhere. Get a multimeter and put it on the 'Amps DC' scale. Disconnect the red cable from the battery and put the meter in series with the red cable and the positive terminal. Read the current flowing. It should 0 with everything switched off. If you have a stereo it might read a few milliamps (that's what keeps the station memory up, and is not enough to drain a battery... )...

To isolate the source of the drain, start disconnecting ancillary equipment, radios, sounders, lights, pumps, ect....

The ideal situation is that the engine system and the accessory systems are isolated, but 99.9% of the people wiring up boats are morons and hook accessories off the engine harness behind the dash... :facepalm:... Makes this sort of troubleshooting a real pain...

The other option, and this is the one I would do in your situation. Separate off the 'non-engine' wiring from the engine wiring. Run a heavy (6mm minimum) pair of wires, one red from the battery switch, one black from the battery negative terminal, up behind the instrument panel and terminate them at a couple of terminal blocks... Run anything that is not related to the engine from those....

These are the terminal blocks I setup in a friend's boat... (BTW, my boat has exactly the same. )...



Chris.........

Re: Mercruiser 120/140 restarting problems

You lost me after you said " You have some current leakage somewhere"

Re: Mercruiser 120/140 restarting problems

DayCruiser said:

You lost me after you said " You have some current leakage somewhere"

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The battery should not drain down when nothing is turned on... Ergo, if you are draining the battery with nothing turned on, something is faulty... You need to find it....

Re: Mercruiser 120/140 restarting problems

achris said:

The battery should not drain down when nothing is turned on... Ergo, if you are draining the battery with nothing turned on, something is faulty... You need to find it....

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I believe you are correct. Just a bit over my head in the electrical department

Re: Mercruiser 120/140 restarting problems

I still think your primary problem is NOT the battery. The battery is just a secondary problem because you can't fire up the engine.

The motor should start up within 2 full rev's if everything is working fine. You should look into why you have to crank it so long that it kills the battery.

Back to the original questions: tune up done ? choke operating correctly ? (this was a problem on my boat). Are the fuel filters good ?

Re: Mercruiser 120/140 restarting problems

CaptainMak said:

I still think your primary problem is NOT the battery. The battery is just a secondary problem because you can't fire up the engine.

The motor should start up within 2 full rev's if everything is working fine. You should look into why you have to crank it so long that it kills the battery.

Back to the original questions: tune up done ? choke operating correctly ? (this was a problem on my boat). Are the fuel filters good ?

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Yeah, like we can read this... :facepalm:... Stop messing with the colours!

Re: Mercruiser 120/140 restarting problems

achris said:

Yeah, like we can read this... :facepalm:... Stop messing with the colours!

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whoa... what happened there ? made my eyes water...

Re: Mercruiser 120/140 restarting problems

CaptainMak said:

whoa... what happened there ? made my eyes water...

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I'd say you went to click on this and missed, hitting this instead....

Now that you've had your little play with the text colour button, can you leave it the default colour (black)... It's quite distracting trying to read your posts in different colours.... I'm sure you have some fine things to add, but I just stop reading your posts because it hurts my head (and I'm sure I'm not the only one)...

Thanks....

Re: Mercruiser 120/140 restarting problems

(and I'm sure I'm not the only one)

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Ayuh,.... 'n you'd be Right...

Re: Mercruiser 120/140 restarting problems

I was having a similar problem and think it was corrected by replacing the coil.... I also did the cap and rotor at the same time.