Can't figure out what's wrong here.. Did I muck sth up? Suddenly lost half power :(

[steve-ribnet]

You may still have weak spark to give good idle and poor performance at higher rpm.
Swap coil and ignition HT lead, plug cap etc between 2 and 3. If you are lazy you might be able to just change the switch box trigger (coil input) from 2-3 and change the HT lead (coil output) from plug 2-3 (if it will reach) but undoing and re-making all connections including the coil ground to rule them out is not a bad thing.

If a timing issue, it seems odd that only one cyl is affected.
Are your three carbs identical - can you swap carb 2 for 3 for example? (do you have 3 carbs? my old mariner 70 did)

Do you have a timing strobe? Looks like you have seen that the manual has a value for correct timing at cranking speed, which will give you a good (enough) value at WOT if you are unable to test on the water; certainly a good enough value to run smoother than you have at present.

You could make two additional timing marks on the flywheel 120 degrees apart (or take the circumference and divide by 3), then trigger your strobe off cyl 3 HT lead. compare to 1 and 2 when running at some revs. This might highlight a weak spark if your strobe on 3 is much dimmer (fires less often) if you don't have a spark gap tester.

mariner test sequence is
1 - check input voltage to coils
2 - check for strong spark
3 - check spark plugs
4 - check timing: trigger/pickup linkage, trigger cable and plugs, trigger magnet ring
5 - check STOP circuit of switch box (ignition control box)
6 - check ignition switch - isolate stop switch/kill chord at the switch box (ignition control) and repeat stop circuit checks [edit: I had an old donkey engine with a weak spark caused by a wet and corroded kill switch]
7 - check stator

I presume you have the service manual and a multimeter to test the correct values?

[Fstarocka]

Hi tx, have timing light yes, I'll make diy spark gap tester, multimeter yes but not the one that can read Max volts..

Do I check input voltage to coils while running or cranking?

Got true tdc using piston stop and set cranking timing at 28 per manual.. Dropped it off with degrees for today's fuel..



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[steve-ribnet]

Originally Posted by Fstarocka

Maybe sync link is way out? On front cover it says to set Max cranking degrees and then carb cam pickup just before the big slope to open carbs, but it doesn't specify whether to do that with Max stop touching or what...

for the 70/75/80HP, timing can be set roughly at cranking speed as 2 degrees more advance (before TDC) than your maximum advance timing value.

e.g. if your WOT maximum timing is 26 degree before TDC, then at cranking this will be 28 degree before TDC

Remove all spark plugs from block except #1, hold your timing control arm at max timing and against the screw stop and crank over on fresh battery. adjust timing stop screw to give your compensated maximum advance value

[Fstarocka]

Steve did that.. Wot timing is set perfectly.. So is Max throttle stop

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[steve-ribnet]

Originally Posted by Fstarocka

Do I check input voltage to coils while running or cranking?

from the mariner 70 manual:
Test procedures and specifications are provided for
checking primary ignition voltage while the engine
is running and/or being “cranked.”

coil input (primary) voltage meter test range is 400volts DC, for a reading of 150-250Volts at cranking, 180-280 volts at 1000-4000RPM.

multimeters that handle 400VDC are cheap and plentiful in the UK - £35 will get you a Vichy VC99 clone).

You can check the stator coils with just an ohmmeter (resistance).

[steve-ribnet]

Originally Posted by Fstarocka

Steve did that.. Wot timing is set perfectly.. So is Max throttle stop

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good job. personally Id try swapping coils and HT leads over first before probing about, having first cleaned the plugs.

[Chris]

could be the coil. they can start to fail when they heat up

[doggypaddle]

is the fuel pump diaphragm ok? may be worth checking if it connects to the crank case at the "wet "cylinder, they can fail and cause flooding, though usually more at low RPM.

[Fstarocka]

Diaphragm is fine, also replaced all fuel lines ..

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[matata]

Ive listened to the excellent little video clip again. I think its defo electrical. Cylinder drop test?? Nik

[steve-ribnet]

Any news Fstarocka? Have you swapped those plug leads and coils over yet?

[Superjetjim]

Plug leads or coils all day, seen / had this many times over the years. Change the no3 plug lead and or coil and you should be good.

They loose spark as rpm and vibration increase due to the break in lead - hence why it's AOK at lower rpm.

[Fstarocka]

Hi sorry haven't been back at boat.. Been fixing motorbikes past few days.. Soon as I'm mobile I'll take some coils with and swap leads..

Did a compression test, 140 almost exactly on all 3..

I'm also going to test stator.. Coils aren't cracked .. But I did see sparks at night swinging..

Could these pack up so quickly? Odd that it was running great and within 4 trips degraded to half power..

Probably have results in a few days.. Thanks so far everyone..

Will try get marine grade plug wires here in city..

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[Fstarocka]

So tested stator again, red high speed was shorting to black ground..

So I tossed it into a fire, burnt away all the plastic, having it rewound this week for 35 quid.. See how it goes.

One trigger wire has 1900 ohms instead of 700-1400..

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[Fstarocka]

Reg rect also toast.. Just my bad luck then.. In for a few grand!

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[Fstarocka]

Originally Posted by steve-ribnet

You may still have weak spark to give good idle and poor performance at higher rpm.
Swap coil and ignition HT lead, plug cap etc between 2 and 3. If you are lazy you might be able to just change the switch box trigger (coil input) from 2-3 and change the HT lead (coil output) from plug 2-3 (if it will reach) but undoing and re-making all connections including the coil ground to rule them out is not a bad thing.

If a timing issue, it seems odd that only one cyl is affected.
Are your three carbs identical - can you swap carb 2 for 3 for example? (do you have 3 carbs? my old mariner 70 did)

Do you have a timing strobe? Looks like you have seen that the manual has a value for correct timing at cranking speed, which will give you a good (enough) value at WOT if you are unable to test on the water; certainly a good enough value to run smoother than you have at present.

You could make two additional timing marks on the flywheel 120 degrees apart (or take the circumference and divide by 3), then trigger your strobe off cyl 3 HT lead. compare to 1 and 2 when running at some revs. This might highlight a weak spark if your strobe on 3 is much dimmer (fires less often) if you don't have a spark gap tester.

mariner test sequence is
1 - check input voltage to coils
2 - check for strong spark
3 - check spark plugs
4 - check timing: trigger/pickup linkage, trigger cable and plugs, trigger magnet ring
5 - check STOP circuit of switch box (ignition control box)
6 - check ignition switch - isolate stop switch/kill chord at the switch box (ignition control) and repeat stop circuit checks [edit: I had an old donkey engine with a weak spark caused by a wet and corroded kill switch]
7 - check stator

I presume you have the service manual and a multimeter to test the correct values?

Hi, sorry haven't been on here for a while.. Still having problems..

To clarify I have two carbs, ive cleaned them plenty times, new filter, lines etc.

I now have a few used stators given to me to try solve my issues..

Oddly I bought another sw box 4 weeks ago and the motor performed perfectly for two sea trips, one very harsh riding..

Day 3 started doing same as before, hun nun nun and no power.

I tested the reeds, all OK, fitted new lower crank seals too, using a motorcycle rect in there now, getting around 13.1v at idle..

On cranking my blue is giving 210 volts, red can't quite recall as I was focusing on low speed, yesterday I noticed a miss on cyl 3,i need to get back tomorrow and write down results.. This thing really is ghostly..

Also, built the gap tester, all 3 coils jumped a big gap like a tazer, arcing blue lines..

I've checked all earth points, compression is almost the same on all 3.. 139 psi..

Always starts super easy.. Bought the parts for a diy dva apapter and for some reason it doesn't give me the readings I'd expect.. Maybe diode or cap has been damaged or something..

So ive been measuring with normal multimeter and getting OK results.. Although my pri coil is showing like 4v dc and an old mech told me it shd be like 300-400!

Either way thats at idle..

Tomorrow I'm going to temporarily try fab new plug leads and disconnect harness to eliminate issues..

Thanks all, hopefully I'll figure it out sometime..

[Fstarocka]

Oh, yes tested kill wire, I'll do some more tests tomorrow with harness disconnected and new leads..

The miss was at idle 3 days ago and yesterday it only showed when I maxed out the fast idle lever, like its moving around..