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..