Mercury 200 - still odd cough/spit at idle. Ideas?

[CamaroMan]

Originally wrote to Joe Reeves on his website but I see he is finished so just pasting all that down here

Hi joe - thanks for offering this service. I have a customer with a 85 (i think) 200, been thru alot of head scratching with it.

Replaced stator, trigger, and both packs from CDI - initially one pack had a bias of 22k ohms, both are now equal.

Carbs cleaned, idling at 10-12 atdc which I think is right, did carbs 5 months back - WH22 carbs, triple checked the front facing jet arrangement. Compression 130-140 on all 6, powerhead was rebuilt apparently 2 years ago..

We just replaced the reed block with chris carson fibreglass reeds after suspecting the reeds, similar issue but it does seem a little better, the tach sits around 850 and now and then spits out exhaust with a burny eye gas.. which im wondering is a weak or intermittent weak spark issue perhaps?

New gas, new plugs, new quicksilver oil mixed 50:1 -

At my wits end with this thing-

Thanks! I hope i have included enough info - If I left anything out please ask -

Here is a 30s video of it idling, you can hear it dip now and then and blow a little thru exhaust by the prop- this is about as good as I can get it, 900 rpms at about 10-12 ATDC-

https://www.youtube.com/watch?v=tw5u_lb08D4


Im going to do a spark gap test again - i have noticed #3 shows a few cuts in the timing light strobe possibly indicating a pack or trigger or coil issue but I have been up and down the chain doing all the cdi tests over and over and got good DVA results all over..

Remote control short shaft

 

[racerone]

How does it idle submerged with boat at the launch ramp .------Sure sounds like lean sneeze to me.

 

[CamaroMan]

its so on and off.. pretty much same - i just found #3 wont jump a 7/16 gap.. spent few hours again messing with it - ill see if I have time otherwise ill try 2moro morning- it seemed to get worse when it got hotter.. i have previously tried swapping coils but had trigger issues so thought none more of it-

fyi - the brass enricher by the carbs.. should it be closed in the clockwise position under normal operation? if not- is it adjustable? I believe its a manual enricher to start in case the solenoid has failed?

 

[CamaroMan]

also - the inside of the prop is powdery black - rich? I might have to pull carbs and check the jetting.. the air bleed jets (front facing) are correct per the WH22 carb diagram in the manual.. I havent verified if the jets are perhaps one size up - past idle it runs like a mad thing..

 

[racerone]

The enricher is ONLY for starting.----The valve should be CLOSED for normal operation----Correct the spark issue on #3 cylinder first.

 

[CamaroMan]

The enricher is ONLY for starting.----The valve should be CLOSED for normal operation----Correct the spark issue on #3 cylinder first.

Thanks - ok so just got back.. more confusing - seems the intermittent spark is moving around.. #3 was worst at first, then #1, no 4 and 6- its all over the place. I suspected coils and that didnt seem to make
a difference.

Once again dva readings at idle:

Stator blue to ground (both packs): +- 245v
Stator red to gnd (both packs): +- 90-100v

Trigger wires (from top to bottom on pack)

Yellow/outside (2,4,6):
2.7
3.8
2.7

Inside pack (1,3,5):
3.0
2.9
3.6

Thoughts? im about to throw this thing in the drink.. weak spark - cannot jump 7/16 gap on some cyls-
If the darn miss was in one place that would really help. Next im gonna try run without the harness and see -

 

[CamaroMan]

Also - when running today its REALLY burning my eyes, is that unburnt fuel? Im wondering if the small batteries in there arent causing problems. Going to put in a new battery this week and re-test. At one point I saw an arc going straight through the plug wire in bright sunlight! Wondering of owner put on cheap wires?

none of the plugs are fouling - when I take them out they are all shiny and a little wet sometimes..

 

[CamaroMan]

does the wire that comes out of each coil need to touch the body/ground or just the magnet?

 

[CamaroMan]

also - do the small wires on each coil have to touch the magnets/ground? whats the purpose of these wires?

 

[Dukedog]

for starters ya need ta re-do idle timin'.. forget manual/merc spec numbers.. put it in tha water, in gear and adjust timin' to whatever tha motor and you like and happy with... pull tha cowl and run it AFTER dark...

make sure all linkages are adjusted right with butterflies completely closed.. leave a small gap between roller and throttle cam..

 

[CamaroMan]

last time I had it running after doing all the setup - it was a banshee just off idle.. but the cough at idle seems to get worse after warming.

Do the wires that come out of the coils need to touch the ground - what is their purpose?

Measured cranking dva on the coils on 2 of the worst plugs last night, both were around 200 on the switch box terminal with the green coil wire disconnected -

with green wire connected to coil but spark plug wire disconnected got about 165-170v..

When spark plug was connected and screwed in - it dropped to about 125v on the 2 i tested - ie the coil load was dropping the volts down quite significantly-

Could the wires be wrong? New sierra ones arriving today..

Coils faulty? (coils pass the ohms tests and no cracks - plus they seemed to work like a charm off idle-serious power there/no missing at all)

Can anyone advise how to use the load resistor from CDI?

 

[BillP]

I can't tell much from the video but chased a similar cold idle cough (and die) on a 140 omc. I bought the engine new off the showroom floor (around 1980), it coughed when cold and died if idled too long. Dealer couldn't find it after multiple visits to the shop but I found it. It was missing the tstat. Evidently they forgot to install one. It took over a yr and a lot of grief to find it but that was the problem. I found it by sqeezing the water hose while on muffs just enough to make a minimal stream out of the telltale. A new tstat fixed it. . I haven't seen a cold engine mentioned yet so that's my input.

 

[CamaroMan]

I indexed the firing order ontot he flywheel using a cam degree wheel.. and ran it - firing was all over the place, could hardly tell anything apart - mostly visible was between cylinders 2 and 3 and 4-5, I initially noticed marks on the flywheel at night jumping in and out of the strobe - indicating cross firing.

Going to try source a flywheel and take it from there..