Re: 1986 Mercury 115 - stalls in neutral
Hi, John, first off, here's a really good thread you should check out regarding idle issues and synchronization:
http://forums.iboats.com/showthread.php?t=413324
Here's a link to the wiring diagram for an ADI system:
http://www.maxrules.com/oldmercs/Wiring/1966ona/37.pdf
Note the idle stabilizer connected to the switchbox. If you have one of these, toss it. They are prone to failure and when they do, usually they fail in a very bad way and can cause preignition/ultimate destruction of the powerhead. An Inline Six in good condition internally and in good tune does not need the Band-Aid of the stabilizer. In fact, if you do have one, it could be acting up and causing at least part of your problem.
Here's some links regarding troubleshooting ADI problems, one of them has a resistance chart for the stator windings:
http://dolphinmarineservice.homestead.com/Ign5.html
http://outboardparts.com/mercury/troubleshooting/troubleshooting10.htm
http://www.maxrules.com/fixsparktips.html
http://www.boatpartstore.com/mercreadings.asp
Note that you need a DVA (Digital Voltage Adapter) in order to do the 'active' checks of voltage when the motor's running. But you can easily do the resistance tests of the stator with a regular meter. If you don't have one, check at Sears as they usually have a digital VOM on sale and even an inexpensive one will do for these tests.
A few other things you can check on the ign, just for checking's sake, are the condition of the ign coils. Any one that's cracked is a problem. You'd need to pull the coils off their mounting plate and peel back the black rubber cover in order to inspect all areas. Cracked coils can arc to ground and if bad enough you can hear them at idle, with the cowling removed.
Fire off the motor after dusk and if you see a 'christmas tree' of lights around the spark plug wires, they need replacing.
Since you say it's running pretty well when cold, I'm thinking maybe it's flooding out due to rich-running when warmed up.
Some possibilities are fuel pump; leaking float needle/seat; 'sunken' float and although you've inspected the floats, perhaps it'd be a good idea to replace unless yours are already the upgraded white plastic items. They are an improvement over the older, foam-composition floats.
On some of these motors, Merc used a very small wire mesh filter screen behind the N.P.T. fitting which attaches the fuel line to the top of the float bowl. The only way to know if you have these is to remove one of the float bowl covers and unscrew the fuel line to check for this filter. These are prone to plugging and it's recommended that they be removed to preclude a lean condition.
I see you've installed an inline filter off your gas tank. Depending on what type of filter, it could cause a restriction that your fuel pump can't overcome at idle. The only kind of filter I'd recommend to install there is one of the clear glass type with a plastic filter element. This type has much less restriction than a paper filter and you can clearly see when there's water or debris in the fuel.
Did you check the wire mesh filter screen in the fuel pump? Also check the black filter housing, it's prone to cracking then will suck air.
Mercury put out a TSB about fuel starvation which included reference to an upgraded primer bulb. Seems the old-style check valves were degrading with the ethanol-blended fuel and causing problems with fuel delivery. The new-style Merc primer bulbs have an improved check valve design.
Unless you've already done it, I'd definitely replace the fuel pump gaskets/diaphragm and inspect the check valves for any problems.
What happens when you adjust the idle mixture screws; does the engine speed up as you're leaning out the mix (clockwise on the screw), then tend to die off as it goes too lean? When you go to the rich direction (CCW) from best, highest idle, does the engine slow down and start to 'blubber'?
Got to make sure that the carb mixture is actually changing in response to changes in needle adjustments; if not, there's something going on in the carbs.
Check all the small oil bleed hoses running around the Stbd side of the powerhead, for cracks. I-6's don't like vacuum leaks, it makes them very cranky. Check the balance hoses on the front of the intake cover for cracks as well.
Here's one thing you'd have to tear into the motor in order to check; the idle bleed restrictors. These are plastic plugs with teeny weeny orifices which are installed in holes in the block, if these are sucked-out it can cause idling issues. I'd only check these once you've gone down the 'list' of easier things to do, externally. You have to remove the transfer port (intake side) covers on the Stbd side of the motor in order to inspect for the restrictors. There are 5 of them altogether and Mercury still sells the pesky little buggers.
Here's something related to synchronization that my compadre Thom (aka "Dr. Frankenmerc") pointed out at the Bigweek Inlines forum recently:
"Since this is an ADI motor:
It is also quite critical for good idle consistently to insure there is no
slack in the motor linkage that would allow the timing to 'drift'
back-n-forth when slowed to an idle as much as 8-10 degrees.
If the spring in the small black circle of the primary pick-up adjustment
and WOT timing adjustment is not properly pre-loaded the idle can drift as
much as 8-10 degrees.
If the plastic piece of round stock that the 1/8" diameter rod (horizontal
link at the top of the vertical throttle arm) threads into is sloppy in the
aluminum of the sweeping piece that opens the carburetors - your idle can
'drift' as much and 6-8 degrees, causing in gear idle issues.
And double check those butterflies to insure they are all closing completely
at an idle. At an idle manually hold each butterfly link closed and see if
you can hear a difference in RPM and or feel notible movement of the
butterfly link. Too much pressure will only flex things and give you a
false feeling for what's going on."
A Most Excellent bit of wisdom from the Dr., if the timing is fluctuating around due to linkage issues, it'll wreak havoc with idle quality. The thing on the carb butterflies is well-taken also; at idle, the strongest air signal thru the carb's idle circuits is gonna be produced thru a carb butterfly that's fully closed. From there you adjust idle speed via an increase in throttle setting (increasing spark advance as the throttle advances) until you get a stable idle.
Ideally, at idle the butterflies should be completely closed and then you set up your 'primary pickup' from there. And if I were going to compromise in the primary pickup setting, I'd first make the motor idle with the butterflies completetly closed, with whatever amount of intitial timing advance (i.e. increased throttle setting) it needs.
Such that your idle speed is a combination of whatever she'll run with closed butterflies and as much advance as it needs to keep from dying off. Then set the primary pickup from there. Some motors are a lot more sensitive to this adjustment then others, so you may have to experiment.
There's other issues to cause running problems, mostly internal such as bad crankshaft seals, bad reed valves, and worn reed blocks. Crank seals will evidence themselves by oil leaks at the top, and water intrusion into #6 cylinder at the bottom.
Unfortunately there's no good way to check for bad reed valves or worn reed blocks without removing the powerhead and splitting the cases. Except in the case of a very badly broken reed, which will cause fuel to be spit back out of the carb.
So, I'd leave the internal stuff for very last, I'm thinking it's very likely you're gonna find this to be fuel or synchronization-related. But you've got a plenty long grocery list of stuff to go thru at any rate!
HTH & keep us posted on your progress...........ed
p.s. goes without saying that a motor with poor compression ain't gonna run so well. Something else to check, although you say it runs strong at the top end.......you never know.............
p.s.s. something else real stupid, a new set of plugs. Slap a set of NGK BUHW plugs in there and see if anything changes. Or pick up a set of Champ L76V sparkies.
