115hp Idle & Starting Problems 1986 Merc

[candu238]

This is making me nuts.
She is really a pain to get started and once it does start it'll die if the idle goes under 2500rpm. Only starts with wide open throttle & with the cold start solenoid screw in the out position.
I also need to keep the cold start solenoid screw out at least half way to keep it running. As I screw it in the idle falls off and it dies.

So far I have here's what I've done:
-new gas tank, bulb, and 94 octane gas (bulb goes firm when primed)
-new plugs (slightly gas/oil wet after running)
-removed & cleaned carbs, replaced floats
-replaced three coils
-replaced water pump (twice!!!!!)
-compression averages 120psi on all six
-replaced intake and exhaust gaskets
-replaced a few bad wires on the switchboxes

Could it be a bad fuel pump? Now that I'm typing, I realize I didn't try squeezing the bulb as it was running.
Could it be bad switchboxes?
Any help please..............ahhhhhh

 

[Chris1956]

Re: 115hp Idle & Starting Problems 1986 Merc

The stator on that motor has high speed and low speed windings. I recommend you get the stator troubleshooting guide off the CDI Electronics web page and ohm out the stator.

 

[candu238]

Re: 115hp Idle & Starting Problems 1986 Merc

The stator on that motor has high speed and low speed windings. I recommend you get the stator troubleshooting guide off the CDI Electronics web page and ohm out the stator.

I took a read through the guide; very good btw, but what confuses me is that I have good spark on all six at cranking speed.

 

[sschefer]

Re: 115hp Idle & Starting Problems 1986 Merc

I would run in the direction of the stator also but before you do that, change the fuel filter and do the bulb squeeze test in that order. That's cheap and a lot less hassle then starting the stator test routines just yet.

 

[verado7]

Re: 115hp Idle & Starting Problems 1986 Merc

sounds like a fuel issue though

what did you set the float height at - when the springs on the needles get compressed -some poor mechanics will redjust the float to get another season out of them but when you replace the needles the next time the float heigth will be off more to the lean side - i watched a buddy of mine do that and i said - but there only 6 bucks -LOL i'm sure he will read this .

 

[Vairpilot]

Re: 115hp Idle & Starting Problems 1986 Merc

Try what Chris1956 suggests, just because you get a spark at cranking speed doesn't mean the high-speed side of the stator is working properly. The high speed windings on mine gave out last year, and yet it still started and ran. Like the another reply said, check the fuel system too for clogged filters, air leaks, double-check the carbs, even if that means removing them and cleaning/adjusting them. My outboard is almost the same as yours, a 1986 90hp I6. Once I got it repaired I loved it, plenty of power and a nice mean sound!

 

[candu238]

Re: 115hp Idle & Starting Problems 1986 Merc

Try what Chris1956 suggests, just because you get a spark at cranking speed doesn't mean the high-speed side of the stator is working properly. The high speed windings on mine gave out last year, and yet it still started and ran. Like the another reply said, check the fuel system too for clogged filters, air leaks, double-check the carbs, even if that means removing them and cleaning/adjusting them. My outboard is almost the same as yours, a 1986 90hp I6. Once I got it repaired I loved it, plenty of power and a nice mean sound!

In this case it's the lower end of rpm that's the problem, from 25000 up it's ok.
I also just remembered something I should have mentioned earlier; when I have the motor running (3500rmp) and I spray gas into the carbs I get this result:
gas into top carb = rpm increase
gas into mid carb = no change
gas into lower carb = no change

Confused......maybe more of a switchbox issue.

 

[Vairpilot]

Re: 115hp Idle & Starting Problems 1986 Merc

Do you have a timing light that you could use just to check for spark on all cylinders? Hook up the timing light and turn the engine over in the normal starting range, check each cylinder see if you are missing spark on any of them.

 

[sschefer]

Re: 115hp Idle & Starting Problems 1986 Merc

Nope, Chris1956 nailed it and my bets on the stator too. Test it, I'll bet it's out of spec. You'll need a multimeter and the spec's from the manual to do the simple tests. For the full tests you'll need a DVA. If that's beyond you then take it to a shop and have them test it. It should only cost a half hour labor unless their minimum is an hour.

 

[turbinedoctor]

Re: 115hp Idle & Starting Problems 1986 Merc

The low rpm side of the stator is around 1500 rpm's. Next time you get it running try pulling the 3,4,5 & 6 plug wires one at a time. If no difference and you say it runs with the enrichener valve open, my next thought would be the reed valves.

With carbs rebuilt and no change putting fuel into carbs 2 & 3 it sounds like fuel is not getting past the reeds. Check to see if there is suction on the carbs when cranking over.

 

[candu238]

Re: 115hp Idle & Starting Problems 1986 Merc

The low rpm side of the stator is around 1500 rpm's. Next time you get it running try pulling the 3,4,5 & 6 plug wires one at a time. If no difference and you say it runs with the enrichener valve open, my next thought would be the reed valves.

With carbs rebuilt and no change putting fuel into carbs 2 & 3 it sounds like fuel is not getting past the reeds. Check to see if there is suction on the carbs when cranking over.

I haven't covered the carbs to feel for suction, but I can see gas being pulled up and into the carbs from the large jet that is in the center of the carbs, equally on all three carbs. As I close the enricher valve, the amount of gas going into the carbs reduces till it stops and stalls.

 

[turbinedoctor]

Re: 115hp Idle & Starting Problems 1986 Merc

How long has this been going on?

Double check the floats adjustments.

The enrichener bypasses the carbs and put fuel straight into the crankcase.

it sounds like a fuel problem in the carbs.

Why did you replace the intake and exhaust gaskets?

Did you try squeezing the primer bulb with it running, any help?

 

[candu238]

Re: 115hp Idle & Starting Problems 1986 Merc

Didn't buther trying to run it today, not keen on hitting 4000 rpm with the hose attachment. However I did an ohm check on the switch boxes as in the CDI troubleshooter. I removed the white/blk stripe wire that bridges both boxes and then checked from that terminal to ground on each box. Looks like the circuit is completely open; no reading at all on the ohm meter for both.
Is this possable? Is this my problem? Could they have been fried by rotten wires running to them that I replaced? The rotten wires were from the upper box to #2 coil and the lower box to #5 coil.

 

[sschefer]

Re: 115hp Idle & Starting Problems 1986 Merc

Pretty sure I read in the service manual that shorted coils can blow switch boxes and damage stators.