1985 35hp mercury wont idle, or run in gear.

[motoman125yztb]

Hey, same motor giving me problems. The motor will only run in neutral when bumped up. It will die even warmed when set to slow idle, or attempting to shift in gear. Fuel filter, fuel lines, and tank are new. New gas, carb is clean and functioning. When I pull plugs they have a dark grey to brown coating on them, smells like gas, but wont ignite when put to a flame. I was getting water in cylinder 1 so I replaced the exhaust port gaskets, and the head cover gasket, to inspect the water jacket. Now no more water. So the plug fouling seems to be the problem. compression on both cylinders is 118 psi. they both get good spark with an inline light tester. When I drop it in the lake I can make the motor scream up and will stay running when idleing high, but will die when returned to neutral idle, and when quick shifted it bogs and dies, I wanna see this motor gallop. I have set the idler screw to 1 1/2, all the way to 3 turns none yielding any positive results. Any ideas are appreciated. Thanks, Don.

 

[motoman125yztb]

Re: 1985 35hp mercury wont idle, or run in gear.

My buddy told me to check my thermostat as that could cause fouling. The thermostat was not in it's housing, so that goes to the top of the list. Would that cause the plugs to foul in under a minute?

When I first got the motor I was replacing bad wires and connectors. The stator wires, brown and white, brown and yellow were kind of gummy at the switchbox. I cut back to where they were good and spliced in new wires of similar gauge. I know there is a low and high idle side of the stator. Would that cause weak spark, or no spark in low idle? what would cause them to become gummy?

 

[jslu]

Re: 1985 35hp mercury wont idle, or run in gear.

motoman

A misssing thermostat is not your problem. After 1983, these engines were issued form the factory without a thermostat. I have had several of these engines dating from 1982 to 1989 (I repair as a hobby) and they all run fine without a thermostat. From what I understand, Merc removed the thermostats and poppett valves in 1984 because they potentially caused greater problems. Go to boats .net and look at the pictorials to verify this.

Are the pics of the plugs before or after solving the water intrusion problems? Looks to me like overly rich fuel mixture at idle speed. Carb needle and seat malfunction maybe.

John

 

[motoman125yztb]

Re: 1985 35hp mercury wont idle, or run in gear.

Thanks John, I saw the blow up diagram and there is no thermostat, so thats not the prob.

The pics are after I replaced gaskets. when it was getting water it was more of a light grey, or silver color. Those pics I fired up the motor just forward enough to hold idle, than died. That pic is the worse of the 2. This carb has fixed needles, and with carb spray I ould see the clean flow through the pilot needle, the main is a straw for the most part. I took this carb off multiple times to soak clean and blowout everything. The only adjustable component is the air fuel mixture screw.

This is a silly question given the limited info. What can I rule out ignition wise? I have spark, cant test how strong yet. The bottom cylinder does seem to be the more consistant of the 2 and doesnt collect as much buildup. I'm gonna switch coils and see if anything magical happens. I found the page with the ohm specs for the stator and trigger, gonna check that.

While I got ya, what does the switch attached at the exhaust cover do? it has a black and yellow wire connecting to the switchbox, and the other wire from the switchbox goes to the stator. It looks to have been replaced at one time. Theres a pic of it. Thanks again, Don

[View attachment 204047View attachment 204046

 

[jslu]

Re: 1985 35hp mercury wont idle, or run in gear.

motoman

1.) The carb does not have fixed needles. It does have fixed jet orifices, one of them is the high speed metering jet. The low speed "needle" that you are adjustind is essentially a variable low speed jet.

2.) The true needle and seat arrangement within the carb is what controls the level of fuel in the carb. This is controlled by the float within the carb. Adjustment of this float setting is critical and is specified in the merc manual. A improperly adjusted float or a faulty float can cause the needle not to seal in it's mating seat, causing carb flooding, most noticable at low speeds.

3. Your switch in question is the tilt/trim limit switch. Not related to your problem. This mercury switch will not allow the engine to start if the engine is eccessively tilted.

4.) You can test for good healthy spark with an inexpensive spark gap tester, availabe at most auto parts stores. Buy one with an adjustable gap. A healthy spark will jump a 3/8 inch gap in air with a bright blue flame. Easy to use.

Good luck!

John

 

[motoman125yztb]

Re: 1985 35hp mercury wont idle, or run in gear.

Thanks John. I am gonna run to the auto store and grab new plugs just for fun. I have done a decarbonizer spray a couple times and some members suggest replacing plugs. I'll see what they have for the adjustable spark tester.

I switched coils, same thing, bottom plug comes off clean, top has a coating. I had the plug light tester connecter while spraying the decarbonizer and the top plug light stays lit for the most part. no obvious misses. Everytime I shut it down theres the coating on the plug after its been ran. I want to lean twards fuel problem but the bottom plug is always good to go.

When I throttle back from high idle to low idle the motor doesnt do a rev down like a chainsaw or dirtbike, it just bogs liike if you turned the key and cant be coaxed back.

 

[motoman125yztb]

Re: 1985 35hp mercury wont idle, or run in gear.

Okay ohm test for stator high speed side and low speed come in the correct range. Trigger also in range. Using the spark gap tester I'm jumpng 3/8 no problem, It isn't blue but its a whitish orange. This is cranking not running. I'm gonna run the motor to clean out the decarbonizer and change my plugs. Try my luck on the lake.

Another question, the tilt switch. It was replaced for sure, the wire coming off runs to the black and yellow bolt on the switchbox along with the low speed wire from the stator is that right. Its the only connection with 2 wires on it. If its only a safety kill switch I'm gonna disconnect it before I run it next time.