Mercury 850 Outboard super high Idle

[thelostkiwi]

Hi Everyone,
I have a 1977 Mercury 850 Outboard that was running fine last year and ran fine once this year but the next time I started it, it started with a super high idle.
Now it wont start unless I block one of the air intakes and then it will be super high idle again.
Any ideas would be most welcome!

 

[matt167]

vac leak. Or a seal going, being it's a 2 stroke

 

[thelostkiwi]

vac leak. Or a seal going, being it's a 2 stroke

Would the vacuum leak cause the high idle or difficulty starting?
Any idea where I would look for the leak?

 

[matt167]

would cause both.. vac leak will cause a lean mixture which causes a high idle. And hard starting because the mixture needs to be richer to start ( choke ) . Check the upper and lower seals, and carb gaskets.. You may be able to use a propane torch BUT, I would put a lot of oil in the gas since propane contains no oil. The motor will burn the propane and your idle should settle down when you find it

 

[thelostkiwi]

would cause both.. vac leak will cause a lean mixture which causes a high idle. And hard starting because the mixture needs to be richer to start ( choke ) . Check the upper and lower seals, and carb gaskets.. You may be able to use a propane torch BUT, I would put a lot of oil in the gas since propane contains no oil. The motor will burn the propane and your idle should settle down when you find it

Matt167 I really appreciate your help here. I will check the seals and gaskets but have no idea what you mean with using the propane torch lol

 

[matt167]

Matt167 I really appreciate your help here. I will check the seals and gaskets but have no idea what you mean with using the propane torch lol

It's an old trick... An un lit propane torch will vent raw propane in a somewhat safe controlled maner. A vac leak will pull the gas in and burn it. It will change the idle/ running quality allowing you to spot the issue. You will have to mix the gas a bit oil rich since propane contains no oil. 32:1 would work I would think.

 

[thelostkiwi]

It's an old trick... An un lit propane torch will vent raw propane in a somewhat safe controlled maner. A vac leak will pull the gas in and burn it. It will change the idle/ running quality allowing you to spot the issue. You will have to mix the gas a bit oil rich since propane contains no oil. 32:1 would work I would think.

Sounds like a great trick but I don’t think I can run the outboard whilst doing this as the idle is so super fast and loud. It’s as if the throttle is stuck open but there’s nothing showing this in the cable mechanism.

 

[racerone]

Serial # of this motor ?-----Not many places where a vacuum leak would be big enough for a motor to roar away.------Air leaks on a 2 stroke causes them to STOP running.

 

[thelostkiwi]

Serial is 7101664(Canadian)

 

[racerone]

Check trigger assembly.----Sounds like linkage came off and timing stays advanced.

 

[thelostkiwi]

Check trigger assembly.----Sounds like linkage came off and timing stays advanced.

That sounds logical but whete do I check the linkage? I hope it dosnt involve resetting timing as been watching YouTube vids this morning and that looks way above my pay grade lol

 

[Chris1956]

The trigger is a lever under the flywheel. It is connected by linkage to the carbs. As you move the throttle, the trigger should move also.

 

[1960 Starflite]

FYI: only. My 850 (1975) idled way too high. Carb linkage was against stop. Ended up being belt off one tooth.

 

[thelostkiwi]

FYI: only. My 850 (1975) idled way too high. Carb linkage was against stop. Ended up being belt off one tooth.

Wow thats really interesting as my linkage is also against the stop. What Belt are you referring to as being off by one tooth?

 

[1960 Starflite]

Timing belt, flywheel to distributor. Timing was too advanced. The 850 changed IGN systems during the mid 70's I just put that out there for information only.

 

[Chris1956]

IL4 motors changed to ADI ignition in 1976. The 1975 and earlier models had the distributor ignition.

 

[thelostkiwi]

Thanks everyone for all your great ideas!
I finally figured out what the problem was and you won’t believe it.
I noticed that the carb flaps were not closing totally so I thought maybe something is blocking them open a tiny bit?
Well I opened the flaps right up and shone a light in the lower throat and low and behold, deep down inside is a straw like one you would get on a can of wd40.
i fished it out with some some thin wooden skewers like chopsticks and problem fixed!
i think it was from the previous owner from fogging.
Who would of thought!

 

[1960 Starflite]

Good Catch