85 horse mercuy outboard falls on its face.

[presque64]

Hello everyone.

I have a 85 horse merc outboard. When I'm running it and I go to open it up it falls on its face and stalls. Starts right back up. If I use the choke while speeding up it will take off. Once wide open it runs great. I've check for fuel leaks,check the fuel screen,check the pick-ups in both tanks.Replaced the plugs.Ran a few tanks of seafoam thru her. Still no luck. Someone told me to turn the low speed jet out a 1/2 of turn? But I'm really not sure which one is the low speed. One is silver and the other is brass and set in some. Hoping somone may have a idea and an help. Trying to avoid big cost if I can...

Thanks for the help...

Glen...

 

[AMD Rules]

Re: 85 horse mercuy outboard falls on its face.

Does your motor have a serial number?

Sounds very much like a lean condition, and the typical response would be to give the low speed just 1/4 turn ccw in unison until the problem goes away. Low speed jet is usually the silver flat head screw facing forward on the port side of the carb. Often it is slightly recessed. Brass fittings are plugs, and should be tight.

It could also be a carb cleanliness issue, or a float setting problem.

It could also be a fuel pump problem, which is quite possible given that you seem to have a better reponse when it is choked.

 

[Laddies]

Re: 85 horse mercuy outboard falls on its face.

First I would try opening the low speed screws 1/4 a half is a lot try opening the not more than 1/8 turn at a time so you don't go to rich. Here is a parts identification chart for you to ck out the low speed needle

 

[presque64]

Re: 85 horse mercuy outboard falls on its face.

I Turned The Low Jet Screw Out Just A Touch. Big Differance. Spits And Sputters Some But Seems To Be Better. Did Not Fall On Its Face At All. Gonna Turn Them Just A Touch More And Try It Next Time In The Water.

Still Think The Carbs Should Be Overhauled And Maybe Even Replace The Fuel Pump...where Is The Pump Located On Here. Is It A Hard Job To Do? Pumps Very Costly?

Again Thanks Everyone For Your Help...

Glen..

 

[Chris1956]

Re: 85 horse mercuy outboard falls on its face.

Glen, First adjust the idle mixture (top carb first), open 1/8 turn. Then do bottom carb, 1/8 turn. Repeat if necesssary. If the motor doesn't run properly, you will need to clean the carbs.

 

[NickBlaze466]

Re: 85 horse mercuy outboard falls on its face.

I'm relatively new to the whole boating scene, but I've done a lot of work on ATV's and cars and such.

I've been reading the posts on adjusting the low speed screws on the carb to get more gas to the engine while at wot to reduce a lean condition in the engine. On everything I've worked on, if its not getting the gas at wot playing with the mixture screw got me pretty much nowhere. I didn't play with the mix until i had the situation pretty much resolved, as it is basically for fine-tuning once you have the basic setup. Pilot jet was gas at idle and up to 1/4 throttle, needle took over from roughly 1/4 to 3/4 throttle, and then the main handled everything above that. Apparently thats not how it goes with boats? Whats the difference?

If there is no difference and what I've just typed out is basically the same as on a boat, and you didn't do anything to your engine to make it more powerful (As i said i'm new to boats, so I don't know if you can put a "better flowing exhaust" on, or change the reeds, something like that on a dirtbike) but if your engine is still stock i would say to pull the carbs and clean them out real good, or better yet rebuild them. cheapest issue i always did was just replace the nasty jet with a new one, for about 5 bucks.

Again I dont know squat about boat engines, I'm actually tearing into mine for the first time this weekend, so i reserve the right to be completely wrong and not feel like a dumb *****

 

[Chris1956]

Re: 85 horse mercuy outboard falls on its face.

Nick, You are correct. The idle mixture setting only affects idle mixture. It has virtually no effect on higher RPM.

I think the problem you are having is why the idle mixture needs to be richer than "normal" on your motor. Those motors do not have any mechanism for enrichening the idle mixture, when you want to accelerate. An auto engine has an accelerator pump, some motorcycles have a bit of fuel sitting in the main jet chamber which acts to enrichen the mixture, whne you open the throttle plate. Your outboard simply needs to run rich at idle, or it will not rev up!