Merc 850 85 hp NEED ANSWERS!!

[kevvjr]

I just bought a merc 850 knowing it had some problems. (Not idling). so we took off the carbs and cleaned them out with carb clean. still woudnt idle. noticed a leak around the fuel pump cover. bought a new and fixed it. motor would finally idle but only in full throttle, if i tried to bring it down the motor died, if i tried putting it in gear motor died. Finally it would idle, Seemed to be running perfect. We put it in the water and nothing, she would run but she would just die after a few seconds of ilding at full throttle and whould die when i tried to throttle down . THen she went into gear and ran beautifuly until we slowed down she died. then wouldnt start,let it sit for awhile she started and died. we got it back on the trailer she ran and idled fine.then noticed white milky stuff coming out if exaust and burned 5 gallons of gas in 20 min while in idle. Soooo... what should i do next, where should i be looking for my ploblem, or what is my problem. if you have any answers please let me know. Im going to go back and clean the carbs again.

 

[dblok4eva]

Re: Merc 850 85 hp NEED ANSWERS!!

ok im pretty new on boat motors but it sounds like you might be getting water or oil in the combustion chamber and to be honest it sounds like the rings are bad please correct me if im wrong i dont want to mke someone rip apart the head if its unnecessary

 

[Chris1956]

Re: Merc 850 85 hp NEED ANSWERS!!

You really need to start with the basics. Buy a service manual, take a compression test and put a timing light on each of the four spark plug wires to see if you have spark to all. Inspect all spark plugs and note their color. Post back with the results.

I will guess that motor has side bowl carbs. If so, the initial idle mixture setting is 1-1/2 turns out from lightly seated. When you cleaned the carbs, did you clean out the high speed jet and the idle passages?

Posting the serial number will tell us the year of the motor.

 

[kevvjr]

Re: Merc 850 85 hp NEED ANSWERS!!

No, any advice is good i just need a direction. but that is very possiable. Now what exactly does the combustion chamber do?

 

[kevvjr]

Re: Merc 850 85 hp NEED ANSWERS!!

Well a friend of mine checked the compression said it was fine. i pulled the plugs all are fireing. No the bowls are on the bottom of the carb, And no we didnt take the carbs fully apart, we only took off the bowl and sparyed carb clean in all of the little holes. the serial number i have is 7101680 but i cant find anything on that number.

 

[dblok4eva]

Re: Merc 850 85 hp NEED ANSWERS!!

ya when cleaning the carbs you have to pull the carb off there are jets in there with very tiny holes that muct be cleaned there should be 2 jets and then the float needle valve get them out but dont forgete which one goes where take a bread tie free of plastic and paper just the metal wire and that should be thin enough to go through if not jus cleaan best you can and make sure you can blow through the main jets its the jet in the middle with the bowl off

 

[OldMercsRule]

Re: Merc 850 85 hp NEED ANSWERS!!

The serial # indicates a 1977 Canadian engine.

As Chris already said: verify that the compression is North of 100 and even, if you have 100% confidence in yer friend OK, but I would do it myself IF I WAS WERKIN' ON IT.

As Chris already said: verify HOT spark on all four plug wires.

As I say: you either totally dissassemble and totally clean the carbs or don't bother doin' anything!

Sounds like the fuel pump is now rebuilt, (if not do it: COMPLETELY), is yer gas line free of ANY air leaks? Is the tank totally dry with fresh mid grade pre mix, (without ANY alcohol if at all possible)?

There is the answers, (some repeated), you were looking for. Good luck! JR

 

[bullbat]

Re: Merc 850 85 hp NEED ANSWERS!!

well firsts things first if you didnt take the carbs all the way apart that was the first mistake , take them all the way apart every single peice and and make sure no passages or jets are clogged, sounds to me that is prolly where you problem is, and i would get a new set of plugs if you havent already like they say start with the basic Air, Fuel and Fire.

 

[kevvjr]

Re: Merc 850 85 hp NEED ANSWERS!!

Yes plugs are new, i checked all four wires, all have a hot spark. I did put freash mid-grade gas in the tank, but i have not checked for any air leaks. but will be sure to do. I didnt rebuild the fuel pump b/c it seemed to be working fine with the way gas was pouring through the carbs. Do you think i should still rebuild it?

 

[OldMercsRule]

Re: Merc 850 85 hp NEED ANSWERS!!



Any water in the tank before the fresh fuel went in it?????????

I already said I would personnaly check the compression BEFORE I spend another dime or additional time on it.

I would then #1 check the fuel line for leaks, and #2 then rebuild the fuel pump, (n ' then see if it runs OK), and then #3 tear the carbs down totally and totally clean and rebuild them, #4 link n' sinc, #5 new water pump, #6 fresh gear oil, n' THEN: rock and roll!

Hope that helps ya focus. JR

 

[bullbat]

Re: Merc 850 85 hp NEED ANSWERS!!

its nor gonna hurt ne thing if your do rebuild it even if you dont need to i would just to be sure but make sure you take those carbs all the way apart and clean them the right way

 

[kevvjr]

Re: Merc 850 85 hp NEED ANSWERS!!

There was no water in tank. I really appreitate the help and advice. Thanks. Another thing, why did she burn almost 5 gallons of gas in idle and why is gas coming through the exaust. is it just pouring out of the carbs and running down th shaft or is it something internal?

 

[OldMercsRule]

Re: Merc 850 85 hp NEED ANSWERS!!

There was no water in tank. I really appreitate the help and advice. Thanks. Another thing, why did she burn almost 5 gallons of gas in idle and why is gas coming through the exaust. is it just pouring out of the carbs and running down th shaft or is it something internal?

One possibility is the fuel pump diaphram is shot, (hole in it), and the fuel is dumping directly into the crank case.

Hard tellin' not knowin', 5 gal in 20 minutes at idle sounds a bit far fetched ta me, [especially since you were whinin' in the same paragraph about some sorta idle problem or some such], (but I was born at night ).

 

[kevvjr]

Re: Merc 850 85 hp NEED ANSWERS!!

well oldmercs you were right huge hole in fuel pump diaphram. now running great. than ks for all the help.