Please note this thread has been inactive for 90 days. For the best results, please start a new thread.
Page 1 of 3 1 2 3 LastLast
Results 1 to 25 of 73
  1. #1
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default HELP.. Mercury 850 (85 HP) Issues

    Ok, so I bought my first boat in April. It is a 1972 Larson Trihull with a Mercury 850 attached. I have taken the boat out approximately 5 times since I purchased it and it has ran like a champ until yesterday.

    It started up and idled great. It went into gear and ran moved nicely across the water. As soon as I crossed the no wake zone, I ran into issues. I put the throttle approximately 3/4 of the way down. The motor started to go, but then fell flat on its face. It would not move at all. It wouldn't open up and I could only go approximately 10 MPH. It kept bogging down.

    I puttered around the lake for 5 hours, mainly fishing, and then brought the boat home. The whole time on the lake it bogged down going more than 1/2 to 3/4 throttle, but ran like a champ below 3/4 throttle. At home, I ran it on muffs and it ran like a true champ (even at full throttle). It did not bog down at all while on the muffs. I thought maybe it fixed itself, ya right. So, just in case it didn't fix itself I went to the local marina and got some suggestions.

    After speaking with them, I came back home and I ran a compression test. I got 115 PSI in each of the cylinders. I then went out and bought some BG fuel additive (suggested by my Marina) and x4 new spark plugs. I added the BG additive to 6 gallons of fuel (nearly double the suggested amount) and changed all of the spark plugs. I was feeling confident that this may solve the problem, so back to the lake I go.

    At the lake, it started and idled just fine. I got past the wake zone and got similar results. This time it seemed to go a little faster, but still the bogging issues. I figured I needed to run the entire tank through the engine to clean it out (with the BG additive). While riding around, the engine would fluctuate and it seemed like it was going to take off, but it never did (it did this several times).

    After I drained the first 6 gallons, I switched to my second tank. This time I disconnected the fuel filter (figured it maybe clogged) and ran fuel straight to the motor. Still no luck and lots of bogging and sputtering. We put the filter back on. I then had my friend pump the primer bulb while I got on it (the engine) and "boom" it seemed to take off. We did this several times and each time it seemed that pumping the bulb got the motor running correctly.

    So, my question is this. Does that mean its a fuel pump issue? To my knowledge, it had never been re-built or replaced. If its the fuel pump, then why does it run perfectly while out of the water? Is there a way to test the fuel pump? What PSI should the fuel pump be putting out?

    If it is the fuel pump, where can I find a replacement? What goes bad in them? I looked everywhere online and cannot find a place to by a new or used fuel pump for my motor. I believe my engine is a 1972 or 1973 Mercury 850 (85 HP), SN 7083192. The fuel pump has the #73433 etched on the top of it (probably a part number). Any help would be great. Thanks in advance.

  2. #2
    Rear Admiral
    Join Date
    Sep 2010
    Location
    New Liskeard, Ontario
    Posts
    4,634

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Jimmy;

    The s/n would indicate that your engine is Canadian built 4 cyl:

    85 1976 EL 4366802 - 4590511 7071373

    From here:

    http://www.maxrules.com/models/Merc_...es/60-100.html

    Parts listing:

    http://www.crowleymarine.com/mercury-outboard/475.cfm

    service manual p/n: 90-86134--4

    http://kingston.kijiji.ca/c-cars-veh...AdIdZ285464523

    If you look under Fuel Pump in the spares listing you will see the Check valve and Diaphram kits which will allow you to repair your fuel pump.

    The reason it runs perfectly out on the water when your friend is pumping the bulb is that the bulb is now providing the necessary fuel pressure in lieu of the defective fuel pump.

    Gerry

  3. #3
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Thank you very much. You are 100% correct about my motor being at 1976. I still don't understand how you got the year from reading my serial number, I looked at the above website and still cant figure it out. I appreciate you taking the time and responding to my post in such detail. Thanks.... I am going to order the diaphram kit.

  4. #4
    Senior Chief Petty Officer
    Join Date
    Jul 2010
    Posts
    678

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    I noticed that you ran it at full throttle on the muffs; don't run it above 1200 rpm when not under load!
    If you have these carbs with the flattop there's a filter inside that might be plugged
    carb-filter.jpg
    remove them, unscrew the fuel fitting and look inside.
    I had one that was full of lint.

  5. #5
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Quote Originally Posted by merc850 View Post
    I noticed that you ran it at full throttle on the muffs; don't run it above 1200 rpm when not under load!
    If you have these carbs with the flattop there's a filter inside that might be plugged
    carb-filter.jpg
    remove them, unscrew the fuel fitting and look inside.
    I had one that was full of lint.
    I didn't run it very long with muffs on, but I will keep that in mind next time. I will check out my carbs and see if they are similar to the ones u posted.

  6. #6

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    ive had the same exact issues for all of last fishin season and tried alot of different things to no avail. i finally decided to take it to a mechanic. by the way i have a 1977 850 merc. anyway he ran some tests and found that my stator was bad. i havent replaced the stator because i now have a hole in the water jacket and am debating getting a newer year. hope this helps.

  7. #7
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Well, today I received my fuel pump rebuild kit. It only cost me $5.00 and was very simple to install. While I was installing it, I noticed a thin fuel line leaking that runs from the bottom of the engine to the top of the engine. I don't know what it is for, but I replaced it with a new yellow fuel line. I will post some pics maybe someone can tell me what it does and what it's technical name is.DSC05948.JPGDSC05941.JPGDSC05947.JPGDSC05946.JPGDSC05940.JPG

  8. #8
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Quote Originally Posted by vadigger View Post
    ive had the same exact issues for all of last fishin season and tried alot of different things to no avail. i finally decided to take it to a mechanic. by the way i have a 1977 850 merc. anyway he ran some tests and found that my stator was bad. i havent replaced the stator because i now have a hole in the water jacket and am debating getting a newer year. hope this helps.
    Thanks for the post. If my latest updates (fixed leaking fuel line and rebuilt the fuel pump) then I will focus on the Stator. I want to rule out the cheap things first. Did the mechanic give you a quote on how much it would be for the part and labor?

  9. #9
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    bump bump bump

  10. #10
    Supreme Mariner
    Join Date
    Mar 2004
    Location
    On Barnegat Bay, NJ
    Posts
    17,563

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    That small rubber tube is the bleed system on your inline 4 motor. Any oil that pools on the lower main bearing is pumped thru that hose to the upper main bearing. Keep an eye on that yellow stuff you added, to make sure it holds up to fuel and temperature conditions in the motor.

  11. #11
    Senior Chief Petty Officer
    Join Date
    Jul 2010
    Posts
    678

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    I have noticed some wires that need attention/replacing.
    bad-wires.jpg

  12. #12
    Supreme Mariner
    Join Date
    Mar 2004
    Location
    On Barnegat Bay, NJ
    Posts
    17,563

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    You might look over the whole motor harness. If it is real bad, consider replacing it. You can try surplusunlimited.com for replacements.

  13. #13
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Quote Originally Posted by Chris1956 View Post
    That small rubber tube is the bleed system on your inline 4 motor. Any oil that pools on the lower main bearing is pumped thru that hose to the upper main bearing. Keep an eye on that yellow stuff you added, to make sure it holds up to fuel and temperature conditions in the motor.
    I watched fuel move from the bottom connection up to the top connection, does it always bleed this way? I will keep an eye on the yellow hose, it was the only hose that i could find with a small size hole. The hose is a Holley and it made for fuel.

  14. #14
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Quote Originally Posted by merc850 View Post
    I have noticed some wires that need attention/replacing.
    bad-wires.jpg
    Yeah, I have noticed a lot of wires that need attention. I guess the times are catching up to the old wires.

  15. #15
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Quote Originally Posted by Chris1956 View Post
    You might look over the whole motor harness. If it is real bad, consider replacing it. You can try surplusunlimited.com for replacements.
    I will check out the website, thanks.

  16. #16
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Ok, I had it on the water today and still "no dice." The motor started easily, idled easily, and would go about 50% but still bogs down at WOT. So far to date I have tried the following to correct the problem: replaced spark plugs, replaced leaky bleed line hose, added fuel additive (cleaner) to the gas, and rebuild the fuel pump (diaphragm kit). I thought for sure the fuel pump rebuild would take care of my problem.

    As a reminder, this problem only occurs when under load (aka in the water). It runs excellent at WOT out of the water on muffs (which I will not do anymore). I am still leaning toward my issue being fuel related. Again, while I was out on the water (today), I had my son pump the fuel bulb and the engine would take off (just not consistently) but it sucked down fuel doing this. Any suggestions? I am thinking of replacing my fuel line connector (metal piece that goes into the motor) and the fuel line (to include the bulb and filter) that runs to the gas tank. Any other ideas?

  17. #17
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    I went out and took the cover off of the carburetor. I took pics of the carbs. I don't know what a "normal" carb looks like so maybe some can tell me if mine look normal. Here are the pics>DSC05998.JPGDSC06000.JPGDSC06002.JPGDSC05995.JPGDSC05994.JPGDSC05998.JPGDSC06000.JPGDSC06002.JPGDSC05995.JPGDSC05994.JPG

    Also, there was fuel below the carb unit, is this normal?

  18. #18
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    I researched the internet and found the melted black thing in the middle of the carbs is a VENTURI ASSEMBLY (part# 1395-6685). I looked everywhere for this part and it appears to be obsolete. How important is this part? Could this be the source of my problems. Any idea on how it would have melted? Should I just buy new carbs?

  19. #19
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Ok, I just thought of something else. I remember about a month ago I opened my motor and discovered a piece laying inside the motor. I did not know what the part was at the time and the motor still started fine (so I didn't think anything of it). Well, while trying to find a solution to my problem, I discovered the part I found laying inside the motor was the plunger and link assembly that sits inside the choke solenoid. Does anyone know if missing the plunger and link assembly would cause my motor to bog down at WOT?

    I know I keep posting over and over. I am just trying to find a solution by ruling out everything possible. What does the choke solenoid do anyway?

  20. #20

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    i swear it sounds like you have my motor in your boat. i had gas in the case surrounding my carbs also. when you give it the throttle try easing the shifter very slowly past the bogging down point. sometimes i could find the sweet spot and i would get full throttle. also the plunger was missing on my choke so i had to use a string to manualy choke the carbs. my mechanic told me the loss of power thing was the stator(400 installed) and the gas coming out of the carb was a hole in the water jacket which eventually led to my bearings goin bad. after you put it in the water drive it for a few minutes the pull each plug one at a time and see if any are wetter than the others. if so then you probably have a hole in the jacket and might want to consider selling the motor before it quits all together.

    Quote Originally Posted by jimmy120 View Post
    Ok, I just thought of something else. I remember about a month ago I opened my motor and discovered a piece laying inside the motor. I did not know what the part was at the time and the motor still started fine (so I didn't think anything of it). Well, while trying to find a solution to my problem, I discovered the part I found laying inside the motor was the plunger and link assembly that sits inside the choke solenoid. Does anyone know if missing the plunger and link assembly would cause my motor to bog down at WOT?

    I know I keep posting over and over. I am just trying to find a solution by ruling out everything possible. What does the choke solenoid do anyway?

  21. #21
    Supreme Mariner
    Join Date
    Mar 2004
    Location
    On Barnegat Bay, NJ
    Posts
    17,563

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Clearly your motor need some carb help. Was it in a fire or did it overheat so badly to melt the venturies. The cowl looks to be a 1976/7, but I never saw air boxes like that.

    I would take a look at the carbs especially the floats, inlet needles and seats. Also the venturies sit on top of the main fuel nozzle. Make sure they are not clogged by the melted plastic or dirt.

    You might post a picture of the carbs w/o the airbox. maybe we can source some venturies for you.

  22. #22
    Vice Admiral bktheking's Avatar
    Join Date
    Jul 2008
    Location
    Carleton Place, Ontario
    Posts
    5,048

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    I'm working on the same motor right now, those venturies are melted, what you need to confirm is the hole coming up through, it it still ok or melted over, pulling the carbs will tell you. Once you get the carb apart you can shove a nozzle up through the top of the venturies to confirm if the hole is still good(I used the red nozzle from a can of carb cleaner) If I were you I would clear out any melted plastic through the center hole (looking from the front) and call it good. My motor is a 76, look at your starter, it's stamped 76. You need to remove 4 bolts, they hold that air cover on (with the 6 holes) then 2 bolts per carb and the carb will come off, start with the top then remove the bottom, be careful not to break the platic link between the 2 carbs. Inspect the needles in the carb as well as the float, check the pilot jets for crud as well.


    Pull the screw out of the fuel pump cover, it's to the left of the switch box. There is a screen underneath as well as an o-ring. Make sure the oring is not compressed and that the screen is clean. Merc dealers sell a rebuild kit that comes with the gaskets and diaphram and check valves for around $25, the diaphram could have hardened from sitting and just needs to be replaced.


    These motors take surface gap plugs, I hope that's what you replaced the old ones with.

    These motors are renowned for holes in the water jackets, you need to confirm before anything else that it isn't water intrusion into the cylinders, it wouldn't surprise me if that's the issue.
    Signature- If you have fuel and spark- Have you checked compression?

  23. #23
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    In regards to your engine, did your engine work correctly if you pumped the fuel bulb? I think mine is fuel related cause when I pump my fuel bulb the engine gets up and goes, indicating to me it is fuel related. I found the stator part for $110.00, before I replace it I want to make sure I replace all the cheaper parts first.

    Where is the water jacket located on the motor?

    Quote Originally Posted by vadigger View Post
    i swear it sounds like you have my motor in your boat. i had gas in the case surrounding my carbs also. when you give it the throttle try easing the shifter very slowly past the bogging down point. sometimes i could find the sweet spot and i would get full throttle. also the plunger was missing on my choke so i had to use a string to manualy choke the carbs. my mechanic told me the loss of power thing was the stator(400 installed) and the gas coming out of the carb was a hole in the water jacket which eventually led to my bearings goin bad. after you put it in the water drive it for a few minutes the pull each plug one at a time and see if any are wetter than the others. if so then you probably have a hole in the jacket and might want to consider selling the motor before it quits all together.

  24. #24
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    It was not in a fire and I am not sure about it over heating. I was told they can melt if an engine backfires, since I have owned it I have not had it backfire. I don't know if this was preexisting damage or not, because I didn't check out my engine till after 5 runs on the water when I started having issues.

    When you say the airbox, are you referring to the metal piece with the 6 holes sticking up?

    Quote Originally Posted by Chris1956 View Post
    Clearly your motor need some carb help. Was it in a fire or did it overheat so badly to melt the venturies. The cowl looks to be a 1976/7, but I never saw air boxes like that.

    I would take a look at the carbs especially the floats, inlet needles and seats. Also the venturies sit on top of the main fuel nozzle. Make sure they are not clogged by the melted plastic or dirt.

    You might post a picture of the carbs w/o the airbox. maybe we can source some venturies for you.

  25. #25
    Petty Officer 3rd Class
    Join Date
    Apr 2011
    Location
    Sterling, CO
    Posts
    80

    Default Re: HELP.. Mercury 850 (85 HP) Issues

    Quote Originally Posted by bktheking View Post
    I'm working on the same motor right now, those venturies are melted, what you need to confirm is the hole coming up through, it it still ok or melted over, pulling the carbs will tell you. Once you get the carb apart you can shove a nozzle up through the top of the venturies to confirm if the hole is still good(I used the red nozzle from a can of carb cleaner) If I were you I would clear out any melted plastic through the center hole (looking from the front) and call it good. My motor is a 76, look at your starter, it's stamped 76. You need to remove 4 bolts, they hold that air cover on (with the 6 holes) then 2 bolts per carb and the carb will come off, start with the top then remove the bottom, be careful not to break the platic link between the 2 carbs. Inspect the needles in the carb as well as the float, check the pilot jets for crud as well.


    Pull the screw out of the fuel pump cover, it's to the left of the switch box. There is a screen underneath as well as an o-ring. Make sure the oring is not compressed and that the screen is clean. Merc dealers sell a rebuild kit that comes with the gaskets and diaphram and check valves for around $25, the diaphram could have hardened from sitting and just needs to be replaced.


    These motors take surface gap plugs, I hope that's what you replaced the old ones with.

    These motors are renowned for holes in the water jackets, you need to confirm before anything else that it isn't water intrusion into the cylinders, it wouldn't surprise me if that's the issue.
    Ok, thanks for the long reply. I will start by removing my carbs and checking them out. I need you to clarify what hole "coming up through" you are talking about. There is a hole in the middle of the melted venturies and a yellow plastic piece in front of the venturies (the jets?).

    I have already replaced the fuel pump diaphragm and seals. I completely rebuilt the fuel pumping thinking that was the issue, apparently it was not.

    Yes, I replaced them with surface gap plugs.

    Do you have a picture of the water jacket? Where is it located on the motor? How do I confirm there is water in the cylinders?

Page 1 of 3 1 2 3 LastLast

Similar Threads

  1. 07 mercury 225 pro xs low rpm issues
    By rtr80 in forum Mercury & Mariner Outboards
    Replies: 1
    Last Post: July 24th, 2012, 05:55 PM
  2. 97 mercury 200 efi issues!
    By ranger492 in forum Mercury & Mariner Outboards
    Replies: 1
    Last Post: April 11th, 2011, 09:31 AM
  3. 50 Hp. Mercury running issues
    By brucedoer in forum Mercury & Mariner Outboards
    Replies: 1
    Last Post: May 16th, 2010, 10:25 PM
  4. prop issues-Mercury
    By brad1756 in forum Prop Questions and Topics
    Replies: 2
    Last Post: June 11th, 2008, 06:07 PM
  5. more '80 mercury 80 issues
    By fishdog4449 in forum Mercury & Mariner Outboards
    Replies: 4
    Last Post: May 31st, 2008, 05:30 PM
  1. iboats Forum Directory - Over 100,000 forum posts organized by topic