MarineEngine.com - Your online store for all types of marine engines and boat parts.
PHONE ORDERS
Monday - Friday
9:00 AM - 5:00 PM EST
Click for TOLL-FREE Number
Online Checkout
Special $9.95 Flat Rate Shipping
(800) 209-9624 | Home | Contact | Shipping | Returns | Cart View your shopping cart.
Part Number Search
Shop by engine/drive part number.
Original & matching parts for sale.
Manuals & Accessories
Shop by description, item number
or manufacturer's model number.
Boat Repair Forum Boat Repair Forum   Boat Video Gallery Video Gallery
   
Get instant online access to repair manuals for your Mercury / Mariner outboard. Online Manuals
MercuryMariner
Order printed Mercury / Mariner service manuals — shipped to your door! Printed Manuals
MercuryMariner
Use engine diagrams to find & order parts for your Mercury / Mariner engine. Engine Diagrams
MercuryMariner
Find parts quickly with Mercury application guides. Quick Parts Guide
MercurySierraCDI
Page 1 of 2 12 LastLast
Results 1 to 30 of 42
  1. #1
    Join Date
    Jul 2010
    Location
    New Hampshire
    Posts
    12

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    I have the above engine on my boat. I bought the engine and controls from someone who started it (idling) on a hose. We shook hands, I paid him and got shafted.

    The problem is; The engine starts and idles fine. As soon as you put it in gear and give it the throttle, the engine revs a little bit higher than idle, stays running, but barely holds 5 mph, a little more throttle and then it craps out. If you put it in neutral, it will start back up. It sounds like it is starving for fuel, but you can see the jets misting fuel and the butterflies opening.

    UPDATE: While in gear and moving at 5 mph, I had a friend move the timing lever back toward the idle zone and it made no difference. The engine still stalls as soon at the butterflies start to open. The engine seems to be flooded when the plugs are examined after the stall.

    Here is what has been checked and or changed: The Timing, the carburetors were cleaned but not adjusted, new fuel pump diaphragm, new fuel filter and all rubber hoses. New ignition module. The carbs are clean and shooting gas and both butterfly valves opening. If you open the throttle as far as you can with the engine in gear and running, and spray carb cleaner into one of the carbs, the engine stalls. This was an idea suggested from my local Merc dealer. The timing is set according to the procedure in my SELOC manual. All the settings seem to line up with the painted/unpainted factory points. The linkage works correctly.

    Compression is good, all 4 plugs are new and have a hot spark. The spark is hot at stall-out. It was getting dark and I pulled one cylinder wire and connected it to an extra plug and grounded the case. Nice spark at all rpms. I have no tach.

    Electric choke works and is not stuck. Tilt cutoff switch disconnected.

    Irrelevant, but the battery is getting charged with 5.5 amps when it IS running.

    Low end shifting is smooth and quiet. Clean oil in lower end and no leaks.
    New water pump impeller and seals. New Shift lever seals. New Drive shaft seals.

    I'm looking for that one tech out there that has fixed a million of these and
    seen these symptoms.

    JP

    JP
    Last edited by jplandry; 07-08-2010 at 02:56 AM. Reason: update observations

  2. #2
    Join Date
    Nov 2005
    Location
    Chesapeake, Va, US
    Posts
    1,111

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    Check for a strong spark at all plugs then do a link & sync exactly as outlined in your manual.
    Bill H PTC USN Ret
    A manual is a cheap investment.

  3. #3
    Join Date
    Apr 2010
    Location
    Bonita Springs FL
    Posts
    1,100

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    Is your timer base under the flywheel advancing as you give it throttle ?Stuck maybe or broken linkage ?

  4. #4
    Join Date
    Jul 2010
    Location
    New Hampshire
    Posts
    12

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    I do have the SELOC version of the manual and the timing and linkage advance to the stops at the right slope and rate. I had a Mercury Dealer check the timing, coils, and spark/throttle advance. All OK. Is it true you cannot test these engines in the shop on a tank? I can't fathom the $90.00/hour for some technician to demonstrate what I have video of on some lake.

    Good Ideas however. And thanks for the support and assistance.

    I read through some other problems that sounded similar on other engines and I found this: "If you can squeeze the bulb on the gas line and see gas coming out of the carb jet, the float valve is leaking by" If this is true, It is the case with my engine as well. If I squeeze lightly, gas dribbles out. From both carbs. I cleaned them, but did not adjust anything. Could the engine be getting swamped with gas when the butterflies open?
    Last edited by jplandry; 07-07-2010 at 11:26 PM. Reason: clarify

  5. #5
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,334

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    ....."the carburetors were cleaned...."

    Describe exactly how this was done.

    Jeff

  6. #6
    Join Date
    Jul 2010
    Location
    New Hampshire
    Posts
    12

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    I marked all the adjustment points with white-out and removed the carbs. I removed the float bowl drain plugs (screw,jet, whatever) and soaked them for two days in a gallon of carb cleaner. Detail: What kind? I bought 10 cans of the big walmart aerosol type carb cleaner, let all the propellant out, and cut the can so I could pour the liquid out. The container I used was a 1 gallon ultrasonic cleaner bought from Northern Tool. I turned on the ultrasonic transducer for the soak.

    Removed the carbs, (they were absolutely spotless) and sprayed more cleaner into the float chamber and drained. All was clean. Replaced jets and re-installed everything.

    Engine did the same thing. I hope this is clear enough.

  7. #7
    Join Date
    Sep 2007
    Location
    Posts
    1,068

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    Check the stator hi-speed windings again. Pretty common in those years. Rechech the spark again above idle when it craps. Use the timing gun is the easy way.
    Last edited by timebandit; 07-08-2010 at 07:52 AM.

  8. #8
    Join Date
    Nov 2005
    Location
    , il,
    Posts
    2,198

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    is it possible its just set to lean, try opening the idle mixture screws a 1/4 turn each and see if it helps, or bumb the choke while trying to go..jb

  9. #9
    Join Date
    Jul 2010
    Location
    New Hampshire
    Posts
    12

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    RE: Lean theory. I haven't tried opening the idle mixture yet, but I will try. I have hit the choke during that gray area where it will barely move the boat but stays running. I tried different levels of choking and it immediately stalled it. So, Choke theory stalls engine immediately.

  10. #10
    Join Date
    Jul 2010
    Location
    New Hampshire
    Posts
    12

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    RE: Check the stator hi-speed windings again. Pretty common in those years. Rechech the spark again above idle when it craps. Use the timing gun is the easy way.

    What do you mean by the high speed windings? It was my understanding that the timing was advanced with the throttle and hits the stop from then on. The same windings are actuating the switch-box through the entire band. I have the wiring diagram and can't see it any other way. Am i missing something?

  11. #11
    Join Date
    Jul 2010
    Location
    New Hampshire
    Posts
    12

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    RE: Check the stator hi-speed windings again. Pretty common in those years. Rechech the spark again above idle when it craps. Use the timing gun is the easy way.

    Can I do this with a hose in neutral? You don't know how many times I've "Test Launched" this boat.

    How High can you rev it in neutral? I haven't dared to do it at all.

  12. #12
    Join Date
    Nov 2005
    Location
    Chesapeake, Va, US
    Posts
    1,111

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    If gas is dribbling out when you pump the primer bulb then you have found the problem. It should not do that. Replace the needle and seats, Check and adjust the floats.
    Bill H PTC USN Ret
    A manual is a cheap investment.

  13. #13
    Join Date
    Jul 2010
    Location
    New Hampshire
    Posts
    12

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    re: gas is dribbling out when you pump the primer bulb then you have found the problem. It should not do that. Replace the needle and seats, Check and adjust the floats. __________________

    This is the case. Gas does dribble when the primer bulb is squeezed. I will do this work before we go any further. I will report back with the results. Thanks for all the input.. This is really a great place to get marine advice.

    Standby....

  14. #14
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,334

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    Since the primer bulb can deliver 15 pounds pressure--and the fuel pump makes only 4 at WOT--I wouldn't be all that concerned if they dribble a bit. (Many techs set them up that way for faster cold starting.)

    First thing to do is set the idle mixture screws properly. This requires warming the motor, putting it in gear, and dialing in the best idle. After this is done, I open the idle screw about a 1/4 turn which helps stubborn motors such as yours.

    Jeff

    PS: I tie my boat to the dock (on on the trailer) when doing the above. Far easier to that way.

  15. #15

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    I have the same motor and am experiencing the exact same problem you have. My motor starts up and idles fine but when I put it in gear and give it throttle it dies. The odd time when I advance the throttle super slow it will build up and run fine but if I throw it ahead quick it just dies instantly. Was wondering if you were able to fix the problem and what you finally did. Also what are the idle mixture screws supposed to be set at? If you turn them all the way in how many turns do you bring them out to be set properly? I do not have a manual.

  16. #16
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,596

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    Classic symptoms of idle jets / adjustment being too lean.---------Turn both in lightly seated and back out 3/4 turn ------------If motor idles good and stalls on takeoff, open both jets 1/8 turn each try untill problem goes away.

  17. #17
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,279

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    ...sprayed more cleaner into the float chamber and drained.
    I have used ultrasonic tanks and they clean great but may not have removed the debris from the tiny fuel passages. Did you blow the carb fuel passages dry w/compressed air?

    Replaced jets and re-installed everything.
    Did you include removing the high speed jets?

  18. #18

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    ok thanks for the info.

  19. #19

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    Just another question there is an idle set screw and another one that has a hole in it to the left i'm guessing that is the jet.

    how much do you adjust the jets? 3/4 turn out as well?

  20. #20
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,334

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    Start there, but adjust them as I wrote above.

    Jeff

    PS: OB carbs don't have accelerator pumps, which makes the idle adjustment so critical.

  21. #21
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,596

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    Do not " guess " when working / adjusting things on your motor.--------Research what that screw with the hole is !!!

  22. #22
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,279

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    Are you referring to item #2? JET, VENT BOWL

    http://www.mercruiserparts.com/Show_...RETOR+ASSEMBLY

  23. #23

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    ok thanks Jeff will do with the idle screws. Yes guyjg that is what I mean jet vent do I adjust that as well?

    do you adjust the same for both?

  24. #24
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,596

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    That vent jet is not an adjustment !!--------------Unless you change the size of the hole.

  25. #25

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    ok thanks this is all relatively new stuff to me....

    so I only adjust the idle set screws and that should fix the problem?

  26. #26
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,279

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    That's correct. Start w/the top carb and slowly turn the idle mixture screw CW until the engine starts to stumble and then turn the screw CCW until the idle smooths out; continue to turn the screw CCW until the engine starts to stumble again. Now turn the screw CW to the midway point between the two stumble points. Repeat on each carb until the idle is smooth. The RPMs may increase a little but that's OK. Idle speed is set in forward gear in the water.
    Last edited by guyjg; 08-16-2011 at 09:42 PM. Reason: correction for 4 cycle carb adj.

  27. #27

    Thumbs up Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    ok thanks I will give that a try.

  28. Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    make sure both carb butterflys are in sync and both are open at wot run without cowling if base gasket is bad exhaust will bog motor have you inspeted reed valves when carbs where off? black stator is two speed newer red is single. carb idle screw 1 1/4 to 1 1/2 ck spark plugs what is the burn are they all the same should be coffey brown wet dry keep in order post findings.

  29. #29
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    583

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    You initial setting is 1 1/2 turns out off a light seat like Midnite posted and adjust in water with back pressure like guyjg posted and you should be fine. And yes some 2 & 4 stroke outboard carbs have accelerator pumps.

  30. #30
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,334

    Default Re: 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP

    Update: I have similar carbs on the triples I run and stumbled (punn intended) on the cure: To prevent bogging, pull the carbs and drill out the three vertical holes in the butterflies to 1/8 ". (THis can be dne without taking them apart. Just be sure to blow out any chips.) One of the holes may already be 1/8 " (or larger). Drill the other two anyhow.

    This little trick TOTALLY cured the bogging issues on my triples where no amount of idle enrichening would. I can now re-adjust the idle for best idle, which makes the motor run far better.

    Jeff
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Carb Fix.jpg 
Views:	119 
Size:	66.6 KB 
ID:	3576  

Page 1 of 2 12 LastLast

Similar Threads

  1. 1984 Mercury Outboard 75 HP 4 cyl Bizarre problem HELP
    By jplandry in forum Johnson Evinrude Outboard Forum
    Replies: 2
    Last Post: 07-07-2010, 07:47 PM
  2. 1984 Mercury IO problem
    By pferreira in forum Mercruiser Sterndrive Archive
    Replies: 2
    Last Post: 09-11-2008, 05:21 PM
  3. 4 HP bizarre Model # and water problem
    By sacam in forum Johnson Evinrude Outboard Archive
    Replies: 4
    Last Post: 11-03-2007, 12:50 AM
  4. 1984 90hp Mercury outboard
    By hipane in forum Mercury Mariner Outboard Archive
    Replies: 1
    Last Post: 06-21-2007, 08:12 AM
  5. 1984 Mercury XD problem
    By Paul Matthews in forum Mercury Mariner Outboard Archive
    Replies: 6
    Last Post: 03-30-2006, 05:14 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •