1996 Mariner 150hp Offshore - problems at 2000 RPM

Discussion in 'Outboard Maintenance' started by iMacattack, Jul 9, 2013.

  1. iMacattack

    iMacattack busy, too busy

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    This is a long overdue issue I have been ignoring. (yea I know, shame on me)

    So here are the specifics.

    1996 Carb Mariner Offshore 150.
    Boat can sit for a month, prime bulb, choke, and starts on the first or second try.
    Starts and idles out of gear brilliantly.
    Idles in gear well. No complaints for a 17 year old two stroke.
    From idle to about 1700ish RPM boat does not exhibit any problems. Some minor hesitation from time to time but nothing of concern.
    Above 2000 RPM Boar runs clean.
    Instant throttle response all the way to WOT.
    WOT with SS prop is about 5600/5700 RPM.
    Boat can hit 50mph with a light load.
    The problem is from about 1700ish RPM to about 2000ish RPM. Boat hesitates, (possible miss can not confirm) Sometimes bogs down. This is where the boat is trying to get on plane. It just plain runs rough. Difficult to get on plane due to possible miss and hesitation.
    Before I just start swapping parts I'm looking for suggestions on troubleshooting ideas.
    Also with a smaller prop (too small will hit rev limiter) the engine can wind up the RPM's quicker and it get's over the 2K RPM hump thus problem does not manifest itself as prominently.

    Thanks.
     
  2. Brett

    Brett > PRO STAFF <

    Had a 140 'rude that did something like that.
    Lost power in the midrange when under load.
    Cause was 2 things, Cracked insulator on a spark plug
    and the brain box was starting to go. Replacing the plug helped for a while
    but the symptoms returned. Tapping on the brain box with the back end of a
    screwdriver would give me a temporary respite, but replacement solved it.
     

  3. grego

    grego Well-Known Member

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    Try bumping the choke while running at the problem rpm range. My 2 stroke merc did the same thing to me a few times and that worked out the jets.
     
  4. danville_marine

    danville_marine I Love microskiff.com!

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    thats why i liked older style choke instead of primer hit button close flap suck it out
     
  5. Creek Runner

    Creek Runner Well-Known Member

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    IMac you forgot the most important thing, and Brett can't believe you didn't ask (lol)  :D Brett beats me to all these post!  :cool:

    Does it do it every time or is it intermittent?

    Creek standing by
     
  6. Brett

    Brett > PRO STAFF <


    Forgive me, I'm only an amateur  :-[   not a trained professional... ;D
     
  7. Creek Runner

    Creek Runner Well-Known Member

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    Easy Brett only my wife gets to call me that! ;D

    iMac give me a serial number, and model there were multiple carb 150hp back then and they used different systems.
     
  8. iMacattack

    iMacattack busy, too busy

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    Have to travel for work. Will get it for you when I return.

    Thank you.
     
  9. iMacattack

    iMacattack busy, too busy

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    PM sent with S/N and other info.

    Thanks! ;)
     
  10. Creek Runner

    Creek Runner Well-Known Member

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    Oh boy you got a fun one!
    IMac your issue could be multiple things, we will need to narrow it down to see which area is causing the problem 1st (IE. Fuel or Spark)

    Also let me say there are certain tools required to test some of the electrical components that you may not have. I feel that if it is a fuel issue we can diag, and if your handy you can R&R anything thing that is required. If it's electrical I can give you steps and pointers but without the proper test tools you will ultimately have to resort to part swapping which is not the correct way to fix something and can get very expensive. (No returns on electrical components)

    Even though I feel this is not your problem, my rule is to always do a compression test on every engine 1st. So do a compression test, lol!

    I would eliminate the boat as being part of the problem,  (primer bulb, fuel line, FWS, Tank, anti-siphon) run the boat on a portable 6 gallon fuel tank with a new fuel line and primer bulb, hooked directly to the engine. If the problems still persist then move to the next step, if the problem is solved then it's either the primer bulb, FWS, or anti -siphon valve.

    On the bottom of the Starboard cyc head is an Air Thermal valve, it will have a vacuum hose going from it to the carbs, Disconnect the hoses from the thermal valve and test run.

    Fuel pump, disconnect the 2 bolts holding the fuel pump on the block (leave all the lines hooked up) pump the primer bulb no gas should leak out anywhere, if it does R&R.  Your engine model/serial # range does have a couple bulletins regarding fuel pumps. (I doubt that's the original pump though, but you never know.  you will need a vacuum gauge digital strongly advised, a foot or so of clear hose, and a Tee fitting. You will disconnect the main fuel line into the pump, install the tee in the fuel line coming from the boat, the clear line will go on the other side of the Tee with the clear line connecting to the fuel pump, the top nipple of the tee is where you will hook the vacuum meter. To begin test, start engine (idle only) and pinch of the main fuel supply line you should get a reading above 2.5'', (if not R&R fuel pump)Next start engine and idle observe the clear fuel line, Air bubbles present you have an air leak somewhere before the fuel pump(ie tank, FWS, etc, etc), start engine at idle again you should have a reading less than 2.5 slowly raise engine RPM and  you should see an increase in readings but never above 2.5, If above 2.5 you have a restriction somewhere before the fuel pump.  If all test good then move to the carbs. See below.

    Pull the carburetor cover, get a good flash light, (going to need a 2nd person) have someone at the helm and the other person at the motor with the cowling off and carb cover off sine the light into the throats of the carbs, bring the RPM's up to 1800RPMS or until the motor begins to (surge, stall, misfire, etc) you should see the same amount of fuel flow in each carb, (thinking 1-2 might be opening slowly) (also check to make sure each butterfly is opening at the same time and all the way this can be done without the motor running on the hill) If you see something that doesn't look uniformed than I would say your issue is carbs, Also while running the boat at the problem RPM take a can of carb cleaner and just squirt it into the carb throats directly one at a time (very little squirt) and see if the RPM's increase. This is basically the same thing as choking it like stated by others, but your engine runs an enrichment valve so it's easier to do it this way. If RPM's increase you have a carb issue.


    If everything above checks fine, then all signs point to electrical and even though Brett said power pack, I would look at the Stator under the fly wheel, it has a low side and a high side, I would say the high side is starting to fail. Mercury had lots of issues back in the day with stators, Black stator, Blue Stator, Red Stator etc, etc plus there are countless non oem parts out there. If the stator is bad you will also need to replace the rectifier, as they should always be replaced in pairs. If a switch box is bad then you should replace both switch boxes at the same time. I will need a picture of your fly wheel to determine what amp charging system you have 9,16,or 40. Probably 16. Also let me know what color wire you have coming from the stator and I will give you the tests for it.  You will not be able to check the Switch boxes, or the trigger without special tools.  I highly doubt it's a coil.

    BTW I feel like it's a fuel issue more than a electrical issue by the symptoms provided.

    Creek Standing by
     
  11. iMacattack

    iMacattack busy, too busy

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    Thanks a TON! I'll start troubleshooting and reply back. It will take a couple days.

    Best Regards,
    Jan
     
  12. cutrunner

    cutrunner Cert. Yamaha technician

  13. iMacattack

    iMacattack busy, too busy

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    So in prep for running the tests you mentioned above I found the following.

    What I believe I'm seeing is the following.

    Note this is based on my observations and my best attempt to follow the wiring diagram in the Service Manual I have. If I am looking at this incorrectly please let me know.

    Red lead shows resistance and overheating. This lead connects the lower voltage regulator to the starter solenoid. Yellow lead is showing similar issue but not as bad.
    [​IMG]

    Upper voltage regulator is cracked and looks burnt.
    [​IMG]

    Closer view
    [​IMG]

    According to the manual it states I have a 40 amp stator.

    Regards,
    Jan
     
  14. Creek Runner

    Creek Runner Well-Known Member

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    Yep that voltage regulator is burnt, and so are the leads. The bad thing is I would not recommend just replacing the voltage regulator, I would also go ahead and replace the stator. The yellow leads go to the stator, and is more than likely the reason the voltage regulator went bad. They always go bad in pairs, if you would have let it go much longer it might have even killed the switch boxes.

    I always recommend OEM parts, but I have had good luck with Pro-marine stuff as well and it is cheaper.

    Stay away from sierra parts!

    If I was a betting man, my money was on a fuel issue due to your comment on the smaller prop allows it to get over the miss easier.

    Creek standing by
     
  15. iMacattack

    iMacattack busy, too busy

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    Creek,

    Thanks for the info. Unfortunately pulling the flywheel is above my capabilities as I have no flywheel puller. :mad:

    Time to pay out the rear take it to a professional. :-[

    Cheers
    Jan
     
  16. Brett

    Brett > PRO STAFF <

    Flywheel puller is not an expensive item.
    Basically a package of various bolts and a multi-arm forged crosspiece.
    A decent puller is less than 60 bucks, a crappie one is about 20 bucks.

    http://www.harborfreight.com/automotive-motorcycle/pullers.html
     
  17. iMacattack

    iMacattack busy, too busy

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    I found one specific for Mercury. I have a crank puller which may work. Need to check it out tomorrow.
     
  18. Creek Runner

    Creek Runner Well-Known Member

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    You don't need 1 specific to Mercury click on Brett's link and the 1st one for $13 bucks will work. Or one like it just take a piece of cardboard and get a bolt hole pattern off your flywheel so when you go buy it you can make sure they line up with the puller.

    You might have to buy additional bolts, if the ones that come with it are not the right threads. But it's a pretty big kit it should have them.

    It's pretty easy Jan, you can do it no need to take it to someone.

    100% disclosure, some mechanics will tell you that you can just replace the voltage regulator, so you may want to do that. In my experience they are better off replaced in pairs and about 75% time when just one is replaced you will be doing it again very shortly.

    Also I'm not going to tell you for 100% that this will fix your problem as I'm not there to diag everything. But that voltage regulator is definitely bad or going bad, and again If I was working on it I would quote the repair with both components regulator/stator. If the client only wanted to do 1 I would refuse the job and recommended another shop as I have to warranty it and its my reputation.

    Creek standing by
     
  19. iMacattack

    iMacattack busy, too busy

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    Let me see if I can get the flywheel off. If so then we are golden. I have a crank puller and a bearing puller. If it will work properly without potential for damage then I'll do it.

    I hope I find parts locally. Supposed to go fish on Tuesday.

    I don't know if this will fix the problem but it is obviously not right. So it need to be attended to. ;D

    Once this is complete then I'll continue the troubleshooting. I hope it is the problem but I am prepared for it not.

    I appreciate all the help. Worst case I take a pile of parts to a professional.

    ;D :D

    Cheers
     
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