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  1. #1

    Default 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    STORY.

    My 2002 Merc 115 ELPTO (0T464942) is giving me low-end rpm problems while running below around 1300 rpm down to idle. Freshwater use (no sand) lakes history.

    Brought to 3 separate mechanics over the last 5 years, 2 were Merc techs in the Twin Cities (Mpls/St. Paul), and all said link/sync was good and that these motors just run cold-blooded. While I know 2+2's can be and are, it's not an answer, as I have a buddy who has the exact same engine, 1 year older, and it's smooth - night and day compared to mine. So it must be possible.

    About 6 years ago I first noticed the issue, with occasional shaking/roughness at idle or slightly above in rpm, and it would always smooth out at about 1200 or 1300+ rpm, then nice and smooth up to 5200. I was beginning to get engine kills when shifting into forward or reverse and earlier this year began to get what sounds like occasional misfires throughout, even in the upper RPM range. It was always worse when the engine was warm, better when it was cold. The issue became progressively worse, so I decided to work through the 12 or so reasons that I've read could lead to the problem. Here's what I've done so far:

    Checked fuel and fuel system (found good with no water), added fuel water separator, replaced all engine fuel filters, and rebuilt fuel pump with Sierra kit.

    Cleaned (they were amazingly clean anyway) and rebuilt all 4 carbs (kept linkages intact), rebuilt carbs with OEM ss needles (had rubber-tipped aftermarket needles in there), verified throttle shutters closed and moving together with linkage arm (carefully eyed after reinstallation).

    Replaced reeds with Boyesen power reeds (for smoother idle, not really for power), and replaced all gaskets with new OEM - on intake reed blocks, intake manifolds, and both sides of cabs. Torqued with proper patterns and torque values.

    Backed out idle jets on carb 1 & 2 (one and a half full turns, or 3 half turns), plus 1/4 turn out rich for the Boyesen reeds (per instructions for those to keep from lean opping)

    Replaced bleed check valves with OEM and bleed hoses with OEM hose cut to proper lengths

    Tested trigger, stator, voltage regulator/rectifier, and found chared yellow wires to rectifier from stator - half of stator tested out of spec, replaced with CDI unit. Replaced rectifier with new. Replaced trigger with CDI unit while in there, just to be sure (though it tested barely within spec).

    Replaced CDM on Cyl 1 (read slightly out of spec) with new blue CDI unit.

    Replaced all 4 spark plugs with proper NGK's at .040" gap and tested spark with CDI tester - looked solid


    Now it still does the same and is even slightly worse than before I started. I have "chattering" from 600-1200/1300 rpm, smoothing out after that and good when I transition to all 4 cyls, with nice power at WOT.

    Where do I go next? I've seen a lot of discussions on 2+2's, but most don't write back about what did the trick or what the issue actually was. Link & sync, timing, scoured cyl walls, or something else? I have no TIMING MARKS or scale of any kind on my flywheel and haven't found a pointer or scribe for TDC. The manual shows there are timing marks for the 3 cyls, but nothing for 4 cyls. What's the best method after establishing TDC, count the cogs and work out the 360 deg picture? I think I'll need a white paint marker ...

    Now the OEM service manual does state that one can adjust idle timing, which I've not yet attempted. Everyone here says that's not needed or even possible, and it's actually done only at Max cranking or 3000 rpm running, and no need to adjust idle for 2 deg BTDC. Right or wrong? I've checked the clearance between the roller and throttle cam, it's right at .020" with feeler gages not very tight (probably +.0005" or so), and the marks are centered with each other.

    I'd REALLY love to be able to get this running right again for trolling. Any help is greatly appreciated. I will send updates on recommendations.

    Best,
    Rusty
    Last edited by rusty51; 09-21-2020 at 06:01 PM.

  2. #2
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Lotta writin there.----What are the compression test numbers ?

  3. #3

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by racerone View Post
    Lotta writin there.----What are the compression test numbers ?
    Last year's numbers, cold with a quick spray of oil in each cyl 1=136, 2=132, 3=138, 4=141. Will check again after engine warmup and post back.

    Thanks
    Last edited by rusty51; 09-21-2020 at 07:31 PM.

  4. #4
    Join Date
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Not sure I want to get into your engine with what you have done. Mine is totally stock except for spark plugs and my cam is set to 0.020 also even though the manual says 0.030....i want it to squirt earlier. I did put a kit in the pump and replaced the 3 and 4 inline fuel filter...little guy hiding behind the rear of the onboard oil tank.

    My plugs were running grey and stayed wet. I went to 6 temp range Iridium and solved that problem....tan and dry now.

    Spec on compression is 120 min so you are in excellent shape there.b

    I also found that I could smooth low speed operation by merely lifting the rear of the engine when running slow about 15*. Not rocket science...just trim it down in the back and wait a minute and it would start wiggling and slight shuddering, then tilt the rear up as stated and give it a minute and it would smooth right out. Other thing is that with the hotter plug and smooth idling, when I punched out it took it smoothly through the transition and moving the throttle on up to WOT it went right to the 5250 rev limiter without stuttering around 5000 for a minute or so and then moving on all the way up....cleaning up the plugs on 3 and 4 my guess.

    Idle is set by the knurled nut on the lower part of the vertical throttle rod that controls engine timing....timing sets the idle speed. Spec is 675 give or take.....fast enough to shift with the engine remaining online and slow enough that you don't eat up your clutch dog in the LU.

    I don't remember looking at the timing on this engine. On my 90 triple, previous engine, there was an index mark molded in the side of the black plastic cover over the flywheel and the timing chart was on the side of the flywheel, easily seen from the right front of the engine, leaning over the transom. Spec on WOT at cranking speed....200 rpms, 22* BTDC per the 2015 revision of the applicable manual for these engines.

  5. #5

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES


    Thanks for the info! I'll look at the plugs again and maybe try iridium's as you did.

    I've also noticed over the years when it was running better that the chugging at lower RPM and idle did even out a bit when trimming the motor up (even) or a few degrees higher. Unfortunately now I get that chugging throughout the lower RPM range , with infrequent smooth/normal running depending on where the RPM sits, say around 1100 +- a few RPMs. It feels like timing ...

    I did find the window and mark in the plastic flywheel cover, just don't have a degree scale on the flywheel to properly use it with a timing light. Strange.

    Best,
    Rusy

  6. #6
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    With what you have done, you probably have the expertise to find TDC on #! and mark the flywheel. From there you can just use the ratio of 22/360 x the circumference of the flywheel and mark your 22* BTDC mark.

  7. #7

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by Texasmark View Post
    With what you have done, you probably have the expertise to find TDC on #! and mark the flywheel. From there you can just use the ratio of 22/360 x the circumference of the flywheel and mark your 22* BTDC mark.
    Exactly. Since these take BP8H-N's, which specific iridium plug did you use in place to get your results?

    Thanks

  8. #8

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    I will say, it's amazing how many people have similar issues and how hard it is to correctly diagnose on these engines. No wonder they don't make 2+2's anymore! I'll get a chance to check the timing this weekend and report back on what I found.

  9. #9
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    Oct 2007
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    1,193

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    I have owned a 1997 115 2+2 for many years. When the boat comes off a plane and the motor is throttled down to idle speed the engine runs rough until the motor is trimmed up several degrees. With that adjustment made, the shaking stops and the motor can be tilted down again and it will run smoothly at idle for hours without shaking. The only reason I can think of would be a fuel related problem such as incorrect carburetor float levels. Has anyone had a similar experience.

  10. #10

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by Texasmark View Post

    My plugs were running grey and stayed wet. I went to 6 temp range Iridium and solved that problem....tan and dry now.

    ...

    I'm curious,

    Which iridium spark plugs are you using with heat range 6? Any chance they're these, "NGK 0127 SIFR6A11 Laser Iridium Plug"? I'd be worried about them failing creating an open circuit based on the non-inductive resistor, vs. say the normal inductive NGK's.

    Let me know - would love to see if it makes a difference for my engine!

    Thanks

  11. #11
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Per the www NGK plug manual, I first got the dimensions of the existing plug from their site and then went down to the iridium section and found corresponding dimensions. NGK increases heat with a decrease in stated number so 6 is 2 heat ranges hotter than 8 in their plugs. The NGK stock number is 4085, the plug part number is BPRGHIX. That plug is gapped 0.030 and the current plugs are gapped at 0.040. I realize that gapping to a wider gap allows the voltage to move on up which assists the ability to fire the plug when it breaks over.

    So I used a wire gauge, and very carefully gapped them out. You are cautioned about gapping in the first place and other places say be very careful....reason is that the tip is tiny and easily broken off. Just be careful and take your time.....I had no problem gapping mine.

    NGK also tells you how, in the catalog, to determine if your plugs are authentic or copies. I bought mine off ebay for $7+ each and they are authentic.

    https://www.ngksparkplugs.co.za/wp-c...logue-2019.pdf

    https://www.sparkplugs.com/Data/uplo...ug_Chart_1.jpg

  12. #12
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    Apr 2008
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    114

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Just thinking of things to check. Have you checked throttle shaft play?
    The crank case under each piston must be sealed off to the adjoining piston/case. Rings on the crank make this seal . I have seen these rings stuck and not sealing.
    You could use the hose from the compression tester, remove the schrader valve, and put pressure in the spark hole, move the piston down and up and listen for air in adjoining spark hole or carb. Not sure how much pressure those reeds can take. Maybe someone has an idea on this.

  13. #13

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by Texasmark View Post
    ...

    So I used a wire gauge, and very carefully gapped them out. You are cautioned about gapping in the first place and other places say be very careful....reason is that the tip is tiny and easily broken off. Just be careful and take your time.....I had no problem gapping mine.

    NGK also tells you how, in the catalog, to determine if your plugs are authentic or copies. I bought mine off ebay for $7+ each and they are authentic.

    https://www.ngksparkplugs.co.za/wp-c...logue-2019.pdf

    https://www.sparkplugs.com/Data/uplo...ug_Chart_1.jpg
    Thanks kindly! I'll give that a try for sure. So just to be sure, you re-gapping the .030" factory gapped 4085's to .040"? Yeah, I see the electrode is crazy small on the iridium's!

  14. #14

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by gene_d View Post
    Just thinking of things to check. Have you checked throttle shaft play?
    Do you mean the bushings at the carbs, or the throttle linkage settings? Since these intake manifolds don't appear to have vacuum ports for syncing, I had the idea of using four .001" dial indicators on the carb throttle shutters, to make sure they're moving together. So far I've only visually inspected their movement.


    Sounds like a great test idea. If I do hear a leak in these rings, is there a way to break them free without splitting the head/case?

    Thanks
    Last edited by rusty51; 09-24-2020 at 12:37 AM.

  15. #15
    Join Date
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    The seal rings are in the bearing race ...dont waste your time as no way to test.
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  16. #16
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    Sep 2020
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    Reading Ma/Newburyport Merrimack River
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    I believe this engine is running rich,I've seen the same problem many times..what is your idle timing set too, the "newer" ones seem to run better at TDC or 2 degrees before which results in a little faster burn.. try leaning out each carb with the boat in the water in forward gear, do it slowly, as the engine begins to stumble, back out the width of a screw driver, repeat with the second carb.. I bet you find a big difference, I'v found most of those engine, epically the 2000 and up dont need to b quite a rich as people think. When right, they can troll and run as god as any 4 stroke..I've worked on a lot of them, and owned 2 , still running 2004 everyday running lobster pots and trolling for stripers.

  17. #17
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by rusty51 View Post
    Thanks kindly! I'll give that a try for sure. So just to be sure, you re-gapping the .030" factory gapped 4085's to .040"? Yeah, I see the electrode is crazy small on the iridium's!
    Yes..........

  18. #18
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    May 2015
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    2,362

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    There is no magic spark plug to fix your motor. Do you have the Factory manual? Have you looked at the accelerator pumps? Is the fuel pump in good condition? Carb floats set right? Link and sync done correctly? On the water and warm motor? Have you tried running with a different tank? WOT timing does not affect the idle.

  19. #19
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by Rockfish9 View Post
    I believe this engine is running rich,I've seen the same problem many times..what is your idle timing set too, the "newer" ones seem to run better at TDC or 2 degrees before which results in a little faster burn.. try leaning out each carb with the boat in the water in forward gear, do it slowly, as the engine begins to stumble, back out the width of a screw driver, repeat with the second carb.. I bet you find a big difference, I'v found most of those engine, epically the 2000 and up dont need to b quite a rich as people think. When right, they can troll and run as god as any 4 stroke..I've worked on a lot of them, and owned 2 , still running 2004 everyday running lobster pots and trolling for stripers.
    May well be, and you obviously have more experience with these engines than I, but the color of the insulator tells me that the plug is too cold and at grey, isn't hot enough to burn off contaminants on the insulator, allowing for misfiring, regardless of the (reasonable) amount of fuel.

    My hole shot is such that I can hop up on plane at about throttle in about 3 seconds so obviously the fuel is there to feed the ponies. Since mine is working sweet, not going to change anything. I have only had this boat for a little over a year so I have no idea as to its history. But with compression running 129, 129, 129, 130, marking on the water jacket by the mechanic at the dealership where I bought it, and being 18 years old, I'm not tweaking the carbs.....besides boating alone, it would be somewhat difficult. Thanks for the info anyway.

  20. #20
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Get the factory manual. Read the link and sync procedure over and over again until you understand it completely and can almost recite it word for word... Then follow the manual and perform it on your engine, follow the directions to the T..... Then you will know your engine is set up correctly.

    Make sure the carbs are installed in the proper order.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  21. #21
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by Texasmark View Post
    May well be, and you obviously have more experience with these engines than I, but the color of the insulator tells me that the plug is too cold and at grey, isn't hot enough to burn off contaminants on the insulator, allowing for misfiring, regardless of the (reasonable) amount of fuel.

    My hole shot is such that I can hop up on plane at about throttle in about 3 seconds so obviously the fuel is there to feed the ponies. Since mine is working sweet, not going to change anything. I have only had this boat for a little over a year so I have no idea as to its history. But with compression running 129, 129, 129, 130, marking on the water jacket by the mechanic at the dealership where I bought it, and being 18 years old, I'm not tweaking the carbs.....besides boating alone, it would be somewhat difficult. Thanks for the info anyway.
    woa there big guy, my reply was to Rusty the OP...but seeing as you are all defensive,just becareful playing with spark plug heat ranges, I've seen many a melted piston.. I'll just keep my experience to myself .. have a great day.

  22. #22

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by flyingscott View Post
    There is no magic spark plug to fix your motor. Do you have the Factory manual? Have you looked at the accelerator pumps? Is the fuel pump in good condition? Carb floats set right? Link and sync done correctly? On the water and warm motor? Have you tried running with a different tank? WOT timing does not affect the idle.
    Ok, fair enough. It never hurts to try something someone else has had luck with. Yes, I of course have the OEM manual, and there is only one accelerator pump on this motor. Re: initial post, I rebuilt the fuel pump and have visually inspected the carb throttle shutters for sync - which is essentially what the manual states.

  23. #23

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by Rockfish9 View Post
    I believe this engine is running rich,I've seen the same problem many times..what is your idle timing set too, the "newer" ones seem to run better at TDC or 2 degrees before which results in a little faster burn.. try leaning out each carb with the boat in the water in forward gear, do it slowly, as the engine begins to stumble, back out the width of a screw driver, repeat with the second carb.. I bet you find a big difference, I'v found most of those engine, epically the 2000 and up dont need to b quite a rich as people think. When right, they can troll and run as god as any 4 stroke..I've worked on a lot of them, and owned 2 , still running 2004 everyday running lobster pots and trolling for stripers.

    Thanks Rockfish9,

    Thanks. That's something I haven't done yet this year and since the replaced reeds, but will do on the water this weekend and will post back results. So far I've added 1/4 turn more than factory recommendation of 1 and 1/2 turns rich (which I know isn't the end-all), to keep from lean popping.

  24. #24

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by Docksidemarineservices View Post
    Get the factory manual. Read the link and sync procedure over and over again until you understand it completely and can almost recite it word for word... Then follow the manual and perform it on your engine, follow the directions to the T..... Then you will know your engine is set up correctly.

    Make sure the carbs are installed in the proper order.

    Carbs are installed in proper order, marked WME80-1, 2, 3, 4 (top to bottom) - first 2 have the idle mixture adjustment screws. I have the factory manual in hard copy, will take your advice and will report back with results.

    Thanks

  25. #25

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by flyingscott View Post
    There is no magic spark plug to fix your motor. Do you have the Factory manual? Have you looked at the accelerator pumps? Is the fuel pump in good condition? Carb floats set right? Link and sync done correctly? On the water and warm motor? Have you tried running with a different tank? WOT timing does not affect the idle.

    Also, as I understand it the accelerator pump handles 2 things, fuel injecting to aid in starting the motor (servo actualtion) and fuel for the bottom 2 cyl's to aid in transition from 2 to 4 cyl operation (button at the top), which normally occurs at or around 1800 RPM or above, on my motor anyway.

    Not sure, but it sounds like that wouldn't have much to do with lower rpm and idle issues, under 1800 rpm... Please correct me if I'm wrong for sure.

  26. #26
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    What is your serial #? As I recall the bottom 2 carbs have accelerator pumps. The primer only goes the top carbs. I.could be wrong but need your serial #.

  27. #27
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by flyingscott View Post
    What is your serial #? As I recall the bottom 2 carbs have accelerator pumps. The primer only goes the top carbs. I.could be wrong but need your serial #.
    the primer has 2 ports ( 1 in each reed block) in the manifold behind the carbs and feeds all 4 cylinders for starting...

  28. #28

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Quote Originally Posted by flyingscott View Post
    What is your serial #? As I recall the bottom 2 carbs have accelerator pumps. The primer only goes the top carbs. I.could be wrong but need your serial #.

    Posted SN in the first post ;-) 0T464942. Pretty sure, based on both visual inspection and the oem manual...

  29. #29

    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Ok, but there is only one pump.

  30. #30
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    Default Re: 2002 Merc 115 HP ELPTO 2+2 LOWER RPM & IDLE ISSUES

    Look at whatever they are using for an accelerator pump. They are known to start leaking by , when that happens they idle goes to crap. Or you could have lower carb have a carb float slightly off. Link and sync are critical on those.

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