Logo
Page 1 of 2 12 LastLast
Results 1 to 30 of 34
  1. #1
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Low RPM? On 1991 30hp evenrude

    Hi clever boaters,
    I have a 30hp evenrude. Runs sweet as a nut all round. However at wot I can only achieve just over 4000rpm? The book say between 5200 & 5800rpm? Iíve checked everything I can....timing is good at wot, all ignition checks out? Could this be a prop issue? Iím running a 10/13, which is within the book recommendations. I guess I could go 10/11 which may give me 400rpm more but Iíll still be below the books minimum? Iím getting approx 15mph which seems underpower for my 15ft sea hog? Could the taco be inaccurate?
    Iíve bought a hand held taco to test & calibrate.
    Apart from the prop idea I canít think of any other reason why Iím having this problem? Could a coil be failing at high rpm? All is smooth & solid but the figures are low?????
    any suggestions would be greatly appreciated.
    faithfully Mike

  2. #2
    Join Date
    Sep 2010
    Posts
    20,529

    Default Re: Low RPM? On 1991 30hp evenrude

    A 30 year old motor.------Post compression test values here.----Check the flywheel key ( timing changes with a sheared key ) on that motor.----No you can not find a sheared key with a timing light !-----Does primer bulb go hard ?---Pictures of you boat ?

  3. #3
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Hi thanks for your reply....the motor is quit old but not had a hard life.
    the flywheel key is fine, prime bulb gets hard.

  4. #4

    Default Re: Low RPM? On 1991 30hp evenrude

    Is the carb opening all the way at wot?

  5. #5
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Hi,
    good sujestion�� But yes, all linked & synced?

  6. #6
    Join Date
    Sep 2010
    Posts
    20,529

    Default Re: Low RPM? On 1991 30hp evenrude

    Did it run OK and to 5500 RPM on this boat last year ???

  7. #7
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    I’ve made a lot of changes lately....new prop, new ignition & a rpm gauge which I never had before so I’m not sure what it ran at previously? The new ignition is a1 & has been set at wot to the correct degrees 30 I think. I’m convinced it’s a load issue �� compression is good & balanced.
    I’ve only had one opportunity to test on the water recently & conditions weren’t great.
    im thinking prop pitch & perhaps the angle pin at the transom?
    Any sujestions?

  8. #8
    Join Date
    Feb 2001
    Location
    Central West Florida
    Posts
    15,845

    Default Re: Low RPM? On 1991 30hp evenrude

    A 30hp engine on a 15' craft is usually pretty well set with a standard prop BUT even a 15' craft can be loaded pretty heavily and require a prop change.

    Do the spark plug electrode ends look close to being identical... and major differences?

    With the engine running at idle and again as fast to still be considered NOT excessively racing... with insulated pliers, pull the spark plug boots off the plugs so as to compare the power loss (drop test) which should be identical... is it? When underway, at full throttle, are you comfortably sure that the engine is running on both cylinders, the timer base (spark advance) under the flywheel is advanced properly, and the throttle butterfly is wide open?

    If so, especially if the rpms increase when the loading is as light as possible... my bet would be with the propeller.

    Note that the spark advance question can be tested simply by (Engine NOT running)... spin the prop and shift into forward gear... advance the throttle fully... observe that the timer base is up against its stop (full spark advance).

    Pertaining to the thrust angle pin.... sighting the cavitation plate just above the propeller... best to have the rig on a trailer so as to set the pin so that the cavitation plate is as close as possible to parallel to the bottom of the boat, and approximately no lower than 3/4" below the bottom of the transom (The most average setting).

    Let us know what you find.
    Last edited by joereeves; 09-24-2020 at 01:17 PM.
    We occasionally have questions. If you fail to answer, it may affect ours.

  9. #9
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    My goodness is this the legendary Joe Reeves?
    ok will address the best I can....
    When you say the spark plug ends are you referring to the gap? As both are new & identical?
    Ill have to do the drop test next time on the water....but timer plate is hitting the stop....& butterfly it horizontal ��
    Can I please ask....what is gained by checking the timing stop with the engine in forward gear? As I’ve tested be releasing the cable at the throttle arm and pushing it aroun by hand?

  10. #10
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Couple of other questions Joe...if I may.
    what is the purpose of the drop test? I’m pretty sure it’s firing on both. Although I know it will run surprisingly well on one.
    also what size prop would you recommend?
    faithfully Mike

  11. #11
    Join Date
    Feb 2001
    Location
    Central West Florida
    Posts
    15,845

    Default Re: Low RPM? On 1991 30hp evenrude

    The electrode portion of the spark plugs (after running some time) should look pretty close to identical. If one is the normal brownish coloration and the other is loaded up with carbon.... a problem of some sort exists.

    The "drop test"... If the drop in power seems about equal on both cylinders... consider the the condition of both cylinders to be equal.

    I thought a mention was made of the compression readings... don't see it now, must have been a different post. What are the compression readings?

    The timer base question... simply pushing the timer base to its stop doesn't tell you exactly where it stops via the control box throttle handle.

    The prop question... I was never a prop man my friend... but others here, I'm sure, will jump in here with that info.
    We occasionally have questions. If you fail to answer, it may affect ours.

  12. #12
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Thanks Joe Reeves.
    Will do a compression test Asap

  13. #13
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Hello again Joe....
    could I please just run something by you???
    firstly I’d like to explain I live a couple of hours away from the water so testing under load is kind of a slow process for me. I will run by the sujestions you’ve made.
    I was just thinking �� when I flush the motor with the muffs or in barrel I’m pretty sure I could reach the hi end RPM...not that I would make a habit of it....Can we conclude anything from this? Ie:- a load issue?
    im not questioning your eta experience, but I’m pretty sure cylinder pressure is good. I’ve lined up the cavitation plate with the hull...makes perfect sense ��
    I’m just try to cover as many bases as possible before next water test��
    Really appreciate you attention on this. Would also like to add....it’s not that I’m to tight to pay an expert to look at the motor, it’s just that it’s awkward in NW U.K. to test the motor at wot without being offshore.
    faithfully Mike Inky

  14. #14
    Join Date
    Sep 2010
    Posts
    20,529

    Default Re: Low RPM? On 1991 30hp evenrude

    You can not test a motor for " power " when it neutral or no load.----It will rev up running on one of 2 cylinders.----But good trouble shooting will find where the issue is.

  15. #15
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Yes I totally agree...it’s just a read this thread write up online about Rpm & load issues....and it was saying that if an outboard will reach high rpm in the barrel it should reach high rpm under load....if it doesn’t reach high rpm under load it’s most likely a prop pitch issue?
    Would you or any other clever boaters know the ideal prop pitch....30hp evenrude on 15ft sea hog

  16. #16
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    I’m running a 10/13
    engine seems sweet it’s just feels like it me being held back��

  17. #17
    Join Date
    Sep 2010
    Posts
    20,529

    Default Re: Low RPM? On 1991 30hp evenrude

    Some will argue----Yes they sound really sweet running on one cylinder !!-----Read all the books and online you want.-----But some simple trouble shooting on your part will find the issue.----Perhaps find a local shop that has a proper " test propeller " to measure motor power-----No point it dropping prop pitch if motor is not running with peak power output.

  18. #18
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Ok fair shout.
    Please don’t take this out of context....so your basically saying....the motor could be running on one cylinder?

  19. #19
    Join Date
    Sep 2010
    Posts
    20,529

    Default Re: Low RPM? On 1991 30hp evenrude

    Or one cylinder at peak output and one that is at 1/2 output.---Check fuel pump impeller ?----Changed water pump impeller recently ?--Your boat ( load ) might not allow your engine to reach peak RPM.-----Do you know if tachometer is accurate , yes or no ?-----Good compression means nothing.----What are your actual numbers ?----Fact ---You have to determine condition of your engine before changing prop pitch !----Bring it over and it would be easy to figure out !

  20. #20
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Hi thank you for your replies.
    Rebuilt fuel pump this season, intend to replace impeller very shortly before U.K. winter. Think i had it done about 18 months ago.
    I can’t remember the compression numbers of the top of my head, but last test, Spring....they were well balanced & good according to manual.
    I can appreciate what your saying about engine condition & I know I could be wrong but I’m pretty sure it’s in good order. I’ve had in in the shop last two seasons & have been given the ok by the shop. However I’m not sure they tested at wot. They reverse the boat on the trailer into the slipway & run it through the range.
    im not 100% sure on my tacho, so I’ve bought a hand held to compaire & calibrate, but have yet to test.
    Pretty much everything I do is by the book & buy OMC parts wherever possible?

  21. #21
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Could a coil be failing at hi RPM? Surely I’d know? Last test reached around 4200rmp & I can tell you it was as running sweet as a nut? The boat load is a valid point, but that said when these boats were built they came with this motor?
    regardles of rpm I’m only reaching approx 15mph?
    don’t get me wrong it’s fast enough not to ruin the day, I would just like to be able to see the max if needed.

  22. #22
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Here’s a clip prior to setting wot full timing.

  23. #23
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    And another on the same day after a bit of tinkering.....think I had not attached fuel line & emptied carb....but just for reference

  24. #24
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Struggling with clips?

  25. #25
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Both coils check out good by the way?

  26. #26
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Try again with YouTube https://youtu.be/H1pnN1fwOEw

  27. #27
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    And the other cliphttps://youtu.be/xQdKpmrkSL4

  28. #28
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    The first clip shows fuel starvation do to empty tank

  29. #29
    Join Date
    Sep 2020
    Location
    NW U.K. England Blackpool
    Posts
    71

    Default Re: Low RPM? On 1991 30hp evenrude

    Hi Joe,
    you’ve been kindly responding to my query....
    For a reference here are a couple of clips (wish I had more & more recent) The first clip is after I fitted new ignition....I used the Joereeves method to set the timing at this stage.
    The second clip is on the same day, after some tinkering....please note the stall is due to fuel starvation, as tank was on empty & fuel line wasn’t attacked.
    Your thoughts on theses clips are fully appreciated.
    faithfully Mike
    https://youtu.be/xQdKpmrkSL4https://youtu.be/H1pnN1fwOEw

  30. #30
    Join Date
    Jul 2014
    Location
    Buffalo, NY
    Posts
    172

    Default Re: Low RPM? On 1991 30hp evenrude

    If I were you I would address that transom ASAP.

Page 1 of 2 12 LastLast

Similar Threads

  1. Advise & help 30hp 1991 evenrude
    By Mike Inky in forum Johnson Evinrude Outboard Forum
    Replies: 4
    Last Post: 09-13-2020, 07:38 PM
  2. 1997 evenrude 30hp no water pump operation after rebuild
    By andrea736 in forum Johnson Evinrude Outboard Forum
    Replies: 3
    Last Post: 05-28-2017, 08:43 AM
  3. 1991 Evenrude vro 200hp initial start no spark
    By JimmyL in forum Johnson Evinrude Outboard Forum
    Replies: 26
    Last Post: 08-26-2014, 10:05 AM
  4. What are Mariner like 30hp 1991 yr
    By jimminy in forum Mercury Mariner Outboard Archive
    Replies: 5
    Last Post: 08-17-2007, 10:11 AM
  5. Converting manual b86 30hp Evenrude to electric start with b88 20 hp Johnson starter
    By martman in forum Johnson Evinrude Outboard Archive
    Replies: 1
    Last Post: 05-08-2003, 10:18 AM

Posting Permissions

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