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  1. #1

    Default BF90 goes into limp mode at full throttle like clockwork

    Hi everyone! Was wanting to pick some brains if I could on an issue my 2003 BF90 is having. The motor idles fine. Runs fine in the no wake zone area. Hit the throttle, the boat gets on plane for about 30 seconds then seems to go into limp mode and goes from 6000-6200RPMs to about 4000-5000. Also when this happens at idle it runs at 2000rpm where when its running normal it will idle at 700. It does this like clockwork.


    We have tried sea foam, draining the gas tank and refilling, new fuel filter, new thermostat, water pump and New spark plugs.


    Anyone else had this issue or any ideas before I have to take to a shop 2hrs away? Thanks!

  2. #2

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Primer bulb stays firm? What about fuel tank vent? Those would be the first two things I would check. Maybe try running it from a different tank if you have a small portable tank handy.

  3. #3

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Thanks yep, Bulb stays firm and vents good. It runs great out the gate but then after about 30sec it just drops the max rpms and you can’t get back over plane. Shut the motor off for 30min or so, starts right up runs like a champ for 20sec WOT then the drop in rpms happens.

  4. #4

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    You have a bf 90 A with carbs to me it sounds like its not getting enough fuel when its demanded because it works on vacuum could be blocked jets or insufficient fuel in the float bowls

  5. #5

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Would that cause it to go into a limp mode with max rpm around 4-5000 and the with a higher idle than normal? Also once it rests for 30min it will run great again, geton plane for again 30sec then limps again. When the motor is on water muffs, I can rev the motor to the same RPM for the same amount if time and it doesn’t miss a beat. Almost seems electrical instead of mechanical?

  6. #6
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    Default Re: BF90 goes into limp mode at full throttle like clockwork

    After it happens do you have to pump the bulb again or will it just start up after sitting without pumping the bulb? Are you getting any fuel in your oil at all (smell like fuel or 'making oil')? I can't remember how the fuel pump worked on our BF90 but the BF50's I seem to remember could push fuel into the oil if the fuel pump started to fail.
    I am thinking that maybe you are emptying the carbs and then when you come back to idle it is running lean and hence revving higher. I wouldn't expect 2000 rpm though to be fair.

  7. #7
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    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Another thought - could the choke be sticking or flapping loose?

  8. #8

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Also don't forget to clean the low pressure fuel filter .

  9. #9

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Bulb still firm and it starts right up with now additional pumping/priming. Checked the oil and didn’t notice any gas smell.

  10. #10

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Also we replaced the only fuel filter that I am aware of this motor has thinking that was the cause. The odd part is it happens like clock work almost like a sensor is triggering

  11. #11

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Irregular fuel pressure from the fuel pump can mess you around too,it should be between 3.5 and 4.7 psi check this .

  12. #12

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    We were thinking that too. It’s just so weird that it’s always at the exact same run Time at full throttle that it cuts back into limp mode. Grrr! Wish they had diagnostic tools for these issues would be a lot easier to pinpoint! Ha

  13. #13

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Best thing for you to do is fit a inline psi gauge and get someone to watch it when you under way .use this as a starting point then work your way through to solving your problem.At +/- 5000 rpm it should read +/- 4.7 psi
    Last edited by Tegweni; 10-14-2018 at 01:46 AM.

  14. #14
    Join Date
    Mar 2009
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    Cincinnati, OH USA
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    Default Re: BF90 goes into limp mode at full throttle like clockwork

    If you squeeze the fuel bulb you are acting as a fuel pump. So, if the fuel pump is weak, squeezing the bulb should compensate. Unfortunately, that does not account for the high idle situation.

    Since this always fails in the same way, that should help the troubleshooting..

    It is possible that it is an electrical issue...

    If you have a timing light or a clamp on kilo-volt meter....get the engine to fail, then reduce it to the high idle. You could do this test at the high speed too, it is just easier and safer to test at low speeds.

    Connect the timing light to each plug wire and compare how the light blinks. They should be the same. One one or two cylinders flash differently, then it is electrical.

    The ignition circuit consists of only pulsars, under the flywheel, to the CDI unit (which internally generates high voltage), then sends it out to the spark coils at the appropriate time.

    If the ignition proves ok, then you might check for air leaks around the carburetors....although it seems an air leak would be there all the time unless it was a crack in the metal which opened when it got warm and closed when it cooled down.

    Mike

  15. #15
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    Default Re: BF90 goes into limp mode at full throttle like clockwork

    I don't know a thing about the 90's. BUT, from your description I would initially think that you could be sucking air under high demand. That would draw air into your carb bowls, and cause the condition you describe. Those kinds of air leaks are a bugger to find. The first suspect is always the fuel line connector, if you're set up that way for a portable tank. The way I try to diagnose those is to put a piece of clear plastic hose from the fuel filter to the fuel pump and look for air bubbles when the condition occurs. If so, you can back up to the problem. Often times it's at a fuel line connection. If no air bubbles observed there could be a failing seal on the fuel pump, so put the clear plastic hose from the fuel pump to it's next connector.
    CHawk 25 DLX

  16. #16

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Thanks for the suggestions! I will give them a shot! I’ll update once it’s figured out. If anyone else has any idea please keep em coming

  17. #17

    Default Re: BF90 goes into limp mode at full throttle like clockwork


  18. #18

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    I pulled off the relief valve cover and found sediment build-up around the valve, the black plastic piece in picture, See attached pictures. I'm wondering if that is causing a flow issue to the thermostat and not allowing the thermostat to open all the way, since this is in the line prior to the thermostat. Tai
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  19. #19

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    I clean this all out and tomorrow will clean out the similar valve on the other side of the thermostat. We will take it out next weekend to test - snow here today in Kansas. I will update if that fix the issue. I’m hoping that it the answer to why it happens at the same time. Will take the voltage meter in case it does go into limp mode still. Thanks again

  20. #20
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    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Are you getting an alarm when the fault occurs? Could it be an overheat? I assume that is the water pressure relief valve you are cleaning and if it is that might explain your problem. Another test is to remove the thermostat and try it briefly with them out. Just been through something a little similar on a pair of BF175's. Unfortunately I never had to do anything to the BF90 we had for 10 years or so and can't remember much about it.

  21. #21
    Join Date
    Dec 2015
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    maplevalley WA
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    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Your under propped if it goes over 6000rpm you can probably add three inches pitch safely.

  22. #22

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    There is not an alarm and the overheat light on the throttle remote doesn’t turn red. With that said I am thinking that due to lack of water flow that the thermostat doesn’t open all the way and that causes it to think it is overheating or maybe it even is and so it goes to limp mode. Will be testing this weekend. Good idea about leaving it out just to test too. Will try that if it goes into limp mode again.

    We are propped right. Before we had this problem we had no issue getting over plane. Towing a tube rider too. We might get to 6500 -I can recal right off since we have been having this new issue.

  23. #23
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    Dec 2015
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    Default Re: BF90 goes into limp mode at full throttle like clockwork

    The BF90 is rated at 90hp at 5800rpm. If you keep running at 6500rpm just start saving now for a new powerhead or a different motor. Your beating that one to death. If you want faster get a bigger motor. IMHO

  24. #24

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Yeah I think the max is usually right around 6k I’m not usually driving but will look. We have the correct prop per Honda’s site

  25. #25
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    Default Re: BF90 goes into limp mode at full throttle like clockwork

    There are too many factors that determine proper prop pitch. Use WOT rpm your model is between 5200and 6200rpm. Ideally you want around 5800 max with a light load. You can easily add three inches pitch that way when someone else takes it out they cannot run it too fast. To increase engine life you want to run around 3/4 throttle for extended periods.

  26. #26

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Thanks again I am not the captain just the mechanic haha. I’ll make sure that is the case next time we can actually get it to that point

  27. #27

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    I had a similar problem and I did a couple of things like fuel pump, cleaned the carburetor and nothing seemed to work. I believe it was sucking in air, even thought I did not see any fuel leaks. I put zip-ties on all the fuel lines in addition to the metal clamps on the hoses for a test and now I dont have the problem. I can say that was the issue since I did a few other minor things at the same time, but it worked. I watched a youtube, where the motor was brought in a second time for engine trouble and the second repair job, the guy put the zip ties on because he suspected it was taking in air.

  28. #28
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    Default Re: BF90 goes into limp mode at full throttle like clockwork

    As I said earlier. You need to check that.

    Not sure I would trust zip ties for a long term solution (or even a short term one.) Small stainless interlocked worm gear hose clamps work best IMO.
    CHawk 25 DLX

  29. #29

    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Yes this weekend we are taking out the boat again to see the poppet cleaning and flush worked. If not we will be looking at the lines and a carb clean. It is my understanding though that The motor will only go into limp mode due to overheating and low oil pressure so again hoping I found the issue. I will update the results

  30. #30
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    Default Re: BF90 goes into limp mode at full throttle like clockwork

    Its never a bad idea to have a spare prop on hand. If sea trials go good do the WOT rpm test with a light load. Rule of thumb is 200rpm per 1 inch of pitch. If it reaches 6500 get a prop with three more inches of pitch for cruising. You will always be able to put the other prop on for water sports.

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