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  1. #1

    Default BF90 2006 Carb Model Must Prime twice on restart to get cruise on hot days 100F +

    I have a center console with a 2006 Carbureted BF90.
    Purchased with only 70 hours in November,ran 100 ours since then. My problem is that when I run it on freshwater lakes where it is hot Nevada (1,300 feet), Utah (3,600FT) it requires that I prime again after restart in the afternoons when weather is hot, 100F +. Prime once before the restart and again during acceleration to get fuel to the carbs after it stutters from fuel starvation. Once at cruise no problem. When running in cool weather at sea level or no problem.
    I replaced the tank as a precaution at 70 hours. I did not replace the check valve but everything else in the tank is new. I just replaced the fuel prime bulb, line and the gas connector to the engine to try and remedy the problem last week but that did not fix it. I will take a portable tank with me in a couple of weeks to verify the fuel between the tank and the primer is not the problem and will also change all the fuel filters and the check valve.

    When it misses it is actually smooth like it is running on one pair of carbs or 2 cylnders. It does not stall ,it just seems to run smooth on 2 cylnders until the fuel fills up the carb or carbs again from priming. This only happens after the day has warmed up and the engine has heat soaked after shutdown. After the problem is resolved through priming it will happen again when I slow down to trolling speeds. This only happens though after it is heat soaked in the afternoon on hot days.


    Kind of wordy but is an unusual problem. Thanks for your help.

  2. #2
    Join Date
    Nov 2009
    Location
    temecula, ca., usa
    Posts
    2,611

    Default Re: BF90 2006 Carb Model Must Prime twice on restart to get cruise on hot days 100F +

    Hi,
    What is your idle rpm set at? If it's under 900. You may not be spinning your fuel pump fast enough. I'm assuming from what you've written is that you have an in hull tank. If you're trying to pull fuel from lower down in the hull, with less atmospheric pressure pushing on the fuel to help the pump, I can see how this could happen.

    I can also see how your portable tank, setting up on the rear deck or, at least, higher up in the hull, might just mitigate the problem.

    I believe you could set your idle up a bit and that could help. I don't have documentation for your 90 but I think you shouldn't go above 1,000 rpm.

    There's a chance you may have a very slightly weak fuel pump but with only 170 hours I think that's the last place I would go. I would hate to throw a new pump at it only to find it made no difference. Although, I do like having spares on board.

    Let us know what happens when you use the portable tank.

  3. #3

    Default Re: BF90 2006 Carb Model Must Prime twice on restart to get cruise on hot days 100F +

    Quote Originally Posted by jgmo View Post
    Hi,
    What is your idle rpm set at? If it's under 900. You may not be spinning your fuel pump fast enough. I'm assuming from what you've written is that you have an in hull tank. If you're trying to pull fuel from lower down in the hull, with less atmospheric pressure pushing on the fuel to help the pump, I can see how this could happen.

    I can also see how your portable tank, setting up on the rear deck or, at least, higher up in the hull, might just mitigate the problem.

    I believe you could set your idle up a bit and that could help. I don't have documentation for your 90 but I think you shouldn't go above 1,000 rpm.

    There's a chance you may have a very slightly weak fuel pump but with only 170 hours I think that's the last place I would go. I would hate to throw a new pump at it only to find it made no difference. Although, I do like having spares on board.

    Let us know what happens when you use the portable tank.
    Thank you for your comments. I did notice the bottom fuel pump was a little oily as compared to the top pump. I think what I'll do is buy a pump as a spare and go back out and recreate the problem. Then see if the portable tank resolves thed starvation. While the problem is happening I'll try to isolate which cylynders/pump are affected.

    Mean time I'll do a compression test and change the filters
    and the thermostat.

    Thanks again. Probably 2 weeks before I can get back out.

  4. #4

    Default Re: BF90 2006 Carb Model Must Prime twice on restart to get cruise on hot days 100F +

    The RPM is 900 at idle.

  5. #5
    Join Date
    Nov 2009
    Location
    temecula, ca., usa
    Posts
    2,611

    Default Re: BF90 2006 Carb Model Must Prime twice on restart to get cruise on hot days 100F +

    Yes, 900 is probably where you will want to keep the idle set at.

    Another thought I had is that, even though she's only got 170 hours, she's got 11 years on the books.

    Time takes a toll on some things and rubber fuel line is one of them. You should give all lines/tubing under the hood a good going over for any cracking that might allow for small fuel leaks or, especially, air getting in the system.

  6. #6
    Join Date
    Mar 2009
    Location
    Cincinnati, OH USA
    Posts
    4,170

    Default Re: BF90 2006 Carb Model Must Prime twice on restart to get cruise on hot days 100F +

    Ditto to most of the things that Jimmy said.

    Idle should be 950 plus/minus 50. I prefer it to be a little high....close to 1000. Carburetor balance makes a big difference too.

    The bottom fuel pump should not be oily. If you buy a new one, be sure to get a new o ring for mounting. Your whole issue might be a bad lower fuel pump.

    Changing fuel filter is good to do. If the motor keeps running good as long as someone squeezes the squeeze bulb, then once the fuel restrictions are eliminated, I would look at the fuel pump/s.

    Mike

  7. #7
    Join Date
    Nov 2009
    Location
    temecula, ca., usa
    Posts
    2,611

    Default Re: BF90 2006 Carb Model Must Prime twice on restart to get cruise on hot days 100F +

    Thanks for pitching in Mike. The oily fuel pump blew right by me! Of course it shouldn't be oily!
    But that might just be a mount seal?

    Anyway jlc1906, Mike's the guy you want to hear from and when he suggests bumping up the idle, then I would definitely do that.

    And something else Mike brought up that had escaped me was the carburetor synchronization.

    You mentioned that it seemed like it might be running on only two cylinders and the carbs being a bit out of sync might be contributing to that.

    More food for thought.

  8. #8

    Default Re: BF90 2006 Carb Model Must Prime twice on restart to get cruise on hot days 100F +

    UPDATE: I Replaced the fuel pumps, Thermostat, Spark Plugs, Fuel Filter under the cowling, the
    external Fuel Filter and checked all hoses for leaks. I’ll run it this weekend and expect it to run without a problem. The
    problem seems to occur when it is very hot. When it starts happening again I’ll use an external tank, some clear tube a to look
    for air, and a vacuum gauge to zero in on the fuel feed system. The idle is right at 900. When it happens again I’ll look to see if it idles slower
    while warm.

    Thanks for the help. I’ll update the thread when it starts happening again but that likely will be when it warms up in May.

  9. #9
    Join Date
    Mar 2009
    Location
    Cincinnati, OH USA
    Posts
    4,170

    Default Re: BF90 2006 Carb Model Must Prime twice on restart to get cruise on hot days 100F +

    Don't forget to raise that idle to almost 1000 rpm.

    Mike

  10. #10

    Default Re: BF90 2006 Carb Model Must Prime twice on restart to get cruise on hot days 100F +

    Quote Originally Posted by hondadude View Post
    Don't forget to raise that idle to almost 1000 rpm.

    Mike
    Thank you for the help and the reminder to set at 1,000. I will do that Saturday. I have all new fuel lines to the fuel connector which is new. I should look at replacing the lines under the hood as suggested to get everything up to date.

  11. #11

    Default Re: BF90 2006 Carb Model Must Prime twice on restart to get cruise on hot days 100F +

    If the above doesn't work, check this.

    I've seen fuel starvation from old fuel lines being soft and collapsing, no leaks but collapsing. The heat may be making the lines from your tank to the carbs soft and or if any of the lines are old, ethanol can mess them up.

    You can buy marine and non marine gasoline fuel line. I used a non marine that i had on hand and it would bend and block the fuel so I replaced it with marine grade.

    The difference is the walls of the non marine fuel lines are thinner than the marine grade, it is much thicker and stiffer and unlikely to bend and collapse. Not sure what size your fuel line is, but I'd recommend 3/8's fuel line. With that heat you have, you need as much clearance as you can get. You can also get insulation for the lines to protect them from the sun, it'll help to keep the fuel cooler in your heat.

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