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  1. #1

    Default Twin BF150's, Different Performance?

    I have twin 2006 BF150s. I've noticed that I have to push the throttle further on my starboard (standard-rotation) engine more to reach the same RPM as the port (counter-rotation) engine. The starboard/S-R engine also appears to consume more fuel that the port/C-R engine, which seems strange because as I understand it, the C-R engine usually consumes more fuel. My starboard engine also runs 10-20 degrees cooler than the port engine. While the temperature difference could be related to cooling issues (I plan to clean the little passages in the block as thoroughly as I can next spring), I have done vinegar flushes and salt-away flushes in both engines and put new impellers in last fall, and I'm pretty religious about flushing them after each use.

    Attached are two screenshots from my displays. The temperatures are being read from the ECT4 sensor and were calibrated using an ODB tool as well as an IR gun. The fuel consumption figures are based on signals from the ECMs, which were very accurate earlier this season (within 1%). Caveat: because I troll a lot and alternate engines, and my electronics only track total fuel consumed for both engines combined, I haven't been able to verify the consumption per engine recently when fueling up. It might be possible that dirty injectors or some other 'new' flow issue on the starboard side is resulting in less actual flow than the ECM is reporting.

    Also, while the port/C-R engine increases in RPM smoothly, the starboard/S-R one seems to get "stuck" in the low-4000's. It will then "jump" into the mid/high-4000's, at which point I gently back it down to my preferred cruising RPM of ~4,500. This phenomenon occurs most frequently when I'm starting out on trips (after a ~5-minute warm-up period), and then seems to get better after cruising for a while.

    The throttle position & fuel consumption difference seems to be getting worse recently; any thoughts as to what might cause it and how to troubleshoot?
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  2. #2
    Join Date
    Apr 2018

    Default Re: Twin BF150's, Different Performance?

    First thing I would do is replace the thermostats and get that temp up, Starboard is running too cold which will cause rich fuel mixture resulting in fouled plugs and high fuel consunption along with poor performance

  3. #3

    Default Re: Twin BF150's, Different Performance?

    Thank you! Great idea; will try. I hadn't even thought of that because I replaced both t-stats last fall (or, a mechanic was supposed to...). Will replace and post results.

  4. #4

    Default Re: Twin BF150's, Different Performance?


    -Replaced both thermostats in both engines. That resolved most of the temp difference between the two engines; as it turns out, the mechanic who replaced them last fall put both 60C t-stats in the port engine and both 50C t-stats in the starboard engine... doh!
    -Replaced all 4 spark plugs in both engines; they seemed OK and there was not a noticeable difference between the port and starboard engines' plugs. Visually, all coils looked OK.
    -Decarbed starboard engine (Seafoam; Dunk's method). Not much smoke; it didn't seem to need it.
    -Ran fuel injector cleaner through both engines.

    Attached screenshots were taken this past Sunday after doing the above.

    I'm still having the same problem of less power and more fuel consumption in the starboard engine. Two other facts:
    -As best as I can tell from the last two fill-ups, the actual fuel consumption is 1-2% higher than what's being reported in these screen shots.
    -I did an experiment where I went into a calm area, then shut each engine down and took the other one up to WOT (i.e., heavy load given the other engine was off). The port engine got a little over 4k RPM and was smooth. The starboard engine only got to ~3k RPM and stuttered.

    At this point I'm thinking there probably isn't an issue with fuel delivery. Any suggestions on what to check next? I'm thinking it could be valve clearance...?
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