Twin 2007 Honda BF90D on a 25 Cruiser - Tach and Throttle Q

[Water-Doug]

Ahoy hoy,

We are on our 2nd trip with VEGA, and we are figuring out most her systems and quirks. The most concerning quirk is the engines (460 hours ) require drastically different throttle to match RPM. The starboard engine requires a lot more throttle and struggles to keep up with the port engine. With even throttles, if the Port is at 5000 RPM the Starboard can be as low as 3800. The differences is less at lower RPM.

At 450 hours she had all her fuel lines and filters replaced, and she's had regular maintenance. My first instinct is electrical, but she's reading 14 volts on the dash.
I've also noticed the water spout on the starboard engine is a spray (seems like more volume) than the port engines steady stream.

Uploaded a video here for diagnosis: https://youtu.be/KHAgWyxqn98?si=leLDcYM6PMp4GiKM

Should I start with electrical, then spark plugs/ reg maintenance, before attempting to calibrate tachometer?

Cheers,
Doug

[srbaum]

Doug, are both props the same diameter and pitch.

[Water-Doug]

100% same diameter. I'm 90% sure they are same pitch.

[Water-Doug]

UPDATE; After cruising on nice glassy water for a few hours, it seems the starboard tachometer is reading high. If we keep throttles even (ignoring RPM) she's steers straight, and the engines sound similar*.
At 5000 RPM on the port Tach (reads 6100 on starboard tach), we are going 24-25 Kts. Does this speed match anyone else's experience with twin 90HP at 5k RPM on glassy water?

Assuming the starboard tachometer requires calibration, I am still curious why the starboard engine's water output is spraying water in a fan vs a steady stream.

[thataway]

Are the engines fuel injected or carburetors? You want both engines running at the same RPM--if not you may be lugging one of the engines.

Tachs can be wired incorrectly, as well as primary tach issues. There are mechanical tachs you can use, or use one of a number of other outside tachs: inductive, timed light tach, and similar. they are not expensive, and a way to get started.

The spray may be a small amount of debris in the hose or oriface==not that unusual.

[C-Wolfe]

I had similar issues on my Honda 50s, tapping on the tach will bring the needle back to where it should be. that lasted a couple year until that didn't work anymore, so I replace the tach and that solved my issues. It sounds to me that you might have a similar problem. Tapping on the gauge was a lot cheaper then replacing them, wish it would have lasted longer.

[-Waypoint-]

Check your throttle control cable on the engines, ensure the pushrod throw on each engine are matching. They may have got out of adjustment or the stopper nuts have loosened.

lower both engines. remove engine covers, with engines off, push both the shifters all the way to the stops (full throttle). Go back and compare the location of the throttle positions to match. Adjust the engine throttle pushrod on the engine to match the rpms of the other engine. You may be able to measure the pushrod and adjust it to see if you can get it to match with the other engine. (nice to have twins for this reason)

[Foggy]

Electronic gadgets aside, a lot of information about twin engine rpm
synchronization can be had by simply using your ears.

When they are in synch, they harmonize. Find it at various speeds. Then
intentionally briefly unsynch them and notice the difference in sound. Then
look at your throttle positions after re-synching them. If uneven, refer to
suggestions above.

Kind of like estimating your latitude by measuring the declination of Polaris (our
North Star) off the horizon when you don't have GPS, like old times...

Aye.

[C-Wolfe]

Most tachometer are not engin specific and need to be adjusted for your application, if you look on the back, you should find a selector dial, normally turn with a small screwdriver. Make sure they are both adjusted the same.

[Water-Doug]

Appreciate all the replies.
1) the Honda BF90D VTEC is fuel injected.
2) after more tinkering, I am pretty sure the Port Tach is reading high.
3) will give several of the suggestions a try!
Look forward to many more hours of cruising around at 18-25 Kts !
Thanks,
Doug

[srbaum]

Doug,
I mess with a lot of outboards each year and I use a simple handheld tach, to just idle and also check rpm at various intervals. My experience is that the older tachs are not accurate (pre NEMA 2000). I have a very inexpensive handheld tach and I have used it on hundreds of outboards over the last 8 years with no issues. I do enough outboards that I had to buy extra reflective material, but even that was not expensive.
https://www.amazon.com/AGPtek®-Professional-Digital-Tachometer-Contact/dp/B004Q8L894/ref=sr_1_6?crid=1HUXOL0U5P40U&dib=eyJ2IjoiMSJ9.HcYK9iBLPRzFoKFI-Ye3tEPfRC0qUQhV4eCFH4IRL7E8nN-OB9Yr4alZKIugyxB3wzkkvu_AIf7z15xWDg8cBvLn5MR3ZsWv_fblwGUQCD-lwuxg6fRdt3h-UU2OMtO2Xz2Mr9FpPAfgRJpHN5JO3TvAAQ7R3Qnfgg_Bd2fVRm-S2F_2TPbecEUAPe3n2lCT-dH0EAq-VIBV0lZ_-VXWwq8kFOESbSt-d23PTIVY6iA.qgb3BGwvQb_ypqW_-moRQZLIJUH1vg37rLOTbX1_2wU&dib_tag=se&keywords=hand%2Bheld%2Brpm%2Btachometer&qid=1713795242&sprefix=hand%2Bheld%2Btach%2Caps%2C127&sr=8-6&th=1

[thataway]

For some reason that long URL didn't work for srbaum (or me), but I believe if you search for "AGPtek® Professional Digital Laser Photo Tachometer Non Contact RPM Tach" in Amazon for about $19, this comes up. It certainly looks like a great product (of China with many similar units and slightly variable prices; This was far cheaper than any hand held non contact tachs I had used in the past. A great way to confirm your dashboard tach.