fuel flow metering for twins

[centerisland]

A separate thread about metering Yamahas got me thinking...I'm going to add a Lowrance LMF-200 for the (2) Honda BF40As...do folks with twins generally install one sensor (for a combined consumption), or separate sensors (for individual consumption)? I recall that for the smoothest flow the sensor is supposed to go _before_ the filter element , which is where the fuel line commonly splits for the two engines.

My gut feel is that it would kind of interesting to see the fuel flow for each engine - and it could highlight a possible tuning problem with one engine - but ultimately a combined usage would be more useful.

[drjohn71a]

While I do not know about the 40 hp Hondas, the Honda twin 150's on my TomCat have the Honda Gauges. There is a separate readout for each engine, or you can toggle to read the combined flow, so there must be separate flow meters on each line.

John

[rogerbum]

Keith,

If you're going to go to the added expense of adding fuel flow gauges, I would suggest that re-design the fuel system to provide a separate filter for each engine and put the flow meters in front of each filter. The factor designed system had only one filter and that reduces some of the value of the twins.

[Doryman]

I researched this for my 22 (there is a thread somewhere about it) and the wisdom of the collective revealed that the fuel flow through those Honda 40s was so small that the flow scan devices were rather inaccurate. I have fuel flow capability with my Yamaha 150s as part of the Command system on the Tom Cat, and it works great, but for the 22 I've decided that the empirical observation method will suffice.

Warren

[hardee]

I looked into this too, and for my Yami twin 40's, carbed, it was way to much money and work for the proposed questionable accuracy. The 50's EFI verson, has internal fuel flow readout capability via the engine electronics display available to the helm, (I think MFD or a separate gauge) Matt at Kitsap helped with that info. He may have more and more recent.

Harvey
SleepyC

[centerisland]

Ah, if only 8 year old Honda motors were NMEA 2000 compatible!

Yes, a single 40hp carb'd motor running at other than close to WOT is unlikely to register accurately on the little flow meters - even two of them together wouldn't be enough.

However, what I think I'm really looking for is a way to measure changes in load, trim, etc at cruising speeds. From my previous experience with an LMF-200 and a Yamaha 90, I know it isn't worth it to try to meaure total consumption when, after all, you can see the level in the tank at a glance.

Roger's point about redoing the fuel system is provocative - but rather than put a filter on each engine, I think I'd rather be able to dynamically switch filters while running if one filter became plugged - I have that setup on my diesel trawler. Except, I dunno - when you start down that road you really want to draw from a day tank and a lot of extra plumbing, and from experience I know that extra connections mean increased chance of vacuum leaks. The KISS principle would lead you to...what the factory did in the first place!

I think you guys may have just talked me out of this!

[thataway]

You want some filter before the transducer--to prevent debris clogging the transducer turbines. Sintered bronze filters will work, as will small automotive type of filters. Remember that the transducers should be aligned in a vertical fashion.

I run separate flow meters on the Suzuki 150's. At ldle I certainly feel that they are suspect--but when you start pulling 20 to 30 hp, they seem to be very consitant. I hav not compared that with the engine computer read out.

I like to know what each engine is doing fuel consumption wise.