DrFeelgood

Throttle position, power setting, etc. Just where the throttle was at and the resultant rpm, load, etc when the failure occurred.

articfriends

iTrader: (1)

When I tune on the water some boats are going 2800, 3000 cruising easy at 15%, 17% throttle at say 77 map/kpa, I would tune for low , maybe mid 13s at that point if i knew the distribution on engine was ok, on the other hand, I seen boats where your going 3200 and its at 40, 50% throttle or at least at 88, 90, 92 map, maybe even getting close to getting into boost, that would be tuned into low 12s. most these boat efi tunes run between 70 and 100 map once under a load, I would tell you to rescale your tune in your holley program to expand the tables in that area so your transition wont be 12.0 to 13.5 to say 14.5 real close together (you could be bouncing in the lean cells). I know you can scale map vs rpms vs fuel. A guy called me a few years ago, was building a 540 for his formula, wanted me to tune his mefi, he chose to just buy holley, skip having it tuned and skip having it dynoed. Never heard back from him, a buddy bought a snowmobile off fb marketplace and I helped him go pick it up. Turns out it was this guy. Started talk9ing to him, he had a boat sitting there with engine out. Tells me yeah he had talked to me about it then just got holley. said he torched a cylinder with the holley and didn't understand why. was a tb mounted holley on poor design open plenum (dart intake), one of the most horrible distribution intakes of the open plenums. I asked him what his wot target was, said real rich like 12.8 or so, I laughed and walked away, wonder how motor 2 went for him!

TomZ

iTrader: (2)

I'll second that being that it was my thread. Smitty, your information is spot on and I have also learned a lot from your discussions and explanations especially around this subject matter. I think I can speak for most of us here when I say that we really look forward to your comments and input.

Back to the thread...

compedgemarine

to add to what Smitty said on throttle position. on the open class race boat with Stirling engines we found that in smooth water with a long straight run you had to pull the throttle back to about 50% to keep it off the rev limiter. this was a 46 Skater so as it aired out it got lighter and rpm went up so at the end of the straight you were at 7800 rpm at 163 mph and half throttle. hard to map for that on a dyno or even in the water. we had to look at a lot of data logging and create a map on the computer to allow for it.

Waterlife

Hey everybody, thanks for all the input and will let you know my outcome...
Thanks Smitty for your time, i had an EFI tech guy look over my engines and he believes its all about the fuel pumps, he said fuel pumps are not good enough to pull out the top of the tank (2 foot High) thru a filter and then push the fuel back up into engine.
Im going to fit surge tanks and use a lift pump from main fuel tank to pre pump filter 100-150 mic - to surge tank -then fuel pump -then filter 75-100 Mic - then up into fuel rail - out to Regulator - return back to surge tank, and then from surge up and back to fuel tank.
Hopefully got this correct... Oh and add a shut off valve.

articfriends

iTrader: (1)

so what pumps are they or were they and in relation to fuel tank what was the height? Ive gotten modded merc mpis to around 560 to 580 on the stock 190 lph, is it mounted quite low though as you know

Smitty275

If your pump is mounted even or lower than the tank bottom, once the pump is primed its no longer really "lifting" the fuel. I know nothing about the pumps you have. But if it was fuel pump you'd have melted parts of all the pistons. Your issue is the fuel map. On fresh engines that weren't dyno tuned you need to keep it 12.5:1 and work leaner from there. Letting it get to 14:1 without testing is asking for trouble.