dealer couldnt find reason for low rpms

[yammif70]

have f70la on a 20 foot pontoon dual 25" logs (manitou). boat is a 2011 model with 2010 f70. first year tach said i was running 6300 WOT. had to get tach replaced along with prop. now runs 5300 with just me. put on old bent prop still runs 5300. It has a yamaha SS 11 pitch prop. recently got back from dealer. boat was there 6 weeks.

They said they checked spark, compression, checked throttle, and they ran it with the yamaha program and they did not find any reason to run low rpms, but the computer confirmed 5300 rpms.

I have changed fuel lines from the tank all the way to the internal inline fuel filter. Changed that little filter and inspected the filter after the fuel pump. changed the fuel water seperator mounted on the boat. i have not changed the VST filter.

What exactly does the yamaha program show?

Anyone have any ideas on what it could be? im at a loss without throwing a bunch of money at it im not sure what to do. Dealer supposedly has master yamaha certified mechanic guru. on top of that my third tach lasted 3 minutes before it shutdown and went to zero.

[99yam40]

I would think they would put the yamaha test prop on the motor to see if it will get to spec RPMs. This should show if it is putting out proper HP and running as it should

What happened to the 1st 2 Tachs?

And what about the speed? Did it drop also?

[yammif70]

first two tachs just stopped working or were intermittently working same as current one. Dealer said he would install a yamaha tach at no charge.

did not have gps first year i had it for the speed. first tach said 6300 rpms WOT no matter the load. im thinking the first tach was bad.

only thing i can think is maybe the vst filter is clogged or something.

not sure what the computer reads like if injectors are working correctly or not. i have used ethanol from time to time. hell the manual says its E10 compatible. i usually used the marina gas since i would usually top off before i left for the day.

i took it out yesterday and my gps said i was running 22 with just me in the boat. i get 17-18mph with family on the boat. i would like to gain a few mph but at this point im more concerned about getting in the rpm sweet spot 5300-6300 fully loaded.

Do you think a 9 pitch would be worth a try? i dont think it would raise speed just rpms.

[rodbolt17]

my advice?
ditch the Faria and teleflex crap.
fairia is how you spell junk in italian.

pay to install the correct yamaha gauges.

then go play.

[yammif70]

update

since i last posted. I got a new yamaha tach. RPM's still read the same.

bought a Solas 9 pitch prop as it was the cheapest i could find. rpm went from 5300 to 5700.

back in august i heard hissing noise. had a crack in a top weld of a pontoon. The toon heated up in the mid day sun.

took it to dealer for warranty work to fix it. they told me they got out about 50 gallons of water. and they changed every filter but VST. they didnt do vst because they said all others look good.

took the boat out and now get 6000 rpms. still only get 22 mph with me in it and around 19 with wife and kids. so no real change in top speed going from 11 pitch to 9 pitch but rpms are up.

still searching for the last 300 rpms. ill probably just learn to change the VST on my own.