Yanmar 4lha STZP & Bravo 1 - 2004

[SampoSam]

So finally had the fuel injection pump re-furbed which had a worn diaphragm and some lose part that was letting too much fuel through. This has helped to get to around 20-22 knots using trim tabs ( from 11) flat out but still hard to get on the plane so still not quite right so still checking. As the tacho is the original for a petrol engine and i am running a diesel ( Yanmar 240 i need to check i am getting the correct rpm - flat out says 4,200 but heard there is a mechanical cut out at around 3,400 so obviously not right ?. I feel the boat is always aft heavy and was thinking should try it by putting some ballast in the bow end ?
Any comments gratefully accepted..- 6 months later and ££££ out of pocket still not fully resolved

 

[SampoSam]

perhaps its just a heavy boat and need to use trim tabs always to get on the plane ?

 

[DavidJ]

Just going back to turbo refurb.
Was it a total refurb ie new rotor, maybe the bore resleeved or just a clean up. I’d suggest that if there is more than 15 thou clearance between the rotor and the bore then that could be the source of your problem. Have you tested the turbo pressure on full throttle?
I don’t know your engine but do you have a supercharger?

 

[SampoSam]

no wasn't a total refurb - i will ask whether rotor has been replaced and pressure tested
no don't have a supercharger

 

[SampoSam]

It could be a 1.5:1 there were a couple we did running that ratio. Going to guess your an 03/4

 

[SampoSam]

Hi Rareplank appreciate any comments especially as you know these boats well !

 

[DavidJ]

no wasn't a total refurb - i will ask whether rotor has been replaced and pressure tested
no don't have a supercharger

Ah! the pressure test is done on the boat at full throttle.

 

[SampoSam]

Thanks. First thing i aim to do is test the true rpm- i am told there is a mechanical cut out on these engines of around 3,400 rpm ?

 

[SampoSam]

It could be a 1.5:1 there were a couple we did running that ratio. Going to guess your an 03/4 boat?

Ah! the pressure test is done on the boat at full throttle.

sorry just checked yes was a total refurb..

 

[salar]

I have exactly the same engine and leg, I get 29 knots with a clean bum WOT. Cruise happily all day at 18. I had a fuel starvation problem once that turned out to be an elusive bit of ptfe in the fuel pipe, which only blocked the fuel flow at higher revs. The other BIG difference is the leg trim angle and trim tabs. My semi displacement hull needs to be well trimmed nose down and that makes at least 5 knots difference. Hope that helps.

 

[SampoSam]

I have exactly the same engine and leg, I get 29 knots with a clean bum WOT. Cruise happily all day at 18. I had a fuel starvation problem once that turned out to be an elusive bit of ptfe in the fuel pipe, which only blocked the fuel flow at higher revs. The other BIG difference is the leg trim angle and trim tabs. My semi displacement hull needs to be well trimmed nose down and that makes at least 5 knots difference. Hope that helps.

Many thanks . can i ask what boat you have and length ?

 

[salar]

Many thanks . can i ask what boat you have and length ?

Harley 25, 25 foot semi displacement like a baby Nelson. Designed by TT. Mursall.

 

[SampoSam]

Harley 25, 25 foot semi displacement like a baby Nelson. Designed by TT. Mursall.

ok thanks

 

[SampoSam]

Harley 25, 25 foot semi displacement like a baby Nelson. Designed by TT. Mursall.

Also can i ask what your prop pitch and size you use ?

 

[SampoSam]

Hi

That’s the correct prop we installed when fitting that engine to those boats. Guess you have a clean hull to start with?

check hose between turbo and intercooler is in good order.

The gaskets on intercooler were they all replaced?

Have you checked in the engine bay? The elbows on the exhaust side of turbo can fail/crack giving lack of power. You will notice soot in the bay.

Hi have now refurbed or replaced virtually everything and getting 20-22 knots which is better but still not 3o- knots ? - i am constantly being told i have the wrong prop ?

 

[ChromeDome]

Nah. You've been told about the factors that affect the speed. Mainly weight

Also that 30+ knots is possible if everything is fine and the boat is empty.

The way to get there is by testing and documenting different adjustments, one at a time. Hence collecting facts to know the as-is before hunting the to-be

 

[salar]

Also can i ask what your prop pitch and size you use ?

15 1/4" by 22P Bravo Stainless prop. You should be able to tell if it is under or over propped by the engine revs. If you can't rev to 3600rpm or you can easily rev to over 3600 under load then it could be an incorrect propeller. However, you stated in your original post that you were originally getting 24 knots now only 11 so it can't be a propeller problem, they don't change! If you are losing power I suspect it's fuel supply. Make sure the fuel flow is good at high revs. I had a Trophy that lost power and it turned out to be crud in the tank part blocking the pipe but only at higher flow rates. It had been converted from petrol to diesel and petrol tanks often have a coarse filter in the tank, so the crud collects there and the filter looks clean. Original diesel tanks tend not to have filters, and collect the crud in the inline fuel filter instead. That experience made me check the power problem on this Yanmar and it turned out to be a bit of ptfe in the pipe. Try running the engine from a 25 litre fuel can instead of the built in tank and see if that makes a difference. That's how I identified the problem. On a previous boat I also had the rubber driveshaft slipping. I could go gently up to 5 knots then it just spun so that was pretty obvious.

 

[ChromeDome]

Agreed, but comparison of a semidisplacement and a fully planing, stern heavy, 30+ knots US boat will need to factor in some basic differences.

The OP made another thread about the same matter over here.

 

[SampoSam]

Agreed, but comparison of a semidisplacement and a fully planing, stern heavy, 30+ knots US boat will need to factor in some basic differences.

The OP made another thread about the same matter over here.

Thanks but can't access that link ?

 

[salar]

Agreed, but comparison of a semidisplacement and a fully planing, stern heavy, 30+ knots US boat will need to factor in some basic differences.

The OP made another thread about the same matter over here.

That's why I made the point about trimming the leg and trim tab placement earlier. An accurate rpm reading would help these dignostics a lot.