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Splash reading above got me thinking, it's been a long time since I got messy with these engines, I think there is an idle screw per say, located near the arm that drives the timer base and below where the timing mark is located (I think) this will achieve what you are looking for but could depending on how much you need to turn it induce a stumble just off idle etc, anyway it's a concert but give it a go when the engine is fully warm - if I am not actually thinking of another engine it should be there, you can always go back to where it was before you started.
Hi BM I sort of agree but because advancing the spark on these even 1 deg must also advance the idle timing an identical degree as a solid block because the timing plate is a solid 1 piece unit, bit like a slot size, not one that can be stretched independently at any end, if I explained it well enough.
Bit like the trap for people new to outboards who think that if the specs call for 28btdc max spark advance they think that if the set it to this figure like say a person can do with the spec for a car it will work and not go pop! always a shame.
No manual I have ever seen actually states the max advance spec must have the idle advance subtracted from it and this figure is the TRUE max advance specification because advance in these is as a solid block of degrees there is no vacume or centrifical advance like in a car. Reliable but in the age of the dinosaurs.
It won't matter if pickup timing was 0 degrees or 4atdc or 4btdc because the max advance is set by the max advance stop screw, so lets say you retarded the pickup timing by 5 degrees that won't alter the actual degrees of max advance.
It simply means the timer base is moving through a larger arc thats all. I understand your thinking, it just not correct.
The idle for splash's engines as with most outboards is achieved via the adjusting of the pckup timing. The Yams differ from this by an actual carb adjustment for idle speed.
Hi BM yeah you could be right about Splashs engine and it's what I thought earlier but an idle screw rings a bell, wish I had a manual still, it should be in there if it exists, might be the 90deg V6 crossflows I am thinking of.
Still cannot agree, unless we are actually near saying the same thing but I have not twigged.
No worries, think we will need to agree to disagree this time around....again??
I'm not quite sure where your confused FNQ but run with me here mate.
Lets say we disconnected the timer base and with the engine running rotated the timer base to the TDC position (using a timing light obviously).
Now, you have two stops for the timer base, one in a retarded direction and one in an advanced direction agreed??
Lets say the max spark stop is set to 24 degrees for example. The distance between TDC and max spark is a set distance. TDC is TDC and we have mechanically stopped the timer base from going beyond 24 degrees of advance.
Likewise with the pickup or idle timing stop. We set that to whatever the case may be.
TDC on the timer base remains a known constant and the arc of the timer base swings between the pickup/idle timing stop and the max spark stop. Therefore, retarding the pickup/idle timing by whatever amount doesn't alter the position of TDC or max spark it simply allows the arc to become larger and therefore retard the engine further.
Took the boat for a test drive after replacing gearbox and left hydrofoil off.
I am now getting 45kph @ 4700rpm.
The motor will reach 4800-4900rpm if I trim the motor up more but then starts porpoising, I had an adult and child passenger and did not make any real difference them sitting at the stern or standing at the helm, boat still porpoises.
The cav plate now sits somewhere between 15-20mm higher than the bottom of the boat.
Is this okay?
Sometimes the prop did ventilate a little on turns.
What prop pitch would allow the motor to obtain the extra rpms needed?
It looks like you are getting an extra 11 km per hour using an extra 700 rpm which you could not get before and then you still have around 200 rpm left.
A question on the porpoising is, What were the water conditions like. Were you on the bay with a little chop or on a waterway with no waves to speak of, near glass.
When you trimmed the boat up, can you trim it to a point where it starts to lose speed and you hear ir start to aerate, or are you not being able to trim it far from the transom because of the porpoising.
Did anyone check to see where the cav plate was when you were travelling at speed.
It sounds like you are on the right track with lifting the propeller (removing the spacer). It may still need to have the prop changed to get more WOT. I cannot offer any more advice there.
In relation to the cavitating during turns, that is why I have the foil on my motor. It stops the air being sucked down easily during highspeed directional changes.
I will attatch some more pics showing
A/ the distance the motor is away from the transom - trimmed in all the way
B/ the distance the motor is away from the transom - trimmed to maximum planing speed at WOT ( any more and it draws air)
C/ the line of the keel when the motor is fully trimmed in
D/ the line of the keel when the motor is trimmed parallel to the keel line ( the cav plate is about 25 mm above the keel line which is a little hard to tell from the picture)
Dave sounds like you are winning, I forget your leg ratio so cannot chase up where you really are with your figures but much better regardless, you have a 13.5 diameter prop which is your problem now it seems, your choices to go down in P really suck, you will get your rpm up easily but at the expense of efficiency. If it were me I would look long and hard to find a 13.25x15p any brand, this will allow more revs + keep the boat traveling forward at an acceptable rate. You are not traveling faster enough ATM to get the hull working so if you can fit a prop with less dia once it gets to over 50kph somewhere the hull will lift prop slip will reduce and the effect will gather up and you should be away toward 60kph - in theory. if you go down in P and keep the same diameter you may not ever travel fast enough to find the sweet spot where it all comes together.
Exactly where my boat is, nothing on the shelf that suits in any way but badly, so I make my own.
You sound handy you could always work the prop diameter yourself and get there, I know how I would fix the prob but each is to their own.
If you decide ot get jiggy with it can let you know basicly how to go about it -back yard style or you can give it to someone, hope it is alum.
One other thing that someone has already stated is that this could be a small motor to be pushing this boat.
With that in mind - it could get to a point where it is doing the best that it can, and will never achieve better results.
It's "Your call" on this given the advice from quite a few minds and the changes you have made
I must say that I had a 5.2 metre fibreglas half cabin with a 115 hp on it and it ran very well. Then again if it had a 85 on it I think it may have struggled. It could be worthwile to look around at other boats that are the same and see what they are powered by.
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