Speed - Page 3

trevbouy · 18 January 2024, 23:08

Sorry about missing the video, the link I saw was black, I missed the other one.

Watching the video what you have appears to be a vacuum jet progression step that is perhaps to large.
As the throttle is opened the vacuum increases and another opening in the throttle tube has more fuel drawn through it. If it's slightly too large a step then the engine revs will rise to balance fuel and air intake accordingly with fixed throttle input such as you are doing. I noticed in the video a further rise at higher revs suggesting a further higher revs port.
As to what could be done I don't know as it's inbuilt to the carbs.

Carbs such as the SU used a varying tapered needle in a fixed jet which gave smooth progression.

trevbouy · 18 January 2024, 23:31

Hmm that led to more thinking.
In a multi carb setup if one idle jet is partially blocked then progression on one cylinder would be a jump that would also effect other cylinders slightly leading to the revs rise.
Also an out of balance set of carbs might give you uneven progression. They need to be vacuum balanced at idle using a vacuum guage and set by adjusting the idle screws on the throttle inkage. Vacuum balance devices can be cheap plastic or expensive garage kit.

Fenlander · 18 January 2024, 23:31

Sadly us oldies with our carb thoughts won't help as it's an efi motor.

>>please explain how a tacho will help me.

Well my thinking is that your hull has a specific speed at which it is super responsive to going on the plane... and the outboard by chance at this speed has a non-linear rev rise. So I wondered if you changed the prop pitch a little would it be possible that the engine revs were no longer rising in this way at that specific hull speed. If there was any credibility in this thought the start point would be to see if your prop is already ideally pitched or under/over. If either of the latter then it would give more leeway for changing the pitch.

I'm interested to hear what they think they can change in the engine's response with the diagnostic kit... I thought such changes would be in the realms of a specialist mapping/tuning company and outside the work a dealer would undertake?

Salty Pete · 19 January 2024, 05:22

https://www.powersports-diag.com/en/...&id_currency=6
G'day Fenlander.
This is the diagnostic tool that I saw. It looks like it can change some parameters in the engine. What do you reckon?

Fenlander · 19 January 2024, 08:33

Hmmm I'm not sure. I had that kit (different brand but same software and 40% of the price) when I owned my 20efi and if anything I reckon you will be limited to perhaps changing the idle speed and maybe max revs but I don't remember it having any menu to alter the fuelling map.

tinker · 19 January 2024, 08:55

Why not take the prop off and run it in a tank to see if it's a throttle adjustment issue, without a prop the revs should increase with a relatively linear throttle movement as the load on the engine is always the same, next to nothing.

trevbouy · 19 January 2024, 09:12

I'm going senile. I didn't see anywhere it mentioned efi, doh !

Salty Pete · 19 January 2024, 23:10

I posted a message yesterday but it got lost. I used quick reply so maybe you can only post small replies.

After consulting with my Suzuki manual it suggest a method of selecting the correct prop. To work out where I am at the moment I think I need to do a sea trial to not only work out more acurately the exact speed the boat is going on the plane but also at what revs.

Hey Fenlander I need a tacho (who would have guessed

)

I have ordered a tacho from Ebay it should arrive early next month. It is going on the next available camel train. Joys of living in West Ozz.

Steve509926 · 19 January 2024, 23:28

Hi Pete, pleased you've taken Fens advice and got a tacho to determine if you have the right prop.
Only one thing to add at this stage, once you've fitted the tacho, cover it in petroleum jelly! They are not 100% waterproof!

Salty Pete · 20 January 2024, 01:16

Quote:

Originally Posted by Steve509926

Hi Pete, pleased you've taken Fens advice and got a tacho to determine if you have the right prop.
Only one thing to add at this stage, once you've fitted the tacho, cover it in petroleum jelly! They are not 100% waterproof!

Thanks Steve

I did have a choice of two. The one I chose stated that it was waterproof. Although in my past experience Ebay waterproof goes by the international waterproof standards of "do not operate this device within 10 kilometers of moisture".

Salty Pete · 11 February 2024, 03:43

Hello again. Fenlander suggested I put a Tacho on my boat so I can workout where I should go in selecting a prop.

I have uploaded a video but since this has now become an Engine/Prop problem I have uploaded it in that section.

Kristoff · 14 February 2024, 13:00

I still don't think you have a problem, I just think you have a boat thats designed to plane easily.

If you give any planing boat enough throttle to allow it to climb up over its own bow wave to get on plane, and then don't back off the throttle, the revs are going to increase once it gets on plane and you'll pick up speed. That's all that is happening here.

chipko · 14 February 2024, 13:03

Quote:

Originally Posted by Kristoff

I still don't think you have a problem, I just think you have a boat thats designed to plane easily.

If you give any planing boat enough throttle to allow it to climb up over its own bow wave to get on plane, and then don't back off the throttle, the revs are going to increase once it gets on plane and you'll pick up speed. That's all that is happening here.

Well said that man.

Salty Pete · 14 February 2024, 23:51

Quote:

Originally Posted by Kristoff

I still don't think you have a problem, I just think you have a boat thats designed to plane easily.

If you give any planing boat enough throttle to allow it to climb up over its own bow wave to get on plane, and then don't back off the throttle, the revs are going to increase once it gets on plane and you'll pick up speed. That's all that is happening here.

Well Kristoff me hearty, let's consider the evidence against your theory.

One is that I am a senior citizen and have owned and driven several boats and although this is the smallest boat I have ever owned one would think I would know how to drive a boat and realise that one would have to cut back on the throttle once a boat gets on the plane. The other is the evidence I demonstrated with my outboard in a tub of water that it is accelerating without me moving the throttle handle.

There is an area between 6 and 15 knots where I cannot control the speed. It goes from 6 knots to 15 knots when accelerating and 15 to 6 knots when deaccelerating. I cannot get any speed between them.

This has been outlined in my previous threads.

Kristoff · 16 February 2024, 13:55

I suppose you should be able to plough the water with the bow up, with the boat half on half off plane, so if you can’t do that I guess you could have a problem. But as a Highfield owner I can confirm these boats don’t like to do that. My 600 is either tubes in the water and displacement cruising, or it’s lifted it’s skirt up and we are off, running on plane. The transition is barely noticeable and there is next to no bow rise. I've never actually tired to balance it on the knife edge in semi displacement mode, like you can do with heavy fibreglass boats. I'll give it ago when our season opens, I bet it will be difficult.

I’m throttle by wire on my boat and its very smooth, not sure what your setup is. I still think what you are experiencing is a sensitive throttle and a small light boat that wants to plane. Hard to tell for sure without helming the boat though I guess.

Adam350 · 19 February 2024, 04:06

Hey Salty Pete, i enjoy your YouTube vids! Just watched your latest one. I have found as per a couple of different setups attached....that the planing speed can be adjusted using a prop hydrofoil, trim tabs, adjusting the outboard tilt and/or switching to a stainless prop with a prop guard. Unfortunately I didnt record the exact speeds and results. I wanted to throw you these ideas as I dont think they have been mentioned yet.

Happy RIBing!

Adam350 · 19 February 2024, 07:08

Beyond just the change of prop pitch...but I did change it when going to stainless with the prop guard

Salty Pete · 20 February 2024, 11:19

Thanks Adam

They're not trim tabs they're airoplane wings. My little 380 will get airborne.
Did a test run today 100% success. I'll put up a video on Outboards and Props.

Steve509926 · 20 February 2024, 12:11

Quote:

Originally Posted by Salty Pete

Thanks Adam

They're not trim tabs they're airoplane wings. My little 380 will get airborne.
Did a test run today 100% success. I'll put up a video on Outboards and Props.

Interested in seeing what you have done, wish you would have kept it all together in the same thread though.

Salty Pete · 22 February 2024, 06:29

Quote:

Originally Posted by Steve509926

Interested in seeing what you have done, wish you would have kept it all together in the same thread though.

Yes I would have preferred that myself Steve but in forums moderators like people to have their posts in the revelant section.

Since this ended up being an engine and prop issue I decided to move it to deprive the moderators the satisfaction of doing it.