New project - Seahunter 520

[Bigplumbs]

Could it be that the gasket seal on the carb bowl is leaking in air. This is often a cause of poor idle.

A new gasket might fix your problems

Dennis

[ChrisParish]

Cheers, Denis. I’ll check that out.
I am going to head down to Poole on Monday and strip / clean / rebuild the carb to see if that helps.

[ChrisParish]

I did some research as to how the advance works on the Selva and it is ultra simple and if the advanced was broken then the entire ignition system wouldn't work. Given that the engine runs at all then we can surmise that the advance / retard is probably working.
So I went down to Poole and removed the carb. I then gave it a darn good clean, paying special attention to the idle jets.
Engine reassembled and test run.
The idle is much better now and the engine starts much more easily - it can now be started with the regular recoil starter, rather than requiring me to wrap a rope around the flywheel.
I bought a cheap laser tacho to accurately measure the RPM - long story short: don't buy cheap laser tachos. Darn thing was useless.

Having established that the engine idles and starts more easily I found an old clean dustbin, filled it with water and ran the engine in the bin rather than on muffs. This is where I encountered a problem - when I drop the engine into gear it stalls. In order to stop the engine stalling the idle rpm when in neutral has to be raised. Unfortunately the idle RPM is now far higher than I would like and the engine goes into gear with quite a bang. Now, given that the RPM still drops massively when you put it in gear then there isn't a lot of energy involved so the chance of breaking the gearbox is not especially high, but it is disconcerting.

So the plan now is to tinker a bit more and get the boat out on the water and put a few hours on the motor in the hope that it improves as it runs in. I will be taking the Honwave as well as a safety / recovery boat in case we have problems.
More pics and info to follow!

[warder54]

Just a thought - is compression OK? not enough power to keep running when trying to turn the prop at idle?

[9-R]

Majority have two separate modes or systems between idling and under load whether carbed or fuel injected. Seems you have the idling side of things worked out and hopefully it runs well enough under way but there is a problem with the transition. Sounds to me that you aren't getting enough fuel or air as it changes over from idle to main jets? If you cleaned the main jets and passages, I'd look at the butterfly valves to make sure it's getting the air it needs when it needs it. Adjustment of them was a little tricky on my old Jeep engine to get balanced right.

[9-R]

Hi 9R,

The carb as a main jet, an idle jet and then a series of three small transitional jets / drillings. It was the transitional jets which were bunged up because even at idle it draws fuel from the first of the transitional jets.

Hoping to get it on the water in about a fortnight and we’ll see what happens!

[9-R]

We have given up on the 1978 Selva. It was just not going to play ball.

Just arranged to buy this from a guy down at Warsash

It’s a Suzuki DF50 from 2004. It used to belong to someone who did powerboat training so it’s had a long life but has been well serviced (apparently)
It started up and ran beautifully on the test stand. A few cosmetic bits here and there but nothing some paint and polish won’t fix. I couldn’t get the dials to work, but someone has bodged the wiring from the remote to the dials so I may have to fix that.

Price was good and collecting on Friday.

I’ll keep you posted.

[Roy54]

Nice one @ChrisParish. I'd love to see your seahunter sometime. I'd love a boat with a cabin

[harrison]

Should go well with the 50 on the back.

Good luck with bolting it all together. Measure ten times, drill once...and all that jazz.

[ChrisParish]

@harrison I am hoping it goes well - it should!
We will make a template from the transom mount, stick it on and then offer the engine up. Then, if we are happy, I will get busy with the drill.

Picked the engine up today (it’s in the back of my car at the moment). Going to redo the paintwork on the plastic parts this winter.
It also needs the anodes changing and a bit of TLC on the skeg. It started and ran nicely and everything under the hood looks good.

There will be pictures.