J30a V6 Bike Carby Engine Build

[Kakapo76]

You are right, the single stage will struggle to hold onto the v6 torque.
My opinion would be try an 18 or 19 bullet, I think a 21 would slip too. 
In reality, I think you will struggle to be ever really happy with the single stage.
I just drove a new 3.9m LVB with j30 (injected) and new flo pro 2 stage. Impressive package, popped up good, cruises along happy as @3000rpm 
Flat out about 4600rpm, 80ks.

Thanks Jeff, my current impeller is a rejigged 19 so will see if it can be bent (pitched up) to its original spec. Appreciate the feedback.

[Kakapo76]

I picked up a new 19 deg Scott bullet from Jetboat Base.
Installed it and took her up the Waimak on Saturday- revs now down to 5600 WOT,
Cruise now happy south of 4000 and she goes like a cut cat. Didn't have GPS so will need to check numbers but I am much happier. I am going to try a 112mm insert and see if that allows me to pull back to around 3800 rpm but still have decent speed.

Oil pressure 80 PSI WOT 20 at Idle.

185deg F water temp- absolutely rock solid. Ran up to the Pylons and back and it never shifted.

Oil temp 60degc- (post cooler) never moves either. Before installing the cooler it was well north of 135 Deg C

I am going to lift the vtec cut-in to 4600 rpm and lean out the mid-range slightly- but otherwise, this is finally doing what I had hoped.

I am getting some fuel standoff above the carb trumpets so think that air cleaner/ airbox setup might be a good idea.

[Kakapo76]

Question Time:

Has anyone modified a Hamilton (or any other big unit, not jetski) to include a scavenge style bilge tube (similar to what jet skis have)? I have a couple of pockets where the water ends up that I cant get my bilge pump to clear due to tight spacing and I am getting water flung around the engine bay on hard turns by the flywheel.

MY solution is to drill a hole in the side of the tail cone and run a venturi tube to the low spot so it's constantly sucking any water out as I am running the engine.

I plan to put in a check valve to prevent it from filling up the bilge when the engine is off (or making it hi-rise).

Thoughts?

[Jeff B]

The venturi tube needs to be positioned after the smallest orifice in the jet unit doesn't it? That's behind the nozzle?
Anywhere in the tailpipe will be making pressure wouldn't it?

[Paul]

You can use the second 'pressure feed' going through a cavity to create a low pressure, which is then connected to the lowest point.  You need to be careful in the hose routing and sometimes add a 'vacuum break hole', to avoid water syphoning back into the boat when at rest.

[Kakapo76]

The venturi tube needs to be positioned after the smallest orifice in the jet unit doesn't it? That's behind the nozzle?
Anywhere in the tailpipe will be making pressure wouldn't it?

Yes, my bad- that's what I meant- I have a trim nozzle so that's adds complexity.

[Warwick Marflitt]

How about something like this run off the second pressure feed off the pump or tap and fit a third one plumb it higher than the waterline with an external hull air bleed and it wont siphon...

[Kakapo76]

That's a clever idea- I like it.

I ended up welding in a siphon, but it's below the waterline at rest and that brings water in, I have a one-way valve I am going to put in the line to see if that works.

I will post pics.

Would have done so already except I managed to blow a couple of litres of coolant out into the engine bay via the overflow tank 1 minute from the ramp, I thought I had blown a head gasket and was about to give the boat a Viking funeral, but let it (and me) cool down, topped it off with a litre of water and it totally behaved itself back home- I think the thermostat stuck shut- no idea why had been operating perfectly the previous 3 runs.

When it cooled down again it siphoned all the excess coolant back into the engine and there's no evidence of water in the oil or a gasket leak- I am crossing fingers it was a stuck thermostat only.

Has anyone else got ideas?

[Warwick Marflitt]

Blocked sand trap,
stone,weed,stick,plastic bag stuck in raw water feed hole inside unit
Did the exhaust note get louder from no water going thru it and Lots a steam not H2o out exhaust?
The cause will be evident. Pull out Thermostat and look for rubbing or binding. Test it buy boiling in pot of water on stove with thermometer to check opening temp? or just replace! But its prob new from your build and only done a few hours and less than 50 temp cycles since new? Check radiator cap rubber..... loose hoses, air in system, Wax in ears

[Warwick Marflitt]

More dry bilge ideas. Diaphragm pump sucking thru a sponge...... Who wood a thunk that?

https://lifeempirically.com/2018/03/12/build-your-own-diy-arid-bilge-or-dry-bilge-system/

[Kakapo76]

Hi Warwick,

I saw that clip on youtube- quite a neat idea, definitely stop you from blocking the tube with leaves or debris.