Vintage Grumble

VGs Tiny Squirty Thing

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2 hours ago, Vintage Grumble said:

Also, not sure what they do about gearbox/clutch/extra junk in bike motors when they put them in boats? Just leave it in there or remove it all? 

A few have done it but its a hassle, most dont even go there and get jetski running gear to drop in. 

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Just something to consider, if you hadn't. 

In terms of a panic situation, in a jet boat you have no steering when you aren't on power. So if you need to turn in a hurry you need to power on, not off which depending on the situation may well go against natural instincts. 

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12 hours ago, tortron said:

how many rpm does a jet unit like, 10000?

It sounds like a lot of big boy jet boats with V6's and small/jap V8's aim to do around 4500rpm, I guess you have to try get the bite of the impeller correct so you have enough grunt to drive it, but not too much grunt that you can cause cavitation? / I don't really have a clue TBH. 

52 minutes ago, anglia4 said:

sequential shifting boat skids sounds pretty rad

I've seen a few mini boats with road bike motors, but never looked into how they do the drive? I'd be tempted to strip the gearbox and clutch out or even remove the housing if possible, to make it simpler and lighter. But as mentioned above, probably not worth the effort. 

23 minutes ago, kyteler said:

Just something to consider, if you hadn't. 

In terms of a panic situation, in a jet boat you have no steering when you aren't on power. So if you need to turn in a hurry you need to power on, not off which depending on the situation may well go against natural instincts. 

True that, I spent a lot of time on stand up jet skis as a young man, so kinda know what to do. Mind you, jumping off a stand up is easier than getting out of a tiny boat in a hurry / i'll probably struggle to get into trouble in such a slow boat, lololololols.

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Yeah I feel like you're gonna be WOT even when slowing down, damn it'll look cool doing it though, if maybe a bit clown car spec though puhuhu.

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2 hours ago, Vintage Grumble said:

It sounds like a lot of big boy jet boats with V6's and small/jap V8's aim to do around 4500rpm, I guess you have to try get the bite of the impeller correct so you have enough grunt to drive it, but not too much grunt that you can cause cavitation? / I don't really have a clue TBH. 

I've seen a few mini boats with road bike motors, but never looked into how they do the drive? I'd be tempted to strip the gearbox and clutch out or even remove the housing if possible, to make it simpler and lighter. But as mentioned above, probably not worth the effort. 

True that, I spent a lot of time on stand up jet skis as a young man, so kinda know what to do. Mind you, jumping off a stand up is easier than getting out of a tiny boat in a hurry / i'll probably struggle to get into trouble in such a slow boat, lololololols.

1.  Yes 'cavitation' is the water boiling because your're drawing too much vacuum into the unit than what you can flow out the back end.  It sounds like you're driving a concrete mixer.

2. From what I read the solution is to drive the jet unit off the back of the clutch, typically have to manufacture a bellhousing up for a new shaft. 

3.  If in doubt, right foot...

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Leave bike motor complete and couple jet unit to the sprocket shaft then select what gear is 1-1 drive and do hoons, leave clutch intact so you can clutch in for no drive

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31 minutes ago, HighLUX said:

clutch in for no drive

That would be so convenient.  I have to take my driveshaft out if I want to run the engine up at home

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41 minutes ago, h4nd said:

Cuuuute.

*cough* expansion chamber *cough*

Would an expansion chamber work on a twin with single exhaust outlet? I might remove the big exhaust block on one of the spare motors and see if it has two ports under there. 

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That's how the Dai is plumbed, and apparently makes a big diff to the performance. Pics of outlet? You might be able to fabricobble something up :)

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