Jeff jet 1750

[Jeff B]

Yep the starter is a monster, with the small gear on flywheel it spins the 125 faster than an old Grenada running at WOT.....only have to touch the starter button and it's running.
Weight is piling up though...
75kg all up with big 20ah battery(no charging circuit...yet) and a full tank of premium gas.
Ready for water test....

[Jeff B]

https://youtu.be/BB7hDriCyFo

[Jimmy Jet]

Brilliant. How did the powervalve go?

[Ross Goldsack - JBNZ Immediate Past President]

Looks quite snappy..... maybe I'm just thinking of the belt?

[Jeff B]

Only pushed the power valve lever once, rpm increased but not sure how much, that video is with the low exhaust port mode so there is heaps of power on tap. Waiting on a tacho so I can get some accurate data but promising first run.
The belt, well the belt is holding up fine.....for now.....

[Henry]

Looks like the relatively big pump and gearing worked a treat. Do you think it would work with a putts four-stroke like a Honda XR250?

When customers have an idea to do something a bit tricky i can almost always send them to the relevant Jeff thread now days. The belt drive was the final missing piece.

Maybe sounds even worse than a 300cc tho....

[Jeff B]

Nup the little screaming 125 does sound slightly better than the lugging 3 hunny......slightly.

Henry, the xr250 is a dead duck...air cooled,
Look at the 4 stroke scooters with cvt belt drive...there are some 250cc models that might work, some of the chinasian cvt buggy engines are the same, I think yamaha knockoff?
20hp might be ok?

[steelo]

Thanks for the quick video Jeff. Looks brilliant. More More.

[Jeff B]

Bit more testing today.
After an initial flooding problem, bit of swarf in needle valve, got some data runs in.
Minimum plane, about 6500rpm, 25k
Cruises nicely 7500rpm, 35k
WOT 10800rpm, 55k
Hull sits up and cruises nicely, pulls nose down at full throttle, no porposing.
Can probably bang the ride plate up a bit and get a bit more speed but it handles good now.
The belt is still holding together too....

[steelo]

I suppose you can just vary the sizes of the pulleys to adjust speed / rpm. Something we can't do in our boats

[Matthewf/Norbert/TuiDog]

I suppose you can just vary the sizes of the pulleys to adjust speed / rpm. Something we can't do in our boats

Stick a lathe gearbox in it jeff🤣

[Jeff B]

I suppose you can just vary the sizes of the pulleys to adjust speed / rpm. Something we can't do in our boats

Yes that is the benefit of this setup.
Although I think I have it pretty close first with 10,800rpm (goal was 11,000)

[Jeff B]

3mm ride plate a bit flimsy and hanging down a bit so fitted some lightweight aluminum turnbuckles to fine tune the handling.

[Jeff B]

Not happy with the crappy heat wrapped exhaust, now that I now the concept actually works (there was a tiny amount of doubt)
So I started making proper jacketed exhaust, this shape has been designed to optimize power with a strong bottom end, punchy mid range and a screaming top end....

[Warwick Marflitt]

You'd win the NZ Sculptured art award with that creation Jeff!