#6

[speedpro]

Box of flash bits arrived today. The CRF250 rotor is a perfect fit on an MB100 crank. I got the whole rotor/stator/reg rec and capacitor. Very nice gear. Need the power for the Ignitech and the powerjet solenoid on the new 36mm carb.

[speedpro]

The carb isn't downdraught but is trick in every other way. You can see in one photo how the rotor fits the taper on the crank perfectly. The reg/rec is a tiny little unit compared to previous units I've played with. The generator is a single phase output but with 8 poles should generate enough power. It'll need to power a water pump as well on the next engine. I'm gonna try using the capacitor as per the original system but will go with a small gel cell if there's a problem.

[speedpro]

and the stator

[Bert]

Hi SpeedPro.

36mm Carb; are you going to do anything to it or actually keep it that size?
I've got its brother sitting in my shed but I though it would be far to big for 100cc even in the state of tune of yours...
I might have to re-think the 28mm now

[F5 Dave]

Its pushing it, but RS125s come std with 39s & they sometimes run 41s.

28? pah! my 50 runs a 28.

Actually that isn't a bad size to be starting with

[speedpro]

28mm is fine for at least low 20s.

The 36 is being tried on the suggestion of the Wobbly one. The 34mm carb is amazingly good. The old 32mm round slide I always thought was a nice carb but the 34mm is better everywhere.

The 36mm carb has a solenoid controlling the powerjet which is the main feature I was after. The TPS may help make it a nicer bike to ride but funnily enough it's pretty nice now. The thing is you're either full throttle or hard on the brakes so the TPS shouldn't be such a great advantage, apart from helping to determine when to stop the powerjet.

[Bert]

...

The 36mm carb has a solenoid controlling the powerjet which is the main feature I was after. The TPS may help make it a nicer bike to ride but funnily enough it's pretty nice now. The thing is you're either full throttle or hard on the brakes so the TPS shouldn't be such a great advantage, apart from helping to determine when to stop the powerjet.

Thanks SpeedPro.
Well that’s something to seriously think about. I’ve got the Kx version but the powerjet is set rather low in the slide position (straight, where yours is pointing upwards).

Here I was pondering if I should close up a part of my 6 petal reed block and reduce the volume of the intake (and a smaller carb ~28mm). Now, not so sure.
I guess I’ll have to wait and see the results that you come up with....

I see your point about the TPS (that was the original point of getting the Kx carb: to expand the ignitech setting options).

Have you thought about a high temp thermocouple (with relay output) in the exhaust/or head to act as a retardant trigger??

Dimensions of the MB100 shaft / CRF rotor ? please; I’m having a shit of a time finding something to fit my project.

[richban]

I might have to re-think the 28mm now

Some number from the flow bench. Might help.

My new head will flow 125cfm. (32.5hp)

28mm Mikuni 110 cfm, (27.5hp max potential)

Carb in the bin. Next.

[speedpro]

The entry to my reed block matches the carb mounting flange and as smoothly as I could (be bothered) flows out to the ends of the reed cage. It almost looks like it would restrict the flow as the view of the reed petals is obscured but I've tried to keep the cross-sectional area uniform until it gets to the petals. With the splitter in the middle it definitely has a restrictive look to it.
The power jet is tapered on the back face, it doesn't open on the end. The position would seem to indicate that it flows at lower throttle settings.
I don't know about the shaft or taper sizes but the rotor is about 75mm OD. After getting the rotor and stator I would reccommend them, though I probably should wait till it's all running. The rotor is reasonably light though I haven't weighed it yet, so the engine should be real responsive now. More than standard as I'm not running the balance shaft.

[speedpro]

I'm running a 6 petal reed block with only one petal each side. I don't think it needed such a big reed block until the software said the engine was going to make some serious horsepower. The thing is that if the engine is going to be revved hard then the free length of the petals needs to be reduced to increase their resonant frequency. This results in shortened reed ports once the reeds open reducing the cross-sectional area. To keep the area you need to go wide, by possibly going to 6 petals. I think something like a Yamaha RD 4 petal reed block with the centre bridge taken out of each side gives you enough area for your average bucket engine. Certainly enough for low-mid 20s hp. You need to sort out the piston port on the MB as well. Pete Sale does a very nice job of grinding in one extra each side. It's nice and reliable and flows well.

[F5 Dave]

Yes that's the logical thing to do with the inlet port, I think a few people have come up with that independently. I did my old H with a dremel & a ball shapped bit, but you have to be careful not to port yourself into a shape that traps the bit.

[speedpro]

slow progress, or it could be because there's more to it than you might think. Finally got the adaptor spun up and carved chunks off the back so it'd fit in the case. Drilled holes, tapped a couple and hey presto, more or less ready to go. Interestingly I dummied it all up on a pair of H100 cases you see in the photos and then found the MB100 cases are different. The oil feed to the main bearing from the transfer area is different and I had to carve a new relief in the bottom. I've decided to cut off sections that aren't needed to mount the stator.

[F5 Dave]

Well there's something. Never thought they were anything but the same cases. Why would 'onda change them?

[jasonu]

Well there's something. Never thought they were anything but the same cases. Why would 'onda change them?

Purely to mess with Bucketeers.

Nice looking work Mike.

[Skunk]

Interestingly I dummied it all up on a pair of H100 cases you see in the photos and then found the MB100 cases are different.

Weren't you listening when I told you they were different? Sketchy has found that out too. It's not just the mounting points that are different... Anyway - enough of my shit.