Will I get my 100 ready in time for Taupo?

**F5 Dave** · 22nd December 2014, 12:46

Barrel back from an extended stay getting honed, this time of year & all, but the good news was a light lick and its all straight, so the extra support is working well.

**Grumph** · 22nd December 2014, 19:25

Originally Posted by speedpro

With this chatter about boring crank webs I've been thinking that instead of working to reduce the stroke why not increase the stroke, run 52+mm pistons and use a 24mm carb into a plenum.
With a stroke of 51mm(+1.5 over stock) and 52mm piston capacity is 108cc. If you have a rod with a 22mm pin and increase the stroke the full 2mm with an 1mm offset bored pin hole you get a stroke of 51.5mm and running the same 52mm piston end up with the engine at 109cc and 53mm piston makes 112cc and if you want to really push it go to 54mm piston for 117cc.
Rob has already proven that the 24mm carb is not actually a restriction.
You could have a velocity stack of the exact right length entering the reed block dead straight and the entry to the velocity stack would be the bottom of the plenum so anything that dropped out of suspension still went into the engine. Either that or have a small diameter hole in the base of the plenum that drained down into a similar hole in the cylinder or crankcases.
This would also have the benefit of not having to try and maintain some sort of acceptable mounting angle for the carb as it could be mounted at any angle feeding the plenum.
The plenum could also be an odd shape to fit around frame tubes without having too adverse an effect.

The limiting factor on the big MB would appear to be the transfers...when you go as big as 54mm in the bore the top angles change - and not for the better. Passage volume is pretty much optimised for 100cc, not really enough room for the bigger ports needed for bigger displacement. that's why i was going to put a DT125 barrel on one...everything is optimised for 125 already.

just how far do you ride the scooter anyway ? looks like plenty of thinking time but a tad dodgy posting while riding...

**koba** · 23rd December 2014, 11:41

Originally Posted by Grumph

The limiting factor on the big MB would appear to be the transfers...when you go as big as 54mm in the bore the top angles change - and not for the better. Passage volume is pretty much optimised for 100cc, not really enough room for the bigger ports needed for bigger displacement. that's why i was going to put a DT125 barrel on one...everything is optimised for 125 already.

just how far do you ride the scooter anyway ? looks like plenty of thinking time but a tad dodgy posting while riding...

My 54.5mm barrel suffers from this badly, the transfers look horrid plus they are far too low with them being cutback with that roof angle.
I'm going to try it anyway.

**Grumph** · 23rd December 2014, 14:01

Originally Posted by koba

My 54.5mm barrel suffers from this badly, the transfers look horrid plus they are far too low with them being cutback with that roof angle.
I'm going to try it anyway.

Might well be Ok for kart tracks - more torque but less peak HP than a well developed 100 has been our result. Some sucesses but in hindsight we'd have been better to stay at 100.

**koba** · 24th December 2014, 06:37

Kart tracks are different and most need spread of power over peak but I think on the balance of it the watercooled 100 is the way to go for an MB.

This 54.5mm barrel is watercooled so I won't compete with it but I think I will give it a try on my road MB100 sometime, just for giggles.

**F5 Dave** · 24th December 2014, 08:28

Well here's my attempt at trying to get a reasonable curvature to the MB transfers. Clearly I've just stuck some inserts in & glued them in place. Next step is about 1/2 doz gluing iterations with grinding in between to get a finished job. I'll also have to look at the outside curve & match to the inner, but it was a bit naff before. Then there is the twist, but I'll try this first.

This should pull it kicking & screaming into the 80s. Wish there was a 100cc MC18 or newer to be starting with.

**Grumph** · 24th December 2014, 08:39

Is this a fresh barrel without the water jacket ? if so at least you're free from the constraints of finning and can add material to the outside of the transfers to get a better curve...If not, it's been welded on once, pull it off again if you have to.

**FastFred** · 24th December 2014, 08:40

I like your work, curving the transfer duct walls and eyebrow exhaust ports, very interesting.

**F5 Dave** · 24th December 2014, 09:36

Its the same WC barrel I brought down to Chch Bob. I hate weld into Honda barrels, despite the LC jacket, but that caused enough issues.

**kel** · 24th December 2014, 10:02

Hi Dave
I use an Pratley steel putty to fill and shape the transfer ducts. The putty allows the shape to be roughly formed by jamming into the duct with a small spatula then using a pre-formed tool to mash into final shape (as Mike also mentioned)

**F5 Dave** · 24th December 2014, 13:37

Hmm that might be easier for the bottom bit, might try some. Repco it seems. The inserts gave me some consistent shape if I got them in the same place. Jolly hard this stuff in such small places.

**F5 Dave** · 3rd January 2015, 18:13

Well I've been tickling any tickling these transfers as
One, I didn't do a very good job initially. So hard to see up there
Two, the MB is a bit lop sided from std.

Anyway enough obsessing and just time to sew it all back together. I'd have liked to do a leakdown test but my new slip manifold means making an expanding mandril dodah.
Engine goes in frame tomorrow and dyno sometime after.

**mr bucketracer** · 3rd January 2015, 18:37

Originally Posted by F5 Dave

Well I've been tickling any tickling these transfers as
One, I didn't do a very good job initially. So hard to see up there
Two, the MB is a bit lop sided from std.

Anyway enough obsessing and just time to sew it all back together. I'd have liked to do a leakdown test but my new slip manifold means making an expanding mandril dodah.
Engine goes in frame tomorrow and dyno sometime after.

post a picture of your dyno run , want to see how pecky it looks , the gt only seems to run of the main so hopfully time will fix that

**F5 Dave** · 4th January 2015, 19:33

Really I was close to crying when I got home.

People seem to sling things together and get great results. But I have to find new problems. So I started with getting the woodruff key off but sorted that out.
First run full of hope and trepidation. I go to sleep every night thinking about my transfers or ex port. So I was hoping for some more spread. Heck even some more power.

What I got was 5hp less and 500 less rpm than the already peaky spread. Some jet changes reduced that to about 2.5 less but the spread is still gone.

Worse still is it jerks really violently on decell. Tried new plug and huge pilot. But I'm concerned to ride it like that.