The Mut

**F5 Dave** · 6th July 2011, 12:47

Check the 32mm one has two air jet inputs that usually live with soilinoids attached to them. At least mine does. I can show you which ones. I think it should run ok with the idle one blocked off (still on in the carb face) & possibly the main one blocked off, or alternatively with a small pilot jet in it.

**koba** · 6th July 2011, 17:33

Originally Posted by F5 Dave

Check the 32mm one has two air jet inputs that usually live with soilinoids attached to them. At least mine does. I can show you which ones. I think it should run ok with the idle one blocked off (still on in the carb face) & possibly the main one blocked off, or alternatively with a small pilot jet in it.

Sweet, When I tried it I blocked them both off.
I blocked the one on the 28mm carb off but now that you mention it the penny drops because the other one wasn't there and instead it had a bleed screw...

**koba** · 27th February 2012, 20:21

Righto...

Working on the bucket constantly gets shoved to the back of the priorities list, well, almost to the back; writing about it is slightly further back.

So, last major news was that it went on the dyno and got it's horsepowers measured.

Mods from std at that point were:

28mm flatslide from RG150
RD350 Reedblock with fibre reeds from RG150
Extra inlet ports each side of the main inlet port
Terrible miss-match (2mm on all sides) in the inlet tract (the 'wrong' way)
Completely std exhaust port, bad miss-match and all
No head gasket with squish at 0.6mm
Leaking head from no gasket or o-ring
Std ignition

Horsepower on the dyno: 11

Yes, seriously, 11 Horsepower.

At 7800 RPM, so it does have a decent turn of torque but that only lasts for 1000 rpm.
There is a wheezy lump of 8 or so horsepower further up in the revs.

My theory is: The terrible ports in and out and the very mild std port timing, combines with dropping the primary compression ratio (With the way I added the carb and reedblock) to not allow the engine to breath and rev free enough to even get on the pipe properly. So, I'm left with most of the charging coming from the now significantly lower crank-case compression.

As an experiment I put the other barrel back on.
This had a "cleaned up" exhaust port which had the standard windows on each side but had been smoothed out between. It wasn't perfect and showed carbon build-up in areas of little flow. I filed and ground until it looked a lot better. I took the chance to widen the port to just under 70% and raised it a fraction. I also changed the shape of the top a wee bit to try and get a bit more area up there while still keeping it ring-friendly. Standard sort of work.

So with this barrel back on and the std reed-block and carb back in place I took it for a run up the street. I soon discovered I'd forgotten the top bolt holding the right footpeg in place had sheared off in the last race.

It gave me a fright for the second time.

From running it up the street (No jetting changes yet) it felt really smooth and linear, definitely revved higher and probably made more power even if just from that. I'd put a new (yes, new!) head gasket in and it had no signs of leaking.

My arse-dyno as terrible so I really can't tell if it has any more grunt or not, we will see if I get it out for a race. It will be interesting to see which basic mod (Ex or In) makes more difference in an otherwise standard engine. Next on the list is to combine both sides.

**Clivoris** · 27th February 2012, 20:59

Thank goodness you are getting on to it. Let Hel's cook her own eggs for a while.

**Henk** · 27th February 2012, 21:00

Originally Posted by Clivoris

Thank goodness you are getting on to it. Let Hel's cook her own eggs for a while.

That's bloody brave from a guy that lives in the same city. Coming to Te Puke fat boy?

**koba** · 27th February 2012, 21:18

Though I'd add a few pics.

Anyone got any thoughts on the funny wee marks on the piston crown?

**koba** · 27th February 2012, 21:19

Originally Posted by Clivoris

Thank goodness you are getting on to it.

There is a high likelyhood my "improvements" could slow it further or kill it...

**Str8 Jacket** · 28th February 2012, 07:24

Originally Posted by Clivoris

Thank goodness you are getting on to it. Let Hel's cook her own eggs for a while.

The way he's going he can move into the shed in Upper Hutt and look after himself......

**F5 Dave** · 28th February 2012, 09:41

Wow it actually looks quite racy from that angle. If you spent as much time on race tuning as you did on finding photo angles you'd be whipping us all.

btw I never bother with head gaskets on these MB engines. Just a ring of Loctite master gasket.

So increasing from 7800rpm to 12,000 one should expect quite some improvement in peak power. Clearly the pipe is a severe mismatch from the std porting. How long is the pipe? Before you start worrying about primary compression ratios, get the porting somewhere near what the pipe needs & or adjust the pipe to what it should be for the rev range you want to achieve.

Sometimes you just have to rip into it & make a few changes at once when you are so far away from the mark. Then get conservative as you get closer.

**speedpro** · 28th February 2012, 12:17

Originally Posted by koba

Though I'd add a few pics.

Anyone got any thoughts on the funny wee marks on the piston crown?

Marks are from gas flow and not a problem. It isn't unusual to get bigger patches which have been cleaned off.

As F5 says, the pipe looks to be way short and a bad mismatch for stock ports.

A good reed block, reeds, and smoothing the whole lot out with devcon is easy free horsepower.

**Clivoris** · 28th February 2012, 13:41

Originally Posted by Henk

That's bloody brave from a guy that lives in the same city. Coming to Te Puke fat boy?

I'm like a fox terrier in a parked car, brave-as I am. Can't make it to Te Puke, I'm chief judge at a cake competition.

**koba** · 28th February 2012, 19:49

Originally Posted by F5 Dave

Wow it actually looks quite racy from that angle. If you spent as much time on race tuning as you did on finding photo angles you'd be whipping us all.

Too true!

btw I never bother with head gaskets on these MB engines. Just a ring of Loctite master gasket.

I'd been using yamabond, wasn't working. Now you remind me I remember you have told me that before and I meant to try it. The idea got lost somewhere.

So increasing from 7800rpm to 12,000 one should expect quite some improvement in peak power. Clearly the pipe is a severe mismatch from the std porting. How long is the pipe? Before you start worrying about primary compression ratios, get the porting somewhere near what the pipe needs & or adjust the pipe to what it should be for the rev range you want to achieve.

My thoughts on the Primary compression are about what I think is happening rather than what I want to be happening!
Port timing changes are on the list but it's still a slap-together effort at the moment.
It think (quick glance at notes) the pipe works out to around 812mm tuned length (piston to mid-baffle).
Porting definitely needs to change, I'll worry more about the pipe once I get that about right.

Sometimes you just have to rip into it & make a few changes at once when you are so far away from the mark. Then get conservative as you get closer.

Totally, I'm beginning to think I'm a bit of a wus, but on reflection I'm happy with where thinga are for the time/money that's been put into it. (Not anywhere near as much as I'd like of either, but I guess it never will be!)

Originally Posted by speedpro

Marks are from gas flow and not a problem. It isn't unusual to get bigger patches which have been cleaned off.

Sweet, I'd just never seen them so 'focussed', got me guessing!

Originally Posted by speedpro

As F5 says, the pipe looks to be way short and a bad mismatch for stock ports.

If you got that idea from the photo, look real close... (plus it has a few twists that aren't obvious in the photo)

A good reed block, reeds, and smoothing the whole lot out with devcon is easy free horsepower.

Funny you should say that, I've just got back from the second day of careful 'sculpting' of the manifold and reed block entry. It's been on the to-do list for quite some time...

Originally Posted by Clivoris

I'm like a fox terrier in a parked car, brave-as I am. Can't make it to Te Puke, I'm chief judge at a cake competition.

Save me some...

**speedpro** · 28th February 2012, 21:15

I devcon the the inlet port on the downstream side of the reed block as well. My idea is to guide the mixture to the piston port with as few and little cross-sectional area changes as possible. Seems to work. You can hear an immediate change in the noise when doing back-back tests on the dyno and the motor runs a lot cleaner and nicer.

**koba** · 29th February 2012, 06:20

Originally Posted by speedpro

I devcon the the inlet port on the downstream side of the reed block as well. My idea is to guide the mixture to the piston port with as few and little cross-sectional area changes as possible. Seems to work. You can hear an immediate change in the noise when doing back-back tests on the dyno and the motor runs a lot cleaner and nicer.

Good to hear, I've spent a few hours on it so far...