Expansion Chamber

[Andy_C]

I was at an autojumble today and came accross one of those expansion chambers for an MZ - virtually unused and the vendor wanted £20 why not I thought.

I have read very few positive comments on these chambers so I thought for the sake of £20 I would find out for myself how good / bad they are.

Fitted it this afternoon and set off for a ride, first thing I noticed was that the noticeable torque that used to come in at around 3000 RPM has now moved up about another 500RPM.

Second thing I noticed was that the engine reved a lot more freely.

Did about five miles before stopping and pulling the plug which looked a little weak so decided to raise the needle a notch.

I then took it on one of my regular rides, and was very happy with the performance.

I gave the standard pipe the caustic soda treatment a while ago so I know that it is not clogged, so unless there is something wrong with it internally it should not be stifling performance.

Bottom line is that the chamber will be staying on the bike - it is lighter, has a nice "edge" to the exhaust note and performance is perfectly acceptable as far as I am concerned.

I would certainly say that for an ETZ in my experience these chambers are fine - no idea how they would perform on other models.

One side effect is that it seems to have all but got rid of the little bit of surging that the bike had.

Anyone any alternative views ?

[DAVID THOMPSON]

make sure you write down all the numbers on it ....so you can maybe find an other one in the future

[Puffs]

Removed

[dirtsurfer]

Let's see a picture Andy

[Andy_C]

Let's see a picture Andy

You asked so here they are.

Pretty sure it is just the "run of the mill" one that is readily available - I think the "Yoshimura" Label was fitted by the previous owner and I'll be leaving it there just as a talking point

[dirtsurfer]

Good find!

[Puffs]

Removed

[Andy_C]

Yes, very good find for £20!

Not at all trying to go into a contest, but just to illustrate what I said earlier, see the exhaust of a '92 YZ250LC:

YZ250 exhaust.jpg

The minimum OD is 54mm, so in x-section some 78% bigger than the standard MZ250 header pipe, of about 41mm OD (assuming 1mm wall th in both). And it tapers all the way.

Not a problem, Puffs - it is a known fact that tapered headers on 2t expansion chambers make better power than parallell headers and I dont doubt that the chamber I have could be improved on.

From my perspective it replaces the original tatty standard item, and performs pretty much on a par - so as you say a good find for £20.

Cheers

[Andy_C]

A quick update.

Chamber has now been on for nearly a week so I have had a chance to experiment with carb settings.

Initially I was a bit paranoid that the chamber would make it run weak, so I raised the needle a notch, and richened up the slow running settings.

Anyway, long story short, it seems to run best with no changes to the carb settings, richening up the settings just makes it feel sluggish and is relucant to pull top revs

I have ridden it just as hard with the "tuningauspuff" fitted as I used to with the standard exhaust and checked plug colour and it looks good to me.

F.Y.I. The settings are 2.5 turns out for the slow running screw and 4 turns for the bypass on the BVF carb.

Just thought I would post this up.