Exhaust Air Filter Overun

[akirasan]

With my old Supa 5 in the 80's it was suggested I cut off the cone end of the exhaust to improve gas flow.
Yes it revved much better.

If you have ever seen inside an original Supa 5 exhaust you will understand why it is so heavy.
A labyrinth of tubes to cut noise and slow gasses.

Roll on 37 years later I have my ETZ 250.
When I bought it and rode 50 miles home it did not seem as lively as the old trusty TS part of this is the porting being so different between models.

So.…….

The pattern exhaust did not sound right a bit restricted in ring ding ding sound and gas release.

I got one from Kultmopeds off Ebay and it does not have much baffelling inside so very light.

The bike had an original yes original 1990 mz airfilter that had seen better days.

I ordered a new one and decided while waiting for the new one to arrive to fit a K & N panel filter I had laying around the garage. I rolled it up to fit inside the airbox and it sprung loose to fit really well.

There was concern with not enough back pressure and too much air with getting a holed piston - had enough of them on my RD400E - but had a go

There is a lot talk about MZ's bucking on the overrun so I adjusted the mixture screw and along with the air filter and exhaust change it is almost none existent.

Took it for a run and it ran a lot smoother I guess because of the extra air flow it just felt crisper with throttle response.

It sounds like an MZ should and along with the electronic ignition I fitted it is much happier running.

Yes I checked the plug colour and all is fine. As it is a low revving engine it should be alright.

Not done this to gain speed or power just day to day running feels better and easier to ride.

I did this last year and it has been great fitted the ignition this year and still going great.

I did put the new correct air filter in but it felt strangles so took it out.

[Puffs]

Good on you!

There is a recent thread on the internals of a Supa 5 exhaust. The standard ETZ exhaust might be similar, but I wouldn't know. In a 2T the exhaust might also be plugged with carbon. If you want to improve performance (without buying an RD or another faster bike), the common approach for the exhaust is a tuned expansion chamber, which is obviously without any baffles.

Yes the air filter needs to be regularly cleaned and/or replaced, without that it will plug and give more pressure drop, so that the jetting will become rich and the breathing choked.

Filtering the air properly, so that no dust enters into the internals, is of vital importance, particularly in a 2T. And in a carburettor engine, the filter also influences the oxygen/fuel ratio. Particularly the size of the main jet might need changing, as especially with a fully opened throttle any upstream restriction will be felt. With a partially closed throttle, the throttle valve will be the main restriction to flow & the flow through the filter will be smaller. (Regardless, the main jet is always the place to start.)

Yes, a lean (= oxygen rich) mixture will burn hotter and may cause aluminium to melt and/or burn. Aluminium is actually a base metal, which combines quite easily with oxygen (= corrode, burn); this process is normally halted by a thin layer of its sealing oxide. A holed piston can be caused by combining a small a main jet & a permeable air filter, but I'm not sure it's common on standard ETZ's (probably a higher compression is required).

[akirasan]

Already have an RD for thrashing.

Got the ETZ for general runabout and its fun to ride.

While I will not be going very fast on the ETZ I feel with a better flow filter and exhaust (not expansion pipes) it runs much smoother