Silencer leaks

[Andy_C]

While I was messing around taking the centre stand off my ETZ last week to grease it up, I removed the silencer, which had always had a slight leak where it joins the downpipe.

When I put the pipe back I thought that I would fix the leak, which as I say was very minor.

Took the bike out yesterday and was suprised at how much better it went, and since I have done nothing else while I had it apart it has to be fixing the leak that has made it run better, so it suggests to me that these bikes are very sensitive to the integrity of the exhaust system.

Anyone any thoughts on the subject ?

[Puffs]

OK, some thoughts.

Two stroke engines like the ETZ are quite sensitive to the exhaust. Particularly a well tuned expansion system, wherein the reflected pulse injects the last 'fresh' mixture back into the cylinder just before the exhaust port closes, can give major performance improvements. The timed reflection of the expansion chamber can act a bit like a supercharger, but usually only in a relatively narrow RPM band (which could be improved by an RPM-dependent exhaust valve).

A conventional muffler is not normally seen as something that gives such a timed reflection, but it does give back pressure. That can help preventing loss of too much 'fresh' mixture into the exhaust, and in that way improve engine performance. But too much back pressure (for instance when the exhaust is plugged) can lead to leaving too much burned exhaust gasses in the cylinder, and/or too high a pressure inside the cylinder when the overflow ports open, and that will reduce engine performance. But if it's a very minor hole that you plugged, I'd expect the difference in back pressure to be very minor, hence its effect to be very minor too.

Just like you hear on the outside, the small hole will give a reflected sound pulse inside the exhaust pipe too, a.o. travelling back to the cylinder. As the hole was close to the cylinder, it will arrive back at the exhaust port not too long after that port has opened, and might interfere with the exhaust process. It might be something like that, although that too I'd expect to have a relatively minor effect. But the reflection might well have a bigger effect than the pressure (or greasing the stand).

[Andy_C]

Yep, I had appreciated that 2T motors are pretty sensitive to exhausts (I also have a Kawasaki Triple) and it took a long while to get the carb adjustment right to get it to run with the Expansion chambers that it has.

Think this just illustrates how sensitive these ETZ motors to the exhaust system being in a good state of repair.

Took the bike out again this morning and it is still going exceptionally well, so it was not just coincidence that fixing the leak made it run better.

Stand also works much better

[DAVID THOMPSON]

had Datsun /Nissan cars in the 1980's
want to drive a bad running car just let the exhaust on a 510 car or 520 truck or 610 car get bad
runs like crap and sucks fuel... bad pipes on there sports cars made them run very bad
dave