Silencer leaks

ETZ(including Kanuni), ETS, ES, TS, IFA-RT, BK, Saxon,

Moderators: DAVID THOMPSON, phlat65

Silencer leaks

Postby Andy_C » Sun Mar 25, 2018 3:11 am

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 ?
Andy_C
 
Posts: 330
Joined: Sun Mar 02, 2014 9:02 am
Location: Somerset

Re: Silencer leaks

Postby Puffs » Sun Mar 25, 2018 6:39 am

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).
User avatar
Puffs
 
Posts: 2010
Joined: Tue Jan 16, 2018 11:20 am
Location: Ardennes, Belgium.

Re: Silencer leaks

Postby Andy_C » Sun Mar 25, 2018 7:51 am

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 :mrgreen: :mrgreen:
Andy_C
 
Posts: 330
Joined: Sun Mar 02, 2014 9:02 am
Location: Somerset

Re: Silencer leaks

Postby DAVID THOMPSON » Sun Mar 25, 2018 9:28 pm

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
Dave 2002 MZ RT125+1995 Saxon Tour(500cc)
1997 MZ 660 Traveller+6/13/09 WV USA
"IN the end times the IDIOTS will be in charge
of everything"
"I like the road less traveled if it's PAVED!"
wd8cyv at yahoo dot com
User avatar
DAVID THOMPSON
Moderator
 
Posts: 5150
Joined: Sun Nov 23, 2003 11:01 am
Location: Parkersburg, West Virginia USA .questions answered MZ 95 up, BMW 1953 to 1979 and ham radio WD8CYV


Return to Vintage Motorcycles

Who is online

Users browsing this forum: No registered users and 18 guests