Science behind fouling and RePacking Silencer

[liesnerj]

I have read on these boards that sometimes a bike that constantly fouls
plugs needs to have its silencer packing repacked. I know that
rejetting can also help to lean it but I have read that you should
repack your silencer first and see if that makes a difference. My main
question is why would repacking make a difference in fouling the plug?


Could someone explain to me the science and thought behind this?

The bike is a 1988 CR125, just put in new main bearings, seals,
gaskets, new ring (piston new last fall with a fresh bore). We have
had the bike for about a year now and it has always fouled a lot of
plugs, generally we have used BR9ES or equivalent. Usually a couple
every time it is ridden. The only exception was that we tried a
hotter plug, an NGK BR6 and this plug did not, and has not fouled (and
looks good when we take it out) but I dont want to run too hot of a
plug and cause other problems.

So I want to solve this plug fouling problem once and for all.
Thoughts?

[Chris Buckley]

Post by liesnerj
I have read on these boards that sometimes a bike that constantly fouls
plugs needs to have its silencer packing repacked. I know that
rejetting can also help to lean it but I have read that you should
repack your silencer first and see if that makes a difference. My main
question is why would repacking make a difference in fouling the plug?
Could someone explain to me the science and thought behind this?
The bike is a 1988 CR125, just put in new main bearings, seals,
gaskets, new ring (piston new last fall with a fresh bore). We have
had the bike for about a year now and it has always fouled a lot of
plugs, generally we have used BR9ES or equivalent. Usually a couple
every time it is ridden. The only exception was that we tried a
hotter plug, an NGK BR6 and this plug did not, and has not fouled (and
looks good when we take it out) but I dont want to run too hot of a
plug and cause other problems.
So I want to solve this plug fouling problem once and for all.
Thoughts?

What pre-mix oil are you using, and how much of it. Also,
what type of riding do you do??

[liesnerj]

Primarily trail riding. Use Gold Spectro, with about a 40:1 mixture.
Also, I am fairly certain the packing is blown, its loud and I am
almost positive the previous owner did not repack it, he only puttered
around his yard for 15 years with it.

So, with a "gummed up" exhaust it could run richer, more exhaust
velocity, therefore more fuel being sucked in. Is this the correct
understanding.

Thanks.

[Wudsracer]

Post by liesnerj
Primarily trail riding. Use Gold Spectro, with about a 40:1 mixture.
Also, I am fairly certain the packing is blown, its loud and I am
almost positive the previous owner did not repack it, he only puttered
around his yard for 15 years with it.
So, with a "gummed up" exhaust it could run richer, more exhaust
velocity, therefore more fuel being sucked in. Is this the correct
understanding.
Thanks.

The exhaust system was designed to work with fresh packing.
Your jetting will be screwed until you repack it.
The spooge is a result of your fuel/air mixture. It is too rich for
how you are running it (elevation & throttle opening you are using
most of the time.)

The B6 is way to "hot" of a plug. If you want to hedge a bit, I would
go to a B8ES plug instead of the B9..

[john]

a 6 is cooler than an 8, not hotter

repacking changes backpressure & exhaust velocity...
engines tuned for specific exhaust (freash packed) will
run different <richer> on gummed up exhaust...
Go to www.eric-gorr.com for more info.

Post by liesnerj
I have read on these boards that sometimes a bike that constantly fouls
plugs needs to have its silencer packing repacked. I know that
rejetting can also help to lean it but I have read that you should
repack your silencer first and see if that makes a difference. My main
question is why would repacking make a difference in fouling the plug?
Could someone explain to me the science and thought behind this?
The bike is a 1988 CR125, just put in new main bearings, seals,
gaskets, new ring (piston new last fall with a fresh bore). We have
had the bike for about a year now and it has always fouled a lot of
plugs, generally we have used BR9ES or equivalent. Usually a couple
every time it is ridden. The only exception was that we tried a
hotter plug, an NGK BR6 and this plug did not, and has not fouled (and
looks good when we take it out) but I dont want to run too hot of a
plug and cause other problems.
So I want to solve this plug fouling problem once and for all.
Thoughts?

[b***@hotmail.com]

BR9ES is one step colder than a BR8ES
BR7ES is one step hotter than a BR8ES
BR6ES is two steps hotter than a BR8ES

Post by john
a 6 is cooler than an 8, not hotter
repacking changes backpressure & exhaust velocity...
engines tuned for specific exhaust (freash packed) will
run different <richer> on gummed up exhaust...
Go to www.eric-gorr.com for more info.

Post by liesnerj
I have read on these boards that sometimes a bike that constantly fouls
plugs needs to have its silencer packing repacked. I know that
rejetting can also help to lean it but I have read that you should
repack your silencer first and see if that makes a difference. My main
question is why would repacking make a difference in fouling the plug?
Could someone explain to me the science and thought behind this?
The bike is a 1988 CR125, just put in new main bearings, seals,
gaskets, new ring (piston new last fall with a fresh bore). We have
had the bike for about a year now and it has always fouled a lot of
plugs, generally we have used BR9ES or equivalent. Usually a couple
every time it is ridden. The only exception was that we tried a
hotter plug, an NGK BR6 and this plug did not, and has not fouled (and
looks good when we take it out) but I dont want to run too hot of a
plug and cause other problems.
So I want to solve this plug fouling problem once and for all.
Thoughts?

[john]

really? okay, I just use stock 8 plugs,
thought the lower # was cooler?
i know it has to do with how much
heat the plug can disapate... or something like
that, so if the plug disapates more heat it keeps
the tip cooler to prevent predetonation... i don't
like the idea of changing a plug to make up for
some other issue going on in there..
john
I blame last weeks the rum umbrella drinks for any...

Post by b***@hotmail.com
BR9ES is one step colder than a BR8ES
BR7ES is one step hotter than a BR8ES
BR6ES is two steps hotter than a BR8ES

Post by john
a 6 is cooler than an 8, not hotter
repacking changes backpressure & exhaust velocity...
engines tuned for specific exhaust (freash packed) will
run different <richer> on gummed up exhaust...
Go to www.eric-gorr.com for more info.

Post by liesnerj
I have read on these boards that sometimes a bike that constantly fouls
plugs needs to have its silencer packing repacked. I know that
rejetting can also help to lean it but I have read that you should
repack your silencer first and see if that makes a difference. My main
question is why would repacking make a difference in fouling the plug?
Could someone explain to me the science and thought behind this?
The bike is a 1988 CR125, just put in new main bearings, seals,
gaskets, new ring (piston new last fall with a fresh bore). We have
had the bike for about a year now and it has always fouled a lot of
plugs, generally we have used BR9ES or equivalent. Usually a couple
every time it is ridden. The only exception was that we tried a
hotter plug, an NGK BR6 and this plug did not, and has not fouled (and
looks good when we take it out) but I dont want to run too hot of a
plug and cause other problems.
So I want to solve this plug fouling problem once and for all.
Thoughts?

[IdaSpode]

Post by liesnerj
I have read on these boards that sometimes a bike that constantly fouls
plugs needs to have its silencer packing repacked. I know that
rejetting can also help to lean it but I have read that you should
repack your silencer first and see if that makes a difference. My main
question is why would repacking make a difference in fouling the plug?
Could someone explain to me the science and thought behind this?

I can't help with the science, but before you repack the silencer ,
(and after 15 yrs it needs it) I'd go back to the stock plug and stock
jetting.

If you've been trying to fix a clogged exhaust with jetting and hotter
plugs, the engine may toast itself when it can breathe properly once
again.

Post by liesnerj
Thoughts?

Yes, every once in a while...

DJ

[David]

Someone will disagree with me.

what I would do is keep jetting same.
Change your mix to 32:1.
Being too rich is too much GAS not too much OIL.
I like OIL .....

Just my $0.02

Following advise from Wudsracer or MXTuner would get you a bike that runs
RIGHT though.

Post by liesnerj
I have read on these boards that sometimes a bike that constantly fouls
plugs needs to have its silencer packing repacked. I know that
rejetting can also help to lean it but I have read that you should
repack your silencer first and see if that makes a difference. My main
question is why would repacking make a difference in fouling the plug?
Could someone explain to me the science and thought behind this?
The bike is a 1988 CR125, just put in new main bearings, seals,
gaskets, new ring (piston new last fall with a fresh bore). We have
had the bike for about a year now and it has always fouled a lot of
plugs, generally we have used BR9ES or equivalent. Usually a couple
every time it is ridden. The only exception was that we tried a
hotter plug, an NGK BR6 and this plug did not, and has not fouled (and
looks good when we take it out) but I dont want to run too hot of a
plug and cause other problems.
So I want to solve this plug fouling problem once and for all.
Thoughts?

[BKR]

The exaust system of all 2 stroke performance machines since the 1960s
has been designed as an acoustical system. They were called expansion
chambers in my day, but the idea is to use the shape of this exaust
system to provide a pressure wave in the reverse direction to time in
just after the exaust port opening. This aided compression in the
cylinder.

If the exaust system is clogged with old oil deposits in the pipe,
or the silencer is matted down with oil, the back wave will not provide
the correct pulse to the cylinder. The design is thrown out of wack and
the way the fuel and oil burns makes the mix and performance out of whack.

Post by liesnerj
I have read on these boards that sometimes a bike that constantly fouls
plugs needs to have its silencer packing repacked. I know that
rejetting can also help to lean it but I have read that you should
repack your silencer first and see if that makes a difference. My main
question is why would repacking make a difference in fouling the plug?
Could someone explain to me the science and thought behind this?
The bike is a 1988 CR125, just put in new main bearings, seals,
gaskets, new ring (piston new last fall with a fresh bore). We have
had the bike for about a year now and it has always fouled a lot of
plugs, generally we have used BR9ES or equivalent. Usually a couple
every time it is ridden. The only exception was that we tried a
hotter plug, an NGK BR6 and this plug did not, and has not fouled (and
looks good when we take it out) but I dont want to run too hot of a
plug and cause other problems.
So I want to solve this plug fouling problem once and for all.
Thoughts?

[liesnerj]

Just an update. We repacked the silencer Friday night. My son then
rode the bike both Sat. and Sun almost all day both days. It is
running fine. We also used a BR8ES spark plug. He is still on the
same plug. In the past he would have gone through at least a couple of
spark plugs in the same time frame.

So, either because of the packing or a hotter than BR9 plug or a
combination, the bike seems to be running good. At least for now.

Post by BKR
The exaust system of all 2 stroke performance machines since the 1960s
has been designed as an acoustical system. They were called expansion
chambers in my day, but the idea is to use the shape of this exaust
system to provide a pressure wave in the reverse direction to time in
just after the exaust port opening. This aided compression in the
cylinder.
If the exaust system is clogged with old oil deposits in the pipe,
or the silencer is matted down with oil, the back wave will not provide
the correct pulse to the cylinder. The design is thrown out of wack and
the way the fuel and oil burns makes the mix and performance out of whack.

Post by liesnerj
I have read on these boards that sometimes a bike that constantly fouls
plugs needs to have its silencer packing repacked. I know that
rejetting can also help to lean it but I have read that you should
repack your silencer first and see if that makes a difference. My main
question is why would repacking make a difference in fouling the plug?
Could someone explain to me the science and thought behind this?
The bike is a 1988 CR125, just put in new main bearings, seals,
gaskets, new ring (piston new last fall with a fresh bore). We have
had the bike for about a year now and it has always fouled a lot of
plugs, generally we have used BR9ES or equivalent. Usually a couple
every time it is ridden. The only exception was that we tried a
hotter plug, an NGK BR6 and this plug did not, and has not fouled (and
looks good when we take it out) but I dont want to run too hot of a
plug and cause other problems.
So I want to solve this plug fouling problem once and for all.
Thoughts?