Whats my plug telling me?

[Guest]

Hi guys,

got a clone of a 1980 honda CG125, recently thought i'd be a chav and cut the exhaust off, taking it from this:

http://i658.photobucket.com/albums/uu307/Sly-Boogie/PICT1535.jpg

To this:

http://i658.photobucket.com/albums/uu307/Sly-Boogie/PICT1541.jpg

Which besides sounding way too loud (and i never thought i'd say that ) appears to have affected my fuelling. I'm immediately gonna go with way too lean, but this is my 3 week old spark plug as of 4 days ago:

http://i658.photobucket.com/albums/uu307/Sly-Boogie/PICT1540.jpg

So yeah, is it begging for mercy?

On a side note - i cracked 70mph on it Nothing special given some of the bieks on here but by this piece of craps standards - thats special

[Martyc]

Was that plug in before doing the exhaust? Really you need a fresh plug and take it for a ride then look at it as it'd still have deposits on it from before the change. But in the pic the plug doesn't look too bad, maybe a bit lean. White is lean, black is rich, coffee is about right and oil is bad.

[Guest]

It was but it was just tan, like a normal plug. Never seen the insulator go pink before tbh As i knew it, completely clean white was lean, black was rich (as per my other bike which couldnt run richer if it tried )

[archiec]

not an expert but as I understand, no exhaust = no back pressure so gonna affect compression in the cylinder

[Guest]

not an expert but as I understand, no exhaust = no back pressure so gonna affect compression in the cylinder

 

I'm pretty sure that only really applies to 2 strokes?

I do know it can make it run richer or leaner though.

[Martyc]

Back pressure does affect performance on n/a cars so i'm pretty sure it would apply on bikes too. Tends to lose power and torque at everywhere but flat out. It's why kids in 1.2 corsas with big bore straight thru exhausts make lots of noise and go slower than they would if they'd stuck with the standard one (but most people have done it anyway)

[Guest]

Check this out.

http://www.verrill.com/moto/sellingguid ... rchart.htm

Stick a new plug in run it and check against the chart

[Guest]

Back pressure does affect performance on n/a cars so i'm pretty sure it would apply on bikes too. Tends to lose power and torque at everywhere but flat out. It's why kids in 1.2 corsas with big bore straight thru exhausts make lots of noise and go slower than they would if they'd stuck with the standard one (but most people have done it anyway)

 

I'm not so sure, but woulda re-map not fix it (if it needs it at all?)

race bikes, or bikes with race exhaust systems are almost like a straight through pipe, or what about a racefit* (edit goddit wrong) on a decat'd gsxr for example?

ah where is w.... wait... no never mind

Edited October 28, 2010 by Anonymous

[Martyc]

Race exhaust systems are designed to increase performance, and normally have a remap (and other mods sometimes) as you've said. I'm just not 100% sure a commuter 125 has the flow or power to make the most of an open exhaust!

[Guest]

If you alter the length ( shorten or lengthen ) a exhaust pipe, you will alter the pressure wave (back pressure ) .

When the exhaust valve opens it releases a low pressure wave which travels along the exhaust pipe, until it hits the end, it then bounces back and arrives a the valve just in time to catch the valve opening again, because it is low pressure it helps to suck the burnt gases out, this is called scavenging.

So you will lose power ,