Change exhaust - rejet necessary?

[adidasguy]

Restyling my 92 and decided it should have a new exhaust since I don't now the condition of what's on it or even what type (its been repainted). And I want it to look nice since I have new gas tank, belly pan, tail fairings and other new parts. (OK, I WAS going to go for factory original everywhere but have since decided to go mostly original and a little customization to make the bike MY bike, if you know what I mean.)

I've heard you need to rejet the carbs when you change the exhaust but I wonder why. After all, the exhaust is just exhaust. I can see rejetting if you change air filters, air box or other things that mix fuel and air. But I can't quite see why you need to do anything if you're just changing the exhaust. (I do street riding and commuting, no racing). To me its like requiring you to change the faucet if you change the drain in a sink.

Maybe a dumb question to some of you. As this is my first bike fix-up, I am wondering about this.

[Stanfield]

On it's basic level, a new performance ehaust allows more exhaust to escape quicker which requires more air and fuel on the front end.  Don't do it if you don't want to re-jet.

[tt_four]

The bikes already run lean from the factory, so you wouldn't really want to do anything to make that worse, but if you're leaving the stock air filter in you can usually get away with putting an exhaust on a bike. Yes the exhaust lets air flow out faster, which potentially could lean out the fuel mixture even more, but if you still have the stock air filter in, and it's not letting any extra air in, well there's not any extra air for the exhaust to let out. If it does increase the airflow and your plugs look like it's running too lean, just put some duct tape over a chunk of the air filter to cut back on some of the air. 

[Big Rich]

Actually, a new exhaust will most certainly call for re jetting. The exhaust will flow more air out, and the intake will be forced to suck more air in. Most likely you will only need one size up in the main jets - it's really not that hard.

Besides, of you are making it YOUR bike, you will probably do the intake eventually anyway. Learn your carbs inside and out while you "want" to, not when you need to.

[Paulcet]

You might just get away with a washer or two under the needles.

[adidasguy]

Big Rich, I agree with what you say. I should learn the carbs and every part of my bike. And I will. As I customize the bike I will have to learn everything. Getting it back to factory original (with a few upgrades) will require a lot of learning as I replace and upgrade parts. I'm looking forward to this project.

For the immediate time, I think I can install the jardine with the silencer. They say the silencer would require rejetting, which I believe would be putting it back to stock since the carbs would have been rejetted when the exhaust was installed. The quiet plug reduces airflow more like a stock exhaust. I'll plan to work on the carbs in January when I am laid up for a month and can't ride (Voluntary surgery during the rainy season to repair a torn tendon in the left (aka shifter) foot) At that time, I'll take your advice and completely rebuild the carbs and rejet them so I know every part in them.

New belly pan came in and was installed. Original headlight cowling came in - needs fiberglass repair and repainting so there's something to learn this week!

[Twisted]

I recently got an aftermarket can put on my GS. All the mechanic had to do was adjust the carb, no rejet was necessary. The rest of the engine/airbox is stock and it runs fine. Actually it runs better than with the stock exhaust on.

[007brendan]

All the mechanic had to do was adjust the carb, no rejet was necessary.

I can almost guarantee you're running lean.  I was running lean just with the stock setup.  Besides, switching out the idle jets to +1, with or without an exhaust, is one of the best things you can do for better idle and warmup time.

[Twisted]

People say the US bike are jetted too lean. I am in Australia. Do we have the same jets in our carbs as American GS's? I have not noticed any problems with my bike running lean. I will try to pull one of the plugs out after I go for a ride this weekend to see what colour they are.

[Clancy]

I recently got an aftermarket can put on my GS. All the mechanic had to do was adjust the carb, no rejet was necessary. The rest of the engine/airbox is stock and it runs fine. Actually it runs better than with the stock exhaust on.

We got similar pipes Twisted... Different length tho.
i.m running 20 65 147.5 with a lunch box. Seems bout right.

[adidasguy]

Whose carrier rack do you have on the tail?

[Twisted]

I was considering the Ixil shorty but went with this Screaming Demon instead.

[Clancy]

Whose carrier rack do you have on the tail?

its from a co called Vertura. (old Pic)


Holds all my and my gals camping gear...

[Clancy]

I was considering the Ixil shorty but went with this Screaming Demon instead.

The Ixil sure does sound good..
http://www.youtube.com/watch?v=ZdZcHScKNNI

[adidasguy]

If that's your make-out spot, you could win the picture contest! Current challenge is your bike at your make-out spot.

[mister]

Whose carrier rack do you have on the tail?

Took a few different shots for the Lets Talk About Racks thread http://gstwins.com/gsboard/index.php?topic=53281.msg601468#msg601468

There was a song in Aust and it went... football, meat pies, Kangaroos and Holden cars. I think it should have Ventura Rack thrown in there cause there are Heaps of bikes with them on down here.

Michael

[Twisted]

Whose carrier rack do you have on the tail?

Took a few different shots for the Lets Talk About Racks thread http://gstwins.com/gsboard/index.php?topic=53281.msg601468#msg601468

There was a song in Aust and it went... football, meat pies, Kangaroos and Holden cars. I think it should have Ventura Rack thrown in there cause there are Heaps of bikes with them on down here.

Michael

Yes, lets talk about racks. Dunno about you guys but I think this one would look pretty good on my bike -  

[Twisted]

All the mechanic had to do was adjust the carb, no rejet was necessary.

I can almost guarantee you're running lean.  I was running lean just with the stock setup.  Besides, switching out the idle jets to +1, with or without an exhaust, is one of the best things you can do for better idle and warmup time.

Went for a 300 kilometer plus ride today. The plugs are this colour -






Which is this one on the spark plug guide by my observation.

[Big Rich]

Actually, that plug is running lean. It should have more of a "brown-ish" color on the electrode - not white.

If you bump the main jet up 1 size, you'll get a little more power.

[Twisted]

I think the flash from the camera is showing the plug lighter than it is. It is a nice brown colour on the electrode in real life.