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I've been doing research reference after market exhaust. I am confused as to how you determine if you have to install a rejet kit after exhaust upgrade. Some folks just assume that you will rejet, others just seem to know if they should rejet or not. How do you know?
 

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Re-jetting affects the fuel/air mix in the engine. Since the exhaust doesn't really affect that (at least not enough) you don't need to re-jet simply for exhaust.

If you put a new air intake on your bike then you would need to re-jet because you'd screw up that air/fuel mix.

I suspect people assume you need to re-jet for exhaust because a LOT of people put new pipes on in conjunction with a new air intake.
 

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Depends how it runs...thats how I tell. Gotta know your bike....thats why I wouldn't recommend dealer installing pipes at purchase - you will never have any reference.
 

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Based on reading here, many assume you will have to re-jet. If you install a new intake, the change in air to fuel mixture can give you problems. The bike may idle fine, but stumble in acceleration, or accelerate fine, but then find a "flat spot" where the bike won't cruise well. Surging is another problem that may be encountered. Or the bike may not idle well, but run fine. There are many different symptoms of a need for "tuning".

So folks come here and try to gain from the experience of others, and buy the right stuff to be prepared when they are going to mess with a new intake or new exhaust. It is fairly safe to say exhaust has less to cause a need for re-jet, although you will hear many talk of increased or decreased "back pressure".

Performing a dyno check both pre and post installation is probably the best way to accurately see what you've done, but that can be expensive in itself.

In some cases the change of pipes or air cleaner was more cosmetic than performance driven, to begin with.

So to answer your question -- it depends. You will know if the bike runs poorly that you've done something to create the problem, then the task is to find the best economic solution to get the performance back. Folks come here with an idea (I want deeper sounding, growling pipes, for instance), and then try to figure out what others have done in the past ... then try to duplicate it.
 

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Double post ... sorry :oops: :oops:
 

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don't know if it will help, but here's my limited experience. When I did my 600 mile check, I pulled the plugs and inspected them just to make sure there was nothing major. They looked very good. A little darker than that tan color, but nothing out of the ordinary. When I checked them, the bike was all stock. Since then, I took out the pair valve, added V&H Big Shots exhaust, and added a K&N air filter to the stock box. I didn't change a thing with the carb, so took it out and rode it about 75 miles total over two days. Pulled the plugs and they were starting to get a very light color, which to mean says that the changes I made have the thing running a little leaner. The bike seemed to run fine though, no weirdness that I could tell. Maybe I just haven't had the bike long enough, but power seemed pretty close to what it was and maybe there was a tiny bit of difference in certain low or high end HP, but really, nothing to write home about. Since the plugs started looking lean in just a matter of days, I went ahead and did the scars carb mod and added one shim (washer) and pulled the A/F screw out 2 1/1 turns. The bike started up great and idled nice. I have a feeling it might be a tad rich but it's been raining here all day so I haven't had a chance to take it out yet. The main thing is that since the bike started running lean with the things I added, like K&N, new exhaust, etc... I needed to do something and I think the scars method is going to work. it seems very popular and I don't see people coming back and complaining about this or that with it. I'll update as I get to ride the bike more, but for now, I did need a rejet. Nothing big and maybe I could have fixed it with just the A/F screw but I figured I'd get in there and do the mod to get a little better response. Good luck and I hope this helped and I didn't ramble too much.

Curtis
 
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