You guys need to pay more attention to offroading in general and not just the quads. Everyone knows about the Yamaha 4 stroke engines being smothered by the exhaust and is the first thing to do for more power. As for the jetting, Ridley, you are way off base. The carbs on the Yamaha 4 strokes require nothing when modified unless you go into the engine. you can change the filter and even to a full exhaust system and not need to touch the carburetor at all. Go to any of the dirtbike sites and they will tell you that the jetkit is a way for them to get more money. There is one guy there who has a pipe, twinairfilter,prolow intake and a thumper racing intake cam on his yz450f bike and still has the stock jetting!

Captain

 

Any time you improve airflow you need to increase the fuel flow to match.

Also try taking off the air lid.

Then when you re-jet 165 main and bump up the pilot jet to a 45. That's if you are at sea level.

Call any dealer and talk to service and ask them if you need to re-jet after pulling out the baffle. If you don't believe me.

 

yeah real cheap until u have to get a new pipe after ur old one is no good

 

What are you trying to do??? Have some poor naive individual with a YFZ ruin their new toy????


THIS INFO IS TOTALLY WRONG!! DO NOT FOLLOW THIS ADVISE!!

 

I do not have a yzf...but.

He is correct....Why do you think your feeling that little bit of power? your lean.

 

I've had the dealership tell me that I shouldn't need to rejet when just installing the new header and exhaust canister.... now I'm hearing all sorts of things.... I haven't done any "real" engine work since I tooled around my old `78 suzuki 125's motor, so some concrete info on whether or not I need to rejet when i plop on my new exhaust would be much apreciated.... :\

Also, if you could post your "jetting" settings along w/ all of your airflow mods, that would be very helpful.

 

Whoever it was you talked to at the dealership, is an idiot. If you install an aftermarket exhaust, you need to rejet.
Just do a search on the forum to try and find the right jetting for your elevation.
Rejetting isn't that hard. Heck, I'm a girl and I know how to rejet! lol [img]i/expressions/face-icon-small-wink.gif[/img]

 

Easy way to tell is as follows:

buy two new plugs.

Put one in and putt around at less than 1/2 throttle for a little while. Pull the plug and check the color. If it's tan you're golden on the pilot.

Put in a new plug, then ride around for a while sticking to 3/4 - WOT. Pull the plug and check the color. If it's tan, you're golden on the main.

If you are a light ash/ white color, you're lean. Increase jet size. If you're dark dark brown / black, you're rich. Decrease jet size.

 

OMG. Carl, WTF?

when i pulled the baffle, i would occasionaly get the flame-out "pop" when i shut the machine off. then i added a pro design airfilter (with the lid still on) and my header pipe glowed orange at idle. than i removed the lid...and it glowed all the time. (no, i was not riding the quad during this)

i then re-jetted added pipe and piston and canceled my prescription for Spam wordSpam word Spam wordSpam word Spam wordSpam word Spam wordSpam word Spam wordSpam word Spam wordSpam word .

Remember folks...when you remove the baffle. you no longer have a spark arrestor. thats a bad thing in California.

 

For those of you that think you don't need to re-jet with any type of exhaust, air filter or air box mods.. just go to the dealer and ask them to provide you the install instructions for the GYT-R exhaust or GYT-R K&N air filter kit.

Right in those instructions you will read to re-jet using the GYT-R jet kit.