Jump to content
Sign in to follow this  

YFZ450

Recommended Posts

Yoshi TRS full exhaust

Cam-Mod

K&N w/ outerwear & no lid

-4 oz flywheel

Dynatek CDI

I have your jetting kit. 48 pilot, 172 main.

Rode it at 3000 feet with the following...

Blue needle #3 stuttered/stumbled down low.

Red needle #4 pops A LOT on decel.

Tried a 50 pilot...no change.

Tried adjusting the screw...no change.

:cry:

Also...I can turn the screw all the way in and the bike never dies, and the idle is not that high. It has been this way since I have owned it.

Thanks.

Share this post


Link to post
Share on other sites

Make sure the carburetor slide plate is installed correctly. If it's upside down, there will be excessive popping and a bigger pilot jet is usually used to compensate.

See the following picture- Slide and Plate

The hole in the plate needs to be in the lower half of the opening facing the air filter. Some bikes have had this upside down from the factory.

The #48 pilot jet is usually too rich, unless the fuel screw is set at ~1 turn out from seated. The fuel screw is also not responding because of this.

===========

The next possible issue is that aftermarket headers sometimes don't seal well at the cylinder head. Adjusting the jetting too rich is not a good solution. Make sure the headpipe is sealed.

============

The standard YFZ450 kit instructions are to run the red marked needle in the middle clip position and a #45 pilot jet. The fuel screw will have a greater impact on idle with this setting. Your rich stutter is a combination of too big of a pilot jet and blue needle.

In your case, with the modifications, I would run the red marked needle in the 5th from top clip position and #45 pilot jet, ~1 1/2 turns out. The #172 main jet should be good.

James

Share this post


Link to post
Share on other sites

Just one more question...

When I go to Glamis in a week, sea level or less and kinda warm still in the 80's and 90's...

What changes, to the jetting specs you just gave, would you suggest for that area?

Thanks! :cry:

Share this post


Link to post
Share on other sites

Use the same setting and turn the fuel screw as needed. The heat will richen jetting, so evaluate as you ride.

It is difficult to be more precise without doing testing considering variations between bikes and your modifications.

James

Share this post


Link to post
Share on other sites

The heat will be just a tad hotter than where I am riding now...I was thinking more about the 3000 foot elevation loss which should LEAN the mixture...correct?

Share this post


Link to post
Share on other sites

I looked into the throat of the carb and the bottom edge of the slide plate is square with that little crescent in the middle...but I do not see the hole indicated in the picture...? Is it on the other side of the slide plate? I'm looking in from the air box side...I did not remove the carb from the head.

I am assuming that if it was upside down I would see more of a triangle shape across the bottom...that would let in more air when the slide is fully down, that would cause it to be more LEAN and pop...right? :cry:

I put in the 45 pilot, put the red needle on #5, I'm at 2000 feet at my house. Still popping like crazy, even after playing with the screw. I'm gonna buy a new header gasket and try that next I guess? Never had a prob before though...did it just rattle loose maybe?

Thanks :cry:

Share this post


Link to post
Share on other sites

The vacuum release plate is on the airbox side of the carburetor slide. If you never had it out, the plate is probably installed correctly.

Occasionally these are installed upside-down from the factory.

James

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×