450x pilot jet size and suspension question.

[Nusk450x]

G'day I'm from north west victoria in Australia and I have a crf450x that is running a bit lean off the bottom I have the standard pilot jet (45) and a 178 main jet I also have a stage1 hotcam a Barrett exhaust system and airbox mods! I'm just wondering what size pilot jet you guys would recommend! I'm at approximately 60m above sea level! Also has anyone had suspension work done what do you recommend for trail riding mainly fast fire trails??

[Jim Dettman]

 In regards to the pilot (slow jet), I would let the motor tell you what it wants.    You follow the adjustment procedure:

 

On a fully warmed up bike (and you might want a fan on it while you do this):

 

1. Lower idle to just running.

2. Adjust pilot screw for smoothest idle.

 

Repeat steps #1 and #2 until you can no longer.   Where the pilot screw ends up tells you what to do with the slow jet.  

 

If the screw is over 2 1/2 turns out, you need a larger pilot jet.   If the screw is less than 1 turn out, you need a smaller one.  The "sweet spot" is 1 3/4 turns.  Getting the correct jet allows the pilot screw to to be more effective in setting mixture.

 

 If at this setting you get a hanging idle or popping on decel, then turn it 1/8 - 1/4 turn out to richen up a bit.

 

 Now with that said, note that this is for idle.  You said your a "bit lean off bottom".  If your opening the throttle, then that starts to play into other things such as the main jet size, needle itself (taper), and the needles clip position.  Also possibly the accel pump if your issue is just when opening the throttle suddenly vs slowly rolling it on.

 

 Where exactly do you have an issue?

 

Jim.

[Nusk450x]

My main issue is not at idle it is under hard acceleration off idle once even marginally off idle I have no worries I moved my needle up to the fourth clip down which made the bog off idle less noticeable which made me think a slightly larger jet would be better! Thanks for your reply!!

[Jim Dettman]

That would be the accel pump circuit.  It's job is to dump in a bunch of gas when you open the throttle suddenly. There are a few issues that might be causing a problem:

 

1. Outlet nozzle in the carb throat is corroded/plugged.

2. The AP diaphragm is torn.

3. A passage in the AP circuit is plugged.

4. AP timing is off.

5. Leak Jet is too big (and this is correct - unlike other jets, a larger jet means less gas for the AP pump - this jet controls the amount of leakage of gas back into the main bowl from the AP bowl, so a larger jet means the gas leaks back faster, leaving less for the AP).

6. Depending on year, the AP spring may need to be replaced (you may have heard of the 'o-ring mod' - which this is related to).

 

  So how to sort all that out. 

 

1. Remove the air filter

2. Put a mirror in the air box so you can see down the carb throat.

3. Whack the throttle open (doesn't have to be running).

 

 You should see a strong stream of gas come out.  Looks like this:

 

 

  This is for the R&D adjustable AP, but it gives you an idea of what your looking for.

 

  What you want is a strong stream of gas that just misses the slide.   If you have a good stream of gas, then it's #4 - 6.  If you have little or no gas (it dribbles out), then it's #1 - 3.

 

  We'll assume yours is good (if not, you need to pull the carb out).    First thing to check is the timing.   If your squirt splashes all over the slide, then the timing it too early and needs to be adjusted as a first step.

 

  You didn't mention the year of the bike, but for 2008 and back, the strength of the spring is critical to when the squirt starts and the strength of the squirt.  You'd want to deal with that first before doing anything.  From '09 up, the design was changed and this is no longer an issue.

 

 So assuming you reach this point, then the only thing left is the leak jet size.  Most drop a couple sizes down from stock (#60) to a #55 or #50 to eliminate any bog.  The leak jet is in the bottom of the carb bowl, and you must remove the bowl to replace it.

Jim.

Edited June 6, 2014 by Jim Dettman

[Nusk450x]

Cheers Jim that is heaps of help I appreciate it this may fix my problem as I have an 08 model!!

[Jim Dettman]

It was late 2008 sometime when the design change was made.   Here's a photo of the two setups:

 

 

 

 It's a little hard to see in this photo (click on it to make it larger), but the old design is on the left, and the new design is on the right.  Find the black plastic arm in the photo, right below the big round cable drum at the top.

 

 Notice on the left that the arm contacts the adjustment screw on the left.

 

 In the new design, the end of the arm is to the right of the screw.

 

 The difference is significant because the linkage rotates clockwise when it's engaging.  That arm is connected to a rod, which pushes down on the AP diaphragm and what  gives you the squirt of gas.

 

  So in the new design, the screw pushes against the arm and the spring is only used to return the arm to the right position when you let off the throttle.

 

  But in the old design, the screw pulls away from the arm and the spring is used to pull the arm along behind it.  The spring is not overly strong and as a result, the AP response lags from what it should be.   The fix then for the old design is to:

 

Replace the spring with a stiffer one from Merge Racing or Toyko Mods.

or

Do the "o-ring mod" and tie the two together (arm and adjustment screw) with an o-ring.

or

Tie the two together with safety wire.

 

  The last two of course will break at some point, so a new spring is a better bet.

 

  If you have the new carb design, then your set and there's nothing you need to do here.

 

  You should be able to pop the throttle cable cover off the carb and see what you have without removing it.   If you have the old design, order a spring and get a #55 leak jet at the same time as you'll probably need both.

 

  I got my '09 barnd new and from day one, it was a 50/50 shot on whether it would stall or not.   I had the new carb design and the only change I made was to install a 55 leak jet (vs 60 stock) and adjust the AP timing.   I've never stalled since.

 

Jim.

Edited June 7, 2014 by Jim Dettman

[Nusk450x]

Ok I have the new carby I'm on an august 08 build the leak is a 60 and I can't get it to squirt using the throttle but pushing the ap rod by hand it squirts a short powerful jet I'll assume I need the 55 leak jet!! Cheers for the help!!

[FORMA MOTO]

The leak jet size fills the cavity (60 fills less than 50) for the pump

The diaphragm pushed the fuel out (if the diaphagm is old or torn, it moves poorly) through the apump nozzle

The Apump linkage spring actuates the diaphragm, via the rod; if the linkage is '08, there is no mod needed

 

 

You should be getting some kind of spray at almost any throttle opening speed. 

A quick open to WOT and held should get you a spray all the way into the head.

 

More than likely, your apump nozzle is partially corroded/closed off, hence the need for more direct pressure to get a stream going.

[Nusk450x]

Ok carb and bike is back together will order a 55 leak and try to get it spraying properly later! It's not too bad I adjusted the timing which made it a little better!!