03 WR450 Jetting and low end performance


31 replies to this topic
  • Thesykboy

Posted October 03, 2011 - 08:25 PM

#1

I took my bike out for a trip around the block the other day and was very curious about the performance I was having. It bogged and cut out a LOT when at very low RPM. When I hit the gas, it bogs for a split second, then takes off like a SHOT! At high rev, it runs awesome, but at low rev, it's terrible.

I'm not all that clear on how the jetting works on these newer bike since I'm used to bikes with just a Pilot and Main. This carb has 3 jets and I'm confused as to what jet (all jets and the carb are a s clean as a whistle) I need to upgrade or downgrade in order to get this rev as clean as I can...



Here are the current sizes...

Left 65
Middle 50 (slow?)
Main 160

Posted Image

  • miweber929

Posted October 04, 2011 - 04:04 AM

#2

Read the Stickys. All you will will ever need to know about carbs and setup is in them.

  • Krannie McKranface

Posted October 04, 2011 - 10:04 AM

#3

The stickys will help, but there is info missing from them.

Carb on un-corked intake and exhaust typical jetting:

* means not stock

*165 main
*45 pilot (the long one)
*NCVS needle 3rd clip
*50 leak jet (in float bowl)
stock air jet
stock slide
stock needle jet tube
stock power jet (choke circuit)
* Merge racing accelerator pump linkage spring (don't skip this it's amazing)
Slide plate seal: replace it every time you take out the slide
* brass fuel screw upgrade: R&D is the best one

--- A dirty pilot jet is the #1 cause of a poor running motor.

--- A varnished float needle and passage is #2. Don't leave gas in the carb for more than two weeks or you will have problems. You can't get all the gas out unless you drain it out.

If you don't have a ultrasonic cleaner, buy a new one.

Read this article:

http://t3.gstatic.co...XCq7ZnNkIyeFmm-

  • - Jake -

Posted October 04, 2011 - 01:52 PM

#4

Read this article:

http://t3.gstatic.co...XCq7ZnNkIyeFmm-


Mate, I don't think that link is what you thought it was! :smashpc:

  • Krannie McKranface

Posted October 04, 2011 - 02:44 PM

#5

Mate, I don't think that link is what you thought it was! :smashpc:


You just have to read between the drops.............

http://www.dirtrider...ld/viewall.html

  • Thesykboy

Posted October 12, 2011 - 02:21 PM

#6

I looked at the sticky and frankly, it was almost overkill. And it still didn't give me what I was looking for.

I looked at CheapCyclePart.com to see what size jets are recommended for my bike. It said that max size of the slow jet is 50 (which is what I'm running and bogging with). The spark plug certainly shows that I'm running rich and the next 2 steps down from 50 are 48 and 45. Based on the color, I was gonna drop down to 45 and see how she likes it.

Also, I'm used to older carbs with 2 jets rather than 3... Is a "slow jet" basically the same as a pilot jet? And what the hell is a leak jet?

  • William1

Posted October 12, 2011 - 04:52 PM

#7

The 65 is the starter jet, oly operates when the choke is pulled
The 50 is the pilot jet (AKA Slow Fuel jet). That in conjunction with fuel screw is for idle. There is also a slow Air jet in the carb bell. These rarely need to be changed.
Fuel Screw/Pilot Jet
Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.
Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.
*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***
Turn the screw in until the idle becomes rough or the bike stalls.
if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.
If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.
Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.
If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.
If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.
If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

You cannot read a spark plug with todays pump fuels.

Leak jet is part of the Acccelerator Pump, used to add extra fuel when you hit the gas. The AP is the root of many if not all bogs. See the sticky at the top of the forum.

  • Thesykboy

Posted October 21, 2011 - 12:49 PM

#8

After reading all that (which I noticed was in the stickies) and the sticky on "how to eliminate the bog", I determined that maybe I had too big a leak jet. I pulled the carb apart, found that the AP wasn't working properly, cleaned it as per the sticky and looked at the size of my Leak Jet... 40! After putting it back together, I turned out the mix screw 2 full turns and started it. It took me about 5 minutes for the bike to be hot enough to take off the choke.

I then adjusted the idle down a bit and CRACKED the throttle. It stalled for a split second then revved. I waited a few seconds and then hit it again with the same results.

So here's my question... Since the Leak Jet "leaks" fuel back into the carb from the AP chamber, is it safe to say that the smaller the "leak", the more fuel going into the squirt? As in contrary to the typical thought of what a jet does, a larger Leak Jet (leaking more fuel into the carb bowl) results in a SMALLER amount of fuel squirt, and a smaller leak gives you a BIGGER squirt? If so, maybe my squirt is richening up the mix causing the bog (stall) rather than simply making my quick acceleration snappy like it should be.

How far off am I, if at all? ;-)

  • Krannie McKranface

Posted October 21, 2011 - 01:52 PM

#9

After reading all that (which I noticed was in the stickies) and the sticky on "how to eliminate the bog", I determined that maybe I had too big a leak jet. I pulled the carb apart, found that the AP wasn't working properly, cleaned it as per the sticky and looked at the size of my Leak Jet... 40! After putting it back together, I turned out the mix screw 2 full turns and started it. It took me about 5 minutes for the bike to be hot enough to take off the choke.

I then adjusted the idle down a bit and CRACKED the throttle. It stalled for a split second then revved. I waited a few seconds and then hit it again with the same results.

So here's my question... Since the Leak Jet "leaks" fuel back into the carb from the AP chamber, is it safe to say that the smaller the "leak", the more fuel going into the squirt? As in contrary to the typical thought of what a jet does, a larger Leak Jet (leaking more fuel into the carb bowl) results in a SMALLER amount of fuel squirt, and a smaller leak gives you a BIGGER squirt? If so, maybe my squirt is richening up the mix causing the bog (stall) rather than simply making my quick acceleration snappy like it should be.

How far off am I, if at all? ;-)


You are correct, in a way. The hole in a 50 leak jet is larger than the hole in a 70 leak jet.

It's very easy to determine if you have a lean bog or a rich bog: watch it work!



Bottom line is you have to tilt up the subframe and watch the apump nozzle squirt. It has to just miss the slide, squirt all the way into the head, and last for .8-1.2 seconds. Don't guess, look. You could have the perfect leak jet (50) and the nozzle could be dribbling (clogged) or the the squirt could be hitting the slide (linkage adjustment).

  • Thesykboy

Posted October 21, 2011 - 02:10 PM

#10

Nope, I've watched the squirt into the carb. Actually, it looked like the size of the squirt coming off a #40 leak jet was dinky, but I also have no frame of reference. I've seen how BIG the squirt can be when I ran carb (it was impressive) but the standard amount coming resulting from that #40 leak jet was about as big as a piece of thread pulled taut.

So I guess the next item would be, what size squirt? Also, I have not adjusted the "timing" for the AP. When I hit the throttle, the squirt typically hits the slide. I imagine it's supposed to go directly into the chamber yes?

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  • Krannie McKranface

Posted October 21, 2011 - 03:50 PM

#11

Nope, I've watched the squirt into the carb. Actually, it looked like the size of the squirt coming off a #40 leak jet was dinky, but I also have no frame of reference. I've seen how BIG the squirt can be when I ran carb (it was impressive) but the standard amount coming resulting from that #40 leak jet was about as big as a piece of thread pulled taut.

So I guess the next item would be, what size squirt? Also, I have not adjusted the "timing" for the AP. When I hit the throttle, the squirt typically hits the slide. I imagine it's supposed to go directly into the chamber yes?


Read what I already wrote.

I don't know what you mean by the 'size' of the squirt....that is irrelevant. It's how far it goes, for how long, and when.

If it hits the slide, it will run like crap.

  • Thesykboy

Posted October 23, 2011 - 02:23 PM

#12

I've learned a couple things over the last 48 hours that I wanted to share/get clarification.

1. Regarding the elusive "bog". When you have your bike as idle... just sitting there minding it's own business and you SNAP the throttle, that split second hesitation is apparently normal and NOT the "bog" I thought it was.

If you snap the throttle over and over a few times, it almost makes a slapping noise as the slow idle stalls, then finally gets the the fuel from the acc pump that it had to wait on since that lazy ass throttle slide was in the way! I tried all the methods in the Sticky and that result did not change. However, during my experimentation, I did in fact learn what the actual "bog" is that the acc pump adjustment fixes. So now that I know what I was experiencing is actually NORMAL, I can move onto the next bit.

2. I've again tried working with all the recommendations that I got regarding my low end performance. I dropped the pilot from a #50 to a #45 thinking that it was too rich only to do a couple other things and go back to the #50. After taking a ride around the block, doing a full oil change and then going to the Spray N Wash, it occurred to me... if the bike runs better with the choke ON (though no perfect) then I must be too lean still! So I continued to ride for another 5 minutes... this time though, as the bike sounded bad at lower RPM, I reached down and very slightly opened the choke (like 3 or 4mm) and held it open as I rode. The moment I did this, she ran perfectly! I let the choke go, it sputtered and cut out. Pulled the choke out a hair and it ran beautifully again.

So my next step is to figure out if I need to jump up to a #55 or if a #52 will do the job.

Anyone got a recommendation?

Oh! and here's a pic of the plug after my experimentation ride... Looks lean to me.

Posted Image

  • Thesykboy

Posted November 10, 2011 - 06:38 PM

#13

I tried the #55 pilot and it still feels lean. When I ride down the road I still find that the bike runs better when the chock is pulled out just a hair.

I experimented with the height of the needle jet in hopes that raising the needle from the 3rd position to 4th might give me the smoothness I'm looking for. No luck. So I raised it again 1 more position (5th) and not only did it not run better, but it blew a little smoke out the pipe. So I think I'm gonna drop it back down to 3.

Could it be that I need to be running a #58? Every shop I've gone to has said that when a new WR450 comes to Colorado it usually has to be jetted DOWN from the stock jetting (#45) due to high altitude and here I am almost 13 increments HIGHER than stock!

Mixture is set fine and when that choke is out like 3 or 4mm, it runs smooth as butter.

Am I missing something or do I really need to look at a BIGGER pilot jet?

  • Krannie McKranface

Posted November 10, 2011 - 07:35 PM

#14

I tried the #55 pilot and it still feels lean. When I ride down the road I still find that the bike runs better when the chock is pulled out just a hair.

I experimented with the height of the needle jet in hopes that raising the needle from the 3rd position to 4th might give me the smoothness I'm looking for. No luck. So I raised it again 1 more position (5th) and not only did it not run better, but it blew a little smoke out the pipe. So I think I'm gonna drop it back down to 3.

Could it be that I need to be running a #58? Every shop I've gone to has said that when a new WR450 comes to Colorado it usually has to be jetted DOWN from the stock jetting (#45) due to high altitude and here I am almost 13 increments HIGHER than stock!

Mixture is set fine and when that choke is out like 3 or 4mm, it runs smooth as butter.

Am I missing something or do I really need to look at a BIGGER pilot jet?


Yes, you are missing something.

You have a lean condition that the pilot jet circuit is contaminated by.

- air leak at the boot
- exhaust crush washer
- sticky hot start
- clogged pilot jet passage above the pilot (common)
- bad o-ring for the fuel screw
- badly worn slide cavity
- missing gasket on the slide vaccum plate

The ONLY way to determine your pilot size is with the fuel screw: 1-1.5 is the correct turns. If you go more, you need a bigger pilot....assuming you have addressed all the above issues.

  • Thesykboy

Posted November 10, 2011 - 07:55 PM

#15

Well, the mixture screw is 1 4/5 way out. I guess that would mean I'm still running lean on the pilot.

  • bg10459

Posted November 11, 2011 - 09:05 PM

#16

You are correct, in a way. The hole in a 50 leak jet is larger than the hole in a 70 leak jet.

I'm sorry, but this is backwards. A 50 leak jet is smaller then a 70 and allows less fuel to leak out of the ap circuit. The smallest, or richest leak jet you can get (make) is a zero, i.e. soldered shut, leaks no fuel from ap circuit, 100% squirt. On an 03, at very cold temps you might need one, but a 40 (smallest you can buy) or 50 should be OK.

Anyway, even in the dead of winter, you shouldn't need more than a 52 pilot jet, and I'm talking SUB zero temps. Probably more like a 45 or 48. Krannie made some good suggestions for what to check, but add to that the slide plate orientation. Has it ever been removed? Could be in backwards :busted: That would cause lean pilot symptoms.

  • Thesykboy

Posted November 11, 2011 - 09:25 PM

#17

Well, I think I got it. Apparently one of Krannie's suggestions got me the right results.

I pulled off the carb, removed everything and resprayed every port on the thing. Apparently there was a small amount of blockage in the pilot jet housing. I get it back together (with my #50 pilot installed), took it for a ride and was able to keep the bike running with the mixture screw completely closed. And it actually idled and sounded smooth at low RPM for a change.

So tomorrow I'm reinstalling the #45 pilot to see how she goes. Now what to do with all these extra jets...

Progress feels good! Hope I have this much luck rebuilding the engine for my VW Bus (the next project)!

  • Krannie McKranface

Posted November 11, 2011 - 10:05 PM

#18

I'm sorry, but this is backwards. A 50 leak jet is smaller then a 70 and allows less fuel to leak out of the ap circuit. The smallest, or richest leak jet you can get (make) is a zero, i.e. soldered shut, leaks no fuel from ap circuit, 100% squirt. On an 03, at very cold temps you might need one, but a 40 (smallest you can buy) or 50 should be OK.

Anyway, even in the dead of winter, you shouldn't need more than a 52 pilot jet, and I'm talking SUB zero temps. Probably more like a 45 or 48. Krannie made some good suggestions for what to check, but add to that the slide plate orientation. Has it ever been removed? Could be in backwards :busted: That would cause lean pilot symptoms.


No, you are right, I said it exactly backwards. I meant to say a 50 is more fuel, not a larger jet.

  • MaxPower

Posted November 14, 2011 - 01:25 PM

#19

check the hot start cable where it enters your carb. On my 450,the cable entered the carb from the top.At point of entry of the carb there was a plastic piece that cracked causing a very erratic lean condition. I replaced it with sm aluminum piece

  • Thesykboy

Posted November 15, 2011 - 09:25 PM

#20

You know Max, I can't tell you how many times I've caught that little plastic nut out of place after wondering why it's still running lean! I have it taken care of now...

So I think I have this baby licked! After hearing it pop and stutter with a #45 pilot and seeing it run GREAT with a #50 (but while being able to bottom out the mix screw with no idle change), I settled on a #48. And my needle clip is on the 3rd place setting FWIW.

It runs smooth on the #48, but if I bottom out the mixture, it doesn't die. It runs REALLY rough and sounds like it could eventually die, but it continues to run. I got the screw out to 1 1/2 turns to have a smooth idle, but I still wanted to check and inquire as to if where I'm at sounds about right. Since it took almost exactly 3 turns out to get the idle smooth (still backfired though) on the #45, I figured the #48 HAD to be the trick.

How'd I do?




 
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