08 wr450 Help with carb issues after cleaning

31 replies to this topic
  • Mbiker_101

Posted October 02, 2015 - 11:59 AM


Bike was running great, jetted perfectly per this forum. Jd red needle, 4th clip down, 168 main, 45 pilot, 2 turns out

Long story short, Crashed and split my foot open with foot peg so bike was sitting for about 3 months and carb was gummed up due to crappy cali gas.

Cleaned carb in detail, put everything back together with new spark plug.... Starts great but has a small stutter down low like not getting enough gas. Checked tps voltage and .782 volts, so i tore the carb apart again thinking a missed something, checked everything and put back together and had to turn fuel screw out three turns to idle smooth and i still have the stutter. I even unplugged tps because i know that is a quick test.

I'm lost as to what to try next? Why do i have to turn three turns on fuel screw now, what happened? How do i get rid of the stutter?

  • Krannie McKranface

Posted October 03, 2015 - 04:43 PM


You need to use some fishing line to clear the passage above the pilot jet

Follow with light solvent and compressed air

You should also verify the apump squirt casue the nozzle usually gets clogged too

  • Mbiker_101

Posted October 03, 2015 - 10:27 PM


I've verified that the a pump works by squirting cleaner through passages and watch it squirt. Also cleaned all the holes above the pilot jet and blown out with air. Did this twice now thinking that was the issue but still seems to have a stumble. If i nail the throttle there is no sputter or hesitation. Seems to only sputter on very light throttle.

  • Mbiker_101

Posted October 05, 2015 - 06:19 PM


Any more ideas, i'm pretty sure all the passages are clean, made sure of that the second time.

  • stevethe

Posted October 05, 2015 - 07:37 PM


Pilot jets are very difficult to clean. You have to use a wire off a metal brush or just replace it.


Posted October 05, 2015 - 09:47 PM


Don't use metal wire to clean jets and pilots. You will end up boring the jets bigger. Use copper wire because it is softer than the brass jets and will not damage them. Find a piece of scrap electrical wire that has the copper wire braided by dozens of tiny wires. Strip the rubber off of it and you'll have plenty of wire now to clean jets for years to come. Also set that fuel screw to factory specs and adjust idle to that. Then if you need to adjust fuel screw from that point, do it in 1/4 turn increments

  • Mbiker_101

Posted October 06, 2015 - 06:43 AM


I used a brand new pilot jet the same size as the clogged one so i know its good. The other jets i used a copper wire.


Posted October 06, 2015 - 07:10 AM


Where do you have that fuel screw set? Is it still 3 turns out? If so, I'm almost positive that's way too far out. I'll try abd double check on that later today but in most cases 1 1/4 turns out is about normal.

  • Krannie McKranface

Posted October 06, 2015 - 07:28 AM


Fuel screw is adjusted by idle speed, not turns.


If you reach peak idle with more than 2 turns, your pilot jet is too small

If you reach it in less than 1, it's too big.


Once you have the right pilot, the the peak idle, you adjust the idle with the idle screw.


The motor must be HOT before you do this. I mean hot, as in the carb body is no longer at ambient temp, but it wicking in the motor temp.

Run for AT LEAST 15 minutes.


IF YOU START with too high of an idle when adjusting the fuel screw, you will neve get it set correctly.

Start with the lowest possible idle, and raise it with the fuel screw.


After all that, you listen to the idle drop speed after blipping the throttle.

Most people prefer the fastest drop in rpm possible, and this can be achieved by careful very fine turns of the fuel screw (1/8 turn at a time) with a blip in between, and listen to the idle speed drop.


Once you have it dropping fast, you might notice that all your deceleration popping is gone.


Some prefer to have a little decel pop, which means a little more throttle response upon opening, but less upon closing (idle hangs a bit). Turn the fuel screw in for this.


The needle jet, slideplate seal, slide plate, and carb slide bore must be in reasonable condition to achieve good results.

Edited by KRANNIE, October 06, 2015 - 07:29 AM.


Posted October 06, 2015 - 09:13 AM


KRANNIE just put into better words what I had in my head but wasn't really putting on here clearly. ;)

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  • Mbiker_101

Posted October 06, 2015 - 11:39 AM


Thanks guys, i've followed Krannie's instruction before and after the carb cleaning, Krannie you sent me the JD red needle a while ago and i followed youre jetting suggestions and had the bike running great.

I know how to set the fuel screw and i know 3 turns is too much out but still don't understand if i've cleaned everything out to perfection how the fuel screw is now 3 turns outs vs the 2 turns before and running perfect. Is it possible it wasn't that clean before with two turns? Now that i've cleaned it out really well it requires a larger pilot??? Is it possible the float height is off but that shouldn't have changed?

i may yank the carb out again to triple check everything.

  • Krannie McKranface

Posted October 06, 2015 - 02:21 PM


If your float is REALLY high it might do this, but it would also probably smoke black smoke too.........

  • Mbiker_101

Posted November 08, 2015 - 04:15 PM


Ok, I'm ready to toss the bike off a cliff....I've tried all your tips... and i've cleaned the carb 4 times now and still can't get it fixed and the third time even took the carb to the shop to have them double check everything and they said it looks great.

Is it possible it is electrical? I've unplugged the tps to check and it doesn't help so that rules out the tps i think?

Could it be a coil or something? When i crashed it hit pretty hard and maybe jarred soething loose?

Edited by Mbiker_101, November 08, 2015 - 04:18 PM.

  • Krannie McKranface

Posted November 08, 2015 - 04:34 PM


You have never been very specific as to exactly what problem you are experiencing


What throttle position

What rpm




Are you using brand new gas ?


Have you cleaned the stator harness plug out yet??



Plug cap?

Stator pickup covered in ferrous debris?

Loose stator?

Edited by KRANNIE, November 08, 2015 - 04:35 PM.

  • Mbiker_101

Posted November 08, 2015 - 04:40 PM


About 1/8 throttle
Both cold and hot
New VP race gas

Have not cleaned out stator harness plug. But did install new plug.
I'll check the stator.

Thanks for the quick reply.

  • Krannie McKranface

Posted November 08, 2015 - 05:01 PM


About 1/8 throttle
Both cold and hot
New VP race gas

Have not cleaned out stator harness plug. But did install new plug.
I'll check the stator.

Thanks for the quick reply.


If it is purely throttle postion ( rpm is irrelevant) then it's carb

  • Mbiker_101

Posted November 08, 2015 - 05:35 PM


Actually thinking about it it is across the board rpm but feels much stronger down low.

  • Mbiker_101

Posted November 11, 2015 - 07:51 AM


I've dropped the bike off at a local shop for them to test ride and see if they can determine the issue.

In my research i've found out how the air cut valve works and how it makes it run lean or rich. I've cleaned the acv out twice now and noticed it had a very weak spring, is it possible if the acv is opening and closing premature this would explain why i need to turn the fuel screw to three turns out not two as before? If the valve was open like stock it would need two turns out correct, valve closed three turns? But if it had a weak spring it could bounce back and forth at low throttle and cause the weird stutter etc? Just a shot in the dark? I could try to block it like others to see if that helped?

Worst case i have my friends 08wr450 that i may steal his carb to test on my bike to quickly tell if its my carb or electrical?

Thanks again everyone.

  • Krannie McKranface

Posted November 11, 2015 - 08:01 AM


Actually thinking about it it is across the board rpm but feels much stronger down low.

Then it's not the carb....

  • KennyMc

Posted November 11, 2015 - 11:15 AM


KISS = it's the carb. Did you remove the fuel screw? Did the small rubber o-ring come out? Did you put it back in in the right order?

I would still replace the other jets you cleaned. There not expensive.

Also, check to ensure to put the float back together correctly.


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