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Bad stutter mid throttle

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Hey guys, wondering if anyone has any experience with this, 07 WR450 has a nasty mid throttle stutter in all gears. Tried disconnecting TPS, no change, tried grey wire disconnect, no change. Only way I can get it to go away is to drop the needle one position. Then mid throttle stutter goes away but bike won't idle (unless its at 2krpm) and backfires like crazy when on decel.

 

Two brothers exhaust and a boyesen quick shot are the only mods. Quick shot is only 1/2 turn out.

 

Any help is appreciated! I've fought with this thing for months to get the jetting dialed in right and now I get this :(

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Known problem

 

What is your jetting, and are you uncorked?

 

Without that info it's impossible to help.

 

Dropping the needle should not get you decel popping, unless you have adjusted the fuel screw starting with a high idle.........

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55 pilot I think the main is a 170. I'm about 4500 feet elevation also... Uncorked? And I had that thought about setting idle off high idle today :/ Definitely possible but not sure what to tweak to fix it. The bike runs great and idles great, except that violent stutter. To make things stranger I put 91 Octane in (I usually only run 85) and it seemed to make it worse.

Edited by Warhog53

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Have to know the actual jets

 

Pilot

Main

Needle

 

45/165/NCVS works great if it's uncorked.

 

You also need an R&D fuel screw, so you can adjust it properly

 

Uncorked means the restrictions on the airbox and exahust have been eliminated, more like a YZ.

 

You really need to read the FAQ section at the top.

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Still corked on the intake side but exhaust is uncorked (two brothers slip on). Needle is off an FMF Powerjet kit that was on the bike when I bought it. I do have an aftermarket air fuel screw so should be good there.

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Krannie helped me with these settings. I live at 4500 ft and ride up to 9000. These are my settings:

Carburetor Settings. 8/2/2013

45 pilot

50 leak jet

160 main jet

NCVS - 3rd Clip

2 turns fuel screw

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Still corked on the intake side but exhaust is uncorked (two brothers slip on). Needle is off an FMF Powerjet kit that was on the bike when I bought it. I do have an aftermarket air fuel screw so should be good there.

 

Uncorking the exahust but not the intake is kind of pointless

At least remove the snorkle

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Messed with the bike all day yesterday, finally got it to where it's running better but I need to drop the main 1 more setting. It feels so strange to have smooth power delivery. I always just figured the 450's were peaky as hell. Thanks for all the help.

Current settings

150 MJ

45 PJ

Closed BQS

Needle 3rd clip

 

My exhaust must be a little more restrictive with the spark arrestor or something. Because it seems to like leaner better. Less and less pop and crackle on decel, and better power delivery the farther I go, still a super minor stutter at mid-high throttle. but it's barely noticeable anymore.

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You are starting to get pretty lean on the main.

On flat ground (no load) you will not notice any problem, but on long uphills, you might notice some detonation. It sounds like little devils with tiny hammers banging around inside the cylinder.

Nothing to be alarmed about, unless you let it detonate it's brains out for months. Unlike a two stroke, it takes a lot of overly-lean riding to do any damge.

  • Like 1

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I'm at 4500 feet too and 168 main. I have a full gytr pipe though. Also, 48 pilot, gytr needle 4th groove all else stock I believe. Runs awesome.

Edited by Summit

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