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Need some insight on jetting on a RM-Z 450.

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Hi guys, first post here. I just picked up a 07 RM-Z 450 Carmichael edition a few weeks ago, and this bike is mostly all good, but this is my first big four stroke and I have a few questions.

 

So the dilemma is, at the very first crack of the throttle, barely moving it off idle as you're slipping out the clutch, the bike has a wicked stumble. It'll stumble for 1 second or so and then catch itself and run perfectly strong. The warmer the bike gets the less noticeable the issue is. The other thing is, on decel it pops and crackles a pretty good amount, more than what I'd think is acceptable. 

 

So I've neared the conclusion that the pilot jet is lean. The bike has a full Pro Circuit T-4 header and silencer combo, and from what I've seen (and cross checked in the service manual), the jetting is stock. I ordered a pilot fuel screw for it so that I can play with the low speed mixture and see if I can improve things, but I'd really like to get the feedback of the community here before I proceed. When pulled apart, I noticed the exhaust valve stems were white (possibly indicating a lean condition??) The plug however looked fairly good by my standards, burning a nice tan color. I've attached a few photos of the electrode and the exhaust valves. Haven't put feeler gauges on the tappets yet, but that is also on the agenda.

 

27067378830_0f22c4b2f3_o.jpgIMG_4643 by oh1slowsix, on Flickr

 

27067379510_2787e5afea_o.jpgIMG_4641 by oh1slowsix, on Flickr

 

Thanks in Advance,

Corey

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Pilot should be a 45, which it probably is, and is for IDLE ONLY.

Adjust the fuel screw for max idle, then lower the idle with idle screw, if needed.

This will addres the decel popping, assuming your hot start is working perfectly, and your exahust gaskets are sealing.

 

Your symptom is one of a RICH NEEDLE setting.

Drop the needle one clip.....BUT FIRST....

 

If the needle jet (emulsion tube) has never been changed, do that first, as they wear out and oval, causing weird rich conditions.

 

Get an R&D fuel screw to make adjusting the pilot circuit easier

 

You can't read a plug unless:

 

- you use non-pump gas

- you cut the threads off to read the BOTTOM of the porcelin

- you do a throttle cut for each 1/5th of the throttle openings

 

....so don't bother trying......

Edited by KRANNIE

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Awesome, just the answer I was looking for. Thanks so much for the help man, I'm still waiting for a few parts to come in, but when they arrive I'll try out your suggestions and report back!

 

Thanks again!

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Has the accelerator pump shot been checked? Sounds like an accelerator pump problem.....have you done "the O ring mod" to your pump linkage? Check out some of the ,any Youtube videos on the FCR for solutions.

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As solid and william said, also check the duration of the squirt and see if its hitting the slide plate as well.

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Carmichael edition RMZ definitely needs octane booster. That will put you very close with the jetting.

The normal (non-Carmichael) bikes don't need the booster.

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Do you know how to set fuel screw and idle speed? Check if the pilot jet is the right size first. Find out if you can find the sweet spot between 1 and 3 turns out. It might be just the fuel screw that needs some adjustment.

 

I have PC T4 full system on mine and it moves the powerband higher up on mine, so what Krannie says is probably right. Drop the needle, but before that find out if the pilot circuit is set.

 

White-grey buildup on ex valves indicate fuel with high ethanol/methanol content being combusted. Can`t really avoid it nowadays to be honest. Do a favor to your engine and use seafoam regularly.

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Carmichael edition RMZ definitely needs octane booster. That will put you very close with the jetting.

The normal (non-Carmichael) bikes don't need the booster.

 

Any specific reason for this? I was under the impression that the Carmichael edition engines were the same as the normal 450's.

 

And update: The pilot fuel screw is sitting at 2 1/4 turns out and idles excellent with NO MORE popping/crackling on decel, so I'm good there! The low throttle stumble however is still not cured. I dropped the needle 1 clip leaner using the existing needle/emulsion tube, and it may have helped just a tad, but was not noticeable. I went ahead and bought a new needle and emulsion tube, set the needle back to the factory clip position, and re-installed (just to get a baseline to see if there was a noticeable improvement over the old needle/emulsion tube) The problem became much worse, with bad stumbling, and a good bit of black smoke being presesnt on a quick rev. Going to play with needle position a bit with this needle/tube combo, but if it doesn't get any better I'll just throw the old needle/tube back in. Have not played with the accelerator pump yet.

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Any specific reason for this? I was under the impression that the Carmichael edition engines were the same as the normal 450's.

And update: The pilot fuel screw is sitting at 2 1/4 turns out and idles excellent with NO MORE popping/crackling on decel, so I'm good there! The low throttle stumble however is still not cured. I dropped the needle 1 clip leaner using the existing needle/emulsion tube, and it may have helped just a tad, but was not noticeable. I went ahead and bought a new needle and emulsion tube, set the needle back to the factory clip position, and re-installed (just to get a baseline to see if there was a noticeable improvement over the old needle/emulsion tube) The problem became much worse, with bad stumbling, and a good bit of black smoke being presesnt on a quick rev. Going to play with needle position a bit with this needle/tube combo, but if it doesn't get any better I'll just throw the old needle/tube back in. Have not played with the accelerator pump yet.

He's joking about the Carmichael edition, same engine.

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Any specific reason for this? I was under the impression that the Carmichael edition engines were the same as the normal 450's.

 

And update: The pilot fuel screw is sitting at 2 1/4 turns out and idles excellent with NO MORE popping/crackling on decel, so I'm good there! The low throttle stumble however is still not cured. I dropped the needle 1 clip leaner using the existing needle/emulsion tube, and it may have helped just a tad, but was not noticeable. I went ahead and bought a new needle and emulsion tube, set the needle back to the factory clip position, and re-installed (just to get a baseline to see if there was a noticeable improvement over the old needle/emulsion tube) The problem became much worse, with bad stumbling, and a good bit of black smoke being presesnt on a quick rev. Going to play with needle position a bit with this needle/tube combo, but if it doesn't get any better I'll just throw the old needle/tube back in. Have not played with the accelerator pump yet.

 

Nothing to do with the apump.

 

Do you know for a fact that you got the correct needle jet (emulsion tube) ?

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I bought a carb rebuild kit for supposedly a (05-07 rmz 450). It wasn't a genuine Keihin part, so I suppose it is possible that the new needle and emulsion tube have a looser tolerance than my old genuine Keihin needle/tube. I'm going to put the old one in and drop the needle one more clip and see what it does, if not I may need to just sack up and buy the genuine parts.

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I bought a carb rebuild kit for supposedly a (05-07 rmz 450). It wasn't a genuine Keihin part, so I suppose it is possible that the new needle and emulsion tube have a looser tolerance than my old genuine Keihin needle/tube. I'm going to put the old one in and drop the needle one more clip and see what it does, if not I may need to just sack up and buy the genuine parts.

I used a "Moose" branded rebuild kit and found out the hard way the parts are sub standard. Best to spring for the good stuff I believe.

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I bought a carb rebuild kit for supposedly a (05-07 rmz 450). It wasn't a genuine Keihin part, so I suppose it is possible that the new needle and emulsion tube have a looser tolerance than my old genuine Keihin needle/tube. I'm going to put the old one in and drop the needle one more clip and see what it does, if not I may need to just sack up and buy the genuine parts.

 

Oooooh, you can't do that.

 

Keihin is the only one that works.

...and it needs to be the same Keihin part number, IF , it is stamped on the part.

If it is not, then it needs to be the same Suzuki part number as stock.

 

No Tusk, FMF, Dyna, etc

Edited by KRANNIE

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I figured lol. I hate to have to ask but is there any way you guys could link me to a place to buy the genuine part? I'm not one to ask others to do my internet research for me but I honestly can't find it anywhere.

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I figured lol. I hate to have to ask but is there any way you guys could link me to a place to buy the genuine part? I'm not one to ask others to do my internet research for me but I honestly can't find it anywhere.

 

To know for sure that you have the correct Needle jet part, get if from your Suzuki dealer, the correct year and model.

 

If the original Needle Jet part actually has a part number on it (rare) then you can order it from Sudco, Jetsrus.com, or JDJetting.

 

If you are using anything but Keihin or JD jets or any other carb parts (Jet Needle), replace them now....

 

Needle jet = emulsion tube

Jet needle = 'the' needle

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I used a "Moose" branded rebuild kit and found out the hard way the parts are sub standard. Best to spring for the good stuff I believe.

ive never had a issue with their rebuild kits, my crf450r has a moose kit in it now and runs fantastic.

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I figured lol. I hate to have to ask but is there any way you guys could link me to a place to buy the genuine part? I'm not one to ask others to do my internet research for me but I honestly can't find it anywhere.

Check the oem parts section at Rocky Mountain and Motosport. Jetsrus.com is anothet good site.

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ive never had a issue with their rebuild kits, my crf450r has a moose kit in it now and runs fantastic.

Mine ran fantastic initially too.

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