Who's the Engine Expert???


35 replies to this topic
  • grayracer513

Posted November 07, 2007 - 01:48 PM

#21

Black smoke is too rich. I will guess that your jetting was borderline fat before the pipe went on, and is over the line now.

But there are 3 other things to look at:
> Is the needle clip still in place, and the screw securing the needle still there?

> Is the float level higher than normal?

> Seems obvious, but is the air filter clean?

  • polarbear

Posted November 07, 2007 - 04:28 PM

#22

I will check those three things. I am going to work on it tomorrow. The spark plug is still the original one from when I bought it. I'm hoping this is most of the problem. But I will check the Valves, (done that many times), and the needle clip, screw and float level. Yes the filter is clean. ha ha ... If it had a 162 and now it has a 158, and still black, does this mean I need to go down even more? It would really be easy if anyone had the same exhaust on the same bike at the same altitude as me, then I could put the same jetting they had. My altitude is 4500 ft, just incase anyone asks.

  • 2grimjim

Posted November 07, 2007 - 04:36 PM

#23

I will check those three things. I am going to work on it tomorrow. The spark plug is still the original one from when I bought it. I'm hoping this is most of the problem. But I will check the Valves, (done that many times), and the needle clip, screw and float level. Yes the filter is clean. ha ha ... If it had a 162 and now it has a 158, and still black, does this mean I need to go down even more? It would really be easy if anyone had the same exhaust on the same bike at the same altitude as me, then I could put the same jetting they had. My altitude is 4500 ft, just incase anyone asks.


Altitude is 4600 feet where I live. This is the jetting I use on my '06 YZ w/FMF pipe:
m.j. 155 summer (>75F), 160 winter
p.j. 42 summer, 45 winter
idle 2.5-3.5 turns
needle NFPS-4,5 summer NFPR-2,3 winter (stock)
float level 9mm

  • polarbear

Posted November 08, 2007 - 07:50 PM

#24

Altitude is 4600 feet where I live. This is the jetting I use on my '06 YZ w/FMF pipe:
m.j. 155 summer (>75F), 160 winter
p.j. 42 summer, 45 winter
idle 2.5-3.5 turns
needle NFPS-4,5 summer NFPR-2,3 winter (stock)
float level 9mm


Wow... that was helpfull.... thanks. I am hoping that after I check the carb I will find something simple out of spec. If anyone has similiar altitude levels please let me know what your jetting specs are. Mucho thanks! :worthy:

  • polarbear

Posted November 08, 2007 - 08:03 PM

#25

Hey, I was just thinking after reading your post... you say 2 1/2 to 3 1/2 turns out... I think that maybe that could be my problem. It is only two turns out. Is that stocK??? Would adding more air to the mix help it burn clean and also give it more power??? Just brainstorming here...:worthy:

  • moto867

Posted November 08, 2007 - 08:34 PM

#26

The more you turn the screw out the richer it gets. It is a fuel screw not an air screw, meaning it meters fuel from the pilot circuit. If you turn it in it will be leaner and it only affects the first 1/4 throttle or so. Generally speaking if you have to go out more than 3 turns you need a richer pilot jet, if you have to go in to one turn out or less you need a leaner one. I think there is a sticky in the jetting forum on setting the fuel screw.

  • 2grimjim

Posted November 08, 2007 - 08:35 PM

#27

Hey, I was just thinking after reading your post... you say 2 1/2 to 3 1/2 turns out... I think that maybe that could be my problem. It is only two turns out. Is that stocK??? Would adding more air to the mix help it burn clean and also give it more power??? Just brainstorming here...:worthy:


My idle mixture varies depending on temperature. Start @ 2 turns out and open as required. When it's right your bike should start hot in 1 or 2 kicks.
If you turn the idle mixture screw in all the way (0 turns) the engine should die. if it doesn't die with the idle mixture screw closed you need to go down one size on the pilot jet.

  • grayracer513

Posted November 08, 2007 - 08:56 PM

#28

Two things to bear in mind:

> Jim's jetting is for an FMF pipe, and for the most part, FMF comp pipes jet up very close to stock. My experience with WB pipes is that they need to be a little leaner.

> A fuel screw that needs to be turned out more than 2.5 turns usually indicates the need for a larger pilot jet.

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  • 2grimjim

Posted November 08, 2007 - 09:04 PM

#29

Two things to bear in mind:

> A fuel screw that needs to be turned out more than 2.5 turns usually indicates the need for a larger pilot jet.


Not to be argumentative here grey, I've heard this before but when I follow this rule I end up with a bike that's hard to start hot and the idle screw has little influence (won't affect idle quality or rpm).

Never really spent any time with a 4 gas trying to diagnose.

Do you think this is just something particular to high altitude operation?

  • grayracer513

Posted November 08, 2007 - 09:36 PM

#30

I haven't heard that from high altitude people before, but there might be something to it. An excessively rich idle circuit does make them tough to start hot, though. Possibly the idle air jet might need to be larger.

Another risk of running the screw too far out is that the reduced spring tension may not hold it in.

  • todds924

Posted November 08, 2007 - 09:41 PM

#31

I haven't heard that from high altitude people before, but there might be something to it. An excessively rich idle circuit does make them tough to start hot, though. Possibly the idle air jet might need to be larger.

Another risk of running the screw too far out is that the reduced spring tension may not hold it in.


I have seen the aftermarket screws fall out rather easily at anything from 2.5 turns up. I like the stock brass ones. Not much harder to adjust with the proper little flat blade bit. There is no reason for the screw to be more than 2.5 however.

  • grayracer513

Posted November 08, 2007 - 09:56 PM

#32

Something I've found is that the OEM spring holds much better that the ones that are sometimes included with aftermarket screws.

  • 2grimjim

Posted November 08, 2007 - 10:05 PM

#33

I haven't heard that from high altitude people before, but there might be something to it. An excessively rich idle circuit does make them tough to start hot, though. Possibly the idle air jet might need to be larger.


Haven't played with the IAJ (other than converting WR to YZ spec jetting after disabling thr Air-Cut).

Maybe I'll contact Sudco tomarrow.

  • todds924

Posted November 08, 2007 - 10:08 PM

#34

Haven't played with the IAJ (other than converting WR to YZ spec jetting after disabling thr Air-Cut).

Maybe I'll contact Sudco tomarrow.


If you call Sudco,ask for John....a good friend of mine i race with every weekend!!!!

  • bg10459

Posted November 09, 2007 - 09:03 AM

#35

Haven't played with the IAJ (other than converting WR to YZ spec jetting after disabling thr Air-Cut).

Depending on which method you used to disable the ACV, you may or may not have needed to change the PAJ to YZ spec.:thumbsup:

  • 2grimjim

Posted November 09, 2007 - 05:25 PM

#36

Depending on which method you used to disable the ACV, you may or may not have needed to change the PAJ to YZ spec.:thumbsup:


Everything plugged off........same as YZ.





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