Pilot screw?


11 replies to this topic
  • jjk

Posted May 09, 2014 - 08:19 PM

#1

I noticed this today, is this a pilot screw?

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  • 72degrees

Posted May 09, 2014 - 10:42 PM

#2

Yes. I have an after market one like that on my 04 YZ450F. Much easier to tweak the adjustment if required.



  • f150jokerstyle

Posted May 10, 2014 - 03:57 PM

#3

No, it is not. It's a fuel screw and I believe it is a TUSK brand one at that. I have the same one. For advice or a procedure of how to adjust it look under the common threads link or do a search. If you don't understand something in the adjustment procedure, post up and most will help.



  • 72degrees

Posted May 10, 2014 - 11:57 PM

#4

No, it is not. It's a fuel screw and I believe it is a TUSK brand one at that. I have the same one. For advice or a procedure of how to adjust it look under the common threads link or do a search. If you don't understand something in the adjustment procedure, post up and most will help.

 

So you don't use it to adjust the idle mixture?



  • f150jokerstyle

Posted May 11, 2014 - 08:17 AM

#5

Yes you do use it for that. The fuel screw is the adjustment from zero throttle opening to about 1/8 or less. Its overall effectiveness is dictated by the pilot jet. If you do not reach optimal adjustment from the the fuel screw from .5 turns out to 2 full turns out from fully closed it dictates you need to change pilot jet sizes. The pilot jet covers zero throttle to about 1/4 opening. So they overlap a bit.

  • 72degrees

Posted May 11, 2014 - 09:31 AM

#6

OK. Another US/UK terminology difference. We tend to call it a pilot screw whether it alters the fuel or air (some Mikunis) flow to adjust the mixture. In this case we might specifically call it a pilot fuel screw, or just  a 'mixture screw'. In any case, the extended, knurled version makes it much easier to do the adjustment in the paddock without grovelling about with just the right screwdriver.



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  • grayracer513

Posted May 11, 2014 - 10:29 AM

#7

No, it is not. It's a fuel screw.


And what exactly is the difference?

Yes it's the pilot screw. For adjustment procedures, look in the Common Threads sticky in the forum index. It will be under the Fuel Systems heading.

  • f150jokerstyle

Posted May 11, 2014 - 05:01 PM

#8

And what exactly is the difference?

Yes it's the pilot screw. For adjustment procedures, look in the Common Threads sticky in the forum index. It will be under the Fuel Systems heading.

 

I have a feeling I'm going to be enlightened :facepalm:  

 

Before I do, I have some logic to my madness. When trying to describe to people what the "fuel screw" and or "pilot screw" is used for I find if you mention anything regarding the word "Pilot" they tend to fixate on that word and jump ahead of your explanation and assume it actually adjusts the pilot jet physically. Then I have to reel them back in and start from scratch. I was unaware that in the UK and i'm now sure other areas of the world refer to it as something els nor did I notice this fine gentleman was from the UK.

 

So in short from what I can tell there is not any discernible difference between the two. Hence the reason why I liked his last post because it gave me an education.



  • grayracer513

Posted May 12, 2014 - 06:35 AM

#9

From the Yamaha parts fiche: "5NL-14105-00-00   PILOT SCREW"

 

Whether anyone is confused by it or not, that's the correct nomenclature, and remains so regardless of whether it's an air screw, as with Mikunis, Amals, and most other carbs, a strictly fuel screw (which is somewhat rare), or a fuel/air emulsion adjusting screw, as it is in the FCR/FCR-MX carbs and most automotive applications, because it trims the air/fuel ratio of the pilot circuit.

 

You could make the argument that "fuel screw" is confusing because it doesn't  adjust the main circuit as in the case of a lot of small implement engines like chain saws.



  • 72degrees

Posted May 12, 2014 - 08:16 AM

#10

Luckily I now only have bikes with Dellortos or a Keihin FCR (or FI) so I don't have to stop and think "which way is richer and which way is weaker on this one?"



  • f150jokerstyle

Posted May 12, 2014 - 06:37 PM

#11

From the Yamaha parts fiche: "5NL-14105-00-00   PILOT SCREW"

 

Whether anyone is confused by it or not, that's the correct nomenclature, and remains so regardless of whether it's an air screw, as with Mikunis, Amals, and most other carbs, a strictly fuel screw (which is somewhat rare), or a fuel/air emulsion adjusting screw, as it is in the FCR/FCR-MX carbs and most automotive applications, because it trims the air/fuel ratio of the pilot circuit.

 

You could make the argument that "fuel screw" is confusing because it doesn't  adjust the main circuit as in the case of a lot of small implement engines like chain saws.

Well, if you have to look dumb and be wrong at least learn something from it. Done, done, and done LOL.



  • grayracer513

Posted May 12, 2014 - 08:14 PM

#12

Yeah, but at least calling it the fuel screw differentiates from it being an air screw so people turn it the right way. 







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