Adjusting the fuel screw


7 replies to this topic
  • snmhanson

Posted May 15, 2006 - 12:51 PM

#1

If I am properly jetted what should the effect of adjusting the fuel screw be? Should my bikes sound change noticeably as I turn it in or out or is it more of a slight adjustment that I won't even really notice unless I pay very close attention? I always thought the fuel screw essentially allowed you to make minute adjustments to the main jet but I've never really bothered to adjust it much other than turning it to the recommended 1-3/4 turns out. I guess it makes sense then that if you have the wrong main jet in, adjusting the fuel screw won't make any difference at all. can anyone educate me a little in this matter :ride: ? Thanks.

Matt

  • odonnks

Posted May 15, 2006 - 02:53 PM

#2

Once properly adjusting the fuel screw should help you get chrisper throttle response, especially down low.
Look at the graph on this page, That screw and the pilot jet work together, not the main jet.
http://www.thumperfaq.com/jetting.htm

  • snmhanson

Posted May 17, 2006 - 09:34 AM

#3

Thanks for the reply and the info. I'd say thanks for the link as well but because of it I just spent the last hour (when I should have been working) educating myself on the finer aspects of jetting and finding even more tweaks I can make to my bike. Pretty soon I won't even be able to call it a WR anymore, it's going to be some sort of mutated freak, albiet a fast mutated freak. When I get the time I will work on the jetting a bit more and also get into the ACV to see if bypassing it will help me get my jetting spot on.

Matt

  • OneToGo

Posted May 18, 2006 - 03:11 AM

#4

Thanks for the reply and the info. I'd say thanks for the link as well but because of it I just spent the last hour (when I should have been working) educating myself on the finer aspects of jetting and finding even more tweaks I can make to my bike. Pretty soon I won't even be able to call it a WR anymore, it's going to be some sort of mutated freak, albiet a fast mutated freak. When I get the time I will work on the jetting a bit more and also get into the ACV to see if bypassing it will help me get my jetting spot on.

Matt

Hi Matt
The WR is quite sensitive to jetting and can be a bit of a pain. I have changed mine three times with just a 15C temp change...Once dialed in though the bike is great. The ACV (disabled) helps IMO set up the fuel screw and off idle jetting ... no "artifical" interference. For info: I have mine permanently activated in the normal position so the pilot circuit is not richened on decel. A little extra popping but much cleaner on-off throttle response and easier to feel effect of the fuel screw IMO.
A search for ACV should reveal a lot when you are ready...
If you own a thumper with an FCR you have to get intimate with jetting...until EFI comes along... :ride:

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  • snmhanson

Posted May 18, 2006 - 08:08 AM

#5

Yeah, I have jetted several times and although the bike feels strong and IMO has more power all around than my friends MXC450 I just don't know for sure how spot on the jetting is. There is no obvious pops (except the occasional one on decel) or bogs (except the off idle bog), I just don't have a great feel for jetting so I am trying to get all the help I can. I don't mind jetting and it's not all that difficult but I don't always have 45 minutes to spend everytime the temperature changes so I usually just leave the same old 170-48-68-3rd clip on the red needle settings which seem to work reasonbly well for most conditions. I may try going down to a 168 and raising the needle one clip for the summer and see what happens. I just wish access to the needles was a little easier so that you didn't have to disconnect or remove anything to get to the needles. Bring on EFI :banana: :ride: . Then it will be all up to the wife. (i.e. - Well honey, I wouldn't have to spend so much time working on my bike if I just had the new 2008 model with EFI...)

Matt

  • odonnks

Posted May 18, 2006 - 10:23 AM

#6

(i.e. - Well honey, I wouldn't have to spend so much time working on my bike if I just had the new 2008 model with EFI...)


I'll need to begin using that one...

Re the needle, I've always been able to get it out by slipping the carb from the cylinder inlet boot and rotate the top a little towards the left side. Remove the top cover and I use a pair tweezers that came with a electronic tool set to lift the needle out. The tweezers are a 90 deg right angle type that works very well.

  • OneToGo

Posted May 21, 2006 - 05:45 AM

#7

Yeah, I have jetted several times .. There is no obvious pops (except the occasional one on decel) or bogs (except the off idle bog), I just don't have a great feel for jetting so I am trying to get all the help I can. .. leave the same old 170-48-68-3rd clip on the red needle settings which seem to work reasonbly well for most conditions. I may try going down to a 168 and raising the needle one clip for the summer
Matt

Good idea, I think you'll find it (168/clip4) works well:
For Info (as recommended initially by the JD kit)
I used 170-48-70-35 Leak and JD Blue 3 until the temp went above 20c (68F)
Then: 168-48-68-40 Leak FS 1.5 and JD Red 5 up to 25c
Then: 168-48-68-40 Leak FS 1.25 and JD Red 4 at 80F + [because the bike Stuttered at around 1/8 to 1/4 throttle] - Fixed... :ride: BUT, all bikes are different in some small way...

  • OneToGo

Posted May 21, 2006 - 05:59 AM

#8

.
Re the needle, I've always been able to get it out by slipping the carb from the cylinder inlet boot and rotate the top a little towards the left side.


Yep, needle (rotate carb left) and MJ (rotate carb right) should take around 20-25 mins.
IMO, It is way easier if you disconnect the Hot Start plunger after you slide the carb back off the boot. :ride: then reconnect it just before you replace the carb on the boots.
See ARins guide if you need a refresher!




 
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