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scrambler fcr39 jetting with zard low cross

5K views 32 replies 8 participants last post by  RumRunner 
#1 ·
Hi there, I know there are lots of threads on fcr39 jetting but not having any luck finding what I'm looking for. Just curious if anyone has a similar scrambler set up as me and wonder what your jetting/needles are set to

Fcr39 / airbox removed (using unifilters) / Zard low cross / stock cams originally it was set up for TORs but with the zard it seems to be lean. For the needle I'm on the 3rd groove from the bottom (2 grooves showing) - still lean even at 160 mains...

Thanks in advance !

This pipe is awesome btw :) will post video soon
 
#3 ·
#11 ·
still tinkering on that as I type :)
150 mains
60 pilot
Clip position 3 (or whichever shows 2 grooves from the bottom)
about to turn the screws - but first tandori chicken...
 
#12 ·
Did you know that with fcr carbs you can have the wrong needle set up that will limit main jet flow? If the taper is to fat at wot or the needle is to low.You may change main jets a few sizes with out changeing a/f at wot at all.I think a a/f gauge or metter is a must for setting up fcr carbs.fcr carbs are way more adjustable then other carbs for these bikes but you must be able to test what you are adjusting to get them right.One thing afects another.The mains must be in control of wot first before you can get the rest of the carb right.alot of people have way to big of mains and dont even know it.
 
#15 ·
...and I just might be one of those people :)
2008 Scrambler - airbox removed, ai removed, zard, FCRs

60 pilots
150 mains
Clip position 4 (FBR)
fuel screw 1 turn out
air screw - no idea

still seems rich...well it is rich - the damn plugs were black after a bit of a highway run.

The weather has since been crap here so I haven't taken the bike to the garage yet where I can get on a bench and my hands on an a/f gauge...I'm thinking that I'll try a different needle... anyone know what kind of needle to try next?
 
#17 ·
get a a/f gauge play with the mains untill you get around 12.8 at wot at redline(dont know for sure but my guess is you will need around 140 mains.After you get the wot right then look at 3/8throttle and 3/4 throttle dont worry about if there rich or lean at first .What you need to look at is if 3/8 and 3/4 are doing the same way (rich or lean) if one is rich and the other is lean then you need to look at changeing the taper the first letter on the needle.If the taper is right then you need to rase or lower the clip on the needle to get a/f right.if you cant get it before you run out of clip slots then you need to change the 2nd letter of the needle so you can rase or lower the needle more .your leter being a b means you have the needle rased moreto lean it you go to a higher 2nd letter such as m.THE 3RD letter is how thick the needle is that controls 1/8 to 14 throttle.set the fuel screw somewhere around 1 1/2 then adj low speed air screw to set idle mix alittle means alot with the air screw 1/8 turn means alot.I may be wroung but I think 55 pilots is all you need
 
#18 ·
Thanks for the breakdown Mike :) - this Saturday I'll head to the shop and get it on a bench again. They have an a/f gauge I can use. My sense is that you are right as well about the 55 pilots and the smaller mains. The bike is definitely ride-able as is but I want to get it right and it's kinda fun trying to figure this out :)
 
#26 ·
I like the lm2 myself its is very easy to get the tune just right with the play back that you can use on your home puter.Its easy to see whats going on and when its going on.I wish I was smart enough to post a play back movie with play back speed slowed down on here .It show the real deal and its easy to use.On the play back you see a a/f gauge and a tach .You can watch the a/f change as the tach goes up in rpms you can freeze the play back at any point in the run.I like that much better then the charts.
 
#28 ·
DOUG it works way better then the pick up on the dyno I wire mine to the tach wire coming out of the igniter (red wire) so it works as good as the tach on the bike.
I know what you mean though I catch hell getting rpms to read right on the dyno and cant figure why I been wanting to call dyno jet and see if they have any tips,some times it seams to work good other times I have gave up and told the guy to just use the mph chart and dont get a torque reading it sure sucks.BUT i will say that when the dyno works the lm2,the tach on the bike and the tach on the dyno all read pretty close to the same.
 
#29 ·
Mike,

Thanks for the info. Still on the fence on a LM2 vs. a single gauge unit, having the ability to log would be really nice. I spoke to Dyno Jet, and they said it was a grounding issue which made sense to me since I've had that with certain engine dyno's in the past. So we hooked up extra external grounds and it did absolutely nothing.

Doug
 
#30 ·
lol I ran a wire from the neg battery post I was thinking the same thing and it didnt help a bit ether.I kinda wonder if its something that goes on at high rpms with it being a wasted spark system .I hooked up my timing light to the bike once it would work the light good untill about 3000 rpms then the light would just quit working.I tired changeing plug wires ,coils boxes nothing seams to help at all.Maybe there is something strange with how these thing fire at high rpms dang if i know does not make since.
 
#31 ·
I too have had the same issue with Dyno Jets and I think it has to do with the wasted spark. They use an inductive pickup and you start to get cross talk from the "dead" cylinder ay higher rpm. It's a radio frequency interference issue, not a ground issue. Using the negative lead on the ignitor as the LM2 does avoids that issue.
 
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