FCR carb tuning

68 replies to this topic
  • Andrew_in_OZ

Posted March 06, 2001 - 02:13 PM


Spot on JOHN,
JAMES with different fuel air ratios entering the needle jet via MJ & MAJ can slightly affect needle and clip position jetting possibly more from better atomization of the fuel particles rather than the amount of fuel/air.today I'll be drilling the MAJ passage, firstly with a 3/32 see how it feels with the #170main and clip#4 then a 2.5 mm if not completely happy with the result.


  • Taffy

Posted March 06, 2001 - 02:34 PM



please go straight to the 2.5mm drill. the jet is the RESTRICTION you need & not the carb body.

for a start you will have to line up a very thin drill bit with the hole.

3mm meant i was cutting aluminium but to go from 3/32" (2.4mm) to 2.5mm is just asking for a

or b

anyways good luck

i would think the time you know you've got the ratio of the air fuel correct andy is when going one MJ up makes it richer from 3/4 to red line & going one MJ down makes it run leaner from 3/4 to red line.

one of the first benifits of getting the above right will be to get a true plug chop reading.

i hope you've got a couple of MAJ's so you don't overdo it. drilling the carb out one step at a time isn't the answer.

don't forget that 34mm of drill bit sticking out the chuck will be spot on.


[This message has been edited by Taffy (edited 03-06-2001).]

  • Andrew_in_OZ

Posted March 06, 2001 - 03:04 PM


thanks for your concern,as I've already drilled the MAJ to 2.5mm before I noticed the smaller air passage(stupid me!)I thaught I'd first use the 3/32 as the 2.3mm passage is verry close to spot on,I'm using high quality(expensive) drill-bits and a cutting compound to keep it cool & smooth so should be OK, If the 3/32 is insufficient I might use a 7/64 drill 2.78mm and size the MAJ, this is a bit safer.

PS. this site needs a chat room I've noticed some of us are online at the same time.Is there one?


[This message has been edited by Andrew in OZ (edited 03-06-2001).]

  • Andrew_in_OZ

Posted March 06, 2001 - 03:58 PM


I could be wrong but I found that by going back 1 size MJ did lean out 3/4 to WOT and also very slightly the needle in clip #4,1/4-3/4 felt stronger & crisper.so I figure using the #170MJ gives best 3/4-WOT and adding a fraction more air(via MAJ)should tidy up everything from 1/4-rev limit.If this doesent work I'll get the MJ & MAJ right and ive got some tiny.2mm thich washers I found in a dead VCR to adjust the needle height between 2 clips.I just like it perfect as posible.

YZ timing,EKN needle, VORTEX dualcurve ignition
SF triple platinum s/plug
open box -unifilter
98oct fuel
Staintune s/s open exhaust& header......
Somebody stop me !!!

  • Shane

Posted March 06, 2001 - 06:43 PM


James...... Correct me if iam wrong... you took out the MAJ and left it out and are drilling it out a bit? is this the case? also which exhaust would you recommend? for a 2000 WR YZ timed and all your carb suggestions.... Ive got the white bros eseries (s-bend) with no disks just an end cap.... I put the ekp and 48 pilot and 100 air into my buddys WR today and hes running a DMC tapered head pipe with the FMF powercore it seems that his rips much harder off the bottom (no hes not yz timed yet) Is this just the WR timing or the tapered head pipe? My brother has a 2000 WR as well with a e series pro-meg pipe and tapered header Iam thinking about trading him some work on his bike for a swap of exhaust systems (hehehe)

Taffy..... Ordered the screw this afternoon, ill give it a try and see what happens....

Shane from Washington

  • James_Dean

Posted March 06, 2001 - 10:31 PM



The jet was removed and nothing has been drilled (yet).

I'm not the person to ask which exhaust is better. My '00WR currently has a stock YZ exhaust.


  • Taffy

Posted March 07, 2001 - 12:37 AM



i'm finding it really hard to follow your results. are you recording them? i'm sure you're not.

when you say "i'll go to 170" i have to go trundling around looking for your previous MJ! when you move the needle i think 'is that up or down?'.

the chat room would be great for chin wagging & moab & double whoppers (you can tell i do enduro!) & triple whoppers (with extra cheese).

we petrol heads would never put anything on paper or have time to reflect...

have i got crossed wires over the drilling? what i meant was bore the carb out to 7/64 or 3mm & have a couple of MAJ's that can overtake each other (No's 230-300).

the bore in the carb body must be larger than the MAJ for valid results!

i'll be very interested in what happens to your needle after you've got the MJ/MAJ relationship right.

over on the "at last more..." i recorded the two sets of tests, james can weave his way through all that stuff, but i can't.

that's why three days after you've said something 5 times someone asks the same question again!

you keep it going aussie boy! & remember the man who put up all the info on this STILL hasn't got any of the bits in. nobody remembers the englishman that invented 'it', they only remember the american that sold it!!!!!


  • Andrew_in_OZ

Posted March 07, 2001 - 04:55 AM


:) Taffy? now I'm :D :D
Taffy, JAMES & others please check before drilling,I noticed the air passage goes in at 90 degres for aprox 5mm then changes direction about 5-10 degres downward, the first part is 3/32 Dia the second/angled part seems to be only 2mm dia, the straight part of a 2mm drill bit will move snugly through it so using this as a guide to get the angle right I drilled a 3/32 hole, this looks good and clean through the passage, angle appears right,the outer 3 threads(where the MAJ screws into) have just been touched but there was no grabbing or cross threading at all when re-installing the MAJ.*WARNING*Using a larger dia drill bit will result in either or both changing the angle or dammage to MAJ threads.If you drill straight through with a 3/32 or larger you may have an 8 instead of a 0 shape on the inside of the emulsion chamber risking loss of performance.
Could someone please virify this!
YZ timing,EKN needle, VORTEX dualcurve ignition
SF triple platinum s/plug
open box -unifilter
98oct fuel
Staintune s/s open exhaust& header......
Somebody stop me !!!

[This message has been edited by Andrew in OZ (edited 03-07-2001).]

[This message has been edited by Andrew in OZ (edited 03-07-2001).]

  • Taffy

Posted March 07, 2001 - 05:32 AM


i was ok with the '99. it's a straight line in.

remember your just letting air in!!

as long as you use the air jet at the front & the hole behind is bigger than the jet you'll be ok.


[This message has been edited by Taffy (edited 03-07-2001).]

  • James_Dean

Posted March 07, 2001 - 09:00 AM


Note of caution:

Yes, the '00 and '01 FCR carbs have the main air jet passage and main air jet threads at different angles. At first glance it looks like it was not drilled clean and almost oval. The angles give this appearance. Drilling the passage bigger than 3/32 (2.38mm) could damage the threads for the main air jet, causing problems if you choose to reinstall the main air jet.

(Thanks Andrew)


[This message has been edited by James Dean (edited 03-07-2001).]

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  • Taffy

Posted March 07, 2001 - 11:42 AM


so are you going to surmount this problem or are you beaten!

(loaded question!)


  • Guest_Guest_*

Posted March 07, 2001 - 01:49 PM


Taffy why are you such a dick? if you talked to anyone face to face the way you wave your pen on this board Iam afraid you would be missing most of your teeth.... shape up dude and start treating people with respect and maybe people would take you a bit more seriously.... and dont bother writing back to this post.... just clean up your act... "a little constructive critisim" never hurt anyone right? ahh "I challenge you to post information with out a smart ass remark to other people" and hey it would not even take you and hour to do this!!!!!!!!!

Signed: Your american friend :)

  • Hick

Posted March 07, 2001 - 02:07 PM


Originally posted by sick:
I challenge you to post information without a smart ass remark…

If he did I would only suspect an imposter and ignore the post. Besides, how can you tell when he’s being a smart-alec? Hell, I can barely understand him, the insults must get lost in the translation. I prefer to think of Taffy as just very enthusiastic and very English (he may have already lost all his teeth). :) :D

  • Taffy

Posted March 07, 2001 - 02:38 PM


it depends how you read this!!!!

it depends how you read this

it depends how you read this?

how did you read this?


  • Andrew_in_OZ

Posted March 07, 2001 - 05:38 PM


aftre a good ride today I'm extremely happy with the results of the MAJ mod,it now builds up power all the way to rev limmiter and gets there almost instantly, I will need to go up to a #172main from #170 as there is mild hesitation felt from 2/3 to WOT when using race/YZ curve on my ignition. EKN in clip#4 feels excelent now (no rich/rough feeling) strong & crisp.
PS. take it easy on Taffy he might ask for it sometimes but remember his bike is out of action and I know I would'nt be a verry nice person to talk to if I were in his position :) Sorry; but I had to laugh when reading the above posts though!
YZ timing,EKN needle, VORTEX dualcurve ignition
SF triple platinum s/plug
open box -unifilter
98oct fuel
Staintune s/s open exhaust& header......
Somebody stop me !!!

[This message has been edited by Andrew in OZ (edited 03-07-2001).]

  • James_Dean

Posted March 07, 2001 - 09:21 PM


Taffy & Andrew,

The last post was a bit too extreme, but I didn't say that it absolutely would damage the threads. Just use caution!

Just finished drilling the passage to 7/64 (2.8mm) and did no damage to the threads! :D

The reason the passages don't line up is they are each on separate parts. There is an upper and lower body to the carb and each has a hole for the main air to flow. The holes don't line up perfectly as it comes. However, they can be enlarged to 7/64 by carefully drilling as an assembly without damaging the threads, which is what I did.

The passages can also be enlarged by separating the two parts and drilling each piece individually. This choice requires removing the painted screws with a 2.5mm hex wrench. This is much more time consuming.

Next step is to turn the #200 into a #220 and try out the newly installed PAJ screw. :)


  • Andrew_in_OZ

Posted March 08, 2001 - 03:53 AM


Thanks for the info, do you think the variation in alignment of the two passages by only a fraction of a mm or so, could explain the difference in jetting required for various bikes with the same/similar mods and conditions(Alt,temp,etc).Also when drilling air passage did you drill straight through or at a slight angle?


  • James_Dean

Posted March 08, 2001 - 07:48 AM


The bend in the main air jet passage should not make a difference from bike to bike using the same carbs. There may be a difference between the '98/99 and '00/01 versions. As you mentioned, a 2mm drill would pass straight through the crooked path but the passageway was actually a little bigger. The angle to drill it oversize and straight was not much. It may have only been 5 degrees.

  • John_in_Long_Beach

Posted March 08, 2001 - 05:00 PM



I have been reading your posts in anticipation of maybe making the same mods. So thanks in advance for your efforts and posting your results.

Your post above where you were happy with the results and the bike wound out to redline easier: Was this with a 238 (3/32") hole drilled and no MAJ installed?

Are you planning on making a custom MAJ by drilling out a #200 MAJ, or will you just leave the MAJ out?

Any thoughts James or Taffy?

  • Andrew_in_OZ

Posted March 08, 2001 - 06:45 PM


Yes this was with a 3/32(2.38mm) passage and a MAJ drilled to 2.5mm (close to having no MAJ)Although I would recomend drilling a 7/64(2.8mm)-3mm air passage VERY carefully (NOT forgetting to remove needle & needle jet)and re-sizing a couple of MAJ's to suit your bike/mods as James & Taffy have sugested.I will be re-drilling to 2.8-3mm air passage and see how the 2.5mm MAJ goes, If too lean
I'll drill a MAJ to 3/32 to get the same results as I now have (unless James/Taffy/? finds a 2.??mm works better. Just as a matter of intrest, did you have any trouble following my results?
GOOD LUCK & let us know how it goes!!


[This message has been edited by Andrew in OZ (edited 03-08-2001).]


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