FCR Carb boring for the XR

a couple before and after shots of the FCR

What diameter did you end with?

And why not a keyhole bore so you won't lose low end?

All right, it for a road racer ,all top end.

im looking to get a fcr-mx 40 bored out to 43 mm, ive seen a site offering this in the states, im wondering if any ones got any feedback about this, ive reached the flow limit of my carb, i like the way the fcr works, just want more!

temporary kiwi wrote:im looking to get a fcr-mx 40 bored out to 43 mm, ive seen a site offering this in the states, im wondering if any ones got any feedback about this, ive reached the flow limit of my carb, i like the way the fcr works, just want more!

I know with stock carb and no airbox mods mine did 55 the other without any problems ?.

ive sent my fcr 37 over to sredrums machining to get bored to 43mm[ with new venturi insert, im only running a fcr 40mx at present, ill be getting a couple of dyno runs prior/ after to compare outputs, ive est rwhp @62ish, so ill see if the seat of my pants are accurate or not, seems to be capable of roll on powerstands in 4th gear at present, cant give it full throttle in 3rd at mid revs without it trying to flip over, ,ye he he

just got me carb back, in a word - 'awesome', sredrums got carb boring sussed, i gave him specs my mtrs running, he suggested the max size for my carb body, as im after more hp everywhere, he also reccommended a alt needle to use , then even ordered and supplied it upon my request, to think id been told that it could only be straight bored to 40.8mm here in nz[ a local m/sport eng shop] only problem is ive just had my back surgery, and wont be able to try it or my new clark fuel tank for a month or two, [torturous just thinking about all those gee gees waiting to be unleashed] ah well sweet dreams await!

just to update progress, ive just carried out a left hand cable driver conversion to my fcr40-mx, this was required to enable use of my clarke 16l tank with the fcr carb, i also removed the std cable housing and roughly remodeled accel pump cover, +lightly blow molded f/tank to get extra clearance, ive also ported intake to suit the bigger 43.5mm fcr, now converting that carb to l/hand cable drive. hoping to be recouperated enough to be able to kickstart her and do some jet testing [ i beleive the stock port is 40mm, id already ported mine previously to suit the taper bored fcr40mx-which is 41mm on the inlet port side, my fcr43.5mm carb has also been taperbored-44.5 on cyl head side-] im now using a crf450-06 inlet rubber manifold, this allows a straighter inlet path,enables a slight amount of extra room around clarke f/tank, this did require some shaving off the frame to allow space for the new velocity stack to suit the larger carb .

Did you ever measure / workout the actual inlet size on the head ?....just wondering what size it is compared to the new carb and isolator ?.

I am almost embarrassed how easily my TM40 fitted, literally plug & play.......

srry, i wont be able to compare the 40mm carb to the 43.5 on a dyno, as ive just sold it along with my xr's only hrc cam & kn air filter, ive started the l/hand conversion, backs still not very willing to bend yet, soon , soon i keep telling myself, ill be back on me bike, ive planned a trip down to our south island in november ,abit of adventure riding+ attending the burt monroe festival in invercargil[ aka worlds fastest indian]so my back better get with the program,

finally completed the stack/adapter" />g" />[img]https://i.servimg.com/u/f72/18/23/50/93/th/dscf_c12[img][/img].jpg[/img]" />" />

finally got my xr back on the road, just about got the jetting sorted, what surprised me [ at first] was needing smaller jets, i had got a richer hrc needle in anticipation of requiring more fuel for more airflow, and yes it is making more power everywhere over the previous fcr40mm, but this is due to my whole mtr's tune/specs were to suit the larger carb, and also because sredrums very good at what he does[ i.e. the tapered boring]this means the carb is being more efficient at vacuuming up the fuel from the bowl[ i.e. higher velocity]now im getting better k's per litre as a side benefit[up to 14/l] just getting my saddlebag mts sorted ready for a 6'000km trip around the sth island, yee hah, im gettin excited

Kiwi, can you give me some pointers on the FCR install?
I have a 41mm one, have not yet tried it. Needs intake extended somehow, any suggestions?
Also how did you convert the cables to the left side, as I think I'll need to do this with Aceribis 24l tank?

you will need a 'nos' carb adapter to extend the airboot to the carb [ its also the velocity stack]the lefty conversion isnt for the faint hearted,i.e. you will need considerable engineering skills/ tools, i first off made a new longer shaft, utilized the tps as a bush to hold the shafts end, cut the cable holder off the accel pump cam, reused the cam in the stock position, made new boss to weld the cable holder too, made up new cable mt once id worked out where i could mt it to carb, this required tapping a thread beside/behind the tps into the boss cast into housing, just drilled the hole deeper, used the tps mt hole as well, made a new front mt thru the slide bore front face, in the recess that allows air to transfer to the choke knob slide [this i made as a stud], made up the s/steel cable holder to suit, then aligned the cable reel to cable holder as close as possible to carb side, id previously worked out the angles required to suit the new cable routing [thru the top eng mt], then cut off std cable mt , remodeled accel pump cover, made a new piece to cover over the hole left by the removal of std cable holder, i also made a new velocity stack as my carb is bored out to 43.5mm, then i shortened some cables to suit cable mt to cable reel length, so not very simple. An easier way is to blow mold the inner side of your f/tank with a hot air gun, work out where the extra clearence is required, use hi powered hot air gun to heat tank in the spot , use a rounded metal object to push the plastic into shape required, do it in stages till desired shape acheived, no need for lefty conversion with this approach, i highly recommend the fcr carb, it just works 'better' than the other options

temporary kiwi wrote:you will need a 'nos' carb adapter to extend the airboot to the carb [ its also the velocity stack]the lefty conversion isnt for the faint hearted,i.e. you will need considerable engineering skills/ tools, i first off made a new longer shaft, utilized the tps as a bush to hold the shafts end, cut the cable holder off the accel pump cam, reused the cam in the stock position, made new boss to weld the cable holder too, made up new cable mt once id worked out where i could mt it to carb, this required tapping a thread beside/behind the tps into the boss cast into housing, just drilled the hole deeper, used the tps mt hole as well, made a new front mt thru the slide bore front face, in the recess that allows air to transfer to the choke knob slide [this i made as a stud], made up the s/steel cable holder to suit, then aligned the cable reel to cable holder as close as possible to carb side, id previously worked out the angles required to suit the new cable routing [thru the top eng mt], then cut off std cable mt , remodeled accel pump cover, made a new piece to cover over the hole left by the removal of std cable holder, i also made a new velocity stack as my carb is bored out to 43.5mm, then i shortened some cables to suit cable mt to cable reel length, so not very simple. An easier way is to blow mold the inner side of your f/tank with a hot air gun, work out where the extra clearence is required, use hi powered hot air gun to heat tank in the spot , use a rounded metal object to push the plastic into shape required, do it in stages till desired shape acheived, no need  for lefty conversion with this approach, i highly recommend the fcr carb, it just works 'better' than the other options

      

Umm, right, I'll be bending the tank out of the way then!! Will put on to-do list...

temporary kiwi wrote:you will need a 'nos' carb adapter to extend the airboot to the carb [ its also the velocity stack]the lefty conversion isnt for the faint hearted,i.e. you will need considerable engineering skills/ tools, i first off made a new longer shaft, utilized the tps as a bush to hold the shafts end, cut the cable holder off the accel pump cam, reused the cam in the stock position, made new boss to weld the cable holder too, made up new cable mt once id worked out where i could mt it to carb, this required tapping a thread beside/behind the tps into the boss cast into housing, just drilled the hole deeper, used the tps mt hole as well, made a new front mt thru the slide bore front face, in the recess that allows air to transfer to the choke knob slide [this i made as a stud], made up the s/steel cable holder to suit, then aligned the cable reel to cable holder as close as possible to carb side, id previously worked out the angles required to suit the new cable routing [thru the top eng mt], then cut off std cable mt , remodeled accel pump cover, made a new piece to cover over the hole left by the removal of std cable holder, i also made a new velocity stack as my carb is bored out to 43.5mm, then i shortened some cables to suit cable mt to cable reel length, so not very simple. An easier way is to blow mold the inner side of your f/tank with a hot air gun, work out where the extra clearence is required, use hi powered hot air gun to heat tank in the spot , use a rounded metal object to push the plastic into shape required, do it in stages till desired shape acheived, no need  for lefty conversion with this approach, i highly recommend the fcr carb, it just works 'better' than the other options

And that dear children was the reason grandad bought mikuni TM40 and lived happyly ever after   


Sorry could not resist , but well done to you kiwi for not being lazy like me and finishing the job