Yamaha TRX850 Enthusiasts Forum

1. The new carbies are great except when it comes to getting going from stationary...I have to get the revs up to around 3K and then feed a little more throttle after the clutch bites. I could live with that if it wasn't for all the roadworks locally and stop/go signs. I'm thinking she's lean and needs more fuel screw/less air screw. Revs cleanly in neutral, runs fantastic everywhere else...just getting off the line is an issue.
2 Does any extended fuel screw for an FCR fit? Or does it have to be fcr41 specific?
cheers

Well, you`re possibly right they could be a tad lean at the bottom end but remember they take much larger `gulps` of mixture over the stock carbs and require the rider to learn a slightly different approach to opening the throttle too.
I`ve had my beady eyes on these for a while now, they`ll fit ALL Keihin carbs but they ain`t cheap so I`ve held off buying some:

http://www.ebay.co.uk/itm/230595990973? ... 1423.l2649

Great idea and if money isn`t an issue why not?

Cheers Mince...unfort I read a user review on those that the cable had snapped early on. I'll probably opt for this kind:

and maybe longer fuel/vac tubes so I can tune with the motor running.
You are correct on the throttle...must stop mindlessly wringing its neck to enjoy the noise/power or I'll start getting some fines

Yes I`ve seen those too Dav, mostly on Ebay and `crosser` sites, being made to suit large single FCR`s.
If you`re certain they are compatible (I personally think they would be but be sure to have that confirmed ) they would certainly make tuning easier and being nicely machined and bright anodised in several colours add a little bling too.
Thanks for the heads up about the review on those flexi types, that`s interesting but I`ll wager it`s more to do with poor maintenance, dirty, dry or corroded thread tappings in the carb body causing the torsional forces to load up while in use and break the coils in the flexi drive section.
Remember there`s always plenty of grit, some very fine particles too around crossers. If they are not be efficiently cleaned away those fine grit particles play havoc all around the bike.

Hey Mince, those R and D flex jets don't fit the fcr41s...I found this out the hard way. In much the same way as you can't remove the fuel screw without taking the float bowl off the flex jet won't fit thru the hole in the float bowl. A bugger cause I was looking forward to easy on-the-fly tuning.

Mincehead wrote:Well, you`re possibly right they could be a tad lean at the bottom end but remember they take much larger `gulps` of mixture over the stock carbs and require the rider to learn a slightly different approach to opening the throttle too.
I`ve had my beady eyes on these for a while now, they`ll fit ALL Keihin carbs but they ain`t cheap so I`ve held off buying some:

http://www.ebay.co.uk/itm/230595990973? ... 1423.l2649

Great idea and if money isn`t an issue why not?

Ichecked with a Swedish dirttrack company and the one´s they had fit all Keihin´s, although you had to cut them some as there are little space for ´em....not worth it me thinks....

Dav wrote:Hey Mince, those R and D flex jets don't fit the fcr41s...I found this out the hard way. In much the same way as you can't remove the fuel screw without taking the float bowl off the flex jet won't fit thru the hole in the float bowl. A bugger cause I was looking forward to easy on-the-fly tuning.

That`s a real shame Dav, I had `wondered` and did say to check that out (you might remember?) that tunnel is pretty narrow through the float bowl. The screws could be extended to sit outside of the float bowl altogether, you would need to have longer ones ones made as brazing the originals would likely cause distortion and a level of re-machining that might compromise them.

I got a reply back from R & D themselves (rather than the ebay reseller)...they said the 3 bolt float bowl (which the 41s have) simply needs to be drilled out. I'm going for it

Is there enough `meat` in the casting wall for that, just how much bigger does the tunnel need to be?

Plenty o' meat and just a gnat's chuff (aka the thickness of the threads). I'll measure properly before drilling and post back (tomorrow)

The hole was ovalised as it was cast rather than machined...varied b/w 5.3 and 6mm. I did a test drill on some scrap titanium and found a perfectly round 6mm hole is a nice clearance fit for the jet/flex jet. Went ahead and drilled the float holes out to 6mm and result! Off to the bike we go:



edit: I found better places to hang the screws than off the bowls. Now to tune

Ahaaa, looking good Dav. Cheers for the update and piccies I think I will eventually go down the same route, makes fine tuning on the dyno so much easier.
By the way UK TRX`ers there`s more up on Evilbay now, again a Duke set devoid of the TPS though:

http://www.ebay.co.uk/itm/Keihin-FCR-41 ... 1c254a67aa

Hmm, well it certainly makes fooling with the bike a lot easier...although I haven't nailed the lack of power off idle issue. I did take notes and changed the fuel screw in half turn steps from 1/2 a turn out to 2.5 turns against the standard air screw setting and then changed the air screw against the standard pilot setting from 1/2 a trun to 2.5 turns. Interestingly the air screw had the most pronounced effect on idle speed (idled highest at 2.5 turns). The answer is in that matrix methinks. Enough for today. Next time around I'll remember to take a fan to the garage. Beer o'clock

I can pull away on my FCR's at 1500rpm no bother and it will run happily at that open the throttle and it goes no hesitation but mine is rich at the WOT. I will be getting some of these adjusters and some jets together for a dyno sesion I think

i Have had a look around but while we are here,
recommended jetting start point for fcrs?
170 odd main, what about the other jets?
I am going to be running 39s, not 41s, split is well underway from a 4 bank.
No big issues, I will do a report.