Yamaha TRX850 Enthusiasts Forum

Can anyone advise the pros and cons of fitting Keihin 39FCRs compared to fitting 41s?

Cheers Terzi

Terzikat wrote:Can anyone advise the pros and cons of fitting Keihin 39FCRs compared to fitting 41s?

Cheers Terzi

Not really, but the 39´s are top on Peder´s TRX....lovely gas response....

when i asked every one who fitted the 39s, they said they wish they would have fitted the 41s !!!!!!!!!!

steve speed wrote:when i asked every one who fitted the 39s, they said they wish they would have fitted the 41s !!!!!!!!!!

Did they say why? I'm genuinely curious as I'm considering 39s over 41s for my bike. They didn't just say that because you trumped their 39s with your 41s? I'm not taking the pee here, just blokes are funny when it comes to the size of stuff...

size of stuff ???? what stuff???

Come on then, what's the real answer. Do the 41's give more top end and the 39's more mid range, or what?

There's a set 41's on evil bay right now, no bids and 3 days to go.
It's only I can't afford them at the moment that I post this here

Terzikat wrote:Come on then, what's the real answer. Do the 41's give more top end and the 39's more mid range, or what?

Like the yanks say, "theres no substitute for cubes". 39's would be a vast improvement over the standard 38's. 41's are another step up. My 41's give great economy, excellent throttle control and brilliant induction roar I imagine that the price difference between the 39's and 41's would be negligible so why would you ? I've never ridden a 39mm equipped TRX and i've never seen a dyno comparison but i wouldn't think that there'd be more than 3hp difference. If you can pick up a set of 39's cheap enough then go for it. Apparently you can get them bored out if curiosity gets the better of you

Peder has as said 39´s, he has a ported head and has taken off on both cylinder and head so high comp. Balanced crank and weighed in pistons.

I have 41´s with NO skimming on either but 878cc set....his bike put´s out more power on the same dyno. Very marginal but anyway...Think i passed him now though with the newly ported head, will see soon i hope!
(Got to skim the head a bit!)

Kevtrx849 wrote:

Terzikat wrote:Come on then, what's the real answer. Do the 41's give more top end and the 39's more mid range, or what?

Like the yanks say, "theres no substitute for cubes". 39's would be a vast improvement over the standard 38's. 41's are another step up. My 41's give great economy, excellent throttle control and brilliant induction roar I imagine that the price difference between the 39's and 41's would be negligible so why would you ? I've never ridden a 39mm equipped TRX and i've never seen a dyno comparison but i wouldn't think that there'd be more than 3hp difference. If you can pick up a set of 39's cheap enough then go for it. Apparently you can get them bored out if curiosity gets the better of you

39s good, 41s better.

From the perspective of a 39 owner...

I have no complaints, and with the Akra currently get an easy 85 rwhp running a jet size too rich. When I get off my lazy arse to put the proper jets in I should be up to 88-89 if I'm lucky.

I've not ridden a 41'd TRX so can't comment, but the difference between the 39s and stardard CV carbs is quite startling - bags more grunt all over, instant throttle response and of course 15 extra horses.

Everybody wants 41s of course which makes them harder to come by and probably more expensive. My 39s were brand new and cost me a shade over £300 from Germany. Admittedly they were kitted for a TDM which has longer inlet spigots, but I managed to make my own spigots for next to nothing.

The difference between 39s and 41s ... the 39's probably have marginally better torque and midrange, the 41's give more power at the top end of the rev range. I'm still getting 10 miles/litre fuel consumption.

G

Greg wrote:From the perspective of a 39 owner...

...bags more grunt all over, instant throttle response and of course 15 extra horses.

That's answered one of my questions, thanks I'd have expected better response and a bit more power and torque but that's a huge increase for a relatively small cost.

I'm going down the route of 878cc hi comp pistons and ported heads (done), plus full akra (saving up!) and FCRs (saving up for those as well!). Already done the YZF750 front and back ends and now in process of fitting R6 tail (tricky).

Looks like 41's could be the order of the day

Has anyone tried Mikuni equivalents?

Tarwetijger, where on e-bay are the 41FCRs? I can only find a pair of 39's with 6 days to go

It's item number 320305639412
Title = TRX 850 Flat slide carburettors
Seller is in the UK.
Hope this helps?
Hurry up, only two days left!