Yamaha TRX850 Enthusiasts Forum

For the first time - almost like popping a cherry!

Anyway - here's the graph,



Dunno if you can see the numbers, but it made 82 bhp at the wheel, and I asked him to limit at 9000 rpm, but looking at the charts the HP figure started to tail off before then anyway.

It was only supposed to be a suck-it-and-see run, so didn't expect a full tune, but the guy in the know said that it was quite rich at idle and WOT, but spot on in the cruising range. Idle can be sorted with a tweak on the air-screw, but from what he suggested regarding WOT, I could probably get the mix right by going down a jet size, but if I do that will I be able to maintain the mid-range by simply lifting the needle, or will I have to mess around with needle profiles as well..??

I can't remember what the needle codes were, but I have a chart to decipher the numbers if needs be, and as far as I remember the mains were 155s. Carbs are FCR 39s, full Akra exhaust, TPS mod.

Interesting morning though ..

G

Greg wrote:For the first time - almost like popping a cherry!

Anyway - here's the graph,

Dunno if you can see the numbers, but it made 82 bhp at the wheel, and I asked him to limit at 9000 rpm, but looking at the charts the HP figure started to tail off before then anyway.

It was only supposed to be a suck-it-and-see run, so didn't expect a full tune, but the guy in the know said that it was quite rich at idle and WOT, but spot on in the cruising range. Idle can be sorted with a tweak on the air-screw, but from what he suggested regarding WOT, I could probably get the mix right by going down a jet size, but if I do that will I be able to maintain the mid-range by simply lifting the needle, or will I have to mess around with needle profiles as well..??

I can't remember what the needle codes were, but I have a chart to decipher the numbers if needs be, and as far as I remember the mains were 155s. Carbs are FCR 39s, full Akra exhaust, TPS mod.

Interesting morning though ..

G

They are same as 41´s but smaller right?
Then there should be a spike from the acc pump...and that dip there....that´s lean as fekk. This is a WOT run right? So no other parts of the carbs are involved?
...did you try it without acc pump??

Killerwhale wrote: They are same as 41´s but smaller right?
Then there should be a spike from the acc pump...and that dip there....that´s lean as fekk. This is a WOT run right? So no other parts of the carbs are involved?
...did you try it without acc pump??

that dip (on the A/F curve) is rich, not lean.

youngy wrote:

Killerwhale wrote: They are same as 41´s but smaller right?
Then there should be a spike from the acc pump...and that dip there....that´s lean as fekk. This is a WOT run right? So no other parts of the carbs are involved?
...did you try it without acc pump??

that dip (on the A/F curve) is rich, not lean.

Oh, thought it was the same as mine. My bad!!

Yaaah ... the target line is the horizontal red one. I guess the big dip is the spike that Whaley was referring to... Dyno-Man reckoned another 4-5hp if the top-end mixture's right which puts me up to 86-87 which I'll be happy with. I do have another head I can flow a bit though

G

do you have an accelerator pump? could that be what's causing the rich area low down? why oh why do dyno operators put road speed on the printout instead of engine speed??

yes you're rich all the way through the rev range. way rich at 12:1. so you want to drop the main jets by 10 and try again. leave the needles alone. there is alot more power to come from that, as yer man says.

ddi you get a torque curve?

youngy wrote:do you have an accelerator pump? could that be what's causing the rich area low down? why oh why do dyno operators put road speed on the printout instead of engine speed??

yes you're rich all the way through the rev range. way rich at 12:1. so you want to drop the main jets by 10 and try again. leave the needles alone. there is alot more power to come from that, as yer man says.

ddi you get a torque curve?

...and the main jet influence the needle (and vice versa) a LOT on keihin FCR´s
I´ve dropped my needle 2 grooves and use 170 mains

indeed so KW. my point was to change the main jet then run it again. it may be then that the needle needs adjusting, but if you change a bunch of things together it's harder to get it right.

Martin - drop MJs by 10 you say ..?? I'd figured that to maintain the mid-range I'd have to raise the needles too. Dyno-Man reckoned 3 grooves on the needle was worth 1 point on the AF mix... Again I'm clueless here so need to be guided by those with real-world experience of our puppies.

Interesting to see just how much can be gained - glad I was wearing ear-defenders too!

G

Greg wrote:Martin - drop MJs by 10 you say ..?? I'd figured that to maintain the mid-range I'd have to raise the needles too. Dyno-Man reckoned 3 grooves on the needle was worth 1 point on the AF mix... Again I'm clueless here so need to be guided by those with real-world experience of our puppies.

Interesting to see just how much can be gained - glad I was wearing ear-defenders too!

G

Look at my dynoruns under my bike in here....
First run is with needles dropped one groove 4th to 3rd from top...167 main jets
Second run is with 2nd from top and 170 mains.....and of cource 878cc JE kit...

BUT...FCR´s should really not be tuned by a single WOT!! You should devide the throttle in at least quarters and run at the throttle openings wich relates to that part of the carb (idle...slow circuit...needle...main jet)
Then do a thru the gears run not wacking the throttle so you can see that all circuits laps over each other nicely.
There are a lot of hidden power in the FCR´s if they only test the main circuit with a WOT run....

....but that´s my thoughts about it....

them runs are close to mine a spike into lean from closed throttle, rich at half throttle and rich at wot I dropped my mains from 160 to 158 spot on at wot now, tried dropping my needles yesterday just to see what it was like to 2nd groove from 3rd bogged down when first whacked open from half throttle with some vibes then went back to 3rd from top bogged down again but less and with no vibes and pulls itself out of the hole quicker I will go back to the dyno at some point to smooth it out but for now I am happy with how it feels if I were you I would drop the m/j try it then try the needle pos yourself, if it feels better bring it back to the same dyno and give it another go just to check your a/f

Whaley...

I take your point, but this was my first dyno experience, and I did it really just to see what the bike was actually doing - to confirm what the seat of my pants was telling me if you like...

DynoMan did a few cycles, but only datalogged the last one, but he did say that the other cycles showed that the idle circuit was rich, pilot circuit and needle circuits were ok through the 'cruising' rev range and that the WOT was way over...
As with most dynos these days, they're mostly geared to FI bikes with Power Commanders (now I know why I was looking at TDMs on Ebog the other day...) and that the latest generation of Power Commander and software is literally just plug'n'play with the software controlling and re-writing the PC with no other input apart from the operator twisting the throttle - hmmmm Big Brother arrived eh? Anyway, what I guess this means is that there are fewer guys experienced enough with carbs to be able to interpret a graph and suggest appropriate jetting on that basis.

DynoMan has offered runs at £25.00 per as I'm doing my own work ... nice bloke! But I still don't want to spend a really big wad of cash unless I really need to (like on my shiny new rear seat cover ..) I've found a guy in the States who is selling jets at a reasonable price, but it's still going to be a tenner a pair... So, I know the Youngster said to go 10 down, but I'm guessing if I have 155s now, I ought to try 152s and 150s and twiddle with the airscrew..

Keep the suggestions coming..!

Cheers

Greg

Killerwhale wrote:10hp more at 5k revs and just over 5hp more on top, got the A/F almost perfect as well! Just a smaller main air...
So 20% at 5k and 6% at the top...if i got the math right...

And for Phuk who had ? about the graph the other time, as i thought there are a function called "smoothing" in WINpep, at level one you see about every rotation of the wheel....on level five a harley is smooth!
NOW IN COULOR!!

Whaley ... interesting to see your graph - similar profile to mine with the power dropping back around 9k., but interesting also to see what difference the big bore kit made. You have 41s and the second run done with the TPS mod too?
Anyone got any spare jets

G

Greg wrote: Whaley ... interesting to see your graph - similar profile to mine with the power dropping back around 9k., but interesting also to see what difference the big bore kit made. You have 41s and the second run done with the TPS mod too?
Anyone got any spare jets

G

Yup, also with TPS mod. I´m trying to keep it as same as possible to only see the gains.

I have a whole lot of jets but you can do as a lot of guy´s over here.
When you need a bigger jet you drill it out and when need a smaller you solder it shut and drill out with a smaller drill.
Opposed to mikuni´s wich number of jet is based on how much air/fuel it shuffles the keihin ones are straight forward mm based.

....but i don´t think allens performance are that expensive...rambling rambling....

here's the graph...



I didn't have the bollocks to go down by 5 on the MJs so I only went from 155 to 153. End result was 85.3BHP max up by 4 or thereabouts from the last run. It's still running rich from midrange upwards so I've regretted not going straight to 150s, but the change I made did smooth out a bit of the dip in the middle of the blue curve which is apparently a good thing . However, the relative change between the two traces shows that 150s should put me bang on the line. Couldn't get an RPM trace this time cos he didn't plug the sensor in , but I'm getting runs for £20.00 now so I don't really give a fok! I've ordered a pair of 150s from Nikkau in NZ (£6.00 the pair delivered) which should arrive here while I'm on holiday so I can have more fun when I get home. I reckon I'll be seeing 88-90 RWHP which I don't think is too shabby!



Greg