I don't think the carb by itself is going to cause the bike to gain horsepower, however, an improperly jetted carb will certainly hurt power. I think that is what is happening here. Before I took my CV carb off, it felt really strong in the mid-range, stronger than now with the FCR. I think it just needs to be tuned. But what the FCR gives you is not so much hp, but it improves the throttle response and the off-the-start response. It is a pretty big difference between it and the CV. I can tell that even though my FCR is not optimally tuned.

I would definitely have liked to do one of these graphs for each set of mods. And no, I have no way of knowing whether their machine is on or not. They claim it is on and calibrated but they also said that many shops don't bother - who to believe?? The only way to know would have been to do a baseline before I did any mods and see if that jives with the 17 or so hp that folks are getting from the stock bike. But I think I'm being pessimized a bit by the jetting on the FCR. If you look at the part of the graph where the mixture shows it to be very close - up to about 4.5k RPM, then look diretly above and see the higher hp curve and torque curve in that same range - I think that is telling. Just beyond that where the mixture richens up, as indicated by the curve being below the dashed line in the air/fuel section, you can see the drop-off in torque. Except for the little blip of both power and torque just around 7K, but notice that that's the only other closest place where the mixure is "almost" right.

By that, I think there are some improvement to be had by fixing the jetting. And at this point I'm not really trying to get all the hp out of it - I'm happy with the power where it is. I'm finally at the point where it does exactly what I want and it did take the 331cc bore and FCR carb to get there for me. But right now I just want to fix the jetting so that it is not sputtering - that's just not right, and to strengthen up the mid-range. I think fixing one will take care of the other.

I really wish we had fuel injection

And of course, even with all the mods in the world this bike is not in the same league as an MX racing bike. But it sure is a nice fun trail bike which is what I think most of us wanted to begin with.

Another thing this goes to show is that with so little to start with (16.9 hp according to the "Dirt Bike Television" guy's dyno) even a 5 or 6 hp gain can make a big difference in "seat of the pants" feel.


While I don't want to be a slave to this thing and have to be tinkering with it all the time, I'm pretty sure I can dial this carb in. The results from today, while they didn't turn out the way I wanted, they were very useful and gave me some very useful information on what to do. I'm just gonna study up and dive in like I normally do. Afterwards, I still may not be an expert, but I'll sure know a lot more than when I started. And at some point when I'm more comfortable with how this bike is jetted, I'll get it dyno'd again - maybe. The dyno is nice to know - even if it is a reality check.

But I'm done with the high-dollar mods. It's just about where I want it, sans a little FCR tuning. Assuming no major engine trouble or anything, I expect this bike to last me for many good years to come.

 

Doesn't this go totally against your "seat of the pants dyno"...??
Didn't you basically say that after the FCR was installed it was a totally different machine (I think you even said "wheelie machine")?

I dunno - if it feels that much better to you, then something doesn't jive with the dyno results.
Also, does the manufacturer claim 18hp at the crankshaft or at the wheel?
I'm assuming these results you got are from the back wheel.

 

It is! Blip the throttle and the front comes up - no clutch.

Well, I'm not in disagreement with the machine. Since I first put on the FCR I've said something is not right in the mid-range and the CV carb pulled stronger there. I don't think there is necessarily a contradiction. Also, the fellow from Dirt Bike Television dyno'd his bike before they started their mods and got 16.9 HP, so the 18 claimed (not sure who claimed that) may be a bit optimistic to begin with.

What I do think it shows is that:

1) my carb is not dialed in

2) in starting with a meager 17 HP, even a 5 or 6 HP gain can "feel" significant

 

Brian dont't worry about the hp numbers becuase without a baseline they don't mean nothing. Trust yourself to tune the carb, if the idle hangs its lean, you know that and you can tune the rest of it. The hardest part will be fiddling with the jets becuase of the starter motor otherwise you could pull that bowl without removing the carb. Start with top end and work your way down meaning main jet/ jet needle/ pilot jet/ float level. That is one school makes sense because if you dont have the right main yet everything else will be screwy.

Don't beat yourself over the guys at the dyno, anybody can tune an efi with a powercommander, but carbs are a different beast.


Do it yourself and show everybody how its done. Its easy for people to sit back and copy ideas when they work but to be the first to try things out takes real guts. I have only great respect for individuals like you.


Francis
In Florida


PS I say you got 30 hp there.....

 

Ps Just in case I am not bashing anybody as I have done some mods described in the forum. The word I was looking for is innovator
or not afraid to try new things.

thanks
my .02

 

Ya man, no big deal. You've got the right attitude, once you get it dialed in it will be pefect and you won't have to worry about it again unless you significantly change elevations. When I first got my YZ426 (FCR 39mm) it had severe jetting issues, hard to start when hot, backfiring, hanging idle (scary thing where the bike has a high idle and won't decellerate, if I wanted to slow down I had to pull the clutch and brake). I performed the BK mod, which is very similar to the taffy mod, got an adjustible fuel screw, and a JD jetting kit. The fuel screw is the one on the bottom of the carb, with an easy adjust one you can tune it with a thumb screw, which adjust the pilot circuit for simple changes do to weather and temp. I suggest you get one of these, they are the same for all FCR's, from the new 32mm one to the the 41mm, it fits all of them. It is unfortunate that someone like James Dean doesn't make a jetting kit for the FCR on a KLX250/300. His kits include a needle and some jets along with directions for which setup to run at what elevation and temp, very easy. After I made those mods to my YZF, it ran and still runs great. I highly suggest that you pay close attention to all of the bikes symptoms, and make a post in the Jetting forum on thumpertalk. Eddie the moderator is an expert at jetting anything, and he has helped me many times. Just make sure in your post you give him all of the specifics, your current jetting, altitude, temp, etc. the more info you give him, the more he can help you.
Hope this helps.

 

Nobrakes, don't be too bent up about the dino, the fcr carbs are a lot of fun (not so)to dial-in, Use high octane fuel, ours in Australia are 91 standard unleaded, use a 96-98 unleaded if you have this, it does make a difference. Can i suggest that you remove the air filter, cut out the backfire gauze (butcher it, this helps also to relieve built up stress ) put a uni filter or better in as the originals are ****, jump on the bike & go hard for three or four miles, stop, check spark plug, light brown tip = main jets perfect, black tip= too bigger jet, clean/yellowish tip = to smaller jet, the needle clip at this open throttle use, makes not difference. If you get this right, you have the most important starting point, the OPTIMUM MAIN JET SIZE for your bike, with this carb, this needle and filter/air-box. All other rev ranges are with the other settings/jets. At what you have said, the main jet, still sounds too small.
Main jet = max power flat out, end of story. Mid range ( your problem 4500 rpm area) are needle clip heights ( can be needle profile/taper, but to change these you need performance after market needles, e.g. red/black/yellow, same needle thickness, just different tappers. Another story )
Clip 4-5th from top, more fuel 1500-5000 rpm, clip 1-2 from top, less fuel. If you ride for say 5 miles at about 4500 rpm and check plug, brown tip excellent, black = reset clip higher, clear/yellowish = clip to lower setting.
Pilot/ fuel mix screw is for idle - lower range ( hard to start etc, if it picks up idle rev's when it heats up, too bigger idle jet, if it slows, erratic = too small, bench mark for Air mix screw 1.5 X turns out.
Will email you Keihin 35mm FCR Pumper Carb Tuning by Dennis Arnold, remember the Taffy mode, 0.5 - 0.8 of a second, snap power. Anyway I myself haven't gone for the Keihin FCR, as I have had them before, not on a KLX, I went for the Mikuni TM33 Pumper carb from mlancer27@bellsouth.net in the USA, as they were on the Suzuki 350 and were very good, easier to work on and once tuned, leave alone. They sell for $261 USD + $25 for shipping (that's to Perth, Australia), the TM36 are $284 and the Keihin FCR35 are $345 USD, unlike nobrakes carb, you'll have to fit them yourself.
Well I'm very slow at this work and maybe the forum's over by now, hope this helps, my two cents worth. I think the is 26-28 hp in there Nobrakes, good luck finding it,

 

I also forgot that you have your airbox lid on, I think it would be interesting to see the dyno results with it removed.

 

Dynos are tuff Brain. I have dynoes between 140 - 168 hp at the rear. Depends on the dyno, the operator, the altitude, the humidity. Dynos are not a standardized thing. WHat a Dyno IS good for, is setting your mods and finding your a/f ratios, etc....

So, a before dyno would show say 10 hp on his machine, with all the mods, you have 23 on his machine. The overall number is almost worthless with no base point. Does that make sense?

So, you know you have a/f ratio prob at mid range. Fix that, then re dyno. At least now you have a base point.

Did they say if those numbers were corrected HP numbers?

I am curious as to what you gained in overall torque values. That's your wheelie power. Going to a bigger jug, you would have gained more torque over hp, and would have gained it more so in the lower band.

I say do it yourself on the pumper. We all know you can bro!!

 

Nobrakes, almost forgot, these bikes are max hp/torque at the lower rev range, they'll rev all day at 8000 rpm and a slight wind or hill wont be felt much, more revs and it will be affected much more, as it's out of it's power range. WR's about 9000-10500 range standard gearing, my KTM needs 90 mph with 17 X 40 gearing to hit max 58 hp at 8900 rpm and then she's off, before that at 17 X 45, it was 76 mph to hit 58 hp, but still at 8900 revs. The KLX are about 7500-8200, after that unless you are in top gear already, you should of changed up as the power has run out, does this make sense to you, as i think you seemed concerned that if they had got 10000 rpm you would of read more hp's, no, it's just revving higher.
If this doesn't make sense I'll think of another example, yer-sure!! GREENKLX is right about the mains .
You have got on an after-market header-pipe haven't you ?, if not "STOP" and get one, it's got to breath.