Nobrakes, here are a few thoughts

-You are the first person to actually get dyno results and post them. Thank you for spending the time, money and sharing the results with us. Now we have some objective results to work from. It's also a good reality check for people who just get the bike breathing right, slap on an exhaust and claim to have a 7HP gain using the precision accelerometer in their buttocks...those who this applies to please take note!

-As a few posters have already said, lack of a baseline test makes it tough to know your actual gain. Even if you have a baseline using the same dyno, results will vary with temp, humidity and pressure altitude. Bike to bike results will differ due to variation in the manufacturing process.

-Upping the main jet might give you a 2 HP gain at the 8K peak.

-A comment about seat-of-the pants mid-range results. Could it be that the midrange with the CVK is just more pronounced because you're not getting that low-end grunt with the extra squirt of fuel and immediate slide opening to better smooth out the curve? It makes sense that you would feel less of a mid-range rush with the FCR due to more uniform fuel delivery across the RPM range. The sputtering definitely needs attention though.

-I know you disagree with me about the HP curve with the large bore mods, but here it is again. All of the the curves I've seen on the the 300CC and up large bore mods have always dropped-off faster from from about 8000 RPM than the one's I've seen for an adequately breathing 250CC. It probably is due to the stock cam configuration combined with the increased moving mass of the larger piston.

Again, thanks much for having the patience and objectivity to get a dyno run. I might go get a base line done on mine before the weather gets too gawd aweful nasty to ride around here.

 

I'm kind of glad we don't have fuel injection! If you think a carb is frustrating, wait until you start tweaking a bike with fuel injection - all you have are numbers (data) to go by. I have a situation on my V-Strom where there is a rough spot - 3500 to 4000 rpm. Thus far I've spent about $250 on a device that emulates a jet kit for a carb. I have gotten most of that out. Remember, the fuel injectin on bikes is not the elegant solution that it is on a car / truck. There is no feedback to say more / less to the ECM. The bike FI is "Mapped" and they just don't care about the feedback - more expense. I must say I've been able to make the mid-range really strong in the bike, I'm happier, but not $250 worth!

As I read your commentary, I can't help but think of the 4000 to 7000 rpm range - our bikes are pretty much the same with respect to the "Sweet Spot" of the motor! Why do you think that is? I would have to say the ability to flow air. The internal combustion engine is nothing more than a glorified air pump! Air in, air out. You have made your air pump pump more air - h'mmm how much air could an air pump pump if an air pump could pump air ? But seriously, think about what you're saying - the engine is limited by the amount of air it can get in and out. All you have essentially done is make the hole bigger, but the goesinto and goesoutof are the same as a stock 249 cc motor. How can you get more air in and more air out - that will give you more gains in horsepower.

If you look at the numbers that HMF put up, they show about 13 foot pounds of torque. You are showing almost 17. That's a 30% increase in torque, about equal to the amount of displacement gains - pretty typical and something I would expect. I think that is pretty close to the transmongified numbers I gave you for torque. Once again - depending on the calibration of the dyno they might or not be off. It's hard to not have a baseline to compare it against.

My question to you, aside from the fact that the mid-range needs some tweaking, are you happy with the bike?

I do think to be able to get the upper rpm pull - you need to think camshaft and head work. Of course, that is just my opinion.

Most butt dynos have never been calibrated either. I remember back in the days when we used to make secondaries open mechanically on Holley carbs. You really felt the opening and the resulting RROOOOAAARRRR of the intake sound. It sounded good, it felt good, so hey, it had to be faster! Well, later on when I started racing and had those little electric timers, I started finding out that a vacuum operated carb, one where you didn't feel the transition was actually quicker. Don't be misled by a non-calibrated butt dyno! I think you might have calibrated yours though, so a bit of carb tweaking is in order. At least now you know what kind of power you're making.

So, did you basically pay for a dyno run?

 

Hey guys, thanks for all the comments and suggestions - lots of good points were made and I have some good ideas to try out.

Please don't get me wrong - I am 100% happy with the performance of my bike and my upgrades, it's just going to take a little carb tuning to dial it in. But I think what I'm hearing from some is that I probably don't want to drop a main jet size as that will limit power - perhaps the thing to try is to do what Deej's guy has done on his bike and that is to remove the airbox lid. That should lean out the mixture a bit and that might just do it for me. Jerry Leighton of Four Stroke Works who set up this carb is probably the foremost expert on the KLX's perhaps with the exception of Larry Roeseler himself. Jerry set this carb up and from the Dyno run results, while it is running a bit rich, it is consistently rich across the whole range - the line is almost parallel with the "optimal" mixture line which is represented by the dashed line, with just a couple of exceptions at round 5500. But from what I'm reading on tuning this carb, that is no small feat to do and requires a careful balance of the "slow air jet" in combination with the fuel screws and slow fuel jet - otherwise you end up with lean at one end of the RPM range but rich at the other, or vice versa. His setup actually looks pretty good, but is just shifted down a bit across the board. So I think Jerry knows his stuff, but I didn't ask him, though, is whether he recommends removing the airbox lid or not, and if he dials them in assuming it removed, then that is probably the first thing I should do.

And regarding the actual magnitude of the number, I guess I'm a bit disappointed in the "number", but certainly not the feel of the bike - believe me it is a far cry from what it was stock and really is a totally different bike, I was not exaggerating that. But if we assume the Dyno is dead-on and 100% calibrated, and we started at 17 hp, then my gain is between 5 and 6 hp over stock with a detuned carburetor. I think that is pretty good and I find that acceptable, considering. We were originally guessing the gain to be in the 7 to 10 hp range, but we did say we were "guessing" and it's not too far off if you take the low end of the guess. And again considering the fuel mixture is not quite right so it is probably not as high as it should be. And as many of you have pointed out, we have no baseline of my bike on that dyno so that could account for some +/- there also.

It'd be cool if anyone in this area had a stock KLX and could take and have it dyno'd on the same machine I just did, that might be enlightening.

So my next step is going to be to pull the airbox lid and see if the mid-range sputter goes away and I'll see how it runs in general after that.

Marty - on your last question, they charged me for a Dyno run and mixture eval - which was $75. What I really wish is that I had the equipment where I could do this without having to take my bike to the shop which is almost an hour away and leave it, and all that entails with having to get time off work, etc. That makes it pretty inconvenient, not to mention the cost. If I could get that report more conveniently, I'd definitely do a number of iterations and some fine tuning. But even the one run is very enlightening - and is worth it to me. My only regret is that they didn't do any tuning for me there. Again, I suspect that might be because of how tight the carb is in there - I bet most of the bikes they work they access the jets, needle, and mixture screws without ever removing the carb. While you can get to the needle on top under the seat / tank, you can't get to the jets and mixture screws without removing the carb on our bike because of the starter motor - there's just not enough clearance even if you rotate the carb.

 

Brian,

I can tell you have never worked on a 4 cylinder motorcycle engine.

Talk about PITA! Access to the carbs mean you must remove them as an assembly. Taking the carb off the KLX is a snap!

I'm quite sure Big Bear will agree on this!

 

I would bet the farm that he does.

 

Man - I can't imagine the pain of dialing in a 4 carb stack! There's enough black magic and witchcraft involved in just one - makes my head hurt thinking about 4.

I pulled the airbox lid off this evening and took a little spin around the yard and made more potential flower beds. But I can't really give it a good test out because my wife is working tonight and I'm supposedly responsible for the kids so I guess I won't just take off and go for a joy ride. [&:]

It still seems fine down low and still wheelies fine with a whack of the throttle in first, no clutch, stock gearing, size 120 tire. I think I might need to richen up the idle mixture screw as I have a hanging idle condition. I had that before but it is a little more pronounced now with the airbox lid off.

I'll have to wait until tomorrow to do more.

 

I suspect you are probably right about that - I had assumed before that poor response in that range was probably due more to the carb not being tuned in that range. But I think you are probably right and it has more to do with the cam profile and perhaps even the CDI.

I must admit, though, that I rarely spend any time above 7 or 8k so this drop-off doesn't really affect me in any practical way, but it certainly does limit that "max" HP reading from the dyno. I'm not really looking to improve that area too much right now. And I wonder if improving that area would come at a cost of power somewhere else as some have mentioned happens when changing the cam profiles. I leave that for someone else to explore - I like my low-end and mid-range power and torque.

 

Hey GreenKLX - great advice. I posted over in the jetting section at ThumperTalk and Eddie responded back within an hour with advice. He also said that the dyno will show low numbers with knobbies because they slip on the machine so that probably explains some of the unexpectedly low results. Here's what he had to say:

I'm going to have to order some jets and the EMP needle to do what he suggests. However, I can change out my main jet to a little lower with the spares Jerry sent with the carb and change the clip position. I think I'll try that and see how it is, then order the actual jets and needle he suggests.

Thanks for that suggestion.

If anyone is curious, here's my post in the jetting section over at TT:

http://www.thumpertalk.com/forum/sho....php?p=3975684

 

It most definitely did. My next step was to basically just lower the needle a bit (lean it out) by moving the clip from the 4th position to the 3rd. But instead, I followed Eddie's advice as closely as I could within the contraints of the jet sizes I had available to me. I reduced the main jet and the pilot jet to 152 and 52 respectively from 155 and 55. I didn't have the 145 and 45 sizes that Eddie recommended. Neither do I have that needle he mentioned, but I did move the clip to the 3rd position.

Well, it's a WHOLE lot better right now, but there still might be a hint of a stutter in the low mid-range, so I'm going to order the jets and needle he recommended and give that a try.

And by better, I mean that it is pulling VERY strong now in the mid-range, similar to what my CVK was doing in that range before I swapped. So now I have both a very strong pull right off the start when I whack the throttle that the FCR provides as well as a good solid strong pull in that mid-range. Before it was stuttering and sputtering there and noticably weaker than what the CVK was delivering. So right now, I'm close to having the best of both carbs.

As I've mentioned before, my baseline grunt test is to whack the throttle open at low RPM in 1st gear. All the times before w/the 300cc and CVK, the front would come up with a little tug. But now I have to be careful of looping the bike backwards - it comes up strong and fast. Remember, this is with no clutch, stock gearing, and a size 120 tire, all of which pessimize wheelying capability.

What is new is that this same test in 2nd gear now brings the front up strong also - and again, I gotta be careful about looping backwards.

And yes, as you've probably surmized about me needing to watch out about looping backwards, I am a beginner at wheelies - basically I can pull them up, ride a short distance and drop back down, but I haven't yet mastered finding the balance point and keeping it up longer.

But suffice to say that 2nd gear, no clutch, stock gearing wheelies are entirely possible now with this setup - just whack the throttle open and give an ever so slight tug on the bar. I was actually pretty surpised by this. In fact, I think it's a bit easier to do it in 2nd than in 1st because there seems to be a little greater control and RPMs left after the wheel is up in order to balance it out.

I haven't tried 3rd yet.

IMO, even with this level of mods, I'm not so sure. Maybe with the higher performance cams and maybe a more aggressive CDI we might get close. But those MX bikes are purpose built for full-time WOT and power delivery. Not only that, but the suspension on those bikes are 100% better for their purpose than ours would be on the MX track - I think ours is just way too soft for that. But all that performance comes at huge maintenance overhead with VERY frequent top end rebuilds and the works.

But honestly, the KLX "331" + FCR is perfect for me right now. Good solid torque where I want it - down low. Snappy throttle when you want it, but very controllable for the slow technical trails that I like. Perfect for popping the front up over logs and streams, yet not so agressive that it is hard to control in the tight stuff. And when you want to, you can wind it out fast to your heart's content.

Compared to stock, or even what I had a few months back w/the 300cc & CVK, it has a totally new character with the larger displacement and the pumper. I wound out the gears a little bit ago on a short straight and before I knew it I was up to 75 MPH with room to spare in very short order. What a blast! I wish I could have tried the pumper on the 300cc to see how that was, but the very long delivery time from FSW just didn't allow for that. While the combination I have was not cheap to do, about $1800 counting the pipe, it has really made this bike the ultra-fun street legal trail and off-road bike that I wanted. I am 100% happy. It's been a fairly long time in getting here and I'm not sure I'd want to go through it all again, but the end result is totally worth it to me.

I really like those, too. Also check out the new 2007 WR's - those look pretty sweet also and shouldn't be too hard to make street legal in states that allow that.