I got my 2nd dyno run today after rejetting to proper mixture and switching to a tire that hooks up better with the dyno. The result was 27 horsepower, and 20 ft-lbs of torque.



This was done by the same shop, same dyno machine, and same operator as last time. They even had my prior run still stored in the machine which is shown as the lower curve on the plot, but unfortunately the red ink cartridge was dry so both curves are blue. Difference is pretty significant from before. The only changes I made was to tune the carb a little and rear tire change.

If you remember the fellow that did the "Dirt Bike Television" show, he dyno'd their stock bike at 16.9 horsepower, so with all my mods I'm looking at about 10 horsepower increase, which is about what I and some others were guessing it would be. The fellow that operated the dyno said that the tire does make a big difference. He said last time my knobbie was bouncing around like crazy. The tire I put on for this run was a 50/50 dual sport tire from Kenda, it definitely hooks up better on the road and is able to transfer more power to the dyno surface than the knobbies. It is downright confidence inspiring on the road - I know what Mav likes his supermoto setup so much now.

While my jetting is a better now than before, the dyno guys said my jetting might still be a tad rich and I could probably get a bit more power output by jetting a bit leaner. But I think I'm going to call it close enough. I do still have the higher flowing K&N air filter to put on if I want to which will make it a little leaner, but I don't really want to drop the jet sizes any more.

And if we compare to a16tony's and scat's runs, and use their runs as the baseline for the carb rejet + pipe of 21.5 HP, the 331 cc displacement gives about 5 and half HP or so on top of that.

Anyway, there you have it. Less ***** + better jetting yields 4.5 HP over the prior run. Just about what I said I thought it would be a few weeks ago and is now confirmed.

BTW, the way the bike feels at this level is great. It's no MX bike of course, but for the KLX and its intended purpose, it is perfect for the trails and having fun and is not lacking for any power anywhere, IMO.

 

Thanks for sharing the info Nobrakes. I recently picked up a klx300 cylinder on Ebay and will go straight to the 331cc big bore. The Mikuni 33mm pumper is also on my list. Big Gun is on as well as the air flow mods: Smog gone, crankcase breather drilled, dual snorkel set up, Uni filter. If I get close to your 27 hp mark I will be one happy camper.

 

You won't be disappointed, I gurantee it. Smart move going straight to 331, IMO. Of course, it's all in what you want - but if you tend to want a bit more power, you will be glad you went with the 331cc since the amout of work is the same between it and the 300, there's just the extra cost of boring it out and plating. And the difference between it and the 300cc is probably 2 or 3 HP. So if you figure you can get 2 or 3 more HP for a couple hundred, then that's worth it when you figure a Muzzy or Big Gun will set you back more than that and that's what we get out of them. Good luck!

 

You would guess wrong. Increased displacement=increased HP and Torque..that's elementary. The biggest difference the pumper carb makes is in throttle response, not HP. There may be a slight power gain from the bore inhis carb being 1mm larger than stock, butthatdifference would bevery small. *corrected* 82cc of increased displacement is where the lion's share of this power gain is coming from.

 

Good on ya, Nobrakes!Thosenumbers makeA LOT more sense!It's very ecouraging that you can get decent, usable power without changing the cams. Thanks for getting that second run, so we could solve the unanswered questions. I will throw mine on a dyno in spring just to add some data to the pool.

 

82cc! Don't short me

 

Thanks - I knew the earlier run just didn't add up so there had to be some explanation. If you find that 2 + 2 does not equal 4, you need to check the fundamentals and figure out what the problem is. Now, 2 + 2 = 4 and the world is sane once again.

Of course, I knew the power was there because I could feel it. Switching the rear tire in large part made the dyno feel it too, though the gains were a combination of both the rejet and the more dyno-compatible rear tire.

I can't wait to see some more results from you and others. I'm perfectly happy with mine the way is though, but it will be interesting to see the effects of better cam profiles and such.

 

Nice lines on the dyno. Nice and smooth. Where tq starts to trail off, the hp is there. Yes abit fat in the a/f on the dyno, but I am sure at speedthose numbers will be different. However, am curious on a plug chop at speed.

Congrats

 

I am still a bit rich, but not too bad at the higher end, which is what I think matters on this type of dyno test. They essentially let the bike idle along on the dyno in 4th gear at the lowest RPM it will stay and then open the throttle to wide open and record the results as the rear wheel accelerates the drum rotation. So down in the lower RPM range the bike is still under significant load which seems to tend to produce a richer a/f in the exhaust vs at the higher RPM when the bike has come up to near max speed and the engine isn't working quite as hard any more.

To make things a little more confusing, on the print out I got today, they overlaid my prior result from a few months ago but the red ink was dry so its hard to seperate them visually. You can tell the new run on the a/f graph, though, by looking at the old run by itself which I have here:



My earlier prior run starts out rich, bumps up to almost about right at 4.5k, then dips steeply rich from 5k to 6k, and recovers slightly at around 7k and continues to be very rich all the way to 9.5k.

The new run starts lean, still dips to be pretty rich at around 5k to 6k but not as much as before, and then recovers to be just about right on the high end from 7k onward as it nearly overlays the dashed "optimal" line.

It's real hard for me to do a plug chop because of the IMS 3.2 gallon gas tank I have installed. I pretty much have to remove the gas tank in order to remove the plug. I installed an O2 sensor in my headpipe so I can now see the effects of not only wide open throttle which is what the dyno graph shows as the bike accelerates, but I can see the a/f mixture result at any RPM. I typically try and find a long steep hill which is no small feat here in NC, where I can set the RPM and cruise up at that RPM and watch the a/f reading from my sensor. From that I have determined that I'm just about right across the board, but still a bit rich at WOT which the dyno confirms. For example, my O2 sensor reads 0.92 volts at WOT, and the same at idle, but around 0.88 and mid throttle settings. This tells me that my sensor at 0.92 volts is a just slightly rich reading if we consider the dyno result to be my O2 sensor's calibration. Lower voltages are leaner, so the 0.88 is slightly leaner which should put my mixture about right.

I could lean out the main jet a size or two, but I think it is so close now and besides I don't really spend a lot of time at WOT, that I think it's good enough. If in a few months I get bored and want another challenge, maybe I'll try my hand at dialing it in even better, but right now I'm pretty happy with it. The last thing I want to do is see if I can get one of those Kouba fuel screws to fit so I can adjust the lower pilot area settings while the bike is running. Problem is that with this FCR carb, it is taller than stock and there's virtually no room between it and the starter motor to fit the fuel screw extension. I've orderd a screw from Kouba and will attempt to cut it down so that it fits. I hope it works out, but I don't look forward to removing the entire carb just to make a 1/4 turn adjustment, put it back on, start it up and try to assess whether it helped or hurt, then repeat. I really want that fuel screw.