Ok, before you guys lynch me, I'm doing my report on the 331cc.

I've been breaking in this cylinder the past two days pretty much by the book. The procedure is basically to take it fairly easy at first, starting in 1st gear of course and run up through the gears to 4th, never exceeding 1/2 throttle. The idea is that you want to rings to wear in, but not load it too much - hence the 1/2 throttle. Once in 4th and your speed catches up to your 1/2 throttle position, drop the throttle to zero and as the RPMs drop, gear down successively back to 1st letting the engine brake slow you down. Then repeat. The engine brake creates vacuum in the cylinder and sucks oil up through the oil rings of the piston helping to cool it down. The whole point of this exercise is that you want to wear in the pistons, so they seat against the piston walls but do it in such a way that doesn't get the rings too hot and sieze. On reference I read says to do this on flat, hard, level surface - no mud or sand because it will cause the engine to overheat too easily and you won't get a good engine brake effect to suck the oil up for cooling.

I've read several variations of this, the one I went by last time said to 2 sessions of the above for 20 minutes with a 20 minute cool-down period in between followed by a third session allowing up to 3/4 throttle.

The README doc that came with my 331 kit says to do this 8 times for 15 minutes each with a full cool-down in between.

I've now done it 5 times for about 20 minutes each and for the last 2 times have kind've wound it out a bit and had some fun, so I feel like I can now give a report.

First the bad news - it is still not a "wheelie machine". My "test" for this has basically been on flat ground, grass or woods with decent traction in 1st gear, just above idle, then slam the throttle open, no clutch. With the '250, I got very little, had to tug hard on the bars to lift the front end. With the 300, it is better, small tug on the bars brings the front up a little. With the 331, it's a little better than the 300cc but it's not night and day. It still requires a tug on the bars to bring the front end up - not that there's anything wrong with that, but its not like if you're not careful it's going to loop out on you. Note that this test works best where there is good traction - if the rear tire hooks up well, the front comes up a lot better, so it varies with terrain. Note also that my rear tire is a 120/100x18 which means it is about 2cm taller than stock so that will tend to pessimize the wheelyabilty. If I was running the stock rear tire size it would come up a bit easier.

Now the good news - everywhere where else this thing really smokes! Note that I've been riding the 300cc for several months so I'm pretty used to what it felt like. With the 331cc, from 2nd through 5th in the mid-range 5000 through 7000 RPM, as my son would say, "Oh Mylanta!" The 331 really wakes this bike up and it wants more. I'm very impressed with what it has done for the mid-range torque.

I have not wound it out any higher than that. What I can tell you is that at the very low end is about the same maybe a bit better than the 300cc. But the mid-range is kick @ss. I don't remember the 300cc feeling like this.

DISCLAIMER: As I mentioned, I rejetted my CVK carb before I ran with the 331cc to richen it up a bit so that is another variable that changed. I thought I might have been just a hair lean in the mid-range with the 300cc so it is possible that the carb rejetting has benefited the feel of the 331cc and that my experience with the 300cc was pesimized a bit. But note that I was very pleased with the 300cc also and fell stronger pull and torque all across the RPM range, so while it is possible my jetting is better suited for the 331 than with the 300, that's certainly not the full story. BTW, my jetting changes seem to work fine on the 331cc. The big bore kit doc recommends running a little rich during break-in as being too lean can make the cylinder even hotter during this high-friction time and they warn against doing that. I'm definitely popping a good bit on decel when running up and back down through the gears so I think that tends to indicate that I'm running rich. Someone please correct me if I'm wrong. I don't notice that mid-range stutter than I did before, so that, at least, has been corrected it seems.

So ... my next step will probably be to run this cylinder in a little bit more and maybe as early as Saturday put on the Keihin FCR and see what that does. If I didn't have the Keihin to try out, I would still be completely happy with the expenditure based on what the 331cc has done to the feel of the KLX, even above the 300cc. It is really shaping up to be an ultra-fun bike for me with some impressive power and pull. In a way, I'd kind've like to ride it as is for a few weeks to get a better feel for it before going to the FCR, but there's no way that's gonna happen.

If you have any questions, fire away. I'm certainly no expert with anything motorcycles so I've just tried to report on those things that are important to me and make my riding fun. I'm sure I've missed some of the finer points as I'm not really a connoisseur - when I used to drink, I preferred beer over champagn, though I liked my beer stout. I guess that philosophy carrys over to my two wheeled fun also.

 

Thanks for the update, can't wait to hear what you have to say after you really open it up after break in. I heard by someone that popping/backfiring on decel means that you are running lean, can someone clear this up for the records?

 

Whoops, almost forgot the mandatory photo for this thread

If someone was with me I'd have a wheelie pic, but garage pics will have to do.




You can't tell any difference on the outside - all the magic is hidden until you fire it up

 

Seems odd that you upped the the displacement another 10% (300-331) but it didn't make much improvement in the low end? As far as the popping is concerned I've read that it is caused by being too lean. Being too lean the air/fuel ratio is off and you don't get a good combustion cycle which leaves unburnt fuel in there the next time around and on the exhaust stroke this is sent into the exhaust and the heat from the pipe burns it causeing the decel pop. However I tend to agree with your rich diagnosis because I had a decel pop that wouldn't go away no matter if the airbox lid was on or off, and no matter what my fuel screw setting was (before I desmogged). I ended up making it so rich the plug came out nearly black but the pop went away as soon as I took off the smog crap, I was then able to open up the airbox (no snorkel) and turn the fuel screw in to 2 turns and it runs like a dream, harder to start than with a fat mixture but rips for a 250 with stock gearing. So you may be rich in some part of the powerband and lean in the other, or perhaps the CVK just can't feed the 331 adequately off idle and the pumper will surprise you.

 

That don't look like no stock stinky fender. uhhh please shed some light. BTW I had a 350 xl and it was pretty much a wheely machine you shoudn't be too far off. Tweak it mang..

 

There you have it, folks, another convincing win for Nobrakes!

As usual, Brian, your write-up is thorough and informative. There's one thing missing in your disclaimer, however, that became obvious after you posted the pics - the performance gains due to the improved aerodynamics of your "rear end" ... every little bit helps!!!

So: 300cc Big Bore Kit, 331cc Over-bore, FCR Pumper ... what's next? I don't have a crystal ball, but I think I can see where things are headed:

 

I'm wondering if the less than stellar results on the very low end is more due to just the way the CVK operates - it takes more time to get the fuel mixture flowing which tends to smooth out the rapid throttle opening. From what I've heard about the FCR, it "uncovers" lots of low-end grunt. Bad Bear is also saying this ... I trust his experience.

Looks like the forecast is calling for heavy rain tomorrow so I may not be able to get out for any substantial amount of time, but it is supposed to clear up on Saturday. I'm going to try and get the FCR mounted and working by then so I can get to the bottom of this!

Another fellow over on thumpertalk did describe the FCR as giving his KLX a ton of low end grunt actually making it hard to keep the front end down - said it pulled stronger than his WR250F. He said he'd much prefer the FCR on his 300cc bike than his buddy's 340cc bike with its CVK carb. Of course, the FCR on a 331 is just going to be that much sweeter (I hope!).

Not to put a damper on the 331cc - it pulls stronger than the 300cc, everywhere else, I'm just not seeing a huge improvement in that immediate zone just off the throttle. Again, this could be due to the way the CVK carb works and not the displacement since if the engine is starved for fuel right there, no amount of additional displacement is going to help that much. That's what the FCR pumper is for.

So depending on the what the FCR does, some options may be:

1) 300cc kit + FCR
2) bore to 331cc and stay with CVK
3) bore to 331cc + FCR

Door #1 is about $1100 or thereabouts. Door #2 is about $800 or so. Door #3 is around $1400. I'm at #3 right now so my path has already been travelled. But for folks still deciding, it may turn out that door #1 is pretty darn good and can save you around $300 or so. But the downside is that if you decide to choose door #3 at some point in the future, it's cheaper to do it up front and save the cost of the 300cc piston, rings, and gaskets.

I'd hold off on any major purchases though until I can report on the FCR, unless of course you already know what you want. This is a learning experience for me but I have a strong su****ion that the new carb is going to be the icing on the cake for me. I had investigated it pretty thoroughly and it wasn't a random purchase. But the proof of the pudding is in the eating ... hopefully I'll know this weekend.

And it should go without saying that my descriptions are not scientific - I try to be objective and report what I actually feel and observe as opposed to what I want to feel and observe. If you decide to do anything or make major purchases based on this stuff, please do some additional research and get confirmation - my "holy moly" might be your "ho hum" or vice versa. Only the Dyno is scientific and completely objective and I don't have one of those, but I plan to get a run done at some point but not in the immediate future - perhaps in a month or so.

 

Thanks Y's Guy and Damn straight! That fender added 5 HP at least!


Ha ha - that's funny right there. That would be the "nucular" option, as GW would say.

 

See the "new rear end" thread ... it's all there.

I ain't tweakin' notin - I'm ripping that CVK off there with authority and ever so carefully installing my fancy new Keihin FCR pumper carb

 

Thanks Brian I wil check it out. Be waiting for the pumper report.

Francis
Sanford
Florida