Now that we have the KLX331S all sorted out, let's turn our attention on another subject . . . . . camshafts.

Basically we have a single source for camshafts for the KLX250S, and that is Web Cam Inc. Never dealt with them, but I do intend to deal with them here quite shortly.

To begin, does anyone have the cam specs of the cams currently in the KLX250S? I would like to know where we're starting at. It might help make a decision a bit easier. The deicison I'm talking about is to which cam would work the best in this application. There are 3 cam grinds available from Web Cams Inc. They are:


Larry Roeseler's favorite. Quick acceleration with plenty of mid and top end power, Grind #101:

.350 lift 272 degrees of duration at .000 clearance 229 degrees of duration at .050 clearance.


Improves throttle response. Great for trail riding. Works best with racing pistons and exhaust, Grind #293:

.360 lift 248 degrees of duration at .000 clearance 226 degrees of duration at .050 clearance.


Excellent mid and top end power. For racing engines only, Grind #55:

.352 lift 263 degrees of duration at .000 clearance 243 degrees of duration at .050 clearance.


I am looking at both the 101 and 293 grinds. I don't need the 55 grind. I do believe that is way too much cam for what we are trying to do.

Ultimately, I would like to see a dyno chart with both of the 101 and 293 grinds installed in a test motor with no other changes. I would like to see which of these has the kind of mid range, without destroying the bottom end torque of the motor.

I see we have a static compression ratio of 11.0 to 1. That should support either of these cams quite nicely.

A bit of semi-pseudo scientific extrapolation gives me a duration at .010 for the #101 grind of about 263 degrees and the #293 about 242 degrees.

I would like other opinions on this. My cam experience comes from building large displacment V-8 engines, not single cylinder small displacement motorcycle engines. I would like to choose wisely, but not over cautiously.

Jump in and let's get some discussion going!



The #55 grind will probably produce a bit more "grunt" down low, under 4000 rpm. The #101 grind will more than likely make the 4000 to 7500 rpm range come alive! That is where I'm looking for all the help. I don't like to run a motor tight all the time. I do like to have it running in it's "sweet spot" and right now the sweet spot on my KLX250 seems to be the 4000 to 7500 rpm area.

It's a shame that they spec their cams in the conventional manner. I would like to see what it is at say .010 of clearance.

 

Seems like you get the best of both worlds by going 331cc, keeping the stock cams and adding a pumper carb. Had I not just read about Nobrakes FCR install, I wouldn't be saying that though.

I you decide to go ahead with the cam change and stay with stock compression ratio, you might want to PM Brewster over at Thumper Talk. He has a procedure for removing the KACR from the stock cam and pressing it onto an after market cam. I say that because I remember asking my Japanese dealer about some Yoshimura cams here in JA. He wants to learn English so bad that he won't answer me in Japanese, but instead made the noise of a severely labored starter motor trying to turn the engine over.

 

Tremor38,

Back when I was running a small block Mopar engine with a 13 to 1 compression ratio and W-2 heads, I found that when warm, it was hard to start. The way I made it simple is similar to the way NASCAR guys start their engines. They have a separate starter and ignition enable switch. You simply hit the starter with the ignition disabled. The starter turns the engine quite easily and then when you hit the ignition, it comes to life immediately. A simply primary wire change makes it a snap to do.

I like keeping things simple and those that I can control. The KACR is something that most folks are working hard to get away from - for reliability issues.

 

While I have zero cam experience, none at all. I would get myself all hot and bothered over the #101 Grind. While I don't have a full exhaust, and have the current stock piston, the description better fits my bike. Mid range- top end power boost? Sweet! My bike loves it from 6 grand up with my skinny little *** on it... If it can bring the sweet range down to 5,500 I'd really love it. Giving me any sort of improvement in the already sweet spot would be excellent.


Although I must ask, will these modifications show up significantly on the 250cc motor? I can't imagine that it wouldnt... but I've been known to be wrong before. I think I'd like to throw in a few more mods on the 250 before I step up in bore.

 

Why would I do all this to the 250 motor?

To be honest, it's nothing more than a migratory path to the 331 cc motor. I'm just going to do it in a different sequence than Nobrakes did it.

Why would I do this? Well, I don't see where it's going to cost me any more to get there this way, but I do see some more benefits for this forum. There will be more information for everyone to choose the path they wish to go. There might be some that are so intimidated by the work required to get to 292 or 331 cc's that they are looking for something less intense.

Camshafts will make a major difference in a motor's charecteristics. It will take a mild motor and turn it into a fire breather. If you take a look at Cheverolets and their engines for many years - ever since 1955 - they have produced a small block engine that was available in the showroom in many forms of tune! You had the two barreled carburated "family" V-8 that made about 180 horsepower. You also had the Rochester Fuel Injected Corvette engine that made 365 horses. Same block and displacement. The induction (carb), cams, cylinder heads and exhaust methods were made better. Kind of sound familiar?

I'm looking at the #293 and #101 grinds from Web Cams, still not sure which to go with, at least not at this time. I am leaning towards the #101, which is what I really started looking at - probably will go that route. From firsthand experience, more displacement always makes more bottom end torque, so the #101 will really help the 4000 to 8000 rpm area. I think my bike spends most of it's time in that powerband.

While the FCR is a nice carb and really proven, I know of several folks around that have had some awesome results from the Keihin pumper carb. It was used on the Suzuki DR350 in 1993 and 1994. There is a fellow over on Advrider that will set one up to fit a KLX250 for a minimal fee. I'm waiting on a response back from him right now. Once I get the go ahead, I'll be ordering the carb and that will be the first mod I'm going to do.

While I don't have access to a high $$$ dyno, I do have access to a very good daily dyno. That is a measured distance and my GPS. You make a few runs and use the "Max Speed" function on your GPS to see how fast you can go in that measured distance. Then you make your changes and then test it again. A gain in horsepower will result in a faster mph at the end of the run.

Just kind of thought this would be of interest to some of the forum readers to see what mods make a difference, the kind they are looking for. I know I wanted to do this with the basic mod package, but I kind of got a bit too busy to find the time to make it happen. I do know this, I had an opportunity to race a fellow on a stock KLX250 one day with the full "free mod" package installed on my bike and his being 100% stock. I ran away and hid from him. But I would expect that to happen with a 2.5 to 3.0 horsepower gain! Considering 18 vs 21 horsepower, that a huge improvement.

That's all I'm trying to do.

 

I await your review of whatever cam you get... and it just might be my next mod as well.

My credit card rests in your hands Marty

 

I think you mean the mikuni TM33-8012. That carb was offered on the dirt model DR350, not sure of what years though. The FCR is a keihin pumper carb, the 35mm being an older version of the FCR's on today's mx bikes. (37mm on 250F's, 39-41mm on 450's). I have a TM33 (33mm pumper) and a FCR 35mm. I first purchased the Mikuni and put it on my bike, and then later, my dad got a KLX so I put it on his bike and got a FCR for mine. The Mikuni is much easier to jet and dial in than the FCR (my FCR still isn't 100% there), but the FCR outperforms the mikuni. The Mikuni is offered in two different sizes, a 33mm and a 36mm (TM36-8012). Most say that the 33mm is better for a 250 or 300cc KLX and that is offers more bottom end, where the 36mm is better for 300 or 300+cc KLX's, and offers more top end, while the FCR is supposed to be the best of both. So, 33mm for singletrack riders and 36mm for desert riders is the dirt logic, but I'm not sure what applies for street use.

My opinions of the carbs' performance was the the mik 33mm made the throttle and rear wheel feel connected, no more lag in power and made wheelies easier. It greatly improved bottom-end response, but I don't think peak HP and torque changed very much if at all. The FCR offered even more of the connecetd feeling, and a feeling of a little more power everywhere.

Someone on thumpertalk had a 33mm mikuni bored out by a machine shop to a 35mm, that might be the best compromise, that way you could run the carb with stock displacement, and then later, if you felt the need, you could have it bored to a 35mm if you go to 292cc's.

I think that that 33mm with cams that you are talking about doing would be a really sweet setup. I have a set of used stroker race cams that I have yet to try out, all this talk is making me want to throw them in. Sorry for the length.

 

GreenKLX,

No apology needed. Great info.

It's always good to hear from someone that has hands on experience with something you're about to try. I appreciate that.

Yep, it's been about too long since I've had my hands into the internals of an engine, massaging away restrictions and allowing more power to eminate from the motor after my attentions have been administered. I'm looking forward to truly playing once again.

Nice discussion on the Mikuni vs Keihin carb. Thanks for clearing that up!

 

Agreed, the Mikuni vs Keihin clarification is very helpful.

Based on Nobrakes experience, it sounds like the pumper carb route is the performance boost that I've been looking for, and GreenKLX's post basically confirmed it. The cam mod sounds interesting as well, but I'm thinking a carb upgrade will get me where I want to be. So for me, I like the power that's there - I think there's enough now, but I'd like it quicker, and at lower RPM's.

Who am I kidding?!??? Motorcycles are like women and computers:

Women: You can never be too rich or too thin.
Computers: You can never have too many gigahertz or too many gigabytes.
Motorcycles: You can never have too much torque or too much horsepower.

(Let's be realistic: I didn't want to get the exhaust system at first, but this forum wore down my defenses. I'll probably be saying the same thing after someone does the cam mod!!! [:@])

"Hello, my name is Mike. I'm a Modaholic."

 

Okay, I can just see the swearing in ceremony now . . . . .

Repeat after me: "Hello, my name is ___________ (state your first name). I'm a Modaholic."

I think Tim Allen really summed it up on the TV show, Home Improvement with his grunted commentary - "More Power!"

It's a never ending battle for truth, justice and the American Way - More Power!

I'm seriously searching for some dyno time at a local shop. If I can get it, I will publish dyno charts for all the mods.

Personally, I do not think the carb will actually provide additional peak horsepower. Felt power is nothing more than making the engine respond much more rapidly to throttle input. The Keihin carb, when you really look at how it works, is nothing more than a very efficient method to control emissions and make the bike run quite well at most altitudes with a minimum of changes. However, the function of the carb is nothing more than letting a signal be passed from the engine to the carb so it can make a decision as to how much the throttle plate is opened. There is no raw shot of gasoline into the intake tract to cover up the high vacuum request with a shot of gas. That is why the Mikuni and Keihin FCR make the bike really wake up.

My personal belief, based on what I have read, is that there is a lot more fertile fields to be opened up on the KLX250. It is a very efficient design that is "corked up" as delivered. But with some massaging, the little bike can make a lot of decent and usable power!

Even if you look at what Nobrakes has spent, it's a whole lot less than the purchase of a KTM, or Husky or similar type bike.