How do I make a KLX300 better?

Wis

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#1
Hello, does anyone have any ideas on making a KLX300 (99) go much better? I would like to perform bolt on mods such as carby, exhaust etc but don't know what to buy. Any help would be much appreciated.
Thanks Wis.
 

Boit

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#2
Stroker Speed Equipment and Thumper Racing are sources for KLX mods.
 
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#3
Lots of information here http://planetklx.dirtrider.net and on the e-mail list there are a great group of KLX riders that can help you transform a stock KLX into a new machine.

Most noteable mods are:
Header pipe ($140 from Stroker)
Pumper carb ($350-$500)
Exhaust ($300-$400)
Airbox & breather mods (free)
Suspension upgrade (depending on weight & style of riding)

Plus the usual cosmetic and guard related additions

Happy shopping!
 

dirt bike dave

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#4
I know it is not technically a 'bolt on', but if you really want to improve the fun factor, look into the big bore, 331cc.
 

DougRoost

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#5
I'm getting ready to do the pumper carb on mine. From a magazine article linked to PlanetKLX:

We only had to ride about forty feet before we were convinced that all the installation struggle was worth it. When we shifted into third gear the KLX did a phat wheelie, all of its own accord, and before the carb it took a conscious effort to pick the front wheel up. As a matter of fact, all the KLX wanted to do is wheelie, which made it now a ton of fun to ride. Where the stock bike is flat off the bottom--as the engine revs have to wait for the CV carb to develop its vacuum--the pumper carb squirts a shot of gas into the cylinder that makes it leap to life like Wile E. Coyote when he backs into the cattle prod. Instead of riding around with the throttle pinned, now the KLX can be ridden at quarter throttle in the tight woods, working off that burst of low-end grunt. Unbelievable! If you do nothing else to the KLX, this is the modification you need.

This was for the Mikuni 33mm, which requires more installation headaches than the more expensive Keihin 35mm FCR. Both available from Stroker (http://stroker.fusionserver.com/).:cool:
 
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#6
If you want some very cheap improvements that help the KLX300 I recommend these: 1. Remove the airbox cover 2. Remove the tip from the silencer 3. Replace the stock 5 weight fork oil with 7.5 weight. 4. Cut out the backfire screen. If you really want to open the bike up put on an aftermarket exhaust, rejet and change the crankcase vent. I used a Supertrapp exhaust and I liked it very much. I kept the stock engine and stock carb and the bike still has awsome power.
 

DougRoost

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#7
One Dollar nailed it. I've done the free mods to make it breathe better and they do help. I just don't see the bang for the buck with exhaust systems -- even Stroker was recommending just using the head pipe with the stock muffler until they finally made their own muffler.

fyi, power is not the issue as my KLX300 has plenty now. I orderd a 33mm Mikuni pumper carb for mine since everyone I've talked to said this really wakes the bike up. The ability to wheelie over a big rock or log is what I'm looking for and the Mikuni 33 pumper delivers. They say -- and I believe -- that this is the carb that should have come stock on the bike.

BTW, I learned that you probably don't want the Keihin FCR unless you've got a 331 or 365 and even then it can be quite finicky (36mm Mikuni probably a better choice in that case). After all, the FCR is a racing carb and has no choke and the accelerator pump is exposed and vulnerable to mud restricting its movement. More importantly, it only has one pair of vents (the Mikuni have top and bottom). The lack of extra vents means if you dump it while hot it fills with gas and you have to kick it over and over and over until you flush out all that extra gas. One guy told me that even with a hot start valve he's kicked for over 10 minutes to refire. Said it's fast but just don't fall in the middle of a race!

Once I get the pumper carb on I'm going to order a headpipe from Stroker. That way I will also be able to better see how much it helps since I'll do the mods incrementally.:cool:
 
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penguin

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#9
One guy told me that even with a hot start valve he's kicked for over 10 minutes to refire. Said it's fast but just don't fall in the middle of a race!
Hey! I resemble that remark. :scream:

To me the aftermarket muffler is a way to save weight more than it is a way to increase horsepower. Since I have owned 3 KLX's in the last 5 years, I have run several combinations of exhaust and carburetors and the 33 Mikuni, Stroker headpipe ,and stock unplugged muffler is my favorite all around setup and the best bang for the buck. Use the money you save on the aftermarket silencer and invest in suspension upgrades.
 

DougRoost

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#10
Yes, Mr. Penguin is correct. He was the wise, experienced gentleman who helped guide me on pumper carb selection once I decided to do it since he's run all 3 carbs. I haven't done the Stroker header but it's in the near future, along with their shift kit and ilder gear fixes. Recall I was cool with the power level but wanted to wake the bike up. I think the Stroker header will add a little of both since the stocker was a carry-over from the 250 and is smaller than the exhuast port!

BTW, pumper carb or not, all KLX owners should install the Ty Davis hot start valve! It is so convenient and works so well it's the best $70 I've spent on my KLX. You can even use it to lean the bike out a little if weather/riding conditions warrant it and it is so convenient being right there on the clutch perch. With this I don't see any reason to go to a manual decompression release (BTW, Honda says the same thing on their CRF450 since a hot start is stock along with the autodecompression, which KLXs already have).
 

DougRoost

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#11
I just put the Stroker header on (still using stock muffler with turn down tip) and am getting back to you guys as promised. The bike now pulls stronger across the powerband, but is especially noticeable from half throttle to wide open. In fact, I now sputter on the top end so it appears a larger main jet is in order. This is quite telling of the improvement!

As Penguin said, this really completes the pumper carb install, balancing out the mods. AsI knew from all the years of restoring and hotrodding cars, you always have to take a systematic approach to hop-ups. I highly recommend the pumper carb/Stroker headpipe combo. In fact, the stock pipe is so restrictive if I could only afford one I'd do the pipe first and perhaps put a lighter spring in the stock carb until I could afford the Mikuni 33.
 

weimedog

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#12
Does the same advice relative to that Mikuni 33, Stroker head pipe and unplugged stoke muffler work on those older 250 KLX's?
 

DougRoost

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#13
Yes it does. The KLX300 actually gives you a carb choice of Mikuni 33 or 36 or the Kiehin FCR 35. With the 250 you definitely don't want to go bigger than a 33.

The KLX300R is much nicer than the 250, though. It was more than just a bore job - new cylinder head, better suspension, etc.
 
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#14
klx 300 mods

where can you purchase the Ty Davis hot start valve? also, any special case breather kit I should use? I was wondering, does the hot start valve really work, after dumping the bike for instance? My bike never starts after laying it over.
 

penguin

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#15
the hotstart definitely works. for the breather kit I used 5/8" heater hose and a couple of hose clamps form the auto parts store and a big bolt t0o plug up the hole in the hose coming off the airbox. I then bought a Uni breather filter and clamped to the end of the heater hose and ran it up into the airbox. Go here for some pictures and other tech tips: http://www.planetklx.com/