'07 EXC 450 General questions

I have a chance to buy an '07 EXC450 that is 100% stock. I've read alot about them and get the impression they overheat easily and run the battery down quickly, expecially if you install and use the fan and don't rewire/install an aftermarket stator. I currently ride an '02 300EXC in tight single track and this bike has been bulletproof and never overheats. It has rad guards on it and I run engine ice in it. I understand the 450 will need to be jetted correctly and I may need to remove the smallest baffle from the pipe, and run a catch tank, that's no problem. I won't be running any additional electrical stuff on it, (GPS, electric grips, etc). Maybe I'm just used to the reliable 300 but the 450 sounds like it's always on the edge of puking coolant or draining the battery if you have to use the e-start often. I guess I'm looking for re-assurance that if jetted and opened up correctly and I don't run any additional electrical stuff on it that the bike has the potential to be issue free without going to a fan and re-wiring the stator. I'd like to get the reliability of the 300 from the 450 without having to throw a bunch of additional $$ at an already expensive bike. Whadda you guys think?


'02 EXC300

'98 RXC620

'89 FXRS

I think the overheating is a bit over stated. I bought mine in March of last year. I did a home made coolant recovery tank, later to be replaced with the better designed RLR tank. I had my bike in some very tight, hot, twisty single track and never had a problem with a boil over. This was after rejet, cutting out the restrictor, and changing out the gearing to something more trail friendly.

It wasn't until this year, about a month or so ago that my bike first overheated. However, I had just replaced the stock coolant with Engine Ice. I later learned that Engine Ice has a lower boiling point than regular coolant. I don't know if that is true or not, but it is suspicious that I go over a year without a problem and then it boils over when I switch to Engine Ice.

At any rate, I did eventually add the fan kit a few weeks ago. I bought that when I bought my bike last year but I never actually installed it because I never had a problem with boil over, and I didn't see the point of the added weight if I didn't need it. It wasn't until just recently after switching to Engine Ice that I installed the fan kit. I have since switched back to traditional coolant, so maybe the fan kit is no longer necessary, but I left the fan kit installed anyway. I may end up removing it, but it hasn't caused a problem. It does come on while bushwhacking through the tight stuff, or through the ultra-slow, standing, lots of clutch and throttle control, trials-like sections, but that's about it. And I have had no problem with draining the battery and I'm just using the year old stock battery.

So, I've put this bike through the ringer in this regard and I have not experienced the boil over problems described by some. I do recommend the coolant overflow tank, though. It gives you a little extra coolant expansion room and ensures that if you do happen to boil over, you don't lose any coolant - it just gets sucked back in as it cools.

I love my '07 450 EXC. It's a great bike and seems to be very reliable. I have not had one problem with it. I just change the oil and check the valves at the proper intervals and change the air filter. That's about all this bike needs, unless you are racing it hard every weekend. I have over a hundred hours on it now and it's been the perfect bike for me.


I should mention, and it sounds like you have done your research and know this already, but the mandatory mods are:

1) Rejet - JD Jet Kit is simple and performs great. Be sure and do the included "O-Ring" mod which strengthens the AP squirt. Also recommended is JD's leak jet float bowl OR JD's optional Honda AP diaphram. These shorten the AP squirt from 3 seconds down to about 1 second. I have tried both and I recommend the leak jet float bowl.

2) Derestrict - cut the restrictor out of the pipe. It opens up the air flow. It does increase the dB a little bit, but it's not a lot. Some also say that the restricted pipe contributes to this bike running hot.

3) Regear. Stock gearing is 15:45. You'll be lugging the bike at 65 MPH with this gearing and 1st gear will feel like you are in 3rd. :thumbsup: Most people regear to somewhere between 14:48 to 13:52. I'm currently at 14:50 and find this pretty nice. I like 14:52 also.

Everything else is optional and to personalize to your taste. Some people make it sound like you need to buy $10k worth of aftermarket parts to make this bike great. The above three are all you really need, IMO. Figure $75 for the JD kit, $65 for the leak jet float bowl, derestricting is free, maybe $50 to regear front and rear.

The above mods will open the bike up and you'll have what KTM wanted to sell you in the first place, but couldn't due to EPA and European regulations.

Throw in a skid plate and hand-guards, set your suspension sag, and you are all set for the most rugged of off-roading.

To your original question - reliability of a 2-stroke? I'm not sure if that is possible. However, as far as 4-strokes go, the RFS is considered one of the most reliable out there. There are many reports of > 10k miles just doing routine maintenance and they are still running strong with no problems. Like anything, you get out of it what you put in. Keep your oil fresh, valves in spec, and your air filter clean and the RFS engine will treat you very well.

I rode the bike about 10 miles this afternoon. The dealer said they raised the needle a notch and that was all. The throttle response was not real good which I kinda expected. I can see if you got the bike dialed in properly it could be a fun bike. There is a bunch of smog stuff that has to come off. What is the small valve to the left of the carb that has about three hoses leading into it? I'm going to sleep on it and decide in the morning.


'02 EXC300

'98 RXC620

'89 FXRS

Ah, yes, the cannisterectomy. Here's the desmog procedure:


There's a mistake in this, though, that is corrected later in the thread. Do not completely block off the black cannister at the base of the swing arm. If you do, the carb won't be able to breathe and it will act like it is flooded. I think most people just end up removing that whole thing, so that's what I'd recommend. It's there to catch the fuel if you have a tip over.

Desmog doesn't really get you anything in terms of performance, so don't expect a lot out of that. It can reduce decel popping which may be mistaken for lean jetting.

If all the dealer did was raise the needle a clip position, do yourself a favor and get a JD Jet kit. Whether or not you do the honda AP diaphram or the leak jet float bowl, the JD Jet Kit includes two needles which really work well, as well as a range of jets to use. It has clear instructions on which needle to install, what clip position it should be one, and what main jet to use depending upon your altitude and temperature. Also included is the important "O-Ring" mod which strengths the AP squirt. The dealer changing the clip position is not going to hold a candle to what the JD Kit will do.

But combine the JD jet kit with the leak jet float bowl or the honda diaphram pump, and now you're cooking with heat. :thumbsup:

Don't forget to derestrict the stock pipe. When combined with a rejet, its makes a huge difference.



I had a 2000 KTM 300exc and switched to the 2007 450exc - mainly because it is street legal. I have no regrets at all. I love riding the 450 on the single tracks & fire roads. It is also nice to be able to pop out of trail and ride legally down the road to get to a gas station or other trails.

The bike handles allot like the 300 so it was any easy transition for me. It took a few rides to get used to the 4 stroke power (+ engine braking). Some decel popping from exhaust (can be reduced with carb jetting and fixing any gaps/leaks in exhaust pipe). The 450 has lots of power when geared properly.

My best tip to avoid overheating - always shut the bike off when you are stopping for more than a few seconds.

Like others have said - get a coolant recovery tank, JD jetting, de-restrict the muffler, ditch the vapor valve/hoses/cannister and vent the gas tank to atmosphere. Add 14 x 52 sprockets (& longer chain), a skidplate, handguards and you will be very happy riding this bike on any trail.

A 450 needs a little more maintenance compared to the 300. The oil change is more time consuming with two oil filters to change. I use stainless steel oil filters and clean them every oil change. There are also two filter screens that need to removed & cleaned (tap cover bolts and remove when engine is hot). Get an aftermarket replacement hex bolt for the short screen filter for easier removal. Do not over tourqe when reinstalling (may seize in the threads and can be very hard to remove & may strip or crack). The 450 also needs the valves checked/adjusted every 15 hours, or so. My intake valves required more frequent adjustments (three times in first season), compared to the exhaust valves (one time). The 450 RFS engine is very strong and durable ans will last for many years if you keep the air filter clean, change the engine oil often and adjust the valves when needed.

Good luck!

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