650R Overheating at low speeds

Hi folks. Stupid question here, but I'm a newbie so please don't flame me if I sound ignorant.

I have been out of the sport for the last 5 years or so, but I just bought a 2000 XR650R with very low hours (really, almost never ridden by original owner). I have ridden it 3 times in moderately warm temperatures and each time it has exhibited a tendency to overheat and blow off excess coolant. The first time, I started the bike and let it warm up and idle for about 10 minutes while I geared up. I noticed it was spewing, so I shut it down, let it cool for a while and restarted with no problems. Once I got out on the trails and wound it out a bit, it ran fine all day and did not bubble over again.

The other two times I have ridden it since, I was teaching my boys to ride on their new XR100. This involved a lot of 1st & 2nd gear low speed riding around and idling while they negotiated a cone course, practiced turning and stopping, etc. The bike boiled over several times on those days, and each time I was able to cool it off by blasting up an open trail and running it up the gears at a moderatly high speed for a while. Both times this happened, I added colant back up between the range lines on the overflow tank, and other than what was blown off, it seems to be holding that level. I don't have any obvious leaks from hoses, radiators, or cylynder head that I can see.

Is this a normal condition for a BRP that is not getting enough air at low speeds, or is it possible that I have a problem somewhere in the cooling system? If this is something I need to troubleshoot, any advice on where to start, or threads you can refer me to would be much appreciated. I have owned a lot of Honda thumpers before (XR's 100, 200, 350 and 500) and a few CR's back in the day, but this is my first liquid cooled bike. Any advice would be much appreciated.


It's pretty normal for this to happen, especially on a stock bike. If your bike is uncorked (airbox restrictors removed, non-EPA manifiled installed, larger exhaust tip, carb rejetted, etc), then it will boil over a lot less frequent.

Some people buy a Kawi KX80 rad cap that increases the pressure in the system which in turn raises the boiling point, but that will just prolong the enevitable. A very few people have gone to the extreme of adding a fan, but there's really no need for that. Sometimes the thermostat can stick and that might be a problem area, but some people (dependong on their riding environment) run them without thermostats with good success. Some people experiment with different coolants and some have had good success with this approach, but this approach might not be necessary.

I never used to have any boil over issues with my bike and then it happened a few time to me when I went riding with some small kids on the hotter days. I switched over to Evans NPG+ coolant quite a while ago. It has a boiling point of ~375 F which is much higher than the 50/50 (H2O/EG) mix. Just because it has a higher boiling point doesn't mean you'll ever get it to that level and I'm not a bit worried with this product as I've been running the NPG stuff for years in some of my cars with good results. It's also a lifetime coolant. I also did a bit of testing after pouring the Evans NPG+ in my bike. I drilled & tapped the frame plug (for oil temp) and the boss on the water pump (for coolant temps) for 1/8 NPT. Then I captured the temperature information using a portable datalogger on a few rides and decided to keep the Evans NPG+ installed because the temps stayed in check during the summer months while riding in the SoCal & Nevada deserts and the temps never got out of control even during extended periods of idling. The Evans NPG+ is a waterless coolant and has some advantages over the tradition 50/50 mix, but it's far from the perfect coolant. The NPG+ doesn't cool as well at lower temperatures as the normal 50/50 mix, but it continues to work when the 50/50 mix boils and that was important to me along with it being a lifetime coolant. Another downside to the NPG+ is that you cannot add water to your cooling system, so if your bike does get a leak due to your rad smacking a rock, then you're screwed unless you happen to be carrying some spare NPG+ with you.

If I were you, I'd first make sure your bike is properly uncorked and get your carbs tuning/jetting right. That should take care of most of your boiling issues even at lower speeds and you probably won't need to do anything else. Most of the other water pumper bikes will also boil over in the super slow stuff, so don't worry too much.

Is your bike stock or uncorked? What kind of jetting are you running? Do you have the stock exhaust tip, the HRC tip or a different exhaust system?

Easy fix, common problem. The bikes come way too lean in stock form for epa purposes. Uncork the bike using the normal power up items; 175 main jet, clip in 3rd position (competition needle, or clip in 4th position for stock needle, 40mm intake boot, 40mm exhaust tip, and airbox restrictors removed. You have to do all the changes for it to run correctly. Honda sells all of the needed parts.

If you make these changes, the bike won't overheat and spew anymore. I still run the stock radiator cap and have had no problems.

Keep in mind making these changes does NOT affect reliability. There are no issues with the above mods, and they allow the bike to run as intended.

Also, the bike is not intended to be idled for more than about three minutes for warm up. After that, of course you would run the risk of a boil over since no air is flowing over the radiators. It's never a good idea to let a bike sit and idle unless it has a fan.

Good luck with it! Once it's uncorked, it's a whole new animal!


Thanks for all your ideas, and feedback, guys. I was sort of going the direction of looking at a better colant, but not until I know the bike is Okay. It's reassuring to hear that this is not an uncommon symptom for a pumper/thumper. On all my air-cooled XR's in the past, I always warmed them up a while before riding. My old' 500 was death if it stalled after the first start without getting fully warmed up. Anyway, I won't leave it idling that long ever again for sure.

smashinz2002: In answer to your question, my bike is bone stock down to jetting, and the factory exhaust with spark arrestor. Are the parts you describe all contained in the "power up" kit that Honda describes? I am thinking about an aftermarket pipe, but I really need to keep the bike CA green sticker legal so I need to keep the noise <96db and it has to have a spark arrestor. If I do the mods you described, will I still be compliant?

Thanks again,

...my bike is bone stock down to jetting, and the factory exhaust with spark arrestor...

Wow! You'll be in for a huge treat when its uncorked and it will feel like a completely different bike afterward with MUCH more power :). It's a night/day difference between corked/uncorked and this will solve most or possibly all of your boil over issues. See the following links for more info...

(see question #4 on the first link)






Thanks for all the links. Now I understand why everyone calls it "uncorking". I think I will get on the DIY mods like the airbox, manifold and muffler this weekend (I must have a 2" whole saw somewhere...). I think I will do this and attemp the jetting before I spend any big money, but I am thinking about asking Santa to bring me an Edelbrock carb this year.

It's ironic that making this bike FASTER may be the best way to minimize my low speed boilover problems. I love my pig, but the power makes me skidmark my drawers every time I ride it, so I am not sure I really need more HP just yet. On the other hand, I can never admit this to my wife, who really wanted me to start with an XR400 this time :)

Thanks again,

...I can never admit this to my wife, who really wanted me to start with an XR400 this time...

I think a lot of us have been through this :)

Make sure to do eveyrthing at once when you uncork it, otherwise your bike won't run too well. If you do the airbox, manifold and muffler this weekend without the jetting mods, then your bike will be too lean with the stock jetting and it will be very difficult to start and it won't run worth a darn. You can modify the stock manifold, but buying a new one is very inexpensive. I'd also suggest using a 172 main jet instead of the 175 that's listed.

If you ever need Honda OEM parts and you've got the Honda part numbers, then first check the prices online at www.servicehonda.com and at www.ronayers.com These two places will have the cheapest Honda parts in the country and you'll usually save ~30% on Honda parts when compared to your dealer, but don't forget to account for any shipping and handling charges when comparing prices. I've ordered from both of these places with good results and like buying from them over my dealer since my dealer never stocks any of the parts I need anyway. Buying from my dealer also requires a 2nd trip back to pick up the part as opposed to having it delivered to my door for less money, but maybe you've got a more friendly dealer in your area.

One more thing, i dont know if anyone mentioned this, i used to get it pretty hot at idle and boiled a couple times when i was still running the stock slowjet, the 68s slowjet fixed this (stock is 65). im at around 1200 ft. fattening up the mix will make it run cooler most of the time. good luck, JR

Hey bro, the links that Qadsan has there are excellent for learning how to uncork the bike. And yes, if your bike is completely stock, then you are in for a shocking difference! For one thing it won't boil over any more and it will be a lot easier to start, both hot and cold.

I wasn't trying to suggest that riding the bike cold is good for it. It's not. Proper warm up procedure is important. Start it and let it run for about 2 minutes. Then ride it easy for another 5 minutes or so. After that, it's ok to hammer it hard.

Oh yeah, if you've never ridden a properly uncorked 650R, then you might want to take it easy at first. The first time I rode mine uncorked, I was struggling to stay on the bike when I got on the gas. After a few rides you get used to it, but it still demands careful throttle application to prevent the bike from coming out from under you.

I'm not familiar with CA laws. But I can say from experience that aftermarket pipes are MUCH louder than the stock pipe with the 40mm tip. Far too loud, and not much of a power improvement in my opinion. Save your money and use the HRC Honda tip, or , modify the stock tip to 34mm or 36mm opening, which is even quieter (however less power). You can find this mod at one of Qadsan's links. I don't recommend it simply because I believe the 40mm tip is quiet enough and produces much better power.

Good luck with your bike I hope you enjoy the heck out of it!!


Thanks again, guys.

It's an old habit, but I always do try to warm up my bike when I ride. Hopefully after I do all these mods, I can let it run long enough to actually change with out boiling over!

I have been looking for some online OEM parts sources, and both of these look like winners. My only experiences so far with this new bike and my local Honda dealer has been the $12 (yikes!) :) I paid to replace the rear axle nut that was rounded off. They are a good shop, and have a few MX racers on staff that they sponsor, but pretty much expect the same routine I have come to expect from any Honda dealer (you know, order the part, wait too long, pay too much, never get called when it comes in, etc. etc.). Anyway, I am willing to try ordering the stuff I need online.

I have decided to wait unitl I can get all the jets I will need, and the new manifold, to do the whole uncorking operation at one time. Of course the last time I decided to get ambitious and do a bunch of stuff to a bike at one time, it was my 1979 CR250, which has been sitting in pieces in a crate somewhere ever since.

I also picked up some new ProTapers and a replacement clutch/decompression perch to install after my last little excursion over the bars last week. Should be a good weekend of getting dirt under my nails.

From what I have read and heard from you guys, all I will need now is some new earplugs, and a few extra pairs of underwear for my first uncorked ride! Yee haw! :D

Only need earplugs if you take the tip out completely, neighbors will love you, but does it sound MEAN :). Highly recommended at least once. Its like lighting up your big block on open headers to see what it sounds like, you just gotta know!!!. Hold on tight your first ride, and dont sit too far back, you need to hold the front end down. JR

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