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Does this sound like an overheating problem????

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Posted by: cheapo---------------------

I recently came out of “retirement” and ran my first race in 3 years (the Delaware Hare Scrambles) this weekend and faced a problem I haven’t seen in the past. About 1.25 hours into the race the bike starting acting up bad. It is best described as follows:

It sounded like the engine was pinging or knocking and would not hold a steady throttle. When I pulled over or put it in neutral it would rev by itself at a higher RMP for a second or two. I was half way through a lap so I had to limp back and pull over every so often.

This hasn’t happened before, but I suspect it might be an overheating problem; however I could be way off. I haven’t been riding in about a year but what leads me to believe it was overheating is the fact that when I rode for a long period of time in the past (not a race) I had pulled over and heard the water/coolant mix “boiling” in the radiator. At that time I had recently installed a pair of Devol radiator guards, however the bike didn’t act up as described above. I’m fairly certain this weekend was the first race I competed in a race with the radiator guards on. Does it sound like a possibility that the guards hold in too much heat for such a continuous period of riding (about 1.25 hours of high and low RPM’s without stopping)? Seems doubtful to me. A few things to note about the conditions and bike:

-Weather at race time: +/-50 deg F
- I noted some coolant on the frame of the bike at the end of the race
- I noted that during this time of the race, there was plenty of coolant in the overflow tank; just below the Full mark
- Although it was muddy, the front of the guards did not appear clogged or impeded.
- The bike is a 2000 KDX 200
- I mix the oil 32:1
- Autolite MP 4063 sparkplug
- Water/coolant mix about 50:50
- I did a top end job on the bike in 2004 – not a ton of time put on the bike after that
- Devol radiator guards on the radiators. The left side radiator (as you sit on the bike) has minor damage due to a side impact (ie one column of fins were slightly pushed in – that’s the reason I purchased the guards).

I haven’t started the bike since the race so I need to check to make sure the water pump is operating correctly. As I understand one way to do this is open the radiator cap and run the bike to make sure the water is circulating. I also haven’t bled the air from the system which I need to do. The bottom line: do the symptoms described above sound like an overheating issue so I can focus my attention on the coolant system? Any suggestions are greatly appreciated. Thanks all!

-Bill


Posted by: dirt bike dave---------------------

Yes, it sounds like overheating to me.

My guess is the muddy conditions contributed, even though the radiator was not clogged with mud. The motor simply has to work much harder in the mud than it does on hard pack.

Imagine how much easier you yourself would overheat if you had to push your bike a mile in deep mud compared to a mile on dry hard ground. Mud and deep soft sand will bring out overheating problems in many bikes.

Did the radiator guards contribute to the problem? Maybe.


Posted by: sr5bidder---------------------

not venting the air out of the left radiator when filling the right will result in the system being only half full
there is another vent bolt on the top of thewater neck on the cylinder head.

if you did not fill it properly I'd say that is the cause of your over heating


Posted by: dirt bike dave---------------------

Oh, and instead of a 50/50 mix, a higher % of water might make a difference.

And maybe the jetting was just a tad lean for the temp/conditions.

I'll guess there is no damage to the motor and it will run like normal next time you use it.


Posted by: cheapo---------------------

Thanks a lot guys! I'll put my focus on the coolant/radiator.

Quote:
Originally Posted by dirt bike dave
Oh, and instead of a 50/50 mix, a higher % of water might make a difference.


Thanks for the tip dirt bike dave - I'll increase the water mix.

Although the bike didn't sound good at all and I had to keep running it to get back, hopefully there wasn't any damage....the KDX is a resilient machine.....


Posted by: pesky nz---------------------

I've also chased my tail on a boiling KDX and it turned out to be a partly loose water pump impeller and as the motor got hotter the impeller got looser and the coolant did not cycle as well and the boiling began. The bolt holding the impeller on had thread lock so the bolt felt tight enough but the impeller could be turned by hand (just) without the crank moving. Don't swing on the impeller as it is driven by relatively small shaft and gears


Posted by: cheapo---------------------

I was going to completely flush out the radiator, but after a search, I've read some say it isn't worth flushing - just drain, visually inspect and refill. Seems like a flush is easy to do, but any thoughts? Also what flushing compound have you guys used? Thanks again!


Posted by: mudpack---------------------

Sounds like the engine is running very lean. This is a fuel flow issue.
Now, a lean condition can certainly lead to overheating, but you have the symptoms backward; it's not that overheating is leading to your running problems (fuel flow), it's that your running problems are leading to overheating.
Comprende'? Check your fuel system first, from tank to carb.


Posted by: cheapo---------------------

I comprende' but I drained the coolant today and only about 20oz drained from the water pump plug and overflow tank (I did not remove the radiators and empty them). Seems light to me when considering 1.1L fills the system (including overflow tank at full, radiator and engine). Now I think - is the rest hiding out in the left side radiator and/or some in the engine - or was there way too little volume in the system? Once again, I had coolant in the overflow tank when I was done running which leads me to believe I might have had too little volume of coolant and air trapped in the radiators?
I'm hoping a flush and refill will do the trick. I'll also check the fuel system as a precaution.


Posted by: Joburble---------------------

Quote:
Originally Posted by cheapo

It sounded like the engine was pinging or knocking and would not hold a steady throttle. When I pulled over or put it in neutral it would rev by itself at a higher RMP for a second or two.


Because of this I think I agree with Mudpack.

Correct me if I'm wrong someone, but if 2 strokes overheat to the point that the performance is being changed don't they go boggy or seize and not rev higher? Sure the bike may have got hot enough to overflow some coolant but I'd be looking at fuel too as a cause.

Also check head gasket maybe?


Posted by: EYY---------------------

Have you ever changed the crank seals? If not, you could be sucking in air and losing crank case pressure. When you drained the coolant, did you remove the radiator cap? How are your reeds?


Posted by: cheapo---------------------

Revisiting this thread. A while back I did a full flush and refill, bled the air through the screw on the cylinder head and filled the overflow. After a recent ride, I noticed I lost some coolant (the overflow was empty and the coolant was low in the radiator). When I refilled the radiator I noticed that when I screwed on the radiator cap, it screwed past the tabs on the radiator - as if it was stripped. It took some effort to do that, but on the other hand it seemed too easy. So this leads me to believe I may have some discharge from the cap - so it's probably time to replace the cap (it's the original cap on a 2000 kdx 200). I've read some threads here about using a higher pressure cap (a 1.6 kg/cm2). However I'm not clear if this causes unintended consequences - ie higher temps and worse off for overheating. Keep in mind I am using the Devol radiator guards so I understand that holds in a little heat as well. I saw a CV4 high pressure cap (30 psi which I believe equates to +/- 1.6) on Rocky Mtn MC.

I've also read a lot about Evans vs. water wetter vs coolant. I am currently using std 50/50 mix right now.

Any thoughts on replacing the std cap with a higher pressure cap as shown above as a viable solution?

Thanks in advance.


Posted by: dirt bike dave---------------------

I'd replace your bad cap with a standard one first, if it is readily available and the same price.

If you are still overheating or have any trouble getting a stock rated cap, maybe then go with the higher pressure cap.

FWIW, I never could keep coolant in the reservoir on my E model. It would just splash out the overflow when the bike was bouncing down the trail.


Posted by: Dirtdame---------------------

Sounds like lean running, like an air leak or something, or possibly a clogged pilot jet.



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