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Pro Jr Overheating!!!

CNM

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Dec 28, 1999
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#1
My son got a 2003 Pro Jr from Santa. The first few short rides were great! It's taking him a little to get used to the quick power but he can't quit smiling! :laugh:

We went riding Sunday and had all kinds of problems. Not long after we hit the trails the bike started overheating really bad. Coolant was boiling over and steaming. Luckily we caught it before it stuck the piston. Since the factory KTM coolant is clear, we weren't sure if there was coolant in the radiator or just water. Especially since we couldn't smell anything when it boiled over. We filled the radiator with Engine Ice pre-mixed coolant and it seemed to run great in the pasture. As soon as we hit the woods again though, it overheated again.

The dealer where I got it says it needs different jetting so it will run cooler at slow speeds. I guess that will help but I'm not convinced that is the ONLY problem. I can see coolant flowing around in the radiator but maybe there is another problem with the water pump. Oh yeah....no water appears to be in the oil to suggest water pump failure.

Help........if it overheats in 50 degree weather what is it going to do this summer when the temp hits 90+.

Has anyone else had this problem and what are your thoughts?
 

Jman271

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Oct 18, 2001
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#2
Did you fill the radiator up to the top before you rode? If so, you may have over-filled it. Just fill it up to the top of the fins. It needs room to expand, and alot of guys were having this problem when filled it up like a regualr bike. Also, the clutch on that bike is designed for more RPM's for MX than woods riding, so your little rider is working the throttle alot to get the revs up to when the clutch engages. Problem is that this causes havoc on the clutch stack and the RPM's are making the bike heat up real quick. If you will be doing more woods riding, shorten the stack to engage the clutch sooner. This will be a problem if you use the stock mx stack height w/ a later engage for mx in the woods. Hope this helps-
 

Jman271

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#3
Tried to edit my previous post, but it won't let me so sorry for multiple posts. This is taken from www.thracing.com. This Guy Todd forgot more about minis than anyone will ever know. Here is what he has to say about the LC 50cc KTM,,,

KTM LC50 Clutch Setup - 2001 - 2004

First off not all clutch washers are the same size. Even a new bag of 1000 washers comes with variable size washers in it. It is not the size of the individual washer that matters. However, it is crucial that all overall washer stacks are the same height! Second it is important to start with good washers. T H Racing offers washers that last longer and are less resistant to heat related breakdown over the stock washers.

The taller the washer stack the higher the engine stalls (more RPMS) before the clutch engages. The lower the washer stack the sooner the clutch engages (too early will create a bog). There is a fine line between getting the bike to engage at its best and overdoing it and causing clutch drums to break.

To setup a clutch properly you will need a set of calipers to measure the stack height. I have seen inexpensive plastic ones in the auto parts stores for around $5.00.

I normally setup racing clutches to an overall height of .650 - .690 depending on the rider’s weight and track type. If you stay in that range you should be happy with the results. A good place to start would be if your rider weighs 50 pounds stay around .650, 60 pounds .670, over 65 pounds go for the .690 setup. I am calling the overall height that of all the cupped washers and flat washers together.

Now we get into the options. A setup that uses a () setup vs a (()) setup. A () setup will throw the clutches quicker a feel a little more responsive than a setup that used (()) washer stacks. In the warmer months a () setup seems to breakdown with heat much quicker than a (()) setup.

Suggested Summer setup – (top of bolt on this end) (())(())(())() plus the flat washers.

Suggested Winter– (top of bolt on this end) ()()()()((((((( plus the flat washers <requires an additional cupped washer>.

It is very important to ensure that ALL THREE WASHER STACKS are of equal height. If 1 or 2 clutch pads hit the drum before the others you are losing hook-up ability.

The bottom line is you will normally need to experiment to get YOUR RIDERS clutches they way they want it. Use the suggestions above as a good STARTING POINT. Clean your clutch washers often. The difference in a holeshot and no-holeshot is greatly due to the clutch in your 50cc bike. I don’t claim to know it all, but the bikes I build have pulled hundred’s of holeshots on across all levels of competition. I hope this helps your racer to do the same.

There are many variations of washer setups. These recommendations are for experienced riders who expect a holeshot. These would be stacked with the left side against the head of the bolt.

Use blue loctite on the clutch bolts and 1 drop of red on the clutch and crank shaft.

Use 8oz on Maxima MTL Extra Light 75wt oil in the crank case. I can promise you that anything else is 2nd best.

Note: These are suggestions that work well for a number of riders. DON'T BE LAZY, take the time to learn YOUR clutch. If your bike does not hit well AFTER following ALL the above steps you may need to fine tune it. You will have to do that. We do not provide clutch stack support via the telephone. If you have a question please email it to techsupport@thracing.com and we'll do what we can to get you a timely answer.

KTM LC50 - 2003 Update

Your bike comes with 2 .02mm cylinder base gaskets. Remove 1 for a better running bike. Your bike also comes with a real hot BR8ECM spark plug. I would not recommend running these in weather over 85 degrees. Go with a NGK BR9EVX or BR9EIX to be safe for year round performance.
 

CNM

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#4
Thanks for the info! I'll pass it along and see what adjustments they want to make. Thanks again!