Overheating?

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May 17, 2001
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#1
I took my 98 xr400 out to a local track today. The terrain was dry with areas of soft sand. The temp was 77. This is the first 4-stroke I've owned. While I was riding the bike suddenly felt like it was fouling a plug. The bike would idle and start fine, but as soon as I twisted the throttle, it would start sputtering. I guess it seemed like the choke was on, but it wasn't. I managed to get it back to the truck by riding at idle speeds. After the bike (and me) rested for about 20 mins, I started it up, and it worked fine, but it did it again. In the same spot on the track as last time. This time, I rode around on smoother sand-free areas without really opening up the throttle much, and after about 5-10 mins, the bike worked fine again when I twisted the throttle. Another guy there said that maybe it was overheating. I don't understand why it would overheat. The first time it happened, the odometer read 9 miles, and I had already stopped once earlier so it wasn't 9 miles of constant riding. Any help would be greatly appreciated.

Oh, the only engine mod that I know of is a Whit Bros. 416 kit. and I run 92 octane fuel.

Thanks,
Jeremy
 
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#2
xrguy,

Have no idea what the problem is, but I do know you can buy a temperature guage that replaces your oil cap from xr's only. I think it's $20.
 

HiG4s

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#3
My son's two Hondas have acted similar. His XL75 had the valves adjusted too tight and when they got hot they would not close all the way. It also would not start hot. And his XR100 acts that way when ever the air filter is getting clogged. Not sure why just does. After I clean the air filter and re-oil it works fine. Not sure if these are relevent to an XR400 but thought I would share.
 
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#4
If the guy who owned the bike before you ran race gas it could be running too lean. Also want to check your airfilter. If you could ask the person who you bought the bike from some questions you may be able to solve the problem a lot faster.
 
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#5
Thanks for the help.

I have heard about that dipstick/thermometer. But what temp should the bike run at?

So the valves could be the problem? How hard are they to adjust? I have the service manual.

I asked him if he ran race gas in the bike. He said no, run 92 octane. I also checked the filter. I just cleaned it a few days ago, and it's still good. No problems.

There is an aftermarket headlight on the bike (acerbis). I noticed that it sits right in front of the oil cooler. Could that be part of the problem? I have a picture of it. The link is in my signature.

Anyone else have any ideas?
Thanks,
Jeremy
 

Wolf

doooode
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#6
I am no expert by any means, but it just doesn't sound like overheating. I have run mine with a #plate and no airflow to the oil cooler, it never overheated. I also do a lot of low end work, chasing my 4 year old on a 50 and never overheated.
I would start with the valves.
Good luck
 

mtngoat

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#7
No expert here either, but I'll try to help.

I don't think it's overheating either. Intermittent problems can be tough to diagnose. I try to look for any events/conditions preceding or surrounding a problem when I diagnose. For example, I really blundered cleaning my air filter and applying oil while the filter (K&N) was still damp. This restricted airflow causing similar symptoms. I did a lot of work before realizing my mistake.

Anyway, without anymore conditions (or if you can think of more, post), this one is really tough. I'd try the following:

plug - pull & inspect
fuel - remove fuel line and check petcock valve/filter for un-restrcited flow.
valve adjustment - do a search on this; good advise already posted. not difficult.
filter - re-clean and oil
carb - pull the access plug (bottom of the bowl) and look for junk. remove the main and slow (aka pilot) jets, inspect and clean. Take note of the jet sizes.

BTW, ever notice gas overflow from the carb when the problem occurs?

Any other symptoms might help to figure this one out.

That's all I can think of for now.