Take a guess (I know this is a car site)
 

Pulled out the XR400 to go riding in the woods after being stored for a long time w/ occasional starts... it is a 1997. It starts up, sounds ok @ idle, no head noise, good compression. Overall, this bike looks like a virgin prom date & has very low hours. Fresh 100 octane fuel, clean air-cleaner too.

In less than in a minute, one of the two header pipes is very hot... in two minutes, it is glowing orange (both are hot) A little popping on downside of rev. Never had a problem with her before... it is air cooled & a 4 stroke which is hard to kill. I have never pulled one apart... it is forien to me. It has 4 valves. Anyone ever heard of this??? Stuck valve???

Sounds like a sticking or possible bent valve to me.

I'd pull the valve cover(s) and do a looky loo, spray some penetrating oil on all the valve stems and spin it over.

The rockers are adjustable, they probably need adjusting anyway, get a manual for it if you dont have one and do a PM on the valve train first.


Goodluck, Cp

Sounds like the floats may be sticking a bit in the carb.Thats where I'd start,sounds gummed up some to me

one side running lean

Lean
 

X2 on the lean condition.

valve train issue.

Yep scoot, sounds lean. I'd pull the carb or carbs and check the main jet if its been sitting over six months I'd put new main jets in it. Even if you can see through them they could be gummed up and make them smaller than what they should be causing a lean condition. Seen it many times on snowmobiles from just sitting for the summer. Jets are cheap. The other parts aren't.

Guys think about what you're saying here.If it was lean the pipe would be stone cold.

The cylinder have an over abundance of fuel and its burning it in the pipe.

Meaning its getting too much fuel :wink:

Carb or carbs need to be cleaned,main jet,pilot jet,also the needle and seat valve.

It sounds lean to me also. One thing you might check while you are working on it is, since it has been sitting, the rubber boot between the carb and head will dry rot causing a vacuum leak. Look at that too.

TS1955

sounds lean to me also ... maybe a mouse made a nest up in the carb ? I've seen that before

Thanks for all the input!! Good ideas... I will look at the carb this weekend first. I will also check the boot as well. I hear 2 conditions... lean & rich. I am going to start with rich possibilities b/c I know that small flames can be seen comming out of the silencer too... it makes sense that it is getting too much fuel.

On the other hand, I originally thought it was LEAN due to high temp. Being this is a different motor for me to work on, I may have a 4 stroke friend help some. I will post the outcome & verify the issue(s) so you guys know what happend.

Thnaks!! Scoot

ive built alot of harleys over the years and ive seen a few of them pipes turn red when the timing is right . found quite a few times one side running real lean. fattin things up and presto.but then again, i use to drink and smoke that stuff alot back in the day!!!lol

I know this is a little late in getting back, but I fixed it this last weekend. All it was: There are two jets in there. One of which had flakes of varnish/crap in it. It was just enough to let some fuel go by.... but not much. I assume it was the low circuit jet. Anyways, cleaned it out, re-set the F & A mixture, & it was good to go. Gonna go riding this weekend. Scoot

Actually you are thinking wrong not everyone else. Normally when you lean one out the egt's run hotter until you pass peak lean then they drop off also causing the power to fall off. If you start adding fuel your egt's will go down because you can't burn the extra fuel. All this is asuming you start at the correct setting to begin with and since his was running okay when he parked it then yes, a leaner condition would cause the exhaust to run hotter.

I have had this happen to a lot of equipment that sits over winter (welders, pumps, etc....) before I start tearing things apart I usualy take 1/2 gal of gas & put one big bottle of gumout and run it on that, nine times out of 10 it works.