XR400 refuses to idle..

I picked up an XR400 that had been sitting for a two years. I got it running at home but it will not idle. It has 160/62 jets, 2.5turns out on fuel screw. I have taken the bowl off about five times and cleaned out the jets. I stuck a wire through the pilot this last time to make sure there is nothing in there. It fires right up with the choke on full, revs through the whole range just like it should. once I take the choke off it dies, even when fully warmed up. If I hold the throttle while I push the choke off I can ride it around and it runs like a top until the RPM drops close to idle, where hiccups and dies.

 

I have taken the jets out and blown them out / carb cleaner, taken the idle screw out and blown that out / carb cleaner, and blown out the side diaphram area + plate of the carb, as well as the bottom of the carb out and all the passageways. I put a fuel filter inline of the fuel line to the carb thinking there is debris coming in and that has made no difference either. I put a new spark plug in too, and a clean air filter.

 

I don't know what to try next. I can't see the O ring where the idle screw is.. if that goes bad, will it cause this? I will try to pick one up tomorrow and try it just for kicks. There about 1/2 tank of gas in the tank which I got it running on, I will dump it out tomorrow to see if that makes a difference, but I wouldn't think it would as it starts up right away..? I haven't checked the valves, but I have not seen out of spec valves cause a bike to not idle...? I checked the boots on the carb and there don't seem to be any leaks. I will pull the spark plug resistor tomorrow and put a piece of wire in and hope...

 

Thanks

Chris

Edited by n16ht5

Will it idle better with the choke on? If so, replace pilot jet. You might think it is clean, but it probably still has some gunk in it after sitting.

If not, maybe valves are out of spec. It's a good idea to check them when you buy a used bike. Super easy to check them on an XR.

Also, make sure you have a clean air filter, that can mess with your jetting.

it idles fine w choke. I have to order jets as part stores are closed on my days off. I will be checking valves as soon as I get it running, maybe Ill check them now.

I would certainly hope replacing 2 year old gas would make a difference. That should have been done before ever trying to start it.

 

Yes, a bad oring or no oring at all on the fuel screw will cause poor running. If the washer is still up in the fuel screw bore, you won't be able to see the oring, as it's underneath it.

Go ahead and check the valves. Make sure you check them at tdc of the compression stroke (ask me how I know!). If your bike has a decompression lever, the cable should be adjusted directly after adjusting valves. Decompression cable should also be adjusted at tdc of compression stroke.

Do these before messing with the carb. Eliminate one possible cause at a time (once again, ask me how I know!).

Oh and motor should be cold when checking valves and what not.

Edited by chattyXR

cleaned the carb out again, flushed all the old gas out and put in new (It came with a little old gas in the bottom, I just poured in fresh on top of it). runs like a champ now. she must have had a case of bad gas :banghead: . This new ethanol gas sucks, I've run +5 y/o straight gas without a problem before. Thanks TrailRyder, I should have tried the obvious thing first! Now to check the valves, grease some bolts, and dualsport it

 

 

I went and celebrated with the bad gas in the yard

 

 

CAM00597.jpg

 

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Now to.... dualsport it

 

If you are just going to toss the rear light, I'll take it. I'll even trade you a beat to hell Baja designs brake light with a plate mount and cracked lens, if you want! My original is buried in a pile of crap at my folk's house in PA, probably never to be seen again.

I like the rear XR tail lights, but I bet you could find one on ebay

I use to store my XR motorcycles for six months to a year, kick them over and they start right up. No more. Not with all of the ethanol in it. The new gas is nasty and goes bad in as little as two weeks. I now drain everything and use Stsbil.

I was told gas will last longer in a steel can. Race gas cans work. Worst is a plastic fuel tank with a vent on top.

cleaned the carb out again, flushed all the old gas out and put in new (It came with a little old gas in the bottom, I just poured in fresh on top of it). runs like a champ now. she must have had a case of bad gas :banghead: . This new ethanol gas sucks, I've run +5 y/o straight gas without a problem before. Thanks TrailRyder, I should have tried the obvious thing first! Now to check the valves, grease some bolts, and dualsport it

 

 

I went and celebrated with the bad gas in the yard

 

 

CAM00597.jpg

 

CAM00594.jpg

Did you jump the fire with the XR? If not, you should have.

I melted a KX80 playing with fire when I was younger.

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