XR400 carb problems

Hey, so my '01 xr400 has been an awesome mount and has run great through the last 12 years however........

it was stored for the last 2 years ( I was building a house) and I forgot to drain the carb. So naturally I have stripped down the carb and cleaned the green gunk out with carb cleaner. Both main jets and pilot jet were soaked and cleaned and blown out with air. (Standard Keihn carb with standard jets). New air filter and plug. So I kick it and it starts first time, sweet, but....... it will only run on full choke. No amount of backing out the fuel screw on bottom of carb can richen it enough to run without the choke on. I'm baffled at this point! Could the jets be "beyond cleaning"? Anyone have any ideas? I hate to admit defeat and take it to the Stealer oh, I mean "Dealer".

"Stripping" the carb means different things to different people. To me it means every part that "could be" removed "was" removed. So, did you remove the fuel assembly and clean that passage? You have to careful with some carb chemicals and o-rings/ rubber parts.

You should have removed the air diverter valve and cleaned those passages too.

Run a small wire thru all carb drillings and blow them out with cleaner and air.

Could the jets be "beyond cleaning"?

Answer: YES

I bought a bike with a pilot jet that was plugged solid, like concrete. I spun it in a drill chuck and then drilled it with a wire from a wire brush. I don't recommend this procedure because the difference between jet sizes is .001".

It's time to install new jets and clean those passages in your carb. I would recommend getting a carb kit as well.

Trailryder42 has a good carb video on here which you should definitely watch.

Thx Trail & Baja.

I just stripped down the the float bowl, jets & floats. I kept the seals away from the corrosive cleaner. So I have to strip the whole thing down, oh well I was trying to avoid that - just out of laziness I guess. I'll order the rebuild kit.

Interesting about the pilot jet, at the time I didn't have any small gauge wire to pass through it and "assumed" the cleaner did its job. Maybe it is completely closed up. I'll order new jets to be on safe side.

I swear I'm never using ethanol mix gas again!!!!

Thx for all the help, most appreciated, will get to work and let you know how I got on.

PS is there a link to that carb vid that Trail guy posted?

First off let me say hi, I'm new to the forum but so far looks like an awesome site. I have an 01 xr400 and was reading through some of these and read your problem with you're carb. I've rebuilt many carbs and imho carb cleaner is horrible on the carbs, it eats up o-rings pretty badly. The best and cheapest way to clean them is pine-sol. Not the cheap dollar store stuff, go to Lowes or home depot they sell it in gallon jugs for around $20. Disassemble the carb completely, pull all the jets, the slide and any other parts you can apart. Get a container the carb will fit into fill it with pine-sol and make sure it covers the carb completely, let the carb and all the parts soak for a good 24hrs. Pull the carb out and use compressed air to blow most of the cleaner off, and make sure you get all the passages blown out. I have seen many carbs that have sat and gummed up like this, this will most definitely be the only way to clean the gunk out. Good luck I hope this helps you out.

First off let me say hi, I'm new to the forum but so far looks like an awesome site. I have an 01 xr400 and was reading through some of these and read your problem with you're carb. I've rebuilt many carbs and imho carb cleaner is horrible on the carbs, it eats up o-rings pretty badly. The best and cheapest way to clean them is pine-sol. Not the cheap dollar store stuff, go to Lowes or home depot they sell it in gallon jugs for around $20. Disassemble the carb completely, pull all the jets, the slide and any other parts you can apart. Get a container the carb will fit into fill it with pine-sol and make sure it covers the carb completely, let the carb and all the parts soak for a good 24hrs. Pull the carb out and use compressed air to blow most of the cleaner off, and make sure you get all the passages blown out. I have seen many carbs that have sat and gummed up like this, this will most definitely be the only way to clean the gunk out. Good luck I hope this helps you out.

+68 :thumbsup:

I have a stock xr 400r and it has been flawless for many years but after sitting all winter it idles fine but it pops and spits when you giver throddle. i fully cleaned my carb out the only thing i found was the backfire flap on the choke plate has a spring to keep it closed but its not doing its job. Could this be the problem?

I'd say no that flap isn't doing anything when the bike is warmed up and the choke is in the off position, because when the choke is off the butterfly is flipped up to let the air into the mix. I'd say the carbs didn't get cleaned out completely, try the method I described above.

But when the choke is off and the choke plate is vertical the backfire flap is swinging down in the air flow. I have had a thousand carbs apart and i tried your cleaning technique and its still not working can that backfire flap cause terbulance in my air flow?

We don't know..fix the flap before it snaps off and destroys the engine,,retest,,

I pulled off the backfire flap and shes good to go

I did the Pinesol dip and didn't like what it did to the mikuni carb body. It came out black inside. After rebuilding it with parts from Power Barn, I noticed they had a rebuild service for Carbs for $95. Aaaahhh. I spent half that price on a rebuild kit and Pinesol.

I did the rebuild myself with parts from them. Nice people on the phone and they had Mikuni parts I couldn't find. Next time... Into the mail.

http://www.power-barn.com/servlet/the-1348/Carburetor-Cleaning-and-Reconditioning/Detail

I also did the pine-sol dip on my stock carb last weekend. It changed the finish on the body making it dull and chalky, but it did take care of a lot of buildup and corrosion with no scrubbing. Hope it still works ok when I get it back together.

XRsOnly makes a choke plate to fix your flapping problem. You can see it in trailryder42's excellent video.

Be sure to use gloves if you do the pine-sol soak. I did not, and now two days later, all the skin is peeling off the hand I used to fish the parts out of the soup. No need to comment on how big of an idiot I am. Sorta goes without saying. Just hoping others can learn from my mistake.

Hi there! today i make the service for my carb, bought the rebuild kit ( moose racing ) and replace everything that comes in the kit, reinstall the carb and start it up, the bike starts just  perfect, adjust the idle needleand idle perfect, the problem is when i slowly throttle up revs perfect but when i make it fast chokes, i noticed that usually happen  when i fully  open the throttle fast...just chokes.. if i open fast ,  less than 50% throttle revs fine, but full open fast chokes...any ideas!!??

tks!!!

 

 

keep riding.!..

Hi there! today i make the service for my carb, bought the rebuild kit ( moose racing ) and replace everything that comes in the kit, reinstall the carb and start it up, the bike starts just  perfect, adjust the idle needleand idle perfect, the problem is when i slowly throttle up revs perfect but when i make it fast chokes, i noticed that usually happen  when i fully  open the throttle fast...just chokes.. if i open fast ,  less than 50% throttle revs fine, but full open fast chokes...any ideas!!??

tks!!!

 

 

keep riding.!..

 

That is normal for the stock carb and the XR 4 stroke engine. You can minimize it with carefull pilot circuit/fuel screw setting but the XR 4 stroke isn't going to respond to that kind of quick throttle opening like a 2 stroke engine does. Just nature of the beast. Don't get hung up on it. Tune the fuel screw for best/highest idle on the rich side and best throttle response and let it go.

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