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yz400rider

My Yz400 starts up and then dies...

15 posts in this topic

My '99 Yz400F has been sitting for about 6 months and I finally took it out of the garage and cleaned it up and changed the spark plug. I emptied the gas that was in the tank and put some new gas in. My dirtbike will start up when I kick it but then it will die after it idles for about 5 seconds or it will die when I give it a little gas. Any suggestions?

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My bike did the same thing but it was the spark plug. Since you already changed it out It must be something with the carb. Take the spark plug out and make sure it has the right gap and all the connections are free of corrosion.

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My bike showed the same symptoms wouldnt idle for caca... turned out the pilot screw passage was gummed up w/ old fuel... :applause: a good cleaning and a new fuel screw and i was back in buisness

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Old fuel gets kinda gummy and dust like with age. It has pluged up your carb. Take the carb off and completely take it apart. Get some carb cleaner and give all the parts a bath. Then dry them off by letting them sit or hand drying, dont use an air hose!!!!!!!!!!!!!!! Make shure that your seals are good and while its apart you should set the carb up with some performance jets!(Itmakes ab ig diff if you have mods) Your looking at about 25 bucks if you do it yourself.........Put on some good music and just have at it. If you get stuck just pm me!(Power now kits kick a*s if you wanna 100 bucks)

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My '99 Yz400F has been sitting for about 6 months and I finally took it out of the garage and cleaned it up and changed the spark plug. I emptied the gas that was in the tank and put some new gas in. My dirtbike will start up when I kick it but then it will die after it idles for about 5 seconds or it will die when I give it a little gas. Any suggestions?

My '99 400F does the same thing for first 4 or 5 trys; runs a few seconds then stalls, and any throttle will kill it. That's normal for those bikes. Does it act any different than before sitting for 6 months, or is this a new thing?

If you had same symptoms beforethe bike sat for awhile, then it's a matter of increasing your starter jet size so it gets enough fuel (at closed throttle) when it's dead-cold. Doesn't hurt to increase pilot jet size too, since the stock (45) size is lean.

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Old fuel gets kinda gummy and dust like with age. It has pluged up your carb. Take the carb off and completely take it apart. Get some carb cleaner and give all the parts a bath. Then dry them off by letting them sit or hand drying, dont use an air hose!!!!!!!!!!!!!!! Make shure that your seals are good and while its apart you should set the carb up with some performance jets!(Itmakes ab ig diff if you have mods) Your looking at about 25 bucks if you do it yourself.........Put on some good music and just have at it. If you get stuck just pm me!(Power now kits kick a*s if you wanna 100 bucks)

How hard is it to take apart the carb if you have never done it before? I have never taken apart a carb before and I don't want to mess it up. Are they pretty simple to clean on yz400's or should I just take it into a shop?

And rdefonce, no my bike never did this before it sat for awhile.

Thanks everyone for the help!

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Now is the perfect time for you to learn your bike. Carb cleaning is relatively simple, and the manual should offer a lot of assistance. If you don't have a manual, GET ONE. They are very helpful and have pictures for illiterates like myself. I wouldn't trust a dealer to do the carb job right.......

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the pumper carb on these bikes are simple compared to some other bikes. you should have no problem..im doing mine on monday..they are simple..and im 17 if that makes any diff.lol

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What if I just took the carb off and sprayed carb cleaner in every hole I see?

Think that would help or should I take the entire carb apart?

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What if I just took the carb off and sprayed carb cleaner in every hole I see?

Think that would help or should I take the entire carb apart?

No, typically that won't help.

1. Get the manual.

2. The carby IS NOT simple. It's actually a pretty complex design compared with the old school stuff.

3. You need to completely take it apart to clean it properly.

4. Old Gas makes a lot of trouble for these bikes. I'd suggest either using Stabil if you know its gonna sit or take your tank off and drain it as well as the carb before letting it sit.

Old gas turns to a varnish like consistency and will totally ruin the small passages in your carby.

WE can walk you through it though. do a search and read up on how to handle your carb.

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Ditto to MotoGoalie. The carb is complex, but not hard once it is off the bike and you go slow. The hard part is the removal from the bike:-) Follow the advice posted and use your manual. Just go slow and use a clean area to work on. You'll do fine.

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