YZ400 only runs with the choke on


5 replies to this topic
  • cuvalaj

Posted May 23, 2009 - 01:38 PM

#1

So i have a 98 YZ400F, i recently took it out of storage while i was deployed and cleaned out the carb and changed all the fluids. i have no experience in pulling apart a carb so i enlisted the help of our forums like any good owner should do. i had alot of gummy build up under the accelerator pump diapragm. so i gleaned it up and got all of the corrosion off of the shaft too. i cleaned the jets which werent obviously dirty but even a little is alot right? LOL. so now that its all together it only runs with the choke on. i have checked for leaks and made sure my fuel screw is at 1.4 turns out i set the idle screw a little high but i did that so i didnt have to mess wit the throttle too much once i got it started. i got fresh gas in her and i cleaned any foul off the plug. its getting frustrating. the only jet i could get an accurate number off of was the needle jet, its a 175. the others im unsure of their sizes. i dont want to take her in but ill be damned if this isnt frustrating LOL please help i wanna ride! :doh: thanks in advance! oh yeah i live in central cali where its hot and dry and about level elevation.

  • 426 NOOB

Posted May 23, 2009 - 04:58 PM

#2

So i have a 98 YZ400F, i recently took it out of storage while i was deployed and cleaned out the carb and changed all the fluids. i have no experience in pulling apart a carb so i enlisted the help of our forums like any good owner should do. i had alot of gummy build up under the accelerator pump diapragm. so i gleaned it up and got all of the corrosion off of the shaft too. i cleaned the jets which werent obviously dirty but even a little is alot right? LOL. so now that its all together it only runs with the choke on. i have checked for leaks and made sure my fuel screw is at 1.4 turns out i set the idle screw a little high but i did that so i didnt have to mess wit the throttle too much once i got it started. i got fresh gas in her and i cleaned any foul off the plug. its getting frustrating. the only jet i could get an accurate number off of was the needle jet, its a 175. the others im unsure of their sizes. i dont want to take her in but ill be damned if this isnt frustrating LOL please help i wanna ride! :doh: thanks in advance! oh yeah i live in central cali where its hot and dry and about level elevation.

It sounds like your pilot jet is plugged running only with the choke on is a classic symptom. I would pull that jet and brake clean it out. Then hit it with compressed air.

  • cuvalaj

Posted May 24, 2009 - 12:51 AM

#3

Ok ill try it again cleaning them out wit pipe cleaners. and ill blow em off before putting it all back together tomorrow. ill let you know what happens thanks for the suggestion man!

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  • grayracer513

Posted May 24, 2009 - 06:36 AM

#4

You will never get a pipe cleaner through any of the jets. Especially not the pilot. Soak them in carb cleaner for an hour, then use single bristles from a PLASTIC (not wire) brush.

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  • cuvalaj

Posted May 31, 2009 - 06:17 PM

#5

So, this weekend was a good time to pull off the carb and try for round two. I pulled all the jets and cleaned them again using a plastic brush i made the holes clear and freee of any debris-which there was a little bit even after cleaning them before....confusing but oh well theyre clean now. and i double checked the float level. all is well so i reinstalled the carb and she fired up right away....only to die a few seconds later and it never did get started again. i put a new plug in and still nothing. i made sure my work area was prestine so theres no way anything got into the carb and got sucked into the jets again. i made sure the circuit was clear too before reinstallation with carb cleaner and it was all good. I called my friend who used to be a mechanic and he says it might need a valve adjustment....SERIOUSLY? would this even be a problem? i dont get it LOL. help me Grayracer youre my only hope :crazy:

  • grayracer513

Posted May 31, 2009 - 08:52 PM

#6

Have you checked the valve clearance?





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