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48puller

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Reply with quote  #1 
i picked up a 99 400ex and it was running rough so i took carb off and cleaned it up. put it back on and will not start or even fire. has spark its in time. it wont even fire on starting fluid. i was thinking the cdi box but someone told me if its the cdi it wont fire at all?  and ideas?


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Reply with quote  #2 
Did you try putting a brand new spark plug in it?
48puller

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Reply with quote  #3 
i havent. it seems to put off good spark and even the smallest spark should ignite either. but i thought about it




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Reply with quote  #4 
For what ever reason- sometimes they will spark during the test but not after they are installed. I have seen this many times. Cant explain why, but often a new plug will make it run when the old used plug wont. 
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Reply with quote  #5 
Sounds like you may be running way too rich. I would turn off the fuel, pull off the air filter, drain the carb, pull the plug, and crank it over a bunch. Then drop a new plug in and try to start it with "starting fluid". If the starting fluid is the only fuel it getting, and you have a new plug - it should run. If it doesnt- your timing is off, the compression is low, valves are out of adjustment, or you dont have spark .
48puller

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Reply with quote  #6 
alright ill give this a try. ill let you know the results!
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48puller

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Reply with quote  #7 
it still is only a 148 main jet though


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Reply with quote  #8 
Im thinking that it was too rich, and running poorly because of that. Then when you cleaned the carb, it got even more fuel and wont run at all. Then the starting fluid just adds to the problem. If it was too lean, then the starting fluid would have caused it to start- which it did not.
48puller

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Reply with quote  #9 
what would you suggets if i do get it to fire tomorrow with new plug on starting fluid? it has stock exhaust uni air filter and im about 1000 feet above sea level


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Reply with quote  #10 

   At that point I would do a full carb rebuild using a kit, and return all the fuel screws to the factory presets. When you took the carb apart before, did you check the fuel screws for proper adjustment?

Another option would be to replace the entire carb. 

http://www.ebay.com/itm/Honda-400EX-1999-2004-Carb-Rebuild-Kit-Repair-TRX400EX-/201107846686?pt=Motors_ATV_Parts_Accessories&hash=item2ed2f6361e&vxp=mtr

http://www.ebay.com/itm/USED-OEM-99-00-01-02-03-04-HONDA-TRX400EX-400-EX-CARB-CARBURETOR-ASSEMBLY-/291284700297?pt=Motors_ATV_Parts_Accessories&hash=item43d1ebcc89&vxp=mtr
48puller

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Reply with quote  #11 
i did reset fuel screws to factory settign when i cleaned it. i got the new plug in and it fired right away on starting fluid so i put the gas to it and still starts. ran out of time but im gonna try to get it fined tuned tomorrow and see if its running rough still or running god. thanks for the advice. seeing that what seemed to be good spark on old plug really made me think against that being it but i was wrong! lol[jumping0018]
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Reply with quote  #12 
Right on. Ya, its kind of weird that plugs can spark outside the engine, but wont fire the cylinder once its installed. Maybe there is oil around the insulator with a bubble of air under it, and the compression forces the oil down the insulator compressing the air bubble far enough to ground it out, but when there is no compression, the little uncompressed air bubble insulates the insulator from being grounding out???? This is just a wild guess, Im not sure what the actual cause is. All I know is that I wish I had known about this spark plug thing when I was younger. 


Kmack

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Reply with quote  #13 
A totally screwed up A/F Ratio can cause such an atmosphere in the combustion chamber that the plug will not fire at all.
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Reply with quote  #14 
Right, but if you have two spark plugs - one new and one that is old, and they both spark outside the engine and only the new one will make it run.... Then WTF? 
LEOGM5150

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Reply with quote  #15 
i have experienced that so many times in my life i cannot believe it. my first answer is always try a new plug and 9 times out of 10 it is the issue.
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Reply with quote  #16 
Why does it spark outside the engine, but wont spark when installed? 10:1 compression, you are compressing 10 atmospheres into that gap, which adds to the resistance. A partially fouled spark plug will make the jump across that gap, but when its under compression its "easier" to short out rather than make that jump.

   This is a theory. 

   Thoughts?
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