400ex only runs with choke on...why?

[oneroom42]

my 05 400ex will start fine and idle pretty good with the choke on..yellow lever up all the way. after a few minutes i swing the choke lever down in the off position. idle goes high for about 5 seconds then shuts off. fires back up with me hitting the throttle but wont idle unless the choke is on. can anybody inform me why this is??

[scuba]

sounds like an air leak or no gas ......

[trikes4life]

Sounds like a fuel delivery issue, bad vent cap, clogged pet cock. would be where i would start.

[swifty]

it has too many wheels! lol carb is pry dirty id try cleaning it or at least drain the bowl

[SWIGIN]

Cold weather make motors run lean. You are probally on the edge of being to lean in warm weather and now it is to lean to run without the choke.

Time to rejet

[oneroom42]

what size needle should i put in? its all stock with the exception of an aftermarket air filter.

[jensenracing77]

when was the last time you put gas in it? did it run fine the last time you had it out? i am finding in my area that if the gas sits in the bowl of the carb for about 20 to 30 days it has gone bad. i drain the bowl and it idles good. if the gas was in it longer, then the gas in the tank is not to good either. my 400EX and 250EX is does exactly what you are saying with the gas in them very long at all.

[oneroom42]

you know jensen...i found that out about a month ago. i completely drained the tank and carb and put fuel back in with some stabil. ummmi guess i'll mess with the jetting.

[jensenracing77]

if it is all stock you shouldn't need to do anything with the jetting other than clean them. there is a problem somewhere and making it run right with other jets wil only mask the real problem.

[bansheekx]

I would have a look at the pilot jet to see if it is blocked.

[Nightmare]

sounds like a blocked pilot jet.

[oneroom42]

here is the deal with the pilot jet. it requires a tool from honda to remove it. its the D type screw wrench part #07kma-mn9a100. so i call the dealer to get my hands on this tool and its just over $300 bucks!!! what is the deal! is there another way to get this screw out? im gonna check ebay for this tool.

[jensenracing77]

i only done one of those, i just took a dremel and cut a slot into the top of it and used a screwdriver. tossed it in the trash and got a normal one. darn EPA getting involved in stuff they shouldn't.

[oneroom42]

dremel lol thats exactly what i was thinking about doing. im just affraid that after i cut a grove in the top one of the taps is gonna brake off and them i have a real problem.

[jensenracing77]

that would suck.

[oneroom42]

well i got some food and a six pack to prepare for the eagles game and...that damn D screw was still in the back of my mind. out comes the dremel and than the pilot screw. YES! the tip was black and wiped clean, other than that it didnt seem clogged. hopefully tomorrow i can slap the carb back on the machine and be ready for our next snow storm. fingers crossed and i keep yous posted. thanks for all your input!!!

[oneroom42]

well i put the carb back in and it still isnt runin right. i tried adjusting the pilot screw and zero change. as it was ideling i sprayed around the carb and also zero change so everything is tight. how often does that vaccum crap fail. its an 05 and im not sure if all the carbs re the same for different years.

[NINJA]

Wait a second, the tip of your pilot screw was black? You may have carbon blocking it's little tiny passageways. Use some carb cleaner(not brake cleaner) and a high pressure air hose sprayer(with the rubber tip) to spray through it's air jet passageway and it's fuel passageway. It may take several attempts, but if it clears, you should see a stream of carb cleaner through that tiny little hole on the bottom of the carb bore, after the slide on the engine side of the carb.

[oneroom42]

i have a steady stream of carb cleaner throuh the pilot screw hole. i,ve cleaned everything 3 times now and it still idles with choke on and shuts off as soon as i turn the choke off. if i turn the choke off and hit the throttle to keep it running it backfires through the carb. really sounds like its starving for fuel. im not giving up on this, but im starting to hate honda!

[oneroom42]

well its now running good with the choke off...???... i put a new stock pilot jet and main jet in and it still wasnt right. so i removed the spark plug and turned it over for about 5 seconds to blow any debris out of the cylinder. fired it back up and continued to mess with the a/f screw and about 4 turns out it seemed to keep idle but still backfire inside the carb. i then incresaed the throttle reving it pretty high and a small puff of black smoke blew out the exhaust, BINGO it stopped the backfires in the carb. i believe something was clogged somewhere and got sucked/blown through and cleared itself at the high rpm's. thanks for all the help guys!

[jensenracing77]

do you have a stock muffler? i had a 250EX that had a baffle inside the stock muffler rust out. it had broke and was up against another part inside and created an enormous amount of back pressure. it acted like what you are talking. i don't think that is likely to happen very often. not likely to be what caused your problem but just putting it out there.

[oneroom42]

yes it has the stock exhaust. i will keep that in mind. thanks jensen!

[oscarmayer]

you probelby need to take the entire carb appart and clean everything. also hae you looked a carb rebuild kit? the needle and jets can get worn over time and not seat properly or clog. a good voer all cleaning and reassembly of everythign will probelby help.