No Throttle Response

[cbrown74339]

Hello,
I have a 1999 400 ex that been sitting for about a year now. It starts and will idle all day long if I were to let it. The only way I can get it to actually move is if i have it set at half choke. the throttle response is perfect at this setting. with the choke off however, it will idle excellent but the very second that I give it any kinda of throttle at all it bogs down to the point of stalling out if I don't let off the throttle fast enough. If i give it full throttle it dies almost instantly. A friend mentioned a carburetor rebuild, but after the reading I have done, it sounds like something more to do with the accelerator pump to me, but i'm no expert. it does have an aftermarket uni foam filter and an FMF PowerCore IV muffler on it with the stock pipe. Any help would be wonderful. I should add that the carb has been completely pulled, disassembled, cleaned (jets and all), fuel drained and replaced, air filter cleaned, with all the same results.

[hondaking52]

if it has the right jets, it maybe the fuel/air screw isnt right, should be about 3.5 turns out if it has DYNO JET jets

hope this helps

[Exrider434]

Sounds like your running lean, putting the choke on would cut off some of the air flow making it run right.... Try bumping up the mainjet size.

What size is in it now?

[QuadManiac]

Were the mods you describe added and it ran ok or did this start immediately after the mods?

[bartlettracing]

watch and see is it squirts fuel when the gas is pressed....

[bigballz400]

check the linkage between in the slide under the top cover of the carb.....if the slides not oping it dies when u gas it....run all day long idleing but once u gased it it fell on its face


idk if thast wats happen but that happen to me....check it

[cbrown74339]

OK...All of those mods have been on it since I bought it. Yes your absolutely correct in that if the choke is on it runs fine. I have no idea what size main jet is in it. It has always been kinda choppy on the take off, but never so badly that it fell on it's face. what size main jet would you recommend?

I don't see fuel squirting into it from anywhere but it must be since it runs with the choke on. where would i look to see this?

[Exrider434]

Originally posted by cbrown74339
OK...All of those mods have been on it since I bought it. Yes your absolutely correct in that if the choke is on it runs fine. I have no idea what size main jet is in it. It has always been kinda choppy on the take off, but never so badly that it fell on it's face. what size main jet would you recommend?

I don't see fuel squirting into it from anywhere but it must be since it runs with the choke on. where would i look to see this?

I had it mixed up, it would be running too rich if it runs with the choke on, as the choke allows more air to flow through. In order for you to see fuel squirt out, you would need to remove the carb from both the intake boot and the boot on the motor, then pump the throttle a few times and if everything is working correctly a line of gas should squirt out the front of the carb.

I have an HMF with a K&N and i currently run a 155 main jet with stock pilot jet and the needle on the 3rd clip i believe...

If you could get the main jet size that would be very helpful, its stamped on either the side or bottom of the jet.

[atvhonda-rider]

if it runs with the choke on, that means its running with not as much air, equaling its running lean right now. if it doesnt have an air box lid, try putting one on then see how it goes, if it does have one on, try moving up in main jet, as it'll let more gas with the same maount of too much air youre getting. keep us updated.

[cbrown74339]

If i'm looking at this thing right, it has 122 stamped on the jet. the manual for this thing says that it should be a 148. amy suggestions on this?

[Exrider434]

122?!?! I dont know if they even make that size jet for a 400ex, if that is really it, then it is wayy to low. Bump it up a size or 10

[cbrown74339]

If I change this jet, will I need to change any other jets such as slow or pilot? I have found a place that sells an assortment of jet kits and they do have a main jet kit in kits of 5 sizes for about $30. Is that a good idea?

[Exrider434]

No, most people that change the slow jet just change it to aid in cold starting during the winter. And Dyno Jets have quad specific kits that give you the range of jets you will most likely need.

[cbrown74339]

OK, I have a dynojet kit ordered. I will let you all know how it goes and thank you very much for your help.