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Discussion Starter · #1 ·
so I just bought a 13 400ex. I just installed the HMF performance slip on UNI filter and jetted the carb. Mind you, there are no instructions so I made my way through it via a you-tube video.
I used the 1 supplied idle "jet" and then per the recommendation I installed a 170 main jet. No needle change(not one in the kit) and no fuel flow change (cause I couldn't find where to adjust it)

ok so now its running, like sh%%. It pops, has a hesitation when you first nail the throttle and feels lower on power than before.
what did I miss? did I over jet? is there a way to increase fuel flow?
why don't they give you directions....pics would be nice :)

lastly, I went to check the plug and cant find a socket to fit it????weird, but what size is it? none of my standards or metrics fit

help is much appreciated
 

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Curious - according to my sources at Honda, the last 400EX was the 2008 model - after that, the 400X was introduced in 2009, but was absent in 2010 and 2011 - it came back in 2012 and it is the 400X that is the current model.

The carb is fundamentally the same, but the fuel screw is capped to prevent tampering 'a la EPA.

Jetting is a science that needs to be studied, but simply put - more fuel is not more power - more oxygen is more power - power comes from the heat and a lean mixture burns hotter.

Try going back to the #38 pilot jet with a 150 or 155 main jet. The needle can be shimmed up if necessary for proper mid range performance. And above all, patience - the carb will be removed and installed an average of 6 times before the jetting is satisfactory.
 

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Discussion Starter · #3 ·
Curious - according to my sources at Honda, the last 400EX was the 2008 model - after that, the 400X was introduced in 2009, but was absent in 2010 and 2011 - it came back in 2012 and it is the 400X that is the current model.

The carb is fundamentally the same, but the fuel screw is capped to prevent tampering 'a la EPA.

Jetting is a science that needs to be studied, but simply put - more fuel is not more power - more oxygen is more power - power comes from the heat and a lean mixture burns hotter.

Try going back to the #38 pilot jet with a 150 or 155 main jet. The needle can be shimmed up if necessary for proper mid range performance. And above all, patience - the carb will be removed and installed an average of 6 times before the jetting is satisfactory.

you are correct, it is a 400X.
I just replaced the main with a 160, the only smaller jet in the kit is a 152.
Kids are asleep so I will try it out in the morning and update the thread. If necessary, I may order the dyno jet kit, it seems a little more comprehensive
I'm assuming since they capped the fuel screw theres no reason to make that change

thanks for the reply and help
 

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The fuel screw may need to be uncapped and adjusted anyway - in Japan they have fuel that is not contaminated with alcohol - their 93 octane is 93 octane - ours is 85 mixed with alcohol to achieve 93, but it results in a fuel with a lower BTU per pound and therefore produces less power - the fuel screw changes the amount of fuel mixed with air for idle - if your idle sucks, get the screw uncapped and adjust it for a good idle - if you have a lag upon acceleration, check the accelerator pump circuit in the float bowl for a leak jet - if there is one, change it to a smaller one for a stronger shot of fuel from the accelerator pump - if no leak jet, see it the linkage can be adjusted so the pump starts to move as soon as the linkage is moved - sometimes creative modifications are necessary
 

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Discussion Starter · #5 ·
the 160 jet is much better, its definitely rideable and making good power, hoever,
rather than continue with this kit, I ordered the dynojet kit. I feel the needle needs adjusting and a 155 jet may be the touch since its still a little fat.

when I take it back apart i'll see if the fuel plug can be uncapped, but I don't think it can.
thanks for the feedback
 
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