my 400ex did smoke a lil white smoke when i first started it up. after riding it for a while it ran fine. Now when i start it up it smokes a lot and will only run with the choke on (giving it some throttle). if i turn the choke off it dies right away. also i was running with my airbox lid off when i rode it last and i may have sucked in a tiny bit of water, but it just started doing this after ive let it sit for maybe 3 days.

 

redrider52 white smoke is a sign of gas smoke it can be caused from improper carb jetting which cause exccessive carbon buildup inside the combustion chamber causing sticky rings ; i would do a spark plug check to determine the jetting is correct !

A grey/white color to lean , black to rich , normal color should be a tan/brown color ; here's a good product for cleaning up exccessive carbon buildup inside the combustion chamber is Sea Foam mixed in your fuel this stuff help's keep the entire fuel system clen plus clean's the combustion chamber as well !

You will get alot of suggestion's of several product's mixed together that will do a mutitude of good thing's for your fuel system and combustion chamber , and i don't knock any of these remedies ; but everything that all these misture's that you will get advice on are all contained in Sea Foam whitch you can get at most any Auto parts Stores and most WalMart SuperCenters !

In over 20 yrs of operating my own Small Engine Service and Repair Shop untill i retired in late 97' i tried every fuel additive on the market ; and none of the products i tried over the yrs compared with Sea Foam i've seen it used from Lawn and garden equipment to automobiles it comes with a money back satisfaction guarrantee and has been on the market since 1942 and still carries this same guarrantee !

I hope this help's you out , and have a good day and lots of safe riding !........

 

great! thanks a lot man. i will definitely give that a shot. i just got a new jet kit as well so ill run some sea foam through my engine and dial in that carb and see how it runs. my buddy suggested a rebuild and i really don't wana have to do that.

 

NO smoke! yess. sea foam is awesome. i also sprayed some carb cleaner through my carb and got that all cleaned up. only thing is that my quad won't idle. i just rejetted my carb today. got a 170 main jet in with the needle set on the third notch and 3.5 turns out on the fuels screw. any ideas?

 

Well the no smoke sounds good but you may have jumped the gun on the rejetting , you should've ran at least one tank full of the Sea Foam Mix through the engine before the rejetting to ensure all the carbon was burned from the combustion chamber first ; and 3 1/2 turnes out on the air/fuel mixture screw is very exccessive for starting point on the carb !

Most adjustment for the starting point i've seen on any carb , the inicial adjustment shouldn't be over 2 1/2 to 2 5/6's turn's out from a light seat for both Keihin and Mikuni Carb's , even if you done alot of mods , pipe , Hi Flo Airfilter and a higher performance CDI !

I would go back to the original carb jetting and run at least a full tank of the Sea Foam Mix , then do the spark plug check with the air/fuel mix starting point at 2 1/2 to 2 5/8 turns out from light seat ; and make sure that when you turn the mixture screw in untill you feel a light seat not to go to far in ( easy to damage the seat if you over tighten the screw !

Let us know how it goes then we can go from there , if i can't get you going there are alot of great guy's an gal's here that know far more about carb jetting than i do ; and i ran my own Small Engine Service And repair Shop for over 20 yrs. before i retired and closed up shop in late 97' and good luck with your ride these Honda 400ex quads are hard to beat for long life and reliabiliy !.......

 

alright ill try that out but do i really need to? i got a dynojet jet kit a while ago because i was gunna rejet my quad because its got an aftermarket pipe on it. i found out while rejetting that the owner before me never rejetted when he added on the pipe. so i followed the directions given in the jet kit and for my elevation and mods i should be 3.5 turns out, 170 main jet and needle set on the third notch. and thats what i have going right now.

i also got my bike to idle. i started it up today and adjusted the idle screw and it runs perfect. still a little white smoke when its warming up though. ive hardly ran any seafoam through it though and its already improving. i think if i get a whole tank through then ill be in good shape. thanks for all your advice, its helped a lot. should i still go back to my previous carb settings?

 

No leave the jet kit in the carb if you've got it idling now and it
's running good from idle speed all the way through the throddle range with out stumbling or back firing any through out full throddle range , and it's normal for the engine to smoke a little while you're running the Sea Foam to fuel mix untill all the exccessive carbon buildup is burned clean from the combustion chamber ; in fact in most case's it will smoke more that it did before untill all the carbon is cleaned out !

I didn't know the previous owner had done any mods on the Quad before you got it without rejetting the carb , just keep a check on your spark/plug paying close attenion to the color of the the plug ; and remember that Black means you're to rich , white means you're to lean the correct color of the spark plug should be a tan/brown color when the jetting is correct !

And once again good news hearing you've got the engine at the correct idle speed , and keep a close check on your engine's oil level to be sure you're not burning oil ; and are you still running with the air box lid removed if you are and it's running good then you're good to go just clean and re oil the air filer and foam outer ware often to keep any dust from getting into the carb and intake this and the oil and oil filter is the key to a long healthy life to your engine !........

 

awesome thanks for all your advice it really helped.