my 416ex blows black smoke wen i start it??WHY??

[quadboy1988]

hi i have a 400ex bored out to a 416 a nd wen i start it it blows black smoke wut does this mean...

[Mr.EX2U]

lean it out a bit your to rich causing excessisve carbon build up. find out where your rich (ie) idle, 1\4, or full throttle and jet accordingly.

Chris

[04'400ex'er]

Wouldent it work to do a plug check and rejet?

[quadmxracer]

Uhhhhh yeah thats how u do it man. Best way is to get a new plug(s) and go and ride it in the throttle you feel you are running rich such as 1/4, 1/2, 3/4, or full and run it in those ranges for like 5-10 min and check your plug and judge from there. where you may need to lean it out.

[Mr.EX2U]

first off if you know what to listen for you can hear the difference between rich and lean just by running at the 3 throttle positions stated above. Second when plug checking run it at the desired throttle position for 10 to 15 secs and shut down not 5 mins you'll end up with a incorrect reading. not trying to flame anybody but plug checking is such a pain on the 400ex so like me you learn new and easier ways. I cheated by putting a o2 sensor on mine with a autometer stoichometer.

Chris

[quadmxracer]

Same here I used a gas analyzer to check mine out.

[HondaMan222]

Originally posted by 04'400ex'er
Wouldent it work to do a plug check and rejet?
thats what mine was doing, i have a 178 mikini jet in it and it works good, before i had a 175 and it was lean

[cals400ex]

what is the reason for running a mikuni jet?? the stock carb is a keihin.

[zephead400ex]

Originally posted by cals400ex
what is the reason for running a mikuni jet?? the stock carb is a keihin.

My buddy had the same problem. He bought the 400ex used. When he brought it home, we took apart the carb and lo-and-behold a Mikuni jet in a Keihin carb.

HondaMan222, if you are using a stock carb, the Mikuni jet is the problem.