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07 400ex jetting question...

4K views 26 replies 7 participants last post by  dave4881 
#1 ·
ok, so i took my 4 wheeler to an authorized honda repair shop because after installing an HMF sports slip on exhaust i kept bogging while trying to run in the winter time. I was also having the problem with the cold start as i see many others are. so the repair place installed a 170 main jet, and a 42 slow jet and adjust the carb, it's still a pain to get it to start in the cold (i live in northern Ohio) but when it does and gets warmed up it will actually run if i keep the choke on a lil over half way.. is that normal? i'm thinking it's probably not for the best to ride it like that but thats the only way it'll run, if i move it up anymore it'll bog out realllll bad..

any help would be greatly appreciated!

thanks,
tim
 
#2 ·
Welcome to the forums..

I think you may actually have to step up the main jet during the cold months, and drop back to the 170 in the summer...Are you running with the airbox lid on or off?
 
#4 ·
Agree also^^^^^^ plus running the choke on builds excessive carbon on the plug causing premature fouling, by running the choke your trying to richen up the carb by restricting airflow to get more fuel delivery, like red stated if your lid is off put it back on and that should help.
 
#10 ·
Don't you mean down on the pilot and up on the main? I think you did you tyoed faster than the old brain could think...lol
 
#9 ·
Welcome to the forums.
 
#12 ·
Pilot controls idle to about 1/4 throttle needle controls 1/4 to 1/2 main jet covers all the rest of the range. Being that if you run your choke on you are restricting airflow....therefore allowing more fuel to enter the combustion chamber. if you were to drop back a size on the slow jet (pilot jet) you should be fine.
 
#13 ·
But Moose, if he goes down in jet sizes he will reduce the amount of fuel being added. Why would he want to take fuel away?

Were getting you there!!! LOL
 
#14 ·
ok Im starting to confuse myself!!LMAO I can phisically do it tell is another story. how about resetting the air mixture screw then instead of say 3 turns out crank it in about 1/2 turn to restrict a little airflow?

DUDE.. bring me your quad I can fix it!! my dad was a tv repair man he has all these cool tools I can fix it!!!lol
 
#17 ·
You guys don't remember that quote? Spikoli from Fast times at Ridgemont high...lol hey the tv option would be cool but it would keep me from hitting my top speed goal of 71MPH lol
 
#20 ·
ROTFLMAO!!!! I forgot that quote ...now I gotta go rent it makes me want to watch it. I haven't seen that movie in years!!!
 
#22 ·
Me either man.Good funny movie.The 80's movies were much better written then todays are.
 
#25 ·
lol you guys..so i feel like i take one step forward when i read one post then when he replies to his own post i take like 3 steps back..how about this...i warm the quad up, then i change the pilot jet down to a 40..try to start it with the choke off and if it runs it should be ok right? lol..or just say F it and rent fast times at ridgemont high and watch that instead of go riding lol..
 
#26 ·
rent the movie!!!! 400s are extremly cold natured beast after reviewing my circle of replies..lol I have come to the conclusion you need more fuel. by turning in the pilot screw 1/4 to 1/2 turn that should restrict enough air to make you run alittle better. you may however have to reset the idle. but definitely watch the movie...LMAO
 
#27 · (Edited)
The 42 pilot jet should be perfect. The 170 main may be a little too much. I run a 42/160 combination and it screams. With the HMF slip on you need to open up the air box some. Be sure the adjust your fuel screw correctly. That is probably why it won't run without the choke. These quads need to warm up a little before they run well.
 
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