2003 z400 backfires and no power

[hhaceesa]

My 2003 z-400 just wemt crazy!!!!Put in i new plug and it runs great for 10 minutes then starts backfiring and sputterring at about half throttle. no matter what gear im in I can ride it, but it has no power. Local repair shop looked at it "checked carb" and said they wanted to "tear into my motor" becouse they did a pressure check and leakdown test was at 150 psi with 10 % leakdown.. I quickly removed my quad from their buissiness.
I have already checked all the jets but didn't know the needle valve comes apart gonna chec k it next. Any help or thoughts woukld be awesome,,..

[hhaceesa]

Also remember bike ran great all winter, then choke cable gto frayed, needle style choke was staying open. Replaced cable with same said new cable and bike has never ran right since then.. Ive taken cable off about four times , there seems to be no way of "seeing" the needle on choke seat in chamber but its free and even tried with lever end off to see if it was holding open no luck

[John Noftsinger]

what about the sparkplug? you might have wrong one. I took off my choke off (IT broke at bars) and it ran fine with no choke had too use hairdryer in winter to start,then got carb for cheap that had choke lever installed on it .sounds like the plugs the problem,you said it didn,t have problem till you put sparkplug in so Id start there first. try running it with choke cable off.

[witech]

We had a z400 have the needle clip in the carb fall off so it was floating around up and down . It would idle and run a full throttle ,anywhere in between it would just die and sputter and backfire .

[hhaceesa]

Went throu four plugs already. New plug runs ok for about ten minutes then just starts backfiring. I always run ngk. gonna take a look a look at fuel flow to carb cuz it has the small filter at top of pitcock but if I have a good flow then I dont know what to do next

[hhaceesa]

tried with choke cable off at lever to see if it was holding open. same .Im gonna take the little needle/drum off the cable and hold it in carb some how and see what that does..Does the choke add air flow or restrict it?

[twincat800]

I had a Kfx for a minute and it wouldnt start to easy but when it did it seemed okay... I could rev it up a little but would bog down when i would try to rev it near past half way.. At the same time i had my dvx and put an fcr39 on it and used the stock carb off that and put it on my Kfx and that solved that problem... i absolutly dont know exactly what the problem was and didnt care, this is just something to think about

[John Noftsinger]

Did you disconnect at carb?(pull end of cable out of carb) thats the only thing that I can think off for now! And your fan running?may be getting too hot?

[hhaceesa]

No the bike isn't running hot cus it does it all the time.. As soon as it starts then it goes to backfiring.. As for the choke its internal so I haven't tried it off the carb, just took it all the way off lever and tried to see uif it wasn't seating.. Tuesday I'll try ir with choke compltetly out of carb....My bro has a kfx 400 so I'm gonna talk w him, about trying his carb..Thanks guys

[350ex]

The choke restricts airflow. Does it shoot flames? If so what color? 10% leakdown is acceptable. Was that when the engine was warm? What do your plugs look like when you pull them color-wise?

[hhaceesa]

Hey guys just wanted to update yall
my timing advance unit had two burnt wires on it, thats why it would start good and run at idle but had no power and backfire like crazy......

[zukirder93]

i have an 06 z400 and i jetted the Main jet ONLY to a 150. it had always bogged a little when you pinned it real hard in 2nd 3rd 4th and 5th gear but just recently it bogs and back fires at half throttle in every gear. i dont know where to start

[350ex]

Well glad you figured it out. You just reminded me that I need to put my extra cdi in my quad bag for trips.

[twincat800]

Zukirider lol do not ride your quad when it runs crappy like that haha fix it. Do you have aftermarket engine parts that need bigger jets? do reasearch its probably the wrong jet/jets