03 KFX 400 Idling Problem... - Suzuki Z400 Forum : Z400 Forums
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post #1 of 55 (permalink) Old 05-07-2017, 12:00 AM Thread Starter
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03 KFX 400 Idling Problem...

Hey guys,.. new guy here

I'm sure it looks like just another dirty carb post,.. but this one is a bit more involved than that unfortunately..

So pick up this 03 KFX 400 about a month ago and it would start and run, but not hold an idle (Just what I thought - carb needs a good cleaning, pilot jet/circuit is plugged....)

Well this aint my first rodeo so I order a carb kit along with a 25 pilot and 155 main (carb was stock) - Fire up my ultrasonic cleaner (Which I've used on carbs for a couple years now..) and run it through with my Branson MC-1 specially formulated for Carbs formula - I ran it through two cycles and everything looked great.

Reassembled - I ditched the cable choke for a pull/push unit. - installed the carb,.. go to fire up and it pops right of and runs for a few seconds then dies. So I choke it and it'll run for a bit, then die.

I thought maybe it was the petcock and I already ordered the Raptor one so I put it on, (Plugged off the vent on the carb that went to the OEM petcock) .. fresh gas 'n all,.. same basic thing. ---- I can keep it running with the throttle, but won't come close to holding an idle...???

My battery was pretty weak, so I picked up a new one today and I'm charging it over night,... we'll see what tomorrow brings.

I never had this much trouble with a "Carb" in my life, so I think I'm missing something -

Any thoughts or suggestions would be greatly appreciated.

Thanks
Rick
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post #2 of 55 (permalink) Old 05-07-2017, 12:20 PM
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does it stay running at low R's when you hold the throttle there or do you have to feather it?

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post #3 of 55 (permalink) Old 05-07-2017, 12:21 PM
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You did T ry turning up the idle speed?

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post #4 of 55 (permalink) Old 05-07-2017, 01:12 PM
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Oem carb or Chinese knockoff? I had a zoom zoom carb on one I bought and the manual pull choke I bought wouldn't seat enough to fully turn close the choke off.

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post #5 of 55 (permalink) Old 05-07-2017, 03:55 PM Thread Starter
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Ok just installed the new battery,... what a difference in cranking power and quicker starting this makes!!!

The best I can do is hold the throttle at about 1/4 and it will steady run,.. it will rev up when I blip the throttle as well. No matter how I adjust the Idle adjustment knob, it won't come even close to idling. Using the choke on or off didn't seem to make a difference either.

I failed to mention that I have aftermarket exhaust on it - FMF Power Bomb pipe and Titanium 4 silencer/muffler which we repacked and installed a quite core insert - The thing is still stupid loud though

I tried putting my hand over the inlet of the carb to try and force it to pull in more fuel, but that didn't seem to work.

I noticed that when I was blipping the throttle that the slide was actuating up and down which is good,.. but there was a bit of fuel spitting out the inlet of the carb almost like air was moving backwards through the venturi or something (?) ... I guess I need to check valves and cam chain huh? ... I've got a Clymer manual, but I've not actually done those things before...

I wanted to say thanks for the replies! It's nice to have a forum were there are actually "Acitve" members..

Last edited by WERNER1; 05-07-2017 at 03:58 PM.
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post #6 of 55 (permalink) Old 05-07-2017, 05:37 PM
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what jetting

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post #7 of 55 (permalink) Old 05-07-2017, 07:50 PM Thread Starter
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Factory other than a 25 Pilot and 155 main ( Up from 22.5 pilot and 130 main due to exhaust and air filter / no box cover) Air fuel mixture screw is 2-1/2 turns out.
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post #8 of 55 (permalink) Old 05-07-2017, 08:02 PM
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Quote:
Originally Posted by WERNER1 View Post
Factory other than a 25 Pilot and 155 main ( Up from 22.5 pilot and 130 main due to exhaust and air filter / no box cover) Air fuel mixture screw is 2-1/2 turns out.
what happens when you turn the Air fuel mixture screw in ?

I remember when I used that carb I used a 27 PJ

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post #9 of 55 (permalink) Old 05-07-2017, 08:35 PM Thread Starter
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Hmmm... don't know, I would assume it would make it worse cutting off even more fuel during "idle" (?)... I could try it though...

I went ahead and pulled the tank and carb back off to just double check something wasn't stuck in the pilot jet or something,... nope,.. all looked good,.. I may disassemble it all again and run it through the ultrasonic clean a time or two just to make sure the carb is 100% ...

Anybody got a FCR lying around...
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post #10 of 55 (permalink) Old 05-08-2017, 12:42 PM
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What is a carb kit, and where did you get it? They only time I bought a kit for another quad, it wouldn't run at all.
You might be on to something with the valves, what is your compression?

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post #11 of 55 (permalink) Old 05-08-2017, 02:19 PM Thread Starter
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Carb Kit: Just comes with new jets, needle, n stuff.

Haven't checked compression yet,.. probably this evening..

Here's some pics
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post #12 of 55 (permalink) Old 05-08-2017, 11:24 PM Thread Starter
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Ok finally had a few minutes to check the valve lash and here's what I came up with:

EX Left: .203mm
EX Right: .152mm

IN Left: Tighter than .152mm
IN Right: Tighter than .152mm

.152mm was the smallest feeler gauge I had,.. guess I need to pick some more up.

From what I've read, tolerance on the EX is .20 - .30 mm, and IN is .10 - .20mm (?)

So if the intake valves aren't seating (Especially at low rpm), then the blow back could be enough to no let any air/fuel mixture in...???

I didn't get a chance to check the cold compression as there's a lot of dirt/gunk down in the spark plug valley that I need to clean out before I pull the plug - Is that hole on the side of the head a weep hole for the plug valley?

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post #13 of 55 (permalink) Old 05-09-2017, 10:32 PM
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Quote:
Is that hole on the side of the head a weep hole for the plug valley?
\

Yes..

2007 LTZ 400.. 94mm J&E piston, +4mm hotrods crank, 536webb cams,wiseco valves, 39mm fcr, tokyo mods throttle spring, honda thumb throttle,spring removed. yoshimura full exhaust, honda 400ex intake tube, no air box
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post #14 of 55 (permalink) Old 05-10-2017, 12:14 PM Thread Starter
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Thought so,.. thanks! I'll be cleaning that out this evening and doing a cold compression check,.. I'm going to pick up another set of feeler gauges as well and double check everything then pull the cams and check shims...

SO,.. I've been reading through a lot of the post in this forum that have anything to do with not idling,.. man they're are a bunch! ... ironically almost all of them don't have a resolve to them,... they just stop (??) ... with such a seemingly "common" problem with these bikes, you'd think there would be a lot more confirmed fixes documented out there ...? just seems a little weird
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post #15 of 55 (permalink) Old 05-10-2017, 02:17 PM
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Jetting is a pain. Need to fool with the air/fuel screw. I think 2 1/2 turns is close but will take some tweaking. Sense you changed your jets I would say it could be the problem. As for the valves not seating, you should go buy some filler gauges that go past the .152 to get a good reading. Bad valvessels WI'll cause it to run like poop.
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