slow letdown to idle? sticking but not cables??? HELP!!!


29 replies to this topic
  • cocomunga11

Posted February 25, 2006 - 03:36 PM

#1

OK well the throttle stays on at about 2500 rpm for a few seconds AFTER I let off !! (doesnt help in the corrners). It is NOT the cables at all and i took the carb appart and dont think it could be ANY cleaner! has anyone else had this problem? i still ride the bike and just keep the clutch in my hand... its driving me crazy!!e :thumbsup: 98 yzf 400 ported, polished, 450 cams, 450 xhaust

  • 2012 450 xc-w

Posted February 25, 2006 - 03:50 PM

#2

Cable too tight? :thumbsup:

  • cocomunga11

Posted February 25, 2006 - 04:39 PM

#3

thanks but nope, its got the push pull cables... both parfect and played with.

I can actually WATCH all of the MECHANICAL parts and they are working properly... the carb IS closing all the way but it still has a high idle for a few moments .... then drops to idle.... sometimes a throttle BLIP will help it come back down.? maybe just because it has the extra few seconds to drop then?

  • jbrooks26

Posted February 25, 2006 - 04:45 PM

#4

This is referred to as a "Hanging Idle". Usually a symptom of lean pilot circuit. Try turning the fuel screw out 1/8 turn at a time and see if that helps. If you end up with the fuel screw set more than 2 1/4 or 2 1/2 turns out then you will likely need a larger pilot jet. Hope this helps.

Josh

  • cocomunga11

Posted February 25, 2006 - 04:55 PM

#5

OK thanks going out in the shop to try that RIGHT NOW!!!! :thumbsup: (dang just cleaned my air cleaner... ill have to wait till it drys to test ) :thumbsup:

  • ovrrdrive

Posted February 25, 2006 - 05:03 PM

#6

This is referred to as a "Hanging Idle". Usually a symptom of lean pilot circuit. Try turning the fuel screw out 1/8 turn at a time and see if that helps. If you end up with the fuel screw set more than 2 1/4 or 2 1/2 turns out then you will likely need a larger pilot jet. Hope this helps.

Josh



Agreed.

  • PK

Posted February 25, 2006 - 05:09 PM

#7

That's a pretty high idle for a lean pilot jet. Something else you may want to look at again since you have a few days to kill, I would look at your throttle cables again. If the throttle doesn't SNAP back closed when you let the throttle go from wide open they are mis-rigged. If you've taken the cables off and all of a sudden this started you need to look at the cables again. It's best to rig them with the tank off. If one of the cables has too much tension on it, it will cause them to hang up. If you tinker around with it, you'll figure it out. To start out though, you would loosen the nuts on the throttle cables where they mount on the carb. With both cables loose, operate the throttle. It should snap closed, from there you tighten up the cables evenly and keep checking for proper throttle operation.

  • grayracer513

Posted February 25, 2006 - 05:46 PM

#8

When you run out of things to blame it on, check your valve clearances. This is a result of a too lean idle mix, and tight intakes are one of the causes.

  • moochie

Posted February 25, 2006 - 06:02 PM

#9

Howdy...Take a quick look at the gas cap vent hose. While putting the cap back on and twisting it closed, the hose can bind and twist enough to kink and become shut off, which can cause a lean situation.

  • cocomunga11

Posted February 25, 2006 - 06:30 PM

#10

THANKS GUYS! I have decided to get new pilot jet(s) does everyone change the pilot jet AND the pilot AIR jet like the manual says to do? and if you do change both what should the pilot air jet be changed to ? im taking my pilot jet from a 45 to a 48 and have a pilot air jet of 100 but have no info of what stock is or what other sizes there or any info at all on this pilot air jet.??? the book just says they should both be changed togher...

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • PK

Posted February 25, 2006 - 06:57 PM

#11

I've changed plenty of pilot jets and never have changed the air jet, just go for it...

  • jbrooks26

Posted February 25, 2006 - 07:55 PM

#12

THANKS GUYS! I have decided to get new pilot jet(s) does everyone change the pilot jet AND the pilot AIR jet like the manual says to do? and if you do change both what should the pilot air jet be changed to ? im taking my pilot jet from a 45 to a 48 and have a pilot air jet of 100 but have no info of what stock is or what other sizes there or any info at all on this pilot air jet.??? the book just says they should both be changed togher...



Sent you a PM. :thumbsup:

  • ovrrdrive

Posted February 26, 2006 - 06:55 AM

#13

I just did the pilot and main jets. I haven't fooled with anything else and the bike is jetted perfectly for my riding conditions.

  • David37

Posted February 26, 2006 - 06:32 PM

#14

I agree with the others, it sounds like you have a lean pilot jet condition. I had a hanging idle problem with my 250F, so I went with a richer pilot jet(s) but that didn't fix my problem. After trying all sorts of remedies, I finally diagnosed my hanging idle problem, my throttle cables were too tight (I don't like play in my throttles) and did not have enough play. If the richer pilot jet doesn't cure your hanging idle problem try this adjust both throttle cable at the crab. with about 1/4" to 1/2" of play and see if that cures your hanging idle problem. I would also clean and lube your throttle tube on your handlebars to make sure nothing is hanging up your throttle tube.

  • WR450F_RDR

Posted February 26, 2006 - 06:37 PM

#15

I was messing with the same problem today on my 06. I just adjusted the mixture screw a little and it went away. You may wish to try that before changing jets. I went out or counter-clock wise a little on mine to get it to stop.

  • Krannie McKranface

Posted February 26, 2006 - 07:47 PM

#16

Don't forget to check the slide plate on the front of the carb. All the '02 FCR carbs came with plates that eventually loosen and even fall out. My CRF450R did the exact same thing. I glued in the plate, and problems solved.

  • DaveJ

Posted February 27, 2006 - 10:20 AM

#17

When you run out of things to blame it on, check your valve clearances. This is a result of a too lean idle mix, and tight intakes are one of the causes.


There are two active threads on this matter at the moment, both filled with a collection of mystical voodoo and speculation, which surprises me given that the high idle matter is something that most of us encounter and resolve at some point.

I deal with this just about every week on either my YZ or my CR, and both bikes seem to require various carb adjustments throughout the day as the engine and outside air warms.

With that, I think a lean idle and pilot circuit is the cause, which means that it can be resolved by adjusting the fuel airscrew or worst case, switching up to a larger pilot jet.

However, that's not to discount the potential for a carb that is being enticed or has internal issues. As mentioned before, an engine will not rev or speed up without additional fuel, and the carb is the source.

So air leaks and such will lead to this, usually from torn or cracked choke and hot start boots, but this matter of intake valve clearance (via grayracer) may be a very valid point as well.

I would assume that with additional vacuum in the intake tract, brought on by the valves leaking during one of the other three strokes, could tease the carb (so to speak) into allowing the idle or pilot circuit to bring in a little more fuel, that is, until the two come to terms which is when the idle settles down to normal. Grayracer - thoughts, inputs?

But, given that it's winter and the air is thick and cold, start with the simple things. Turn the fuel screw out, test and go from there.

  • grayracer513

Posted February 27, 2006 - 12:07 PM

#18

I would assume that with additional vacuum in the intake tract, brought on by the valves leaking during one of the other three strokes, could tease the carb (so to speak) into allowing the idle or pilot circuit to bring in a little more fuel, that is, until the two come to terms which is when the idle settles down to normal. Grayracer - thoughts, inputs?

Quite the contrary, in fact. Leaking intake valves reduce manifold vacuum by allowing positive pressure from the preceding compression, power, and exhaust strokes into the intake port, which leads to a weaker intake pulse, and less gas delivered per intake stroke, and so, a leaner mixture.

You are quite correct in that the FCR carb seems to be somewhat more fussy about the idle mixture than a two-stroke with a Mikuni, and that some of these problems are the result of guys impatiently hauling their bikes out into the cold with the same settings they ran on the last warm day of fall, when they put them away, but I've seen tight intakes do exactly this on several occasions. It might really be as simple as an fuel screw adjustment or a pilot jet not quite big enough for the weather, but don't spend hours inside a carb looking for micronic particles until after you've checked the valves.

  • cocomunga11

Posted February 27, 2006 - 12:10 PM

#19

Bigger pilot jet is on the way,(im already 2.5 turns out on the screw) im just changing the poilt jet and not the pilot air jet ... any one think thats a bad idea? book says to do both but the concensus is that nobody really changes the pilot air jet?!?!?!

  • grayracer513

Posted February 27, 2006 - 12:24 PM

#20

any one think thats a bad idea? book says to do both but the concensus is that nobody really changes the pilot air jet?!?!?!

When going one or two steps up on the pilot, changing the air jet is not strictly necessary, and is not generally done. That would be something that you would be more apt to do when taking a carb from a completely different engine and adapting it to another.

But, as I said, don't change the jets to correct this until after you've established that your valve clearance is OK, and there are no other causes. Remember, it used to work with the current jetting, right?





Related Content

Forums
Photo
Supercross

Wilson the Blue Privateer by jetfuel


Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  50 replies
Forums
Photo

Snake pit oct 30th by The Anvil


Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies
Forums
Photo

YZ450FX OR YZ450F by MESSMAKER


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 replies
Forums
Photo

2016 YZ450 by CaptainKnobby


Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies
Forums
Photo

BIGBORE FOR YZ450F 2006? by Taattie94


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies
 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.