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TOPIC: Hanging idle

Hanging idle 01 May 2019 01:41 #803131

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Hi guys I'm having some tuning problems. This site has been invaluable but I still haven't quite solved the issue.

When the bike is warm it will idle at around 800-900 rpm nicely. But if i give the throttle a blip I will have a slow return to idle. Once the bike is proper warmed up after a ride the revs will hang at 2000-3000rpm for up to 10 seconds then slowly return. I sometimes need to adjust the idle screw to drop this. Or release the clutch to "pull" it back down.
Throttle snaps shut, I am confident the slides aren't hanging up.

Here is a list of things I have done to try rectify this.

Replaced old cracked carb boots after testing with carb cleaner around the mounts ect. This did help a bit but didn't solve.
Bench synced slides
Adjusted float levels
replaced throttle cables (nothing wrong with the old but may as well rule it out)
Replace pilot screw o-rings
Returned to original air-box from pods I tried out.

I have not yet Vacuum synced yet with the air box back on.

Bike is running 4 into 1 Vance and Hines currently. With airbox. I am unsure if the bike has been jetted to suit. But am trying to rule out any other issues first before messing with them.

Hope someone can help before I pay someone to do it! Thanks

Jim

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Hanging idle 01 May 2019 03:12 #803132

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Good to know what bike your are talking about?
Carbs air ports, main and pilot jets are clean?

Please introduce your bike with some pics.

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Hanging idle 01 May 2019 05:36 #803145

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Vacuum sync'ing and richening up the idle mixture will typically help a hanging idle. Also, check the advance mechanism cam to make sure it moves smoothly (twist the rotor against the springs and release to make sure it snaps back to the base position).

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Hanging idle 01 May 2019 09:53 #803154

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In addition to the usual possibility of a vacuum leak, if you are idling on the main circuit you will get behavior as you describe. Idling on the main circuit is usaully the result of a clogged pilot jet or pilot-air-fuel mixture system clog.

More often than not, when I come across a bike with that problem, it's idling on the main. And then after fixing that we can start actually troubleshooting vacuum leaks... so having both problems is common.

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Hanging idle 01 May 2019 14:11 #803162

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loudhvx wrote: In addition to the usual possibility of a vacuum leak, if you are idling on the main circuit you will get behavior as you describe. Idling on the main circuit is usaully the result of a clogged pilot jet or pilot-air-fuel mixture system clog.

More often than not, when I come across a bike with that problem, it's idling on the main. And then after fixing that we can start actually troubleshooting vacuum leaks... so having both problems is common.


More times than not when the pilot circuit is plugged the cylinder won't fire at idle. Checking to make sure the headers are getting hot from a cold start is a good check.

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Hanging idle 01 May 2019 21:17 #803179

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Hi Guys, thanks heaps for the replies.

The bike is a 76 KZ900. See attached.

I did give the carbs a clean a few months back when I had them out. And checked all the jet ports, were clear. with wire (not recommended i know).
I will check the advancer tonight. hopefully have some luck there.

After that if the Vac sync and richening the idle doesn't solve it, I'll have to strip them down and give another clean to rule out the pilot circuit being blocked as mentioned.

Cheers!

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Hanging idle 02 May 2019 09:40 #803199

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Nessism wrote:

loudhvx wrote: In addition to the usual possibility of a vacuum leak, if you are idling on the main circuit you will get behavior as you describe. Idling on the main circuit is usaully the result of a clogged pilot jet or pilot-air-fuel mixture system clog.

More often than not, when I come across a bike with that problem, it's idling on the main. And then after fixing that we can start actually troubleshooting vacuum leaks... so having both problems is common.


More times than not when the pilot circuit is plugged the cylinder won't fire at idle. Checking to make sure the headers are getting hot from a cold start is a good check.


But it will run when the throttle is held open because it's able to run on the main. Then people turn the idle speed adjustment until the throttle is held open far enough to run on the main. The mixture is so far off, the bike seems to idle even though the throttle is held open much farther than it should be. This is a meta-stable condition, unlike a normal idle which is stable. So, at first it leads to the appearance that the bike is idling, but if they blip the throttle the overly rich mixture clears out and the proper mixture for the now far-open throttle takes over and the RPMs run away... losing the meta-stable condition. You can restore the meta-stable condition by loading down the motor to force the RPMs down or reducing the idle adjustment and increasing it just before the motor dies.

I see this most commonly with bikes that use white tank creme coating. The bike I'm currently working on has this problem. It runs fine after you clean the jets, but just a few hours later the pilots get gummed with white goo again. So the plan is to get a new tank, but I've been toying with the idea of cutting the bottom out of the cremed tank, cleaning it out, and tigging it back together. With any luck, only the underside of the tank will need painting... in order to preserve the factory paint job which is still in good condition.

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Hanging idle 14 May 2019 09:59 #803863

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Just putting this out there since this is something that messed with me on my 440 since I got it (And I only just got figured out last weekend).

If your 900 has points, double check that both sets of points have the correct gap and that they aren't pitted. I had been having issues that looked a ton like a lean condition, even after cleaning out the carbs and ensuring proper back-pressure on the exhaust. Until we took off the points cover and saw that they were barely opening at all. Setting the points made everything get completely better and the bike now runs like a dream.

It should be pretty easy to check the gap, so might not be a bad idea if you're not fond of pulling the carbs.

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Hanging idle 15 May 2019 13:41 #803928

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I see this most commonly with bikes that use white tank creme coating. The bike I'm currently working on has this problem. It runs fine after you clean the jets, but just a few hours later the pilots get gummed with white goo again. So the plan is to get a new tank, but I've been toying with the idea of cutting the bottom out of the cremed tank, cleaning it out, and tigging it back together. With any luck, only the underside of the tank will need painting... in order to preserve the factory paint job which is still in good condition.


No experience with this but it looks worth a shot: POR-15
If it works, it's certainly easier than cutting & tigging.

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Hanging idle 15 May 2019 17:56 #803940

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That's the type of stuff I'm trying to get rid of.

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Hanging idle 15 May 2019 19:37 #803950

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I've stripped failed liners out of two different tanks. It's doable but not for the faint of heart. I used heavy duty paint stripper and uncoated aquarium rocks to scrub the metal. If you can get real MEK in your area it's reputed to cut Kreen. I'd try that before the stripper if possible because it's less harsh.
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Hanging idle 16 May 2019 08:51 #803977

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Nessism wrote: I've stripped failed liners out of two different tanks. It's doable but not for the faint of heart. I used heavy duty paint stripper and uncoated aquarium rocks to scrub the metal. If you can get real MEK in your area it's reputed to cut Kreen. I'd try that before the stripper if possible because it's less harsh.


I used MEK to remove kreme liner in my tank. AKA, liquid death. Nasty stuff, but a better choice than stripper for sure. MEK, will eat the kreme, rubber gloves, your paint, your fingers, and anything else it gets on. ::S:

Remove anything in the tank and make up block off plates for all of the openings.



I found an expanding "freeze plug" at a parts store fit my fill hole perfectly.

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Located in the Saint Louis, Missouri Area.
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Hanging idle 17 May 2019 08:56 #804027

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Over the years I've become more and more averse to chemicals... hence I'd rather cut and weld. Welding is way more "fun" at any rate... though it is not without fumes either.

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Hanging idle 17 May 2019 09:55 #804034

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loudhvx wrote: Over the years I've become more and more averse to chemicals... hence I'd rather cut and weld. Welding is way more "fun" at any rate... though it is not without fumes either.


Soooo, your solution is to cut the gas tank open and scrape the kreme off then weld it back together? Sounds reasonable. LOL ::S:
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Located in the Saint Louis, Missouri Area.

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Hanging idle 17 May 2019 10:13 #804037

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old_kaw wrote:

loudhvx wrote: Over the years I've become more and more averse to chemicals... hence I'd rather cut and weld. Welding is way more "fun" at any rate... though it is not without fumes either.


Soooo, your solution is to cut the gas tank open and scrape the kreme off then weld it back together? Sounds reasonable. LOL ::S:


Yes, simple no? :)

It'll probably never happen, but if done properly, I think it can be more thorough, as it seems any left over liner is going to gum the carbs, and I'm already sick of cleaning liner gunk out of the carbs. Also, i'm hoping if the cuts are placed in the right areas, it won't affect the top-side factory paint job, which is in very nice condition. What will stripper or MEK do to paint? I hate painting ... more chemicals and a bunch of tools I don't have and don't want to have.

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Hanging idle 17 May 2019 12:24 #804041

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loudhvx wrote:

old_kaw wrote:

loudhvx wrote: Over the years I've become more and more averse to chemicals... hence I'd rather cut and weld. Welding is way more "fun" at any rate... though it is not without fumes either.


Soooo, your solution is to cut the gas tank open and scrape the kreme off then weld it back together? Sounds reasonable. LOL ::S:


Yes, simple no? :)

It'll probably never happen, but if done properly, I think it can be more thorough, as it seems any left over liner is going to gum the carbs, and I'm already sick of cleaning liner gunk out of the carbs. Also, i'm hoping if the cuts are placed in the right areas, it won't affect the top-side factory paint job, which is in very nice condition. What will stripper or MEK do to paint? I hate painting ... more chemicals and a bunch of tools I don't have and don't want to have.


I used to have a girlfriend that would over complicate EVERYTHING, then do nothing because it was too much work. LOL

Simple NO. lol

Of course, I'm sure this is only for "what if?" purposes, since very few have OEM paint that is pristine enough to save. Let alone, the welding equipment and skills necessary. In the end, you have a tank with scratched up OLD paint that looks like crap on a welded up tank.

When I decided to remove my liner, I had also decided it was time to put some nice paint on the bike at the same time. Of course, if you are careful enough, and really really really want to save a paint job, it would require the most careful masking , covering and pouring like no one has ever seen. I even put screws in the tank and rotated it in both directions ~1/2 hour each way, packed into my clothes dryer to make sure I got everything out.

Don't try this at home! :-)

Of course MEK and stripper WILL ruin any paint it gets on. so will a welder and cutting torch, and rolling it around on a bunch of welding and grinding debris, to the point that saving the paint will no longer be an issue. . Considering that MINE had a full on " custom" rattle can paint "improvement" . Along with the KOOL kreme job. The paint is of usually of no consideration at this point.

Could you post a few pics of the tanks that you have done this to? Inquiring minds want to know.



I foresee a very lucrative future doing tank coating removal for the patrons on kzrider. lol
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Hanging idle 17 May 2019 16:59 #804063

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I've had very good success soldering pinholes on a tank without doing undo damage to paint. It just looks like a tiny silver spot on the paint in place of the pinhole. I can also mig parts with doing minimal damage to paint. Obviously I would re-spray the underside of the tank, but the top-side, which is what matters, would be untouched.

I don't think it's overly complicated compared to spending days removing the liner with a chemical then spending days trying to repaint the tank with stock stripes etc. And I'd rather cut and weld than deal with stripping and painting any day.

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Hanging idle 18 May 2019 01:10 #804070

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loudhvx wrote: I've had very good success soldering pinholes on a tank without doing undo damage to paint. It just looks like a tiny silver spot on the paint in place of the pinhole. I can also mig parts with doing minimal damage to paint. Obviously I would re-spray the underside of the tank, but the top-side, which is what matters, would be untouched.

I don't think it's overly complicated compared to spending days removing the liner with a chemical then spending days trying to repaint the tank with stock stripes etc. And I'd rather cut and weld than deal with stripping and painting any day.


There is a whole lotta difference between cutting open a fuel tank, compared to soldering a pinhole. Then trying to scrape a bunch of crap out of it, that would dissolve in a chemical would be an exercise in futility. But HEY, you have at it! It's your tank. :whistle:

If you are getting crap in your carbs, your petcock screen is damaged or gone, and fuel filters can normally catch any small pieces of left over crap. BTW, Your pinholes are exactly what the tank liners are meant to fix.



I removed my kreme job then flushed the tank several times. I worked the MEK a while to make sure, the kreme was loose inside running screws with the MEK, and using a clothes dryer to automate the procedure a little. Shaking it gets really old fast. I poured the used / contaminated MEK back into the metal can for disposal,. I then flushed it with lacquer thinner then water before I filled it with metal rescue to remove any metal oxide that was trapped under the kreme. The end result is a perfectly clean tank on a bike that starts / screams like a bat outa hell. Always.
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Hanging idle 18 May 2019 03:38 #804073

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Have you sprayed carb cleaner round the boots when running, see if the revs kick up.
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Hanging idle 18 May 2019 06:55 #804075

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When cleaning the carbs, be sure the #6 orifice is clear [see below].

And remember to wear eye protection, because the carb cleaner spray always backfires. ALWAYS.







Good Fortune! :)
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