Topic: 1973 CB500K2 HANGING/SKIPPING IDLE! HELP!!!

[Coliver24]

I'm new here and have seen a few similar posts but nothing that seems to have solved my issues. So i apologize if i am not poating this in the correct spot. I purchased this bike in the fall and have completely rebuilt it and after reassembling everything and firing her up I am having an issue where the bike starts fine, will idle right around 1100 like it should (bike is fully warmed) but as soon as I apply any throttle, even if it's the slightest amount, the RPMs immediately shoot up to 3,000 to 4,000 and stay there. The only way I can get it to go back down to idle is by either pressing down on the 2 gold nuts on either the 1 and 2 carbs or the 3 and 4 carbs (the gold nuts are where you adjust the slide height). Or if I put it in first then slowly let out the clutch it will drop back into idle. Not sure if I would call this a hanging idle or if it is skipping the idle circuit completely. I will list everything I have done so far.

- Top end rebuild (valve job, honed cylinders, new rings, all new gaskets and seals
- 4 into 1 exhaust
- Pod filters
- Full carb rebuild (fully cleaned, all new gaskets and jets)
       Main - #110
       Pilot - #42 (tried 40s at first but just switched to 42s)
       Needle clip - 4th position from top (have tried middle position
       Mix screws - 2 turns out (have tried just about every position)
- Bench sync
- Cam chain adjusted
- Valve timing adjusted
- Points gap adjusted
- Ignition timing adjusted (static)
- Brand new intake boots so they are not leaking
- Brand new spark advance so has great springback
- Brand new plugs (NGK D7EA)
- New coils and wires
- New points and condensers
- New throttle cables (have full range of motion)

I feel like I've tried just about everything at this point so I am looking for any input. One of the only things left i can think of is the new jets I am using are not Keihin and are aftermarket purchased from 4into1. But i am possitive they are clear and all passageways in carbs are clear. I have not done any plug chops, I don't have a carb sync or strobe for dynamic.

Please let me know if I am missing anything that could be possibly because causing this. Thank you!

[newday777]

Welcome aboard Coliver24
Have you tried using carb cleaner with short quick spray on the intakes to see if there is a vacuum leak?

[Coliver24]

Welcome aboard Coliver24
Have you tried using carb cleaner with short quick spray on the intakes to see if there is a vacuum leak?

I have not but because I have brand new intake boots and brand new o-rings on the intake manifold. So i wouldnt expect there's a leake but I will still give this a try tomorrow.

[DT Tyson]

Check my remedy in the similar issue post.

http://forums.sohc4.net/index.php/topic,190423.0.html

[newday777]

Check my remedy in the similar issue post.

http://forums.sohc4.net/index.php/topic,190423.0.html

http://forums.sohc4.net/index.php?action=profile;area=showposts;u=59162

[Coliver24]

Welcome aboard Coliver24
Have you tried using carb cleaner with short quick spray on the intakes to see if there is a vacuum leak?

Okay so I tried this today and there appears to be no vacuum leak.

Check my remedy in the similar issue post.

http://forums.sohc4.net/index.php/topic,190423.0.html

Just to clarify, all you did was back the idle screw all the way out? I've messed around with the idle screw a lot. When I back it out all the way the bike will die.

[wolf550]

had same problem with mine.
when I blip the throttle would hang and would not rev back down.
I had to push down on the throttle links on the carbs and it went down.
I did not use the correct thickness bolt when setting throttle chambers height correct.
my adjustment screws were way up instead of just 3 or links
circled in pic.

when you can take a pic of your carbs.

[Coliver24]

had same problem with mine.
when I blip the throttle would hang and would not rev back down.
I had to push down on the throttle links on the carbs and it went down.
I did not use the correct thickness bolt when setting throttle chambers height correct.
my adjustment screws were way up instead of just 3 or links
circled in pic.

when you can take a pic of your carbs.

Looks like mine are only 3 or 4 links as well

[DT Tyson]

Just to clarify, all you did was back the idle screw all the way out? I've messed around with the idle screw a lot. When I back it out all the way the bike will die.

In my case, yes. And your result is what I had expected from mine, but that wasn't the case for me.
I'm running a bone stock carburation setup, which looks to be nothing like yours.
Good luck my friend, I hope the good folks here can help you find a solution.

[Coliver24]

Here is a video of what is happening.
- Idling normal and at 1100 RPMs
- Give smallest amount of throttle.
- RPMs race to 3,000-4,000
- Press down on throttle linkage on carbs
- Bike returns to idle and around 1100 RPMs

[Scootch]

It seems as though the throttle linkage or cable(s) or something is hanging up or sticking or....  Maybe a spring that was left off or put in the wrong place?

[Coliver24]

It seems as though the throttle linkage or cable(s) or something is hanging up or sticking or....  Maybe a spring that was left off or put in the wrong place?

Throttle linkage and cables seem to have full range of motion and aren't sticking. What's odd is even with the slightest bit of throttle the RPMs shoot right up to over 3,000 and then stays there. It's not like I'm reving it up to 3,000 and then it stays there

[Scootch]

If you watch the linkage when this happens is anything moving so as to indicate that throttle increase is being commanded?

[Coliver24]

If you watch the linkage when this happens is anything moving so as to indicate that throttle increase is being commanded?

Nope, it stays exactly where it should. Here is a video of the linkage freely moving when I move the throttle

[Scott S]

 The pods aren't exactly helping, but take a read through this thread:

http://forums.sohc4.net/index.php/topic,184299.msg2133716.html#msg2133716

[Coliver24]

The pods aren't exactly helping, but take a read through this thread:

http://forums.sohc4.net/index.php/topic,184299.msg2133716.html#msg2133716

Scott, thanks for the reply. I'm trying to adjust for the German method but I can't get the 49mm measurement. Even with the idle screw all the way in and the slide adjusters all the way down. I see there were a few others that were having that same issue not being able to adjust that far

[TwoTired]

There are four travel adjusters used for syncing carbs.  Later carbs have a master that can't be adjusted.  It is possible to tweak all the adjust so that the slides can't reach to the travel floor, making the idle knob lose dominance of slide position. 
Back out the idle knob, pick a carb for maser duty and adjust so that the slide bottoms out in the carb throat. Lock that one down and never adjust it again.  Use the idle knob to set it's position thereafter.  During mechanical sync or vacuum sync never touch the master's adjuster again.  While the slides don't normally ever need to rest on the travel floor.  The individual adjusters can compete for idle slide position with the idle knob adjuster, yielding erratic idle consistency.

I also notice that the SS keepers you have under the adjuster nuts are bent.  They should be flat.  Bent ones can apply sideways pressure on the slide actuators and cause binding.

[Johnny340]

There are four travel adjusters used for syncing carbs.  Later carbs have a master that can't be adjusted.  It is possible to tweak all the adjust so that the slides can't reach to the travel floor, making the idle knob lose dominance of slide position. 
Back out the idle knob, pick a carb for maser duty and adjust so that the slide bottoms out in the carb throat. Lock that one down and never adjust it again.  Use the idle knob to set it's position thereafter.  During mechanical sync or vacuum sync never touch the master's adjuster again.  While the slides don't normally ever need to rest on the travel floor.  The individual adjusters can compete for idle slide position with the idle knob adjuster, yielding erratic idle consistency.

I also notice that the SS keepers you have under the adjuster nuts are bent.  They should be flat.  Bent ones can apply sideways pressure on the slide actuators and cause binding.

+1

[Coliver24]

There are four travel adjusters used for syncing carbs.  Later carbs have a master that can't be adjusted.  It is possible to tweak all the adjust so that the slides can't reach to the travel floor, making the idle knob lose dominance of slide position. 
Back out the idle knob, pick a carb for maser duty and adjust so that the slide bottoms out in the carb throat. Lock that one down and never adjust it again.  Use the idle knob to set it's position thereafter.  During mechanical sync or vacuum sync never touch the master's adjuster again.  While the slides don't normally ever need to rest on the travel floor.  The individual adjusters can compete for idle slide position with the idle knob adjuster, yielding erratic idle consistency.

I also notice that the SS keepers you have under the adjuster nuts are bent.  They should be flat.  Bent ones can apply sideways pressure on the slide actuators and cause binding.

Thanks TwoTired, I will give this a shot tomorrow if I have a free minute. If not, definitely this weekend. I also noticed the keepers were bent but didn't think it would really affect anything as when i watched the slides move up in down i didnt notice anything odd with them. I will flatten those back out/possibly get new ones just to be sure they aren't a contributing factor.

[Coliver24]

There are four travel adjusters used for syncing carbs.  Later carbs have a master that can't be adjusted.  It is possible to tweak all the adjust so that the slides can't reach to the travel floor, making the idle knob lose dominance of slide position. 
Back out the idle knob, pick a carb for maser duty and adjust so that the slide bottoms out in the carb throat. Lock that one down and never adjust it again.  Use the idle knob to set it's position thereafter.  During mechanical sync or vacuum sync never touch the master's adjuster again.  While the slides don't normally ever need to rest on the travel floor.  The individual adjusters can compete for idle slide position with the idle knob adjuster, yielding erratic idle consistency.

I also notice that the SS keepers you have under the adjuster nuts are bent.  They should be flat.  Bent ones can apply sideways pressure on the slide actuators and cause binding.

Okay so I was able to give this a try and did not have any luck. I have the keepers perfectly flat and used your method for setting the carbs. I thought I got lucky but as soon as the bike gets up to temp it starts doing it. I'm so lost

[OldGreyBeast]

That makes 2 of us my dude.  Mine's a 550 but I've been fighting these idling issues for months.

[Coliver24]

That makes 2 of us my dude.  Mine's a 550 but I've been fighting these idling issues for months.

I was just reading through your thread hoping to find a solution. I've been fighting it since I got the bike put back together in April. I've taken these carbs apart now more times than I can count. I just keep putting more money into it hoping that will be the fix anddddd nothing. We need to figure this out!

[OldGreyBeast]

Same my dude.  It's so frustrating.

[TwoTired]

Can you post pictures of the spark plug tips?

[Coliver24]

I'm new here and have seen a few similar posts but nothing that seems to have solved my issues. So i apologize if i am not poating this in the correct spot. I purchased this bike in the fall and have completely rebuilt it and after reassembling everything and firing her up I am having an issue where the bike starts fine, will idle right around 1100 like it should (bike is fully warmed) but as soon as I apply any throttle, even if it's the slightest amount, the RPMs immediately shoot up to 3,000 to 4,000 and stay there. The only way I can get it to go back down to idle is by either pressing down on the 2 gold nuts on either the 1 and 2 carbs or the 3 and 4 carbs (the gold nuts are where you adjust the slide height). Or if I put it in first then slowly let out the clutch it will drop back into idle. Not sure if I would call this a hanging idle or if it is skipping the idle circuit completely. I will list everything I have done so far.

- Top end rebuild (valve job, honed cylinders, new rings, all new gaskets and seals
- 4 into 1 exhaust
- Pod filters
- Full carb rebuild (fully cleaned, all new gaskets and jets)
       Main - #110
       Pilot - #42 (tried 40s at first but just switched to 42s)
       Needle clip - 4th position from top (have tried middle position
       Mix screws - 2 turns out (have tried just about every position)
- Bench sync
- Cam chain adjusted
- Valve timing adjusted
- Points gap adjusted
- Ignition timing adjusted (static)
- Brand new intake boots so they are not leaking
- Brand new spark advance so has great springback
- Brand new plugs (NGK D7EA)
- New coils and wires
- New points and condensers
- New throttle cables (have full range of motion)

I feel like I've tried just about everything at this point so I am looking for any input. One of the only things left i can think of is the new jets I am using are not Keihin and are aftermarket purchased from 4into1. But i am possitive they are clear and all passageways in carbs are clear. I have not done any plug chops, I don't have a carb sync or strobe for dynamic.

Please let me know if I am missing anything that could be possibly because causing this. Thank you!

Just thought I'd open this back up to see if anyone has any new ideas as I have been dealing with this hanging idle issue for almost a year now!