Erratic idle and nothing helps

[Macjoyrider]

Hi all,
I have been having an idle problem with my 2001 Honda CB600 for nearly 6 months now. The idle is slightly erratic, it jumps between 1300 and 1500 revs. Also whilst crusing below 2,500 revs the bike judders slightly and it is very annoying when filtering through traffic . There is no issue with running in mid and top ranges. It happens regardless of whether the engine is cold or hot. It also occurs when cold and on choke. I have read hundreds of posts and followed all advice I found but the problem still persists.

So far I have :
- removed the carbs, cleaned them 3 times using carb cleaner and compressed air. Eventually I had them ultrasonically cleaned. The jets, passages and mixture screws are clean. Diaphragms and seals are fine. The floats are set properly and not sticking. In other words, the carb assembly is fine.
- I had the valve clearance checked and adjusted.
- I balanced the carbs
- I checked for vacuum leaks by spraying carb cleaner all over the carbs whilst running, no change in revs. Just to be sure, I sealed the airbox with black silicone. All the vacuum lines have been checked and have no leaks.
-new air filter
-new battery
-new plugs
-new oil and filter
- used Redex fuel line cleaner
- checked the fuel lines, cleaned them and blew dry

I have been playing a lot with the mixture screws and the idle seems a bit better with more fuel getting in. At the moment all screws are 3 turns out. Its more than recommended but it simply runs slightly better.

I have no other ideas and would appreciate your help in resolving this issue.

[Itchy]

A left field suggestion is the starter relay.

On Hondas they tend to rot causing funny electrical gremlins that will result in erratic running.

Look for a big wire off the battery and check the relay itself if it's oozing green copper liquid... it be dead.

Two of my old Hondas had this problem. I tore the bikes apart to find out what it was.
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[mudcow007]

are you firing on 4, ie is it a misfire?

what do the plugs look like?

[Macjoyrider]

Thanks for quick replies.

I will have a look at the relay tomorrow.

The plugs are fine. They are dry and have a nice tan colour.

With the misfire, its hard to tell. It does not sound like its missing and it pulls great when I open the throttle. There is no loss of power under load.

[redeem ouzzer]

Needles and emulsion tubes knackered. Such expense.
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[Macjoyrider]

Needles are fine but I have not checked the tubes for wear. It could be it. I take it that they are not removable, are they? Do you think lowering the needles a notch could improve the leak?

[redeem ouzzer]

[temeluchus]

[Macjoyrider]

Right, I have looked at a few photos of my carbs and it seems to me that when you put the emulsion tube into the internal passage, it will be separated from the needle by a round metal seat. That seat is in direct contact with the needle. Surely that would be the first thing to wear, wouldnt it? And that seat, I dont think is removable

[camcam]

Try getting a volt metre and checking your stator. The problems your having are identicel to what I had last year on my gsxr
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[chris-red]

I'm with Itchy on this, check the starter relay, I had a similar thing on my TDM, it also struggled to start and gave symptoms of a dying battery. Starter relay replaced and all the issues disappeared. Clean up the connections either way.
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[Fizzer Thou]

I cannot see why it would be the starter relay when the OPs initial comments were about the bike running at low revs,not about having problems starting the engine

I would be looking at the spark plug caps and the end of the leads where the caps screw into place.I have had several problems where the caps have had a slight crack in them and the spark energy from the coil has jumped to the engine casing.The resistance of each plug cap should be between 5,000 to 10,000 ohms.

Also,check that the green earth cable to the coil bracket is clean and not corroded.
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[chris-red]

[Vincent]

My first guess would be needles and jets too......maybe someone has damaged the bore on one of the jets by sticking something up there that they shouldn't....like a piece of snipped wire for eg. Next would be to replace the seals.
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[Macjoyrider]

Thanks for all the replies.
In the last two weeks I followed the advice about the oval emulsion tube and replaced the whole carb assembly with a dynojetted one from Ebay as I thought it was a good deal. I cleaned it and fitted but the problem is still there. At least the dynojet kit makes a massive difference at the top end so I am not too upset about the cost of the new carbs.

I also had to replace the reg/rectifier as I had a charging problem. Whilst diagnosing it, I checked the resistance and voltage on the stator and it was spot on.

The plug caps, leads and coils have already been replaced and it did not help.

I also had a look at the starter relay and it looked fine but I will have a look at a replacement.

Any other ideas?

[Kawasaki Jimbo]

[Macjoyrider]

Just replaced the starter relay... no effect on the rough idle.

In relation to the charging system, I doubt it has anything to do with it as the idle problem started long before the regulator failed. Also when I replaced the regulator, I did try to run the bike on battery only and the idle problem was still there.

I also tested the TPS and it reads voltage OK.

Anynone got any more ideas?

[Snowdonia Rider]

My bike had this problem due to a lead starting to come away from the spark plug cap, with that sorted it cured erratic idling. But seeing as you've already done that :hmm:
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[Macjoyrider]

Right, applying logic to my problem: problem with my idle can be caused by low compression, issue with fuel/air mix, or ignition.

I had the compression tested a while ago and it was near enough perfect. I don't remember the actual results but they were high and consistent. So the compression is not an issue.

Fuel/air mix:
- vacuum leak- having stripped the carbs apart about 20 times, I have examined all intake boots and seen no cracks or holes. I sprayed carb cleaner all over the intakes, carbs and air box but there was no change in idle speed. I can safely assume there is no leak.
- clogged pilot jet- I have cleaned the carbs thoroughly a few times and once had it ultrasonically cleaned. No effect on rough idle
- fuel leak through the emulsion tube- having bought another carburetor, which has been rebuilt using dynojet and lower mileage, there has been no improvement.
- mixture screw- played with those a lot and no matter what settings, the idle still plays up.
- other carb components- upon visual inspection, there was nothing of concern. Diaphragms are fine and sliders work properly. Choke works smoothly.
-fuel supply- the fuel is flowing and the petcock works fine.
I dont think there is anything else I can blame here.

Ignition:
- battery, alternator and regulator- all in good order. Battery and reg have been replaced. Battery is charging.
-coils and leads- replaced all to no effect
- starter relay- replaced... no effect
-TPS-tested and works fine.
- plugs- I bought new ones last year but now I am thinking thei might have been faulty. I just order new iridium plugs and see if they make a difference.
If the plugs dont make it then I am stuck but having gone through the above, I am led to think it might be sth to do with the elctrical system. Anyone has any ideas as to what I should test? Have I missed anything?

[iooi]

See below...
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[iooi]

[bugeye_bob]

Do the cars mount on those little rubber stubs, a few people I know had issues when one of these was split.

[A100man]

[Macjoyrider]

A100man, I was actually going to ask the forum if the ignitor could be the cause. I have not replaced that. I might pop round to a local breaker on saturday and see if they have some there for me to test.

[mudcow007]

I dont particularly know your bike, but do your carbs have caps like on Bandit carbs for balancing them?

I know on a Bandit, if one of these caps are missing/ split etc its a whole world of pain with wonky running etc

Also, is there a chance an inlet is cracked or anything?

#clutchingatstraws