Topic: CB500/4 tickover problem

[Honda-Rog]

I guess this may have come up before, so apologies if so, I have had a search.

This bike is in standard mode and is good, runs really well, smooth and fast (enough), but for the idle, which is irregular and has an occasional misfire. Doesn't seem to matter what the actual idle speed is set to.

I've gone through the bike - new plugs gapped, new points gapped, static timing, camchain tensioned, carbs checked and rechecked, slow jets (stock) removed and cleaned through (can see clearly through all the orifices), carbs balanced and rebalanced (on the bike). Thanks BTW to all on this forum for posting the 'how to' stuff on all the above.

Starts readily with the usual open throttle and full choke.

All I can think of now is to run a timing light on the points, and maybe replace the slow jets with new ones.

Any ideas - anyone else had this and solved it? I love my bike and don't want to live with this niggling problem.

Hey, I know this is minor compared with the problems some folk have - for anyone in the east coast areas, hope you're OK and can cope with the devastation.

Regards,

[MoMo]

Possbily bad spark plugs caps-should read 5k but more than likely you need to trim the plug wires back and tightly reinstall the plug caps.  Good luck...Larry

[flybox1]

note the voltage of your battery at different RPM's.
idle, 2k, 3k, 4k...
pull your plugs after idle, what kind of deposits?
report back.

[Greggo]

For some reason, my brain is telling me to tell you to check the dwell on your points.

[iron_worker]

I think the improper dwell would bring on more problems at higher RPM instead of idle.

Checking battery voltage at idle isn't a bad idea but if you battery is going dead you would probably know.

I'm thinking mixture... possibly lean. You said you hold the thottle wide open and choke it when you start? Does it have carbs with an accelerator pump (I'm not familiar with the 500s as much as the 750s)?

IW

[Honda-Rog]

Cheers Larry, thanks for the thought. I've already trimmed the leads and replaced two caps, think I'll replace the other two as well.

Possbily bad spark plugs caps-should read 5k but more than likely you need to trim the plug wires back and tightly reinstall the plug caps.  Good luck...Larry

[Honda-Rog]

No accelerator pumps, mixture may not be right on all four carbs. Will check plug colour as suggested earlier and report back.

Battery less than a year old, hold charge fine, don't think this is a problem.

I think the improper dwell would bring on more problems at higher RPM instead of idle.

Checking battery voltage at idle isn't a bad idea but if you battery is going dead you would probably know.

I'm thinking mixture... possibly lean. You said you hold the thottle wide open and choke it when you start? Does it have carbs with an accelerator pump (I'm not familiar with the 500s as much as the 750s)?

IW

[Honda-Rog]

Of the four plugs, two were rich (black), one was weak, and one about right. Have adjusted mixture screws and will road test later.

Thanks,

Roger

No accelerator pumps, mixture may not be right on all four carbs. Will check plug colour as suggested earlier and report back.

Battery less than a year old, hold charge fine, don't think this is a problem.

I think the improper dwell would bring on more problems at higher RPM instead of idle.

Checking battery voltage at idle isn't a bad idea but if you battery is going dead you would probably know.

I'm thinking mixture... possibly lean. You said you hold the thottle wide open and choke it when you start? Does it have carbs with an accelerator pump (I'm not familiar with the 500s as much as the 750s)?

IW

[dave500]

im with momo on the plug caps,,if they are old they will be dud,,its also best to use a timing/strobe light when setting timing,,the static setup gets it close(a bit like "bench"syncing carbs)but a proper tune up is that edge better.

[Honda-Rog]

Plug caps ordered, and I already had a strobe light ready to use. Here's hoping!

Thanks all, will let you know.

Hey, these are still great old bikes!!

im with momo on the plug caps,,if they are old they will be dud,,its also best to use a timing/strobe light when setting timing,,the static setup gets it close(a bit like "bench"syncing carbs)but a proper tune up is that edge better.

[MoMo]

Keep us posted...Larry

[Honda-Rog]

Posting, posting . . .

Guess what, a spark plug cap - such a cheap repair!

Now idles much more steadily, just need to refine the timing and carburation, then, wah hay!!

Many thanks to all for taking an interest, safe riding.

Honda-Rog

Keep us posted...Larry

[MoMo]

Congrats, and a good feeling of accomplishment, isn't it?...Larry

[Honda-Rog]

Hmm - seems I was a little hasty. The plug cap does seem to have sorted the misfire at idle, but the idle is still variable - the engine note varies with a noticeable 'surge' every few seconds. Trying to idle it around 1100-1200 and it's 'orrible!

I've reset the timing both static and with the strobe. All plugs are now showing light brown so I assume the mixture is pretty well right. I've resynced the carbs, assuming my vacuum gauges are calibrated - checked them against a common vacuum source.

The bike certainly goes well. Could it be a carburettor issue - maybe I haven't cleared the slow jets properly? Pretty sure there's no leak from the carb rubbers.

All suggestions considered (excluding selling the bike . . .)

Posting, posting . . .

Guess what, a spark plug cap - such a cheap repair!

Now idles much more steadily, just need to refine the timing and carburation, then, wah hay!!

Many thanks to all for taking an interest, safe riding.

Honda-Rog

Keep us posted...Larry

[MoMo]

When you cleaned the carbs did you remove and clean the midrange emulsifier jets? ....Larry

[flybox1]

Honda-Rog.
after idle, now, do your plugs show the same mix deposits?  does the erratic idle go away if you set your idle to 1300-1400rpm?
did you adjust your idle mix screws so they were all the same, or are they adjusted differently based on the plug deposit for that circuit?

clear tube float bowl level test...a float off by 1mm can make a huge difference in fuel level and jet saturation...
I would go back to all A/F screws set the same.  remove that variable(if not already).
ensure all floats are set the same AND achieve the same bowl fuel level (4mm below bowl gasket seam)
re-gap plugs.
what is your battery voltage at idle?

[Honda-Rog]

Well, we still have the problem! I've checked and adjusted (using drill bit) the slide heights, i.e. bench sync, adjusted the float levels to 22mm, then resynched the carbs and checked and adjusted the mixture - they are all set to show light brown at the plug.

I also opened up the carbs and sprayed cleaner into every orifice.

I'm not convinced that my vac gauges are right, despite calibrating them.

To Flybox1, the idle improves at c.1400 rpm - what could this signify?

Only other thing I now have is a little hesitation when I open the throttle. But it still drives well and revs right up to the red line.

Getting just a little frustrated now . . .

[Bootlegger56]

+1 on the float level test recommended by Fly......

[Honda-Rog]

I didn't, but am now thinking of doing that. But would any blockage there affect idle? And it does rev fine.

When you cleaned the carbs did you remove and clean the midrange emulsifier jets? ....Larry

[MoMo]

I didn't, but am now thinking of doing that. But would any blockage there affect idle? And it does rev fine.

When you cleaned the carbs did you remove and clean the midrange emulsifier jets? ....Larry

All of the half dozen or so 400 fours I had that sat with fuel had the midrange jets clogged with lacquered gas. The tiny holes are usually blocked and the chamber that the tube sits in has that white powdery stuff. I clear the holes with wire and the chamber with a stiff bristle circular brush .  The jet and needle control quarter to 3/4 throttle...Larry

[Honda-Rog]

OK, so I've removed the midrange (emulsifier) tubes - they were pretty dirty. Good clean with carb cleaner, plus all around inside, recleaned the slow jets. Needles look clean and not worn. Reset float heights again to make sure they are all the same.

Bike now goes even better, very smooth, faster too, but still idles like it's on something nasty. Occasionally it seems to settle a little, then off it goes again.I guess I should upload a video to Youtube - would that help anyone with diagnosis?

I noticed the float needles were a little worn, but as I get no leaks I don't think they're for replacement yet - could they have any effect on idle? Checked again for leaks on the inlet rubbers, rechecked timing with strobe. And reset the carb sync, as after cleaning they were well out of balance. I'm not convinced that the balance is right - there's still a little banging noise at tickover.

Any more ideas? I'm running out. Maybe I just have to live with it . . .

[MoMo]

Your description of surging idle does sound like an air leak.  Positive the intake manifolds are tightly sealed? Air screws are not damaged and set properly? What are you using to sync the carbs?...Larry

[bollingball]

Try some fresh gas from a different station. Might not help but it sure won't hurt.
Ken

[Honda-Rog]

Update for anyone still interested.  Having thought about feedback from you all, I changed the inlet O rings, AND the inlet rubbers, AND the slow jets, AND the air filter. AND rechecked the float heights. I didn't change the fuel.

The result - one steady idling machine, ready for a proper carb sync! Now I'm one happy bunny. My guess is the old slow jets were the main issue, even 'tho' I thought I'd cleaned them - compared to the new ones they were clogged. There must be a lesson in there . . .
Moving on soon to a repaint (not a DIY one). Any UK riders out there care to recommend a paint shop?
You guys are the tops! :-)

Safe riding,

Roger

[MoMo]

Glad to see all has been straightened out.  Congrats...Larry