Mike's CB550 Project

[Mike_Berkshire]

So is that why I have a hanging idle yet also symptoms of running rich like sooty plugs and strong fuel smell?  Sounding like another carb off job

I have exact same symptoms Dom

[McCabe-Thiele (Ted)]

To save me trawling right through this thread are you both running on 087A carbs?

Is there any sign of wear on the main jets or needles?
Needles in the middle position(3).

My 069A carbs had needles with no middle poistion, all changed to original needles & jets courtesy of Ken.

[Oddjob]

069a carbs are for a CB550F not a CB500K Ted, as I'm sure you know. a 500K made for the UK should be wearing 627B carbs. The 069a carbs have 4 slots on their needles and it runs at 2nd from top as standard IIRC, the problems here sound like flooding to me, if you can smell petrol there's something wrong. Flooding will cause it to run really rich, hence the black plugs, it's like the engine is running on fast idle setting on a car with auto choke.

As these bikes get older we don't know what's been done to them before we bought it, it may no longer have the same brassware it was made with, a lot of people tended to think they'd be better replacing it with stuff like Keysters etc thinking it was wearing etc, worst thing they could have done IMO. The next owner then has to suffer that mistake and a lot move the bike on because it's not running as it should and they don't know why.

[DomP]

Mines an F Ken on 069a carbs with all original jets etc (some bits supplied by you to replace damaged items) I've adjusted the floats to the specified 21mm? from memory, it will definitely start happily with no choke whatsoever even in cooler weather.

[McCabe-Thiele (Ted)]

What needles & Jets are fitted to your 550F Dom?
Something sounds wrong if it starts without choke.

[Mike_Berkshire]

069a carbs are for a CB550F not a CB500K Ted, as I'm sure you know. a 500K made for the UK should be wearing 627B carbs. The 069a carbs have 4 slots on their needles and it runs at 2nd from top as standard IIRC, the problems here sound like flooding to me, if you can smell petrol there's something wrong. Flooding will cause it to run really rich, hence the black plugs, it's like the engine is running on fast idle setting on a car with auto choke.

As these bikes get older we don't know what's been done to them before we bought it, it may no longer have the same brassware it was made with, a lot of people tended to think they'd be better replacing it with stuff like Keysters etc thinking it was wearing etc, worst thing they could have done IMO. The next owner then has to suffer that mistake and a lot move the bike on because it's not running as it should and they don't know why.

All 4 carbs on my bike are stamped 087A - its a US import 1976 K2 CB550

[Oddjob]

Yeah, different markets got different carbs, 087a sounds right for the states. You checked if it still has Keihin brass? They’ll be marked with a stylised K if they are.

[Oddjob]

Mines an F Ken on 069a carbs with all original jets etc (some bits supplied by you to replace damaged items) I've adjusted the floats to the specified 21mm? from memory, it will definitely start happily with no choke whatsoever even in cooler weather.

If it starts from cold with no choke that’s usually indicative of it running too rich Dom. Seem to recall it’s 22mm not 21 btw.

It could be aftermarket float needle and seats, renowned for not sealing properly.

[DomP]

All jets, needles etc are the correct size with the Keihin 'K' stamped on them.  I wonder if it's a blocked passage but they all appeared to be clear. 

[Mike_Berkshire]

Yeah, different markets got different carbs, 087a sounds right for the states. You checked if it still has Keihin brass? They’ll be marked with a stylised K if they are.

all brassware is kosher. I did swap out the main jets as they were mixed sizes - Julie let me have some original main jets in the right size. I have replacement slow jets also from Julie and in original Honda packaging. New Viton rubber throughout.

[DomP]

That's true Mike, also all new carb o rings from Julie here too.

[Mike_Berkshire]

Thanks all for the help. I stripped and cleaned the carbs paying particular attention to the idle circuits giving it a good squirt through with carb cleaner, blowing out the residue and leaving overnight to evaporate away thoroughly. I rebuilt the carbs this morning with the new idle jets (thanks Julie, I forgot I had bought them but not fitted them!) and checked and adjusted the float heights - a couple were out by 1.5 - 2.0 mm. I re-synched the carbs; this time I set all sliders at the just opening position; previously I had set at a bigger gap. I fitted 2 of the in-line Aeroline filters (thanks Ted for the photos).

The bike ran much better and I have just got back from a blast up and down the road - about 5 or 6 miles; flipping cold but very satisfying :-)

There is still a slight hang now and then but nothing like it was; the bike hesitates when pulling away from a standstill and needs quite a lot of revs. Its been years since I rode a 4 cylinder bike so partly the 'hesitation' might be that I am more used to big twins with low-end torque? The bike still smells as if it running rich.

All in all a pretty good mornings work though

[JamesH]

Mike - not sure if this is a red herring, but I've had a 'slow to return to idle' situation on a couple of bikes in the past; both occasions turned out to be a 'sticky' ignition mechanical advance/retard mechanism. Have you cleaned/lubricated the advance/retard cam that sits behind the points plate?

[Oddjob]

I should have said to do this but TBH I sometimes presume that people know things when they don't. I always recommend when setting float heights to actually check the fuel is being shut off when the float reaches the required height. To do this you need to leave the float bowl off, connect a fuel feed somehow, maybe even connect to the tank and do it by the side of the bike. Then using the same float gauge you used to set the float lift the float up whilst the petrol is turned on, a small bowl under the carb is recommended to catch the petrol. Slowly lift the float using the gauge and it should stop the fuel when it reaches 22mm or whatever the fuel level is on your particular bike. Do this for all 4 carbs. At least that way you are making sure the fuel is actually being shut off and can avoid yet another carb demount because it isn't a lot of the time. Clean the float pin, polish it if needed, make sure the float moves easily. Check to see the pin isn't bent.

Good shout on the advancer James, always worth a check.

I'm not over keen on bench syncing carbs TBH, most times people set the gap too big and wonder why the bikes revving it's nuts off, hence why I asked if you had gauges, I prefer to set mine so as you just move the butterfly you can see a really small gap at the bottom on all 4 slides, you can then lift them all the same amount with the idle screw on the bank if required. With gauges you can get them spot on after fitting.

[Mike_Berkshire]

I don’t have gauges but now the bike is running reasonably well I can set the timing using a strobe light and get someone with vacuum gauges to accurately set the carbs up.

I have previously checked the advance mechanism and it was fine.

I set the carbs so that as you say the sliders are just opening-vacuum gauges should enable me to fine tune from there?