Topic: 1971 CB500 running lean after carb clean

[drj434343]

Hopefully I won't get too much grief for my order of operations.

I had old varnished gas in my CB500, enough so that 1 or 2 of the floats stuck closed and I couldn't get the bike to idle correctly.

I removed and disassembled/cleaned the carbs.  This included the idle and main jets and float needles.  Got everything cleaned up and reassembled.

The bike starts on the first crank and runs, but seems to be running really lean.  Only runs with the choke applied, and even then I get slightly sluggish throttle response and some minor lean popping.

I didn't touch any of the carb settings when cleaning, and the bike ran perfectly prior to the old gas.  Short of doing a full stage zero on the carbs, I'm hoping someone can chime in with perhaps something I may have done during cleaning and reassembly to affect the mixture so much.

[robvangulik]

Did you remove the Idle Mixture Screws, and blow the passages behind that with carb cleaner and/or compressed air? The idle jets may be clean, but if those small passages are (partially) clogged fuel still won't get where it's supposed to go....

[drj434343]

Yes, removed the screws and used copious carb cleaner everywhere.  Perhaps not enough?  Are they notorious for clogging?

[Deltarider]

The easiest first. I don't know if you had the carbs removed. If so, are you sure fuel lines (the right dimensions ofcourse*) are fitted well, without useless inline fuel filters, so fuel can reach the floatchambers unhindered. In other words: check fuel level in the chambers.
* 18 and 30 cm length resp. with an ideal inside ⌀ of 5,5mm. Later model fuelcock (the one that has no bowl) requires 17 and 28 cm resp.

[drj434343]

All other things, including fuel delivery remain unchanged.  I'm trying to focus on what I may have changed by removing the carbs for cleaning.

Is it easier to remove bowls, floats, and idle screws and blow with compressed air from the bottom?  Removing the carb assembly as a whole was a PITA.

[Deltarider]

Is it easier to remove bowls, floats, and idle screws and blow with compressed air from the bottom?  Removing the carb assembly as a whole was a PITA.

For me it is, but that's after I had the carbs on the bench before. That made me familiar with what is inside and what to expect. What helps a lot, is to have the 16 crossheads replaced by allen bolts (see pic below).
With the bowl removed, you can access and remove:
main jet and spring leaf,
Just wiggle and pull downwards. Examine tiny O-ring on main jet. It should seal well. Renew when needed.
float and its swivel pin,
When you cannot extract the pin with your nails, you may use pliers, but do not pinch the pin. Careful, you don't want to damage the towers! Have your hand cupped under the float whilst removing the float, because the float needle above it, will drop. It is tiny and easily lost.
If needed - normally not - float needles seat,
slow jet
loosen with small screwdriver sideways in slot and then unscrew with your fingers
needle jet
Simulate full throttle which raises the needles. Often the needle jet (aka emulsion tube) drops down. When not, maintain 'full throttle' and insert wooden toothpick or whatever from below, cant it and wiggle the jet out. Squirting some WD-40 in there may help.
For cleaning - if needed at all - I use a can of carb cleaner and one of compressed air with a straw and some copper wire. That's it.
I should add that this method works when bike has run, let's say, at least once a year. When bike has sat for years, it might be better to remove the rack in total.

[jc914]

Taking the carbs apart is not as bad as it seems.  It took me a couple of hours to changed the needle position, swapped out some jets, then reassemble.  Check out Youtuber, "Classic Octane" he posted a hour + long detailed video on how to clean out a CB500/550 carbs and assembly.  Remember to clean out the emulsion tubes and bench sync afterwards. 

[drj434343]

I want to post a follow up because I fixed this issue.  It took several uninstalls and tear downs of the carbs, but I figured out that 2 of the idle jets were completely blocked and 1 was partially blocked.  I was only able to determine this by setting up a back light through the bore and using a magnifying glass.  No amount of soaking in carb cleaner, mineral spirits, or even acetone overnight did the trick to clear the idle jets however. 

Eventually with a bit of googling, some old guys on another bike forum suggested 50/50 Pine-sol and water.  Five minutes of soaking in that and all 4 idle jets were clear and it ran like new!

[123 Four]

Had the same problem this week on my 550 f. After cleaning the carbs the bike was only running on 3 cylinders an idling badly. Idle jet 4 was fully blocked so cylinder 4 was not firing and at least One other idle jets was a bit clogged, too.
I have used a slim guitar string to get the dirt out and now the bike is running way better. Tomorrow I will buy some engine/ carb cleaner and add it to the gas to take care of the rest. Hope that will be enough to get my season started.
Cheers