SOHC.co.uk Forums > CB500/550

550f running rich?

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DomP:
I agree with plugs out, I hate the idea of plug chops to tune a bike

K2-K6:

--- Quote from: McCabe-Thiele (Ted) on October 13, 2025, 08:24:25 AM ---
--- Quote from: deltarider on October 13, 2025, 08:11:15 AM ---I always use a T-handle and a 23 mm socket when cranking some millimeters a CB500 for timing. I estimate the risk of damage by removing the spark plugs far higher than cranking that WASHER, SPECIAL which, btw, is still the original... Things may be different with a CB750. I've seen more than once that problems that can occurr on CB750s, were bluntly transferred by experts to CB500550s.

--- End quote ---

Luckily in my case as it was an engine rebuild the plugs were still out from the head decoke.

I share your fears every time I take a plug out of an alloy head.

--- End quote ---

Take them out hot to avoid many problems ... makes a significant difference.

Recently in technical/advisor and oversight capacity  :) (son bought his first car) a significantly complex all aluminium V8 with plugs right down the end of long tubes, they seemed too tight and felt risky to me when he tried to remove them to inspect, bringing it up to temp through running and they came undone easily.

Although against advice from many manufacturers, I use a smear of copper grease on thread when installing.

DomP:
I got mt Trafic glow plugs out this weekend in the same way, I'm also a copper grease fan on threads but reduce tightening torque slightly as ive read it can cause inaccurate torque settings due so the slippy surfaces

exvalvesetdabbler:
A bit of a long shot but here goes..

On my 400 F I had rich running, tail pipe smelled a bit too much like the choke wasn't coming off.
After a lot of poking around and swapping carb internals it turned out that the emulsion tubes had  worn a bit oval internally where the throttle slide needles go. 

The other symptom was stumbling of and on the throttle at low revs and the adjustment of the pilot air screw made little sense. Plugs were a dark colour bordering on being sootey.

Put some new needles and emulsion tubes in and the problem disappeared.

Regards
Dave

The difference between old and new was visible if the needles were inserted into the emulsion tubes and rocked side to  side.

deltarider:

--- Quote from: exvalvesetdabbler on October 13, 2025, 10:51:35 PM ---[...]
After a lot of poking around and swapping carb internals it turned out that the emulsion tubes had  worn a bit oval internally where the throttle slide needles go. 
[...]

Put some new needles and emulsion tubes in and the problem disappeared.
[...]

--- End quote ---
This is in contrast to what I experienced the other day. For a silly reason - to be explained later - I had the carbs on the table. I closely examined needle jets and needles. On reassembly I accidently have mixed up jets and needles - so they were not the pairs they were before, and to my surprise bike runs nicely. The same accidental mix up happened to float needles and their valves and again: no negative effects. These parts have been in service over 140.000km. Makes me wonder what parts have been in your carbs: aftermarket or OEM and the same question to which parts you have put in now. 

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