Honda-SOHC

Small update:

Bike runs fine from cold, for about 2-3 minutes. Then, once warmed up, the erratic idle starts showing. I have (abundantly) sprayed carb cleaner on intake manifolds with no change at all, so for now I tend to exclude an air leak as I could not find any evidence of it (and both rubber intakes and manifold o-rings are new).
I keep on thinking it could be something in the timing (or rather advance mechanism springs, maybe kicking in too soon) and/or unbalanced carbs (only bench synced visually, with a drill bit).

Maybe I'll start playing with the spring combination again, after all I am keeping the original ones as they are and just adding different ones, so anything I do can be undone quite easily.

Cheers

Michele, a long shot, but is the petcock gauze clear. I had erratic fuel flow and cleaned it in vinegar and very gentle brush with an old toothbrush. Then a column of water from a tap would pass freely through it uninterrupted.

I find even when all clean, fuel often only manages to flow through one pipe at a time, so eg from empty, carbs 1&2 and 3&4 don’t both get full flow at the same time, and maybe a slight restriction could cause flow to fluctuate.

As I say very much a long shot, but quick and easy to check, and always good to know it’s ok.

Hi Jeremy, that has been one of the many things I have tried in the past. I have a new petcock filter (the one inside the tank), but I must admit I have not opened the petcock as it's not one of those that can be opened via a couple of screws. Petrol flow seems fine and constant though (I have observed while filling a bottle straight from the petcock) and I have a new fuel line, with no kinks and no inline filter.
I have therefore eliminated this as a possible source of my problems.
Cheers
Michele

Remove the resisted plugs and fit non resisted (D7ES or D7EA) . You only need resisted plugs fitted if you have non resisted plug caps fitted. Too much resistance weakens the spark. I don't think it will solve your problems but having both plugs and caps fitted with resistors won't help.
The DR7ES were the standard fit with the metal, non resistor caps, which were changed at PDI usually (well, thrown in the bin as I understand it).

A-ha! that is useful info indeed, I had not realised. Well it may not solve this problem, but it can't hurt and it is more correct. In fact from older pics I can see my bike came with D7EA, so I must have bought DR7ES just reading old specs around.
Thank you Nurse Julie!!

Update of the day:
Just before thunderstorms hit (although it's still well sunny here) I decided to have a check at the timing.
-Points gaps were at 0.3mm and 0.35mm, so I made them both 0.3mm now.
-Static timing is spot-on for 1-4 and 2-3

I have tried using my strobe but the idling seems too unstable that I am not sure about anything, so I have not tried to adjust anything. I will try again just to see if I notice it being too far advanced at higher revs, but from first examination it does not look that way. It may be that it advances too soon though. I have tried in the past to use different spring combos in the advance mechanism but never really solved anything, so I reverted to the original setup (I was probably jumping the gun anyway).

Here's a video I shot today, just to give you an idea of what it sounds like when idling. Note that unless you see my hand on the throttle or idle screw, she's doing everything else by herself!

https://youtu.be/ESx_E8mv2vM

Carbs are standard PD46A with. standard jetting, This may not be ideal for the Delkevic 4 into 1 the PO put in, but it should not give problems when idling

As suggested above, I will try spraying carb cleaner on and around the inlet manifolds to check for air leaks there, but I have new manifods and o-rings so I doubt it will be that.

To help in the interim,  it's sounds possible from your above observations that you may have a  cylinder not firing.  The points each run two cylinders so if either is a problem you get both from that supply stopping and it's even hard to pull away,  so doubt if it's that.

More likely it could be just one.  If you start it from cold and run for about 20 seconds,  switch off and then feel each of the exhaust pipes youll tell if you've a cold one ( that will feel more like the "something stuck in your throat" you describe) if that's the case then ordinarily you're looking at a fault of the HT part of the system from coil through plug cap to plug itself as initial suspect.

Anyway,  post how you get on and shout if you wish to have help.

Thanks K2-K6, all 4 are firing, I check by default every time I run the bike for 20 secs or so as I did have that problem in the past (but it was carb related).

Hi guys,
I've been chasing gremlins (and possibly ghosts) on my 1977 CB550K3 ever since I got it 20 months ago. Done very little riding (almost none), lots of tinkering, got burnt by a mechanic that did some things right and some other he messed up completely, I cleaned the carbs several times, changed spark plugs and caps, air filter, manifold o-rings, new condensers.....basically everything I could think of that could cause my problems.

Aaaanyway, with 30 years of Vespa riding, I am a novice when it comes to Hondas. I have a great passion for mechanics and I believe I have done all I should have done so far (mostly a 3k tune-up) to a decent level, BUT, I have nobody to be able to check that for me, so I may be chasing my tail forever.
The bike starts fine, just a little choke, and idles ok, but as soon as it warms up (2 mins or less) the idle fluctuates, with no input from me, between 1000 and up to 3000 rpms. This is a great improvement to what it was as it used to shoot up to 5k and would hang in between gear shifts, which made it unridable.

The battery is fully charged....but then again, I am not riding this often at all and have recharged several times, so it may well be the battery itself giving me problems, but I need to eliminate other things before I think about replacing that.

The last 2 things I "believe" I need at this point are
-Timing set with strobe light (I have done the static, but assuming the advance mech. springs may be a bit weak only the strobe lamp will shed true light on this (sorry, this is a terrible "dad" joke....my kids would be ashamed)
- Carb sync: I have the necessary gauge tool and I have watched several videos on how to, however I have never done before and I don't have a proper space to do it (without annoying a few neighbours...)

My question to the audience:
Anyone in North London area (I am in N5) who could help me with these last 2 tasks? I have an old strobe light and the gauges set for the sync, but never really used them before and I would appreciate an expert and watchful eye from a more experienced member.
I tend not to trust my bike too much (it's probably all in my mind) and I am weary of getting stuck on the side of the road, but there are worst things in life and I will of course travel 10-20 miles to reach you.
I will also wear a facemask and keep social distancing, needless to say.

Anyone available around here?
Alternatively, anyone knows a good mechanic around here who would do it (and knows how to) without skinning me alive?

Cheers
Michele

[Edit]
Went for a short ride today (4 miles, city roads) and I have a feeling the bike is not as sharp as it should be, it feels it can't get all the power out (and I am just opening the throttle in 1st, 2nd or 3rd) a bit like when you have something stuck in your throat and your voice's not clear.
So, re-checking points gaps and timing (will try using my strobe light) will be my priority this week.
Any other suggestions are welcome, as I said, I have no real term of reference in my experience....

Thank you guys, but my grab rail has no mountings for the indicators (they must have snapped off as 2 holes are there, you can see them in one of the pictures I have posted.
I'll see if I can find any kind of clamp that may do the job. Something like this may work
https://www.amazon.co.uk/dp/B07L4RM9DS/?coliid=I16V898LLHPKQ7&colid=1NS5EFPD8B8IA&psc=1&ref_=lv_ov_lig_dp_it
but may not be pretty.....

Hi ..Not sure I was looking for 500K0/K/K2  627B  carbs myself, which is why the guy brought them for me to look at but they were deffo stamped PD on the side. I did put David onto them (see baove)  so you need to ask him if he has contacted the guy at all.

Thank you Ash, I have just sent Dave a PM