idle jet differences , 069's

[Bryanj]

 The 500/550 respond incredibly well to getting the points gap and static timing spot on, this can be very frustrating to do but is worth getting spot on F with a 0.35mm gap

[fogrider]

Quite so. Mine ended up at .32mm which gave a dwell of 50%, done static then checked with dwell meter and the strobe and it's all now bang on. Just the carb synch to re-do since having the carbs to bits again. Regarding the timing, the F mark is at 5 deg. Very short for a hemi head.  I rotated the backplate until it ticked over best. That was about 12 deg btdc. As that would put max advance too high, I re-set the advance stops to 34 degrees, ( factory worked out at 33). It runs way better bottom end and starts easier. As they are fully advanced at 2500 revs, ( how much time riding less than that ? ) no harm can be done and it goes better, it was an experiment but I'm leaving it like that.
New plugs and a proper air filter should ,hopefully, make the final touches for perfect running.

 I still think the sparks are weak, ( pinky /purply ), work in progress, but the improved  smoothness makes it much more pleasure to ride.

[Bryanj]

As it is put in the trade " they are all like that sir"

[fogrider]

That's good to know - I can forget looking for the fat blue thing now !

[K2-K6]

Something strange in that you've advanced timing to improve starting. It's an area they are never usually compromised in and notable for just very easy instant starting.

Being a "hemi" or semi-hemi  as they don't use much piston dome at all, they don't seem to follow convention for that arrangement as recognized by other non Honda applications.  If static advance is producing better result then it suggests something isn't quite right as they don't generally need much spark "lead" to run effectively. Have you checked compression yet as that may give more insight.

Giving extra static advance will usually pull up the idle rpm on engines, which has to be countered by having the throttle slides lower to hold onto revs. It may give you an unexpected effect as you go from overun with throttle closed as it pulls raised vacuum against the slides that makes them harder to modulate in that initial phase as you try to bring the throttle back up on entering a corner for example.  You could see it just at that point in erratic off on effect.

[fogrider]

OK, it's not a usual thing to do, but it likes it, no side effects, just runs better. I think it confirms the mystery weakness at the bottom end. All 4 plugs are identical colours so whatever is causing that weakness is built in, not like one faulty carb.

I altered the slides to 2.2  from 2.5 and there is hardly any difference. I'm halfway through fitting the Lambda sensor and reader.  What that shows will be very interesting.

Next few days.........

[K2-K6]

It'll be interesting to see the results of AFR monitoring, I like investigative things to clarify what you are getting.

Flat spots are always going to be a "non burn" or partial of the combustion content, and usually too lean. Maybe getting close to 14.7 to 1 or just over during that acceleration phase.

The compression would add more to the analysis I feel, especially if it's stood for some time as the rings are often stuck on examples seen here.

Maybe worth running with the breather pipe submerged in a glass of oil too as they can suck air from crankcase on induction stroke to give unmetered air content in cylinder. It'll draw the oil into the cases if it's got poor sealing.

[fogrider]

Lambda sender fitted and have had a run about. When fully warmed up, stopped and read the idle, slightly rich. ( on return, I turned the air screws out to between 1 .1/2 to 1.3/4 turns out  from 1.1/4 which now reads right ).

Shocking to see that from even the slightest opening of the throttle right up to half open, the weakness was off the scale.
From half throttle on, goes well rich !          I had bought an aftermarket carb kit, fitted the float valves as mine were shot, left the idle jets in, left the needle jets/emulsion tubes in but fitted the new needles.  Fitted the main jets as they had new O rings on but were marked 98, whereas the old ones were 105.  From the results, I can only assume there is a serious discrepancy with those needles ( in clip 2 the same as original ) and there is almost no transition from idle to needles via the slides.
I'm sure the mains should be 98, had someone already put 105's in hoping to cure weakness ? or is it just the new needles ?  Carbs to come off again, old needles back in.  Test run again next week.

[Bryanj]

Afterarket needles are notoriousy inncorrect in both diameterand taper, clip position is usually middle and i thought mai jet was supposed to be 100

[deltarider]

His is an 'F' that had 98. Below an overview of the oldstyle carbs on CB500/550. Feel free to comment and/or suggest corrections.

[fogrider]

That's a useful chart, great details and part numbers, only missing the cutaway, mine are 2.5 for the 069a and genuine Keihins. Not sure about the others. 
Looked at the old needles, correct part numbers. I'll have a critical comparison of the aftermarket ones,  once I've got them out. Sincerely hope that that's it.
Regarding it going very rich top end, will have to check the hole size in the new mains, maybe they're duff too. If these latest changes cure it, I should be able to go back to standard ignition.

Had a belt around Notts and Lincs on the VFR for a day out, nearly 200 miles , a couple of great cafe stops, lovely cake in Tiggys in Epworth. Great ride out with an ex bike cop on his 1300 Pan.
Made a pleasant change from tinkering. 

[deltarider]

... only missing the cutaway, mine are 2.5 for the 069a and genuine Keihins. Not sure about the others...

All CB500/550s have the same slides/cutaway.

... Regarding it going very rich top end...

Expect to need 6% CO, to have it run right.
I don't know if you have the Shop Manual and in particular the CB550F addendum. They're here in a good resolution:  https://www.dropbox.com/s/88zdzlj8olqi8pl/Honda%20CB500_CB550%20%20Four%20Service%20Manual.pdf?dl=0
As for the various CB550 Parts Lists, they're all here: http://www.honda4fun.com/materiale-documentazione-tecnica/parts-list/parts-list-cb550
Just compare the engine- and framenumbers of yours with those listed in the first 4 pages to determine what goes for your model.

[deltarider]

Talking cutaways, what does this 2.5 refer to?

[fogrider]

The cutaway is the curve cut into the bottom of the slide. 2.5 means the cutaway is 2.5mm deep at its' deepest. The less cutaway, the richer will be the mixture at off-idle openings.
I went from 2.5 to 2.2 as an experiment only to find negligible difference.  Goes instantly weak off idle. I'm more used to Amals and SU's and they never do that, however bad they're set up. All very odd.

I expect I'm missing something totally obvious, but what ?

Carbs off again today while the sun's hot on the rubbers.

[fogrider]

Deltarider, thanks for the 2 references above. It confirms the slides are 2.5. One thing I noticed is a reference to a slow jet. There is'nt one on the parts diagram so presume it's a drilling. Must check that for size.
Carbs are now off (again ).
Have to be really thorough this time, especially the needles.