Honda-SOHC

Carbs are sync'ed manually using individual cables Nigel. No provision for use of vac guages (that I know of anyway) like the fours.

'Possibly look at opening the static tickover rpm to lift it slightly, then make idle circuit richer to calm it down, that can give better "quenching" of throttle shut idle establishment.'
- Just going out now but will have a go at that tomorrow

Are the idle adjustment within decent range when you set the screws ?
- they decrease revs when screwed in or out from 3/4 turn out setting - (3/4 turn out is half way ish from engine hesitation when screwed in or out) but not sure if thats a decent range?

Both sides of float same (checked for twisting). Idle jets defo clear and engine revs rise in response to the air screw being screwed in and out

Reference my similar issues to Ben's 350, I've eventually - after few hours off using a .35mm drill (that eventually broke!) and Ted's suggested wire brush wire method, cleared the slow running jet. Re-checked all passageways/jets and all clear. I also bought a cheap carb kit that included floats after comparing images with those on the advert to the one on DS site, they were the same - and they are rubbish! The pivot hole is 1mm too thick and the 'tang' on the float that prevents the float dropping too far (and the needle valve falling out) is missing. Bought the kit as it obviously included the slow running jet just in case I couldn't unblock the original. Didn't want to use a pattern jet but Honda item not available now - but luckily not needed.
Anyway, as the original brass 'bread bin' style floats had a small amount of petrol in them, I checked whether there was any obvious leaks, which there wasn't when submerged in jug of water. so drilled a 1mm hole in each float and allowed to drain over night on some kitchen roll. The petrol was stagnant and obviously been in there for some time. Soldered up the holes. Set floats at 19mm. Idle screws sync'ed and carbs sync'ed via cables. Timing/points re-checked and spot on. As per previous post, compression 160psi on both sides.
After re-assembling everything and starting the bike, the bike didn't need choke (cut out if choke applied) and generally running rough (sounds too rich to me). Also 'hangs' on returning to idle. Revs fine in middle and upper range. Although only warmed up and run in the garage, the plugs are sooty.
I'm wondering whether the floats are too high and causing rich running.
Also got a noisy tappet that I've checked as OK when stone cold (but going to check again). As these have the eccentric cams adjustment from the side of the cambox, I've adjusted the tappet in question while the engine is running and 'tap' only goes when the engine revs drop (clearly holding valve open). On rebuild, checked rockers visually and all looked ok - didn't check eccentric rocker shaft with a micrometer.
Thought I'd get your opinion before doing any further work (possible engine out again).
Thanks again in anticipation

Sounds like we are having identical issues Ben! My slow running jet just wont clear. It's been soaking in carb cleaner for 2 days. I've ordered a .35mm drill. As a back up, I've ordered some pattern jets (as genuine not available) as a back up. Also ordered some pattern floats.
Hopefully I'll have your success!

Welcome to the forum Rob. Right place for 550 help - loads of 550 guru's on here! Enjoy your resto!

Sent from my moto g(50) using Tapatalk

Further update Ben. Today I stripped the carbs and found a few issues! Found both floats had small amount of petrol in and R/H slow running jet blocked (hence the lack of adjustment on that air screw) - soaked in some carb cleaner but can't shift what ever is blocking it. I should of spotted it first time. Sent for some new float and slow running jets.
So maybe your lack of adjustment on your air screw is a blocked slow running jet?

Started up after actions taken in previous post - revs returning to idle better but still little response to slow running screw adjustment on R/H cylinder (and now no leak on intake manifolds) with misfire (pop) when slow speed screw backed out more than 1/2 turn. Should have checked that curcuit while I had the carbs off! I'll take the carbs off again and check the low speed curcuit for blockages - I'll feed any progress back Ben.
Also got a noisy tappit on R/H to sort when engine back to cold and strangely, the R/H silencer is far louder than the L/H (both new).

Had a day on the 350. Rechecked all the settings - points bob on but timing (using the strobe) altered slightly, fiddled with carb setting and much improved but still intermittently hanging before settling to tickover. When I was building the engine on the bench and when fitting the carb manifolds, I thought the design of using JIS cross head screws and a gasket didn't seem a good design. The last thing I checked today was for air leaks on the carb manifold to head (using the carb cleaner method) and there was a clear movement in the revs when carb cleaner squirted at the joint.
Just spent the night stripping and re-assembled using a slight skim of silicon sealant and hexagon bolts.
I'll report back tomorrow
As an aside, its taken me back 50 odd years taking the tank off (when I had a 250k) and that bloody awful petrol balance pipe that goes from one side of the tank to the other under the frame - you have to juggle taking the tank off while trying to stop petrol coming out of both sides - its a bludy pain! I have put 2 tiny inline taps on the pipe (and disconnect the pipe in the middle between the taps) but there is so little space, its more trouble than the standard pipe.
Coincidence that Ash posted the same thing at the same time!