SOHC.co.uk Forums > CB500/550

Ongoing PD46 carburettor woes (possibly)

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keithtraffic:
Thanks everyone for the feedback.

Have been 'playing' a bit today to see what happens. I adjusted the idle screw all the way in and then unscrewed it (as suggested by K2-K6). All the way in and No 1 cylinder pretty much stalled but it did pick up as I unwound it (which I think is as expected). I did find that unwinding it too far also seemed to cause the cylinder to get very erratic. I am not sure if I expected that to happen - is that how its supposed to work? Anyway I returned it to 1.5 turns out.

However things do seem to have 'calmed down a bit and I can get the engine to run with all cylinders seeming to be working - at least they are all getting hot! The tick-over is a bit high - 1800 rmp and the engine still doesn't seem particularly happy at a lower tick-over.

I am inclined to take it out for a run and see how things go.

What are the options for changing the carbs to non PD types - is that a viable option?

K2-K6:
That's exactly how it should work if the idle circuit is clean and operating correctly.

You should be able to take it from too rich to run well all the way to too lean to again prevent good running. Tentatively, that appears to show the carb as ok.

Unless you've already tested it,  I'd test and record compression for each cylinder next.

Reality check also for carb sync,  have you set them with a bench method otherwise referenced on the site?

keithtraffic:
I don't have a compression tester (yet!).

Is there a good one that comes 'recommended' Having watched a couple of videos on this it seems that the 'best ones' have their pressure valve close to the cylinder?

The actron cp7828 which was recommended in the video I saw seems pretty expensive from Amazon - nearly £80!

K2-K6:
This one should work ok,  but you'd ordinarily need to hold it in the centre cylinders while someone else turns it over for you as it's contorted to do both together.

https://www.mandp.co.uk/products/compression-tester-push-in-type-594478

Usually they have a schrader valve in the end that you push to release, also you don't have to screw anything into the plug threads as some of the kits don't have the correct thread pitch!

keithtraffic:
Hi All,

Will need to think about the compression tester, but took the bike out yesterday to see how it performed.

Despite previously reporting that things had settled down and I could achieve a smooth tick over, albeit a bit fast, went out to the bike and started it up and again No1 cylinder was not really firing. Nevertheless decided to give it a run to see if things improved.

The throttle response was initially was pretty sluggish until about 3000 to 3500 revs and then things picked up and the bike really accelerated - like a bat out of hell - actually much better than I remember it (which could be the result of the carb rebuild and also getting the timing correct?).

After a good blast it did seem that No1 cylinder was running OK but then I stopped for a while and when restarted No1 cylinder was again not really running properly.

I am getting the feeling that this is still something to do with carburation but as mentioned before I really don't want to take the carbs off again if I can avoid it. So apart from compression is there anything else I can do as a diagnostic before committing to removing the carbs again?

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