SOHC.co.uk Forums > CB500/550
Ongoing PD46 carburettor woes (possibly)
philward:
I agree with K2-K6 ref the maybe a duff lead. I had a break in a lead and worked fine most of the time but on start up and initial slow running, run intermittantly on that cylinder. New coil/leads and instantly cured.
K2-K6:
Appears that you've got the response needed.
Although not absolutely conclusive, it certainly is most of the way to confirming that the HT supply to number 1 is compromised intermittently.
The carbs just seem to work as they should with the response you're getting with mixture screw etc. Your diligent cleaning here seems to have payed off.
Coil 1 and 4 obviously fired by same points so low tension triggering not suspect, but route out from coil down to #1 would be the definite location. If original coils they are extremely reliable, but certainly not infallible.
Wouldn't be a surprise to see it come back though if it's just got it by moving the leads around.
The fact it "chuffs" now and again when cylinder 1 wasn't firing shows fuel is present in the combustion chamber, just unlit and passes into exhaust to be later ignited.
keithtraffic:
Thanks for all the help - took the bike out today and generally ok, but did again develop a little chuffing and reluctant No1 after stopping for a while.
I agree tick over at 1800 is definitely too high. I thought the proper figure was about 1000 according to the shop manual?
I have looked at replacement coils and plug caps and they are pretty expensive for original types - over £100 each with VAT for the coils and the plug caps are another £25 each.
David Silver has repro ones at a more palatable £30 + VAT for the coils although they don't seem to be handed (same one for both the left and the right side as far as I can see) - has anyone had experience of these?
deltarider:
--- Quote from: Oddjob on June 14, 2020, 03:30:48 PM ---... the 600 was to show that with an engine in fine fettle they will go much lower...
--- End quote ---
You beat me. Once I was able to have it idling at 800. Not that I recommend it. You want that oil up there. Most bikes of that era wore up there, not at the bottom.
--- Quote ---I'm toying with the idea of changing the HT leads to red instead of black, they'll match the NGK caps and look a little different.
--- End quote ---
Long time ago I went for silicone HT leads and dito plugcaps. Great stuff. At the time there was yellow only. Now even Louis has black.
JezzaPeach:
Hi Keith. Not that you need to but I’ve used a small right-angled Torx bar with a JIS or Philips driver tip to undo all bowls and remove/clean the main and idle jets with a set of abrasive wires/brushes off eBay, but fiddly!
Re the coils cylinders 2&3 had been slower to warm up.
I bought DSS copy coils and just needed to fit female bullet connectors to I think the yellow adapter leads. There is + and - so note. They then fit fine. Cool screw mounts 11cm apart unlike a set I bought on eBay and returned.
Old ones screws tight to undo. A decent JIS T bar driver useful.
Might be possible to recoup some £ by selling the old coils for refurb.
Other issues, a faulty no 2 plug of all things. Have replaced all plugs with non resistor ones, replaced plug caps with NGK resistor ones, and all working well. CB500/4 K1)
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