SOHC.co.uk Forums > CB500/550

Ongoing PD46 carburettor woes (possibly)

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Bryanj:
Use it regularly or those carbs will be off again

deltarider:

--- Quote from: keithtraffic on July 04, 2020, 05:50:14 PM ---... albeit still a little high at 1400 - 1600 revs... but I guess I still need to set up the idle adjustment properly ...

--- End quote ---
Verify the RPM with a true tacho. I once worked on a K3 and couldn't achieve a nice idle. Then I connected my automotive DMM. Guess what... a true 1000 RPM showed 1400 on the ND tacho. No wonder that when I tried to dial the RPM down to a 1000 on the onboard tacho, it didn't run well. Not saying it is also with yours, but I'd check it.

JezzaPeach:
That’s very interesting about tacho accuracy, it would explain a lot. 
PS re jet etc cleaning I found these pretty good, and used a mini bit holder in situ on the bowls, with some contorting (mini rachet on order)

Bryanj:
Carefull with the wire thingies the pilot jets have a sort of cast in spider for some reason, maybe to atomise better?

K2-K6:
"I am sure I have seen some guidance on the forum for how to do that properly but can't find it now - does anyone have a link to the relevant thread?"

From a Honda manual,  set the adjustment screws at recommendation for turns,  warm bike to stable tickover off choke, then turn screw on one carb anti clock* and observe engine revs rise (this is where the accurate tachometer comes in) you should reach a peak revs after which the combustion will start to get worse if you keep going. Turn screw back to "peak" revs and then keep going until you see a 100rpm drop ( because you've made it richer) and that's the final calibrated position for that carburettor and jet.  ie. You are getting it set to juuust slightly rich of the leanest burn position.

Now adjust the overall tickover with the manual single screw if the revs are too low or high,  then work individually through the remaining carbs one at a time.

This routine gives ultimate parity of tick over setup as you'll have just created the same combustion level bespoke to each single cylinder and it's associated carb.  The number of turns out should now be recorded as a baseline setup for your bike.

* some carbs are opposite depending if the idle mixture screw is located on engine side of throttle slide or airbox side.

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