SOHC.co.uk Forums > CB500/550
Ongoing PD46 carburettor woes (possibly)
deltarider:
--- Quote from: K2-K6 on July 05, 2020, 12:07:49 PM ---... From a Honda manual...
--- End quote ---
What manual is that? It's probably a good method for a 2 cylinder engine. For a 4 cyl. I have my doubts...
Bryanj:
Its in the 750 F2 manual that has PD carbs, not sure about the 550 K3 supplement
K2-K6:
--- Quote from: deltarider on July 06, 2020, 08:11:28 AM ---
--- Quote from: K2-K6 on July 05, 2020, 12:07:49 PM ---... From a Honda manual...
--- End quote ---
What manual is that? It's probably a good method for a 2 cylinder engine. For a 4 cyl. I have my doubts...
--- End quote ---
From a CB 750 "shop manual" dated September 1970 , also still in last CB750 K8 / F2 shop manual too. Both official Honda directions for their technical support.
It's something that's effectively been extended into most fuel injection (both diesel and petrol) systems that evolved, ie. The individual setting of each cylinder demand by calibration of it's slow speed circuit to equal the combustion effort across all pistons. Mostly it's done on the fly currently by monitoring the pulse time of the individual power strokes via crank sensors, and then altering fuelling parameters for the next firing of relevant cylinder to produce smooth idle speed.
The philosophy is the same just faster and more resolved.
In the last 750 sohc manual, it describes this routine as one done at the factory and should remain as a datum point for running the engine. It accepts that the adjustment screws don't have to be an even blanket setting to achieve combustion parity.
Essentially it's saying you can't get an accurate enough setting from the tolerances within the idle circuit just by observing the physical screw position number of turns out from base. In deferring to engine rpm it gives you what you are chasing, even tickover and best combustion parity at that speed from a true calibration routine. :)
It really is the icing on the cake of smooth tickover, which is not vacuum balancing. That doesn't have the resolution to do what this routine does. Although it is a prerequisite of this one that the carb slides are previously set correctly.
deltarider:
The method itself makes sense. I recommend an analogue tachometer that shows say 40 rpm increments.
Also realise that CB500/550s with old style Keihins need a relatively rich idle to facilitate a good driveability in the lower region, at least in my experience. The K3 is a different story.
JezzaPeach:
Bryanj yes I think some models have a gauze or something built into one of the jets.
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