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CB650 carbs

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Nurse Julie:

--- Quote from: Raymond_Y on April 04, 2019, 11:01:56 AM ---What is it specifically people don’t like about PD carbs.  Is it just that they are a bit more difficult to set up accurately, because they are a “lean” carb to meet emissions regs?

Raymond

--- End quote ---
They are a pain in the arse if the bike is not ridden regularly, ie, daily. They need constant fiddling with. Best place for them is the USA or in the bin.

matthewmosse:
I loved my cb550 carbs. Mpg especially on motorways was pretty good, Fort William across the A9 then down to nearly Whitchurch, Shropshire on a tankfull one time - could be s frugal beat

K2-K6:
As above,  not liked because they have very fine jets and air passages to get clean if not running. Some have pushed in jets too, making routine dismantling and cleaning harder than straight screw in types.

However, the jetting strategy is a better way to run an engine in pure, pedantic accuracy terms. They are referred to as lean burn,  but really they are more towards optimum fueling for constant running with accelerator pump facilitated extra fuel to accelerate when needed. 

"Conventional" carbs have to be run richer than ideal constantly to make sure they don't go too lean on snap throttle opening,  in effect the inverse of PD carbs.  Effectively running too rich under most light load conditions and resulting in more unburnt fuel passing through the engine.

It seems odd to say it,  but most advancement in engine oil condition has come from running jetting leaner so that less unburnt fuel is washed past the rings to dilute the oil.  It also impacts exhaust life too, with the liquid deposits containing significant acid concentration the more fuel is left unburnt. That should be of concern to those running new sets of four pipes on these bikes given the cost they are, along with limited mileage. None of the pipes being in any way protected from corrosion internally.

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