Nice to have a proper test/tool to figure out a mysterious carb.
I'll report back in a couple days once I work on this. So close to running properly!
> Bill Mazzacane Wrote:
> I have never tuned a PHBG 19 before, so below, I am describing how I
> tune other carbs with similar pilot fuel-air screws.
> From what I have seen, the PHBG 19mm has a fuel screw for the pilot
> circuit. The pilot screw is responsible for starting and idling. The low
> jet supplies the pilot screw with fuel, but the low jets actual
> responsibility is to control low end throttle response, not starting and
> There are 2 styles of fuel screws. 1). is a fuel only screw, that does
> not have any airflow added to the pilot circuit. Hence "fuel only." 2).
> is a fuel air circuit, and as the name implies there is an air-bleed
> somewhere up-stream from the pilot circuit. It is important to know the
> difference because they require different adjustments.
> I like using pilot screws to help determine low jet size by doing an
> idle drop test. Before you perform an idle drop test, the throttle cable
> must have free-play, the fuel level must be correct, a new spark plug
> (and gaped) and if the engine has points, the points must be clean and
> at the proper gap.
> If you have had the intake manifold off recently? was the gasket wet? A
> wet gasket is a tell-tale sign of a vacuum leak. When there is no vacuum
> leak, the gasket will be dry.
> With all the details I mentioned tested and ok, preset the pilot screw
> to a known rich position. Warm up the engine and set a low idle at
> approximately 800 rpm. Slowly turn in the pilot screw until the engine
> wants to die. Then kill the engine and finish turning the screw in till
> it lightly bottoms. Count from where the engine died, then reset the
> screw to that position and increase the screw by 1/2 turn out.
> For example: the engine felt like it was going to quit, so you shut off
> the engine. When you turned the screw all the way in, you discovered the
> screw was at 1/4 turn out when you shut off the engine. Reset the pilot
> screw to 1/4 turns out. Next you turn out the pilot screw another 1/2
> turn (to 3/4 turns out). Then evaluate the idle and throttle response.
> If the idle speed increased after the test, reset the idle to 800rpm and
> perform the idle drop test again.
> If the pilot screw closes and the engine remains running. Then the low
> jet is too rich. If the engine shuts off near 1/2 to 3/4 or more, the
> low jet is too lean, or some other problem exists.
> Bill M.
> If you get in the habit of using this test, you can use to determine if
> a vacuum leak is present, or how many sizes to increase or decrease the
> low jet.
> When rejetting a carb, always start with the pilot or low circuit first.
> And depend on good jetting habits or procedures, not spark plug color
> (unless you are using leaded gasoline).
> The circuit chart is from a late 70's Kawasaki technicians training
> manual for round slide carbs.