Re: Idle under weight! w/ VIDEO!

Ben Subz /
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Hey Bill,

This is an awesome asset--Thank you!

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!

Thank you again

> 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

> idling.


> 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.

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