Carb Needles
- Thread starter benelli7d
- Start date
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The screws regulate the fuel flow on most carburetors. There are also some BIS (balanced idle system) carburetors were the adjusting screw regulates some airflow.
This will get you started
Thanks, I've seen it both ways over the years and I just wanted to make sure what I was dealing with here.
That helps a lot! I'll definitely bookmark the attachment. Thanks. I knew you guys would come through with the good info.
You're welcome.
It's a PDF just download it. I have a folder "saws" , with sub-folders,,,,,,,,,,,,great to have all the IPLs/Shop manuals and such for all your saws.
028S038AV
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Thank you for the Walbro Service Manual
How carbs work....
Now you have some of the names/pcs of carb.... can search on youtube and will find lots more info.
The Carb Venture, the large smoothed hole thru carb is the "air flow regulator" so we match the Venture Size Hole to the cc of the engine. WE need a certain air flow thur the carb for it to work well. The vacuum generated on the piston side of carb is what pulls the fuel thru the carb. Like the wing of plane, the cylinder side of Venture, gets larger and creates vacuum on that side & sucks fuel in the air flow.
True for cars, saws, motorcycle, lawn mowers. That is why we have to size the carb for the cc of engine. Next time you have carb in hand.... look at the throttle plate, see the 2 small holes, when the throttle plate just breaks open, the small holes exposed (transition circuit). Those little holes can hose up your low idle efforts if the throttle plate does not close all the way.
Throttle plate closed, the idle circuit supplies fuel, when you open the throttle plate, the main jet is for running, put the idle circuit kick in some of the fuel needed to run. "Run Fuel" is the main jet & idle jet
How carbs work....
Now you have some of the names/pcs of carb.... can search on youtube and will find lots more info.
The Carb Venture, the large smoothed hole thru carb is the "air flow regulator" so we match the Venture Size Hole to the cc of the engine. WE need a certain air flow thur the carb for it to work well. The vacuum generated on the piston side of carb is what pulls the fuel thru the carb. Like the wing of plane, the cylinder side of Venture, gets larger and creates vacuum on that side & sucks fuel in the air flow.
True for cars, saws, motorcycle, lawn mowers. That is why we have to size the carb for the cc of engine. Next time you have carb in hand.... look at the throttle plate, see the 2 small holes, when the throttle plate just breaks open, the small holes exposed (transition circuit). Those little holes can hose up your low idle efforts if the throttle plate does not close all the way.
Throttle plate closed, the idle circuit supplies fuel, when you open the throttle plate, the main jet is for running, put the idle circuit kick in some of the fuel needed to run. "Run Fuel" is the main jet & idle jet
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