Re: Walbro carb

Posted by jdemaris on December 02, 2005 at 05:48:15 from (69.67.229.76):

In Reply to: Walbro carb posted by CH (upstate NY) on December 01, 2005 at 16:53:27:

I could tell you whatever you need to know about the carb if you give either the carb. or saw model. Usually, Walbro and Tillotson give adjustments specs. with the kit, though.
The needle arm adjustment should be self-evident anyway. Depending on the carb model, it is either set flush with the carb body next to it, or flush with the gasket surface where the cover bolts on (one bolt for small carbs and four bolts for large ones). Gasket goes against carb first, then diaphram. And yes, the kits come with multiple gaskets etc. depending on their application.
Most of the time, when a chain saw acts as your's did - the carburetor is blamed but is not actually the problem. Two-stroke engines are highly dependent on several conditions that four-stroke cycle engines are not. And, this also depends on the type of fuel-charge system used by the saw - there is "roto-port", "reed-valve" and "piston-port" just to name a few. Most modern chain saws use reed-valve or piston port. If there is any wear on the cylinder wall or piston, or a reed valve is broken, or any of the crankshaft seals leak, etc. - the saw will not idle correctly and not rev. up properly - and in general - run lean.
Any good chainsaw mechanic - if the correct tools are available - will pressure test a saw first, and if the crankcase holds pressure - then pull carb. and muffler off and inspect the piston and cylinder for scoring. Usually, if there is damage, it will be most evident near the exhaust port. If it IS scored - no carburetor will make it run better. If the crankcase will not hold pressure, fuel from the carburetor will not have a way of getting delivered to the combustion chamber. Most often, with chainsaws with leaking crankcases, the problem is the crankshaft seal on the sprocket side.
And - as already mentioned, these carbs have internal vacuum operated fuel-pumps. On some saws - like mid-range Stihls, there is separate hose that connects the fuelpump in the carb. to the engine crankcase. If it breaks - #1 you will have a big crankcase leak, and #2 the fuelpump will not be hooked up.

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