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Re: BCDD Adjustment and Bench Testing

Subject: Re: BCDD Adjustment and Bench Testing
by NoferTrunions on 2022/4/24 17:07:53

ddgonzal: Thank you so much for the BCDD pages from the engine manual

My DCH-340-12 has the solenoid.

Mine was working last time I rebuilt the carb, now it is not working - it does nothing.

I seem to recall the adjusting screw was similar to the idle screw: turning it CW resulted in more hang. ALSO gently pushing the adjusting screw is equivalent to turning it in (CW) - you can feel the servo action on the diaphragm. Currently nothing happens no matter how I adjust screw.

It is my understanding that when the solenoid is energized, the BCDD is turned off.

There are articles about how to keep solenoid energies to completely disable the BCDD.

To disable, why not remove the solenoid plunger which appears to be a needle valve that is opened when energized

Last time I rebuilt carb, I wanted to disassemble the BCDD to check the diaphgarm (is there just one? cutaway drawing is too complicated) but I aborted because I was afraid that I would tear the diaphragm trying to separate the housing halves - the diaphragm adheres to the sealing surface with great force. If one HAD to remove, perhaps heating with a blow dryer would help separation.

I think I'm going to try to bench test my 2 spare BCDD's before I rebuild the carb.

NOTE: the Tomco 5321D kit is amazing - has 4 air horn gaskets including the one I need that I have NEVER been able to find in a kit. Talked with Tomco and they consolidated kits that varied by only a gasket of two reducing the typical kit inventory of 600 to 200. So the 5321D is the Gold Standard in my opinion. AND the gaskets and needle/seat are alcohol resistant.