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BCDD removal

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If it's working properly, leave it alone, but if you can't get it to work right with adjustments and you can't find a good replacement, take it off. I plugged mine and all is fine.

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I am slowly putting everything back together and would like to eliminate any future headaches. It did keep a high RPM for about 5 seconds when I came to a stop. So it's going in the "extra parts box". Reading old post from SEARCH is nothing like 1st hand experience. Thank you all for your replies.

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I was able to remove the BCDD from my throttle. I made a cover plate and screwed it on, with a little RTV sealer. I needed to verify which of the vacuum tubes went to the little hole in the throttle throat for the distributor vacuum advance. I haven't been able to tell what effect having the BCDD solenoid unplugged has on the engine's operation.

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Only remove the BCCD or other emissions control devices if you have SOLID evidence they have failed and/or negatively impacting the operation of your vehicle. Theoretically all the BCCD is going to do is cut fuel while your engine returns to idle as you coast or engine brake down, also preventing backfires. That's a good thing, a single backfire can destroy your AFM. And cutting fuel when the engine isn't supplying power saves fuel. There's simply no real benefit to removing it unless it has failed in some way. Instead learn how it works, test it, read the Datsun fuel injection manual on adjusting it IF you think it's misbehaving, (manual available online as a .pdf) and in general LEAVE IT ALONE unless you have a valid reason to remove it.

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I disagree:

Per the FSM, it doesn't affect the fuel delivery.

There is nothing "theoretical" about the device.

The purpose of the BCDD is to let a little extra air into the intake manifold when you let off the gas, while coasting, to keep the mixture a little more even, so the engine doesn't pass a puff of unconsumed fuel out the tailpipe.

See attached. Page EC-5

post-2169-14150818862447_thumb.jpg

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So far, the removal of the BCDD hasn't affected the engine's operation in any bad way. We still need to check how the vacuum advance is working, as it gets the vacuum through the BCDD. Otherwise, there aren't any vacuum leaks.

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It means the BCDD adjuster wasn't frozen like most of our's are. He turned the screw on the bottom of the BCDD per the FSM.

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Yeah. It would keep a high idle for too long. I turned it clockwise 1/2's at a time until it would fall about 500rpm to idle when I push in the clutch pedal. So now it hesitates at 1500 to 1300 for a second then falls to 800 or 900.

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We still need to check how the vacuum advance is working, as it gets the vacuum through the BCDD.

I am 99% sure that the BCDD and the distributor's vacuum advance are not tied together. The distributor should be connected to its own ported vacuum source, on the throttle body.

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My deletion of the BCDD was successful, there are no vacuum leaks, and the distributor's vacuum advance is working correctly.

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Good to hear. Do you still use your dash pot? I took mine off for a short trip and didn't like the clunky feel while changing gears so I put it back on and found a small screw under the white cap for adjusting. It was holding my RPM's up about 300 more than idle so I had to pull the pedal up with my foot to bring it back down. Now it barely touches the linkage stop at idle. I've just about de-bugged everything finally.

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Thank you, Mr. Blake, I didn't know that.

Is the mount for the dashpot of any use otherwise? It just seems to occupy space, and can probably be removed. I wonder why I didn't ask while I was servicing the throttle body.

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As a summary, the BCDD was removed, a block-off plate was made and attached (with some RTV sealer and screws) and the distributor's vacuum advance was connected to one of the small tubes that are coming from the bottom of the throttle (test which works first.) I was considering drilling out or enlarging the vacuum hole in the throat, but I think you don't really need that much vacuum to operate the advance (for most driving types) so it was left as-is.

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As a summary, the BCDD was removed, a block-off plate was made and attached (with some RTV sealer and screws) and the distributor's vacuum advance was connected to one of the small tubes that are coming from the bottom of the throttle (test which works first.) I was considering drilling out or enlarging the vacuum hole in the throat, but I think you don't really need that much vacuum to operate the advance (for most driving types) so it was left as-is.

Do you happen to have a picture of how it looks now? I'm thinking of doing this myself if it is possible.

Thanks

Jan

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