Qjet 7040205 Dash Pot

[Harold #43147]

Dash Pot

Terry can you send me photo? Is this part suppose to be on this carb 70 454 4 sp 7040205 Carb I have the one off the carb no # on it that I can see but the end is missing found a guy has one working order $50.00 I don't want to buy it if it is not correct.
Thanks Harold

[Terry M.]

Re: Dash Pot

Harold,
One can not send attachments through the email links on the discussion board. Click on my name to send me an email, and include your email address. The picture file is 225Kb, so if you are on a dial-up ISP it will take a while to download.
Yes, I have seen it on original 1970 454, and also on 1970 small blocks. The photo is of a small block, but the dashpot looks the same for either engine. Note I said LOOKS the same, I don't know if it is actually identical.

[Joe L.]

Re: Dash Pot

Terry-----

I'm "hot on the trail" of this now, but I won't know anything for several more days. This thing is really wierd. Without a vacuum connection I don't see what the "chamber" is for on the forward end. I suppose it could be intended to be some sort of "air cushion" but I just don't see how that would really work in practice.

I'm wondering if it is possible that this thing was added to some of the cars as part of a service campaign to correct some common complaint? It would have been very easy to add----just remove the idle screw and screw this thing in its place.

[Terry M.]

Re: Dash Pot

I'm not aware of any campaign related to idle in that time range. I thought it was emissions related. Engine will run rich when the throttle is suddenly closed -- fuel (being heavier than air) keeps going and air shuts off = rich deceleration condition, but I can't point you to any tech information to support that concept right off the bat.
We see so few unmolested Rochesters that it is hard to know how common this dashpot was. As I told Harold in one of the above posts, I have seen it on both large and small motors, and my best recollection is I have seen it more on early 1970 cars; but I would stop short of calling it an early feature. Just not enough examples to have a statically significant survey.
If someone has hosting abilities, I can send them the picture to post so we all can see this illusive creature.

[Mark #28455]

deceleration valve

I have one on the carb for my 1970 454 w/ ac car. I was told it was a "deceleration valve". There is no vacuum connection, it threads into place instead of the usual idle screw and has a small plunger tip that presses against the throttle arm to set the idle speed. This plunger sticks out maybe .030" and is somehow spring loaded. The carb guy explained that under high vacuum conditions such as deceleration, this allows the vacuum to pull the throttle plates closed a little more.

I don't know why they would want that, but didn't the old fuelie motors do something with high vacuum conditions too?