Slant Six Forum :: Talk to me about dashpots.

I'm still having the problem with the Scamp stalling after a slightly quicker than normal stop. SlantsixDan suggested a dashpot sometime back in another thread of mine. I got thinking that this may be the solution to my stalling problem. After reading a bit about dashpots, that is indeed the purpose of a dashpot as well as eliminating backfiring. But I noticed in a 1973 Chrysler manual they only describe the dashpot adjustment for a manual tranny.

Did the original Holley 1920 on a 74 225 with 904 automatic have a dashpot?

I no longer have the original carb. My application is the Holley 5200/Weber 32/36 progressive on a 2 barrel manifold with carb adapter plate.

Wouldn't the dashpot have returned to idle already before the complete stop?

Do different dashpots have differing travel length?

I will need to fabricate a bracket and position it for optimal travel.

Also what do the vacuum and electric dashpots do? Are they controlled delays?

could this be the reason why our 1922 argentinian holleys have a vacuum leak hole opened on the base of the carb? it's original, it's a hole that goes from the base of the carb to underneath the throttle plates.

Quote:

Haven't seen these terminate *under* the throttle plates, though open holes (small, about 3mm diameter) have been used on lots of North American carburetors for idle circuit and distributor vacuum calibration, they all terminate ABOVE the throttle plate. Yes, it's possible this is a "gulp hole" to prevent wet manifold flash.

textoad, Much better

So what does it do? Cant be a venturi thing...

Author:	textoad [ Thu Mar 10, 2005 3:30 pm ]
Post subject:	Talk to me about dashpots.
I'm still having the problem with the Scamp stalling after a slightly quicker than normal stop. SlantsixDan suggested a dashpot sometime back in another thread of mine. I got thinking that this may be the solution to my stalling problem. After reading a bit about dashpots, that is indeed the purpose of a dashpot as well as eliminating backfiring. But I noticed in a 1973 Chrysler manual they only describe the dashpot adjustment for a manual tranny. Did the original Holley 1920 on a 74 225 with 904 automatic have a dashpot? I no longer have the original carb. My application is the Holley 5200/Weber 32/36 progressive on a 2 barrel manifold with carb adapter plate. Are dashpots common on cars with automatic transmissions? Analysis: The purpose of the dashpot is to slow the carburetors return to idle from about 2200 RPMs. As I am driving and approaching a stoplight I let my foot off the gas and roll to a stop using the brake. This takes say 5 to 15 seconds before coming to a complete stop. Give or take a few seconds. Wouldn't the dashpot have returned to idle already before the complete stop? How long does it take a dashpot to return to low idle? Do different dashpots have differing travel length? I will need to fabricate a bracket and position it for optimal travel. This might take some trial and error but I hate to do anything if you guys think its futile or their may be other problems I'm not addressing. The car runs beautifully otherwise. I just need to set the "In Park" idle to 1100 or so such that the "In Drive" idle is around 850 or 900 to prevent the red light stall. Also what do the vacuum and electric dashpots do? Are they controlled delays? Thanks and sorry for so many questions. (Large image deleted. Please keep images down to 30k and a max width of 400 pixels. Chuck)

Author:	SlantSixDan [ Thu Mar 10, 2005 6:08 pm ]
Post subject:	Re: Talk to me about dashpots.
Quote: I'm still having the problem with the Scamp stalling after a slightly quicker than normal stop. SlantsixDan suggested a dashpot sometime back in another thread of mine. I got thinking that this may be the solution to my stalling problem. After reading a bit about dashpots, that is indeed the purpose of a dashpot as well as eliminating backfiring. But I noticed in a 1973 Chrysler manual they only describe the dashpot adjustment for a manual tranny. Yep, dashpots were mostly found on cars with manual transmissions. That's because with an automatic, the torque converter "cushions" the throttle snap-shut action both in terms of avoiding car judder from the sudden throttle closing, and in terms of avoiding engine stall for the same reason. But sometimes non-stock setups don't work like factory setups and a dashpot helps out in an automatic application. Quote: Did the original Holley 1920 on a 74 225 with 904 automatic have a dashpot? No, 'cause the '74 225 didn't have a 1920 originally. It had a 1945. Quote: I no longer have the original carb. My application is the Holley 5200/Weber 32/36 progressive on a 2 barrel manifold with carb adapter plate. See above regarding nonstandard setups. If there is a dashpot and bracket available for your carburetor, install it, adjust it, and it'll probably solve your snap-shut-throttle stalling. Quote: Wouldn't the dashpot have returned to idle already before the complete stop? Irrelevant. The reason why the dashpot works is that it prevents "manifold wet flash", which is when the sudden drop in manifold absolute pressure caused by a throttle snap-shut causes the air/fuel charge to spike rich. By slowing down the throttle closing, the wet flash doesn't occur and the mixture doesn't spike rich. It's not a question of timing so much as it is a question of throttle closing speed. Quote: Do different dashpots have differing travel length? Yes, and they're adjustable. Really, the dashpot only needs to be active on the last few degrees of throttle closing travel. Any more than that gets in the way of normal driveability. Quote: I will need to fabricate a bracket and position it for optimal travel. Check for availability of an OE bracket and dashpot off a manual-trans original application of your carb, or a factory setup available as an accessory in the aftermarket. Quote: Also what do the vacuum and electric dashpots do? Are they controlled delays? They're not quite "vacuum and electric dashpots". They're solenoids (electrical) and kickers (vacuum). The solenoids are used for one and/or both of two purposes: To allow the throttle plates to close completely when the ignition is shut off to prevent engine run-on, and/or to open the throttle slightly when the A/C is turned on to prevent engine stall. The kickers are used to maintain constant idle speed in response to changing vacuum levels (as when the power steering is held against the stop at idle). There are devices that combine the function of a slow-closing throttle dashpot and a solenoid. They are called, appropriately enough, "solepots".

Author:	argentina-slantsixer [ Fri Mar 11, 2005 8:56 am ]
Post subject:
hey dan could this be the reason why our 1922 argentinian holleys have a vacuum leak hole opened on the base of the carb? it's original, it's a hole that goes from the base of the carb to underneath the throttle plates.

Author:	SlantSixDan [ Fri Mar 11, 2005 10:17 am ]
Post subject:
Quote: could this be the reason why our 1922 argentinian holleys have a vacuum leak hole opened on the base of the carb? it's original, it's a hole that goes from the base of the carb to underneath the throttle plates. Haven't seen these terminate under the throttle plates, though open holes (small, about 3mm diameter) have been used on lots of North American carburetors for idle circuit and distributor vacuum calibration, they all terminate ABOVE the throttle plate. Yes, it's possible this is a "gulp hole" to prevent wet manifold flash.

Author:	'74 Sport [ Fri Mar 11, 2005 11:28 am ]
Post subject:
textoad, Resize your pic and re-post. I was just getting a good look and Chuck had to remove it. Looks like a nice clean engine bay. Jerry

Slant Six Forum https://slantsix.org/forum/

Talk to me about dashpots. https://slantsix.org/forum/viewtopic.php?t=12173	Page 1 of 1

Author:	textoad [ Fri Mar 11, 2005 2:07 pm ]
Post subject:
Oops, here it goes again and another view

Author:	steponmebbbboom [ Fri Mar 11, 2005 3:03 pm ]
Post subject:
Quote: Quote: could this be the reason why our 1922 argentinian holleys have a vacuum leak hole opened on the base of the carb? it's original, it's a hole that goes from the base of the carb to underneath the throttle plates. Haven't seen these terminate under the throttle plates, though open holes (small, about 3mm diameter) have been used on lots of North American carburetors for idle circuit and distributor vacuum calibration, they all terminate ABOVE the throttle plate. Yes, it's possible this is a "gulp hole" to prevent wet manifold flash. Hey, my BBS has a hole in the throttle body that goes below the throttle plate. I remember when we were speaking about this last year my 1920 had one about midway up, and I assumed the hole in the BBS was for the same purpose, but now I'm wondering about that. An unused vacuum tap, maybe? Maybe I should tap it and throw in a setscrew...

Author:	SlantSixDan [ Fri Mar 11, 2005 3:20 pm ]
Post subject:
Look again: The hole in the throttle body of your BBS is ABOVE the throttle plate when the throttle plate is closed (idle). It's on the left (driver's) side near one of the carb hold-down bolts. There's no reason to plug it.

Author:	Chuck [ Sat Mar 12, 2005 1:05 pm ]
Post subject:
textoad, Much better on the pictures! With a bit more compression you can get them under 30k. You might want to look at http://slantsix.org/forum/viewtopic.php?t=4434 for future reference. Thanks,

Author:	SlantSixDan [ Sat Mar 12, 2005 1:12 pm ]
Post subject:
Quote: textoad, Much better What we have here is enlightened dashpotism.

Author:	SlantSixDan [ Sat Mar 12, 2005 1:13 pm ]
Post subject:
Quote: So what does it do? Cant be a venturi thing... It helps smooth the transition from idle to power circuit, and assists with calibration of the vacuum advance signal.

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