Throttle Return Dashpot

[FastWoman]

Hi all,

I notice when I let off of the gas that the engine RPMs plummet as the throttle slams shut. It's not a serious problem, but it's still a bit inelegant and ill mannered. I realize the job of the dashpot is to ease the slamming shut and possibly prevent the momentary dip in RPM below the normal idle set point.

I remember when I was much younger and owned an 8 year old '75 Z. I refurbed and adjusted the dashpot and apparently kept it. However, I can't remember whether it really did anything or whether it was somewhat of a "rhubarb" (useless part) that I never bothered to remove and toss in the trash.

So... Question to all you old-timers who remember these machines when they were young...

Does the dashpot really do its job and gracefully ease that last bit of falloff? Is there any benefit to keeping/restoring it?

And then the corollary questions...

Is there such a thing as a functional 280Z dashpot? And if not, is there a dashpot from some other vehicle that will mount up? (Mine is quite rotted and is sitting in a box of odd parts.)

Thanks!

[kjphilippona]

Hi FastWoman, i removed mine thinking it did not function and my car started stalling out at redlights, reinstalled it and the stalling went away. I searched and could not find a new one because mine looks like crap also.

[Zed Head]

I knew I has seen a thread on this out there somewhere.

I just adjusted mine in a turn a few days ago, to give a more consistent feel during shifting. At certain times during warmup, the revs drop faster than usual, causing a "clunky" shift. I've adjusted it in the past to avoid the engine dieing problem kjp... mentioned, but I added a little more fine-tuning for driveability.

I think that there is a factory spec. on where it should be, but with my worn engine and throttle parts, I just adjust until it does what I want it to do. It seems to have made a difference, I can't remember a clunky shift since doing it and I can see the tach moving down more slowly.

If you can find a pot with a similar form you might be able to rig it onto the bracket. The bracket keeps it centered over the throttle lever. It's just a spring and leaky diaphragm gizmo.

[John Coffey]

Throttle dashpots are evil things. Throw them away, properly tune your car, and enjoy an engine that moves up AND down the rpm range like it should.

[Zed Head]

Funny, I almost added a comment about the racer types who believe mastering the engine via throttle and clutch control is all that's necessary. Behave beast!

The dash pot is a luxury and it does allow easier shifting. Call me lazy. I can take it.

[cozye]

Mine doesn't have it and runs fine. my BCDD still works though, and when properly adjusted does slow the rpm drop a little.

[FastWoman]

I suppose it all comes down to shifting style. I think a dashpot helps to establish a certain rhythm in shifting. I see others agree and experience clunkyness and stalling without one, so I'll probably search for a solution somewhere. I know there's a dashpot on a Miata (which I own), so logically I should pop the hood of my Miata and see if a Miata dashpot would fit a Z. Duh! (Too many projects, too little time.)

Thanks, guys!

[sparrow6190]

they used way too much vacuum and not enough mechanical advance after the 240z in order to get better mpg.

Vacuum sucks, at least a lot of it, and it REALLY sucks because it doesn't work. I personally want to just order a dashpot from summit with only like 10+ vacuum advance on it, that would match up nicely with my timing, 16-18btdc and 36-38 mechanical total by 2500rpm. I can only imagine how amazing she would run on the highway at with a low advance vacuum dashpot....

Stock ain't better, they don't make it anymore for a reason

[TomoHawk]

Many Carburetors used a dashpot for the same reason. There are also oil-filled thingies that operate like the dashpot, and look like a little shock absorber.

[FastWoman]

Thanks, Sparrow, but wrong dashpot. I don't mean the one on the distributor for the vacuum advance, but the one on the throttle to ease its closing. I'm afraid you're over my head with timing tweaks. I do just stick with stock on that one, because I'm afraid of getting myself in trouble. Perhaps with my new digital advance timing light I might get a bit fancier. (My trusty old Sun light -- late '70's era -- finally bit the dust. )

Tomo, an oil-filled dashpot would probably work better! Those OEM air-filled dashpots are horrible, ill-conceived things! I think I'll just need to wander through a wrecking yard someday.

[sblake01]

Stock ain't better, they don't make it anymore for a reason

And your point is??????? Remember, this is a classic car site............

[sparrow6190]

I wish I still had the little plastic cap on mine.... it fell off so it stopped working right,

good thing my BCDD is working... have you checked that?

They don't have them on the zx's, I wonder what they use.... I've actually just been thinking about taking it off...,