Qjet 7040205 Dash Pot

[Harold #43147]

Any one know were to get one. Also anyone know the part#
Thanks

[Joe L.]

Re: Qjet 7040205 Dash Pot

Harold-----

The part you seek was originally GM #7038538 which was discontinued in June, 1971 and replaced by GM #7043676. Unfortunately, the latter part was discontinued through the GM parts system a few years ago. However, I think that it may still be available through Delco dealers.

I warn you, though, I believe that the 7043676 is a different color than the original was. So, if you show up on the judging field with one of these, there may be a lot of "snickers". If all you're interested in is functionality, though, the 7043676 will do you well.

[Harold #43147]

Qjet 7040205 Dash Pot

Joe the one I have is no functional the color on it is a Bronze color its all metal never looked for a number on it. Is this the correct color? Is the replacment all metal?
Thanks Harold

[Joe L.]

Re: Qjet 7040205 Dash Pot

Harold-----

I'm not sure about this one. I believe that the originals were plastic bodied. I think that the replacements were, too. If I'm correct, I don't know what you have. I know that later ones, beginning about 1971 or 1972, were metal. Look on it for a number. There may be a 4 digit number that could be useful in ID'ing it.

[Terry M.]

Re: Qjet 7040205 Dash Pot

The originals that I have seen (all of them on carburetors) are all metal. I've never seen anything but the metal type on the cars I have judged. The options seem to be metal or missing.

[Joe L.]

Re: Qjet 7040205 Dash Pot

Terry-----

Now that surprises me if we're talking about Q-Jets. Most Holley carbs used the all metal vacuum break. While later Q-Jets did use the all metal style vacuum breaks, 68-69 models definitely used plastic vacuum breaks for most, if not all, applications.

I was not sure about the 70-71. However, I now believe that they were plastic, too. Here's why I think that:

1) I looked at some engine photos of 70-71 Corvettes in the Vette Vues Fact Book, second edition. These are on pages 108, 109, 133, 134, 140, and 141. All of these vacuum breaks (all of them on carburetors), with the POSSIBLE exception of the one on page 141, appear to clearly be the plastic variety. The 1 on page 141 may well be plastic, too, but it's not clear from the photo that it is.

2) I checked out a GM #7043676 that I have in my collection [not for sale]. This is the vacuum break that has been availble for 70-71 Corvettes for the past 30+ years. It's plastic, too. This vacuum control is the original part used for 1971 Corvettes and it became SERVICE for 1970 Corvettes after the original 7038538 was discontinued in June, 1971.

[Harold #43147]

Dash Pot

Joe maybe Iam using the wrong word when I say Dash Pot thats what I always called them also Decell Valves lets the throddel go back to idle slowly.
Thanks harol

[Terry M.]

Re: Dash Pot

I thought we were talking about the decelerate dash pot also. Mounts on the driver's side of the carburetor. Harold, you and I are on the right track -- now let's get everyone else over to our side of the street.
Lets sweeten the pot -- ever see the Rochester with the big red letter R on the passenger side? I think the decel dash pot and the red R are unique to 1970, and maybe not all of that year either.

[Terry M.]

I sent a photo to you Joe *NM*

[Joe L.]

Re: Dash Pot

Terry and Harold------

Well, I see we're suffering from a "confusion of terms", here. When I first read Harold's original post, I interpreted the term "dashpot" to mean the vacuum break control on the passenger side of the carburetor. This is the part that is often referred to as a "dashpot" and it's common to most Q-Jets, although there were many different part numbers used over the years.

Subsequent to Harold's most recent post, I got to thinking that maybe he was talking about the device found on the driver's side of a small number of Q-Jets and VERY RARELY found on Chevrolet Q-Jets of the late 60s-early 70s. I wasn't even sure that Corvettes ever got these. However, I find that they may have been used on the 7040205 Q-Jet and a few other 1970 Q-Jets.

This device is, in general, called a throttle return check valve. However, according to GM, such a device was never used on a Corvette Q-Jet and GM never had available such a part in SERVICE. Of course, we know better because we've seen them and there are "hints" to it elsewhere. Believe me, I SCOURED the books on this one, upside and downside. It just ain't there and it never was. So, this is a real mystery item, all the way.

Terry, I got your photo and it clearly shows the part. I can't see a vacuum connection on it, though. Is it on the other side of the "bulb"? Also, where does the vacuum signal originate?

[Clem Z.]

Re: Dash Pot

i have seen those throttle linkage "dashpots" on some truck "Q" jet carbs if you are talking about the unit that replaces the idle speed adjustment screw

[Jack H.]

Hum....

IF we happen to be talking about the 'pull-off' (RH side of carb-cracks the choke after initial startup), then here's piece of trivia. I've seen two kinds, one being all metal and the other being half metal/half plastic. In my experience of walking scrap yards and looking at various 'untouched' (how do you REALLY tell?) from the era, it 'appears' there's a correlation between pull-off construction and carb mfgr source.

The all metal parts appear almost exclusively on Rochester built Q-Jets while the half metal/half plastic units (prone to leaking vac at the can crimp interface) seem to have been used on Carter built Q-Jets. Mayhaps there were two sources and freight-in cost considerations favored one assy site using one over the other...

[Joe L.]

Re: Hum....

Jack-----

That's the part that I originally THOUGHT was the issue here, but I was incorrect. The part in question mounts on the DRIVER'S side of the carb. As clem mentioned, it replaces the idle speed screw. It's rarely seen on Corvette Q-Jet carburetors and the only known examples that I'm aware of are found on SOME 1970 Corvette carbs. Other Q-Jets for other car lines did use these devices, although not of the same configuration as the 1970 Corvette units. They are generally referred to as "throttle control vacuum valves".

[Joe L.]

Re: Dash Pot

clem-----

With that lead, I'm "hot on the trail" now.

[Terry M.]

Dash Pot

No vacuum connection Joe. It is really just a shock absorber of sorts. It holds the throttle shaft from slamming closed.