Hello!
As the restoration of my Qjet goes on, I've encountered an issue I can find little to none information about online.
Let me explain:
Working on my 75 Eldorado (non-cali) Qjet with number 7045230, during reinstalling all bits inside, I compared the idle pickup tubes with each other.
The older ones seem to be about 41mm (~1.61") long, with the "inner tube" level with the "collar" onto of it.
The new ones turn out to be about 39mm (~1.54") long, with a "well" between the top of "collar", to the top of the "inner tube".
The collar lengths seem to be identical, however.
Pictures below.
Talking to the supplier, they mention they've never seen anything but the "short" one, and claim it's overall use.
Confused as one could be, am not really sure what to do from here.
Could it be as simple as that, with a 2mm difference isnt a biggie, as the end of the pipe always appear below fuel level siphoning?
Do you have any thoughts?
Thanks in advance!
//Filip A
(https://cdn-19.fuskbugg.se/N4q9A9A1n0/45565291-1573598408/bild4.png)
(https://cdn-25.fuskbugg.se/K5q9A7A2nc/27177956-1573598431/bild3.jpg)
(https://cdn-18.fuskbugg.se/L4q9AbAen4/32670ac9-1573598451/bild2.jpg)
The original pictures were there, and HUGE. But, the new ones don't work.
Bruce. >:D
EDIT: Fixed them!
Realized that too! Hoped they'd auto-edit to a viewable size!
These new ones work better I think!
//EDIT
Hmmm, it appears the direct link to photos seem to not work.
Photos are found here, unless the initially posted ones "get back to work"
https://fuskbugg.se/N4q9A9A1n0/bild4_png (https://fuskbugg.se/N4q9A9A1n0/bild4_png)
https://fuskbugg.se/K5q9A7A2nc/bild3_jpg (https://fuskbugg.se/K5q9A7A2nc/bild3_jpg)
https://fuskbugg.se/L4q9AbAen4/bild2_jpg (https://fuskbugg.se/L4q9AbAen4/bild2_jpg)
//Filip A
Those tubes aren't a wear item. If it were me, I would use the originals after a good cleaning.
Quote from: hornetball on November 12, 2019, 06:10:51 PM
Those tubes aren't a wear item. If it were me, I would use the originals after a good cleaning.
Hey, and thanks for your reply!
At this point, I certainly would have if I was able to.
But picking them up ruined them, as a drywall screw was used to grab it and a set of pliers to aid it as it came up a bit.
//Filip A
Hello Filip,
You may have seen the video in the link below, in which the idle tubes were removed with a drywall screw and a diagonal cutter. The video producer has several videos on the subject of Qjet rebuilding. Another source of information is Doug Roe's "Rochester Carburetors" (HP Books).
I don't recall that either source indicated there is a problem if the tubes are a little shorter than original. I think the diameter of the opening is more critical than the length. Feel free to review the sources, and let us know how your carburetor performs.
Respectfully submitted,
Christopher Winter
Hello!
Can't tell exactly where I got idea from, but it worked!
I also think you are on the right track, with the siphoning tube diameter having a greater impact rather than length (in this case, just 2mm).
Not exactly sure how the "main fuel wells" are designed, besides that they seem submerged in the casting unavailable to spot, and that they're fed though the main metering rods&jets.
These "main fuel wells" also turn out, when looking at cross-cut-section in the 1975 Cadillac workshop booklet (is it allowed to post a photo if it here, or does it violate?), be the source from which the idle pick-up tubes draw fuel from.
Seems unlikely to me that the 2mm difference would cause the tip och the pick up tube to always stay above fuel level instead siphoning air?
Especially when engine vibrations alone probably would slosh the fuel around enough, not to mention parking in different steep roads with smooth operation kept.
Still, of course curios about the lengths, hence the question to the pro's in here!
I will try them out, and report back if it's drivable as spring arrives in northern europe :)
Regards
//Filip
These may help next time.
https://quadrajetparts.com/-a-50.html
I found some online but listed longer than yours? http://www.carburetion.com/Products/ProductDetails.aspx?Part=CU1774
The inner orifice diameter is the critical flow parameter, but they're different lengths for different models. The '75 7085230 is a R4-M4MEA which is later than this manual but they're all similar. At least addresses some of your questions.
Can't tell without the exact parts diagram which one is correct. You might want to search that more with the carb parts sites. The ones in there might be wrong or right. These carb models were adjusted to the yearly engine requirements not necessarily the standard issue, so parts maybe rarer.
I did not read every response above, but to add my 2-1/2 cents worth, the 75 carburetor is a ONE YEAR ONLY GIFT TO THE WORLD, so if any of the unique components are needed a 1975 core would most likely be needed.
Greg Surfas
Thanks for your inputs guys! :)
That qjetparts-tubes are too short, and the other one (1.8" ish) is slightly too long!
The '75 sure seems like a one-off, agreed! Thinking of repairing my old tubes and just try, but this has turned interesting so still not made my mind up I guess.
As I read through the 75 supplement manual, I found this cross-section image on the idle mechanism (see below)
The yellow-filled parts would be the pick-up tube.
The blue would be, as far as I see it, the necessary level of fuel in the float chamber, for the pickup tube to be able to siphon fuel. (Meaning slightly higher float chamber fuel level with the new, shorter tubes?)
I assume the main metering rods always allow slight fuel passing through, as they feed the idle pickups?
Can't find any info however, of the fuel level height in the float chamber.
Actually, am also a little confused of that to search for on the internet? (Float chamber fuel level quadrajet?)
Perhaps someone could fill this knowledge gap of mine, like what the fuel level would be at as the needle-and-seat seals the inlet?
(https://i.ibb.co/yymVcc7/bild.png) (https://ibb.co/yymVcc7)
Regards
//Filip A
Hi Filip
The fuel level must be way higher than the line you have drawn.
- Fuel level is engineered to give a pressure to push fuel through the circuits and of course also from the pulling force of the vacuum. So there needs to be enough height to establish this force.
- Fuel level is engineered to give you enough "storage" if the car moves side to side or up and down to not expose any holes to air.
So I am guessing the the fuel level is maybe half to 2/3 way up the float. Maybe a bit more. If the fuel float would be of a material without mass the level would be half way. Since the float does has a mass the level must be somewhat higher. Maybe up to 2/3 of the height of the float.
So in essence, if your tube is, say 1mm longer, it does not matter.
Just make sure there is some room on the bottom for to fuel to make its way into the tube.
There is a collar at the top, so maybe the collar is not at correct position. When you install it it may fit well.
The point of pickup (that is the depth of the tube into the fuel) does not alter the pressure difference that the fuel sees. It is purely a difference between fuel level and pressure at the exit (idle discharge hole). (As a simplification you can take the bernoulli equation)
As long as the tube reaches deep enough and does not bottom out you are good to go.
Best regards,
Nicolas