'75 Eldorado Q-jet Driver's mix screw no impact

[Benji808]

Hello!

I recently rebuilt my Q-jet (#7045530). First time rebuilder, but it seemed to go smoothly, and the car runs much better, and now starts right up from cold with 1-2 pumps (I think accelerator pump was bad, so that's a big difference - she floats down the road again! I also soaked the disassembled carb in chem dip and replaced carb float.)

Issue(s) I'm still trying to sort out: she idles a bit rough, low, and rich (I've been playing with idle speed and mix screws and it's better, but still feels a tad off)...probably related the driver's side mix screw doesn't seem to have any effect...passenger side shuts the car right down when turned in but driver's doesn't. Also, if I turn the idle screw to a certain point, the engine starts surging - sounds just like someone stepping on and off the gas intermittently. Driving it seems great, but that idle is weird.

I've sprayed carb cleaner around the carb and not finding anything...was going to start replacing vacuum lines, even though they all look fine. What else should I check out?

[Cliff Ruggles]

Did you use one of my kits? 

If not did you put a brass float in it?

Were the idle tubes removed or at least cleaned manually so you know they aren't  plugged?

[Benji808]

Got the kit from quadrajetparts.com. I did install a brass float, and soaked the metal parts... I did a bit of spraying but perhaps not as much as I could have...internals were pretty clean overall.

After posting I did further testing, and it seems like the throttle body/base plate gasket is leaking (engine rev from carb cleaner spray near the idle screw), so that is hopefully all it is...not exactly sure how I screwed that up but life happens... planning to pull it and install a new gasket today or tomorrow.

The screws worked before the rebuild so I'm not anticipating anything else - main impetus for the rebuild was a bad accelerator pump - but definitely open to any thoughts you have.

[Benji808]

Ok...hopefully last question and hopefully you can help me. Take a look at this video (youtube link below). The engine clearly surges when I spray carb cleaner around the idle screw. At first I thought it was the throttle body/base plate gasket, which it could be, but this is now the 3rd gasket I've had on it in the past week. I suppose it's possible I over tightened and crushed it, but I was pretty careful the 3rd time to get a firm torque (tightening in a circle) but not push it.

Am I going crazy? Is there some trick to that gasket? Alternately, the surge seems most consistent right around the idle screw...is there a gasket or something that connects the idle screw to the throttle body? I assumed it was just on the outside, but could be wrong obviously.

https://www.youtube.com/watch?v=h92DhLQ81ug

Attached is a picture of the gasket I'm using (this is one of the old ones I removed...I wasn't overly careful to preserve when I took it off)

[Cliff Ruggles]

Never put a brass float in one of these carburetors and most likely you got a "windowed" N/S assembly with a small hole in it. 

Using incorrect parts doesn't help the issues.......

[old cars]

your spaying way too much carb cleaner to be a valid test. the carb can suck in the fumes at that rate

[Benji808]

Ok, thanks for the tips! What are the dangers of using a brass float?

Windowed needle and seat…what does that mean, and how would it impact the potential gasket leak? I will retry the test with less spray.

Thanks for the tips- it’s my first rebuild so I appreciate the education!

[Cliff Ruggles]

The factory went to a solid N/S assembly in the mid-1970's to help prevent drain-back. 

Brass floats do not spec out the same as nitrophyl and they can leak at the seems and sink.

I'll bet the kit had a windowed seat with a small hole in it.  This seemingly minor differences change the fuel level at the correct setting so you are starting somewhat out of spec so the issues could be fundamental simply from using the wrong parts in it.

Nothing mentioned about installing primary shaft bushings, how much play there?

[Benji808]

Thank you for the explanation! I actually did not replace the seat (I'm assuming the seat is the brass-looking thing that screws in that the needle drops into)...it looked fine so I soaked it in chem dip and hoped that would be fine.

The primary shaft - that's the "throttle rod" that runs through the quadrajet and attaches to the smaller two throttle blades, right? If so, I think those bushings are where my issue lies. I didn't do anything to it, and they seem to open and close freely, but there is a  bit of play, and right there at the throttle arm/rod seems be the spot I get the most consistent reaction from spraying carb cleaner (see the earlier video), and the throttle side is also the one where the mixture screw doesn't seem to change anything.

Could bad bushings cause these three issues:  1) rough idle 2) engine jumps from carb spray 3) mix screw not having effect?

If so, do you sell a kit and instructions on how to do that? (I've watched a tutorial or two so I'm generally familiar, but want to make sure I have everything I need before I take it apart.)

It's really close to running in a way I am happy with...if I didn't know the mix screw was supposed to do something and the rich smell bugs my wife I would almost leave it alone, because it's starting and driving really nicely now.

Thank you for your help!!

[Kenth]

I guess the check valve in fuel pump would prevent drainback?

Here is what Delco/Rochester says about the non-windowed inlet seat:

[old cars]

stop spraying carb cleaner . Throwing more parts at it won't solve mixture screw not responding. Windowed/ non windowed, brass float or not, bushings, all of these have little to do with your problem if the one mixture screw is truly not responding at all.
If you have Cliff's book read it. If not , get it. You need an understanding of how the carb works. Clean your circuits.
I'm not saying the use of good parts ( as suggested ) was not good advice.

[Benji808]

stop spraying carb cleaner . Throwing more parts at it won't solve mixture screw not responding. Windowed/ non windowed, brass float or not, bushings, all of these have little to do with your problem if the one mixture screw is truly not responding at all.
If you have Cliff's book read it. If not , get it. You need an understanding of how the carb works. Clean your circuits.
I'm not saying the use of good parts ( as suggested ) was not good advice.

My assumption was that if there was a leak in the side of the carb, the impact on the air fuel mix would render the mixture screw on that side mostly irrelevant, and addressing that would be a good first step so that I can get an accurate understanding if I do have an idle circuit issue. Is that not the case?

[Cliff Ruggles]

Good results ALWAYS start with good parts, and the correct parts. 

The very FIRST thing I do when I get calls to the shop or emails  from folks with carburetor issues on any sort is to have them install one of my kits.

It was a natural course of evolution that I went into the parts business anyhow, so here's a short version of the long story.  WAY back when I went full time into this business we got really busy so I brought in more help and were cranking out hundreds of carburetors.  I was using brass floats in them and the accl pumps and N/S assemblies from the two biggest suppliers.  Things went well initially for a few months, then one by one we started getting carbs sent back here.  The issues were either the float filling up with fuel and sinking or the accl pump or seal failing.  The seals were swelling up and sticking in the bores and the pumps were pulling apart lacking a crimped ring to keep the plastic end on the shaft.  Before anyone asks the answer is yes, the seals on those pumps were "blue" in color.  I have over 50,000 of them here in spare parts removed from accl pumps over the years.  If you think they make the grade just pay the shipping and I'll gladly send you a bag full of them.

I immediately switched to nitrophyl floats and cured that issue and coaxed them to have a crimped on retainer added to the pumps.  They continued to supply the "soft" blue seals on the pumps however, so to this day I still have to remove them and install a seal that is impervious to any type of fuel or fuel additives.  I didn't like their pump springs (coil binding) or their selection of power piston springs so had those custom made as well.  It was a little painful at first as USA companies woln't even talk to you for less than 1000 pieces per order and most want at least 10,000. 

As soon as I started installing all the upgraded components comebacks went to ZERO, none, NADA.  So when I recommend installing one of my kits it is for good reason as it takes the use of crappy parts causing any issues OUT of the equation.

Anyhow, getting back to the task at hand here, most of these carburetors need primary shaft bushings installed in them for two reasons.  It eliminates a vacuum leak at that point and insures that ALL the incoming air is filtered (assuming no other vacuum leaks anyplace).  Additional air coming in around the primary shaft is just like adding more bypass air so it does effect idle tuning.......Cliff

[Benji808]

That's quite the history - thanks for sharing, Cliff!

As you said, to the task at hand - sounds like I need some bushings, and probably new base plate gasket and throttle body gasket, as the chances are not zero that I screw them up during removal. Can I buy these things - bushings and gaskets - from you, or can you provide a source?

I've watched some videos on the "drill in" technique to install the bushings...I may beg/borrow a moment from a really busy guy in town to help me, or I may attempt...any advice you have would be appreciated.

[Cliff Ruggles]

Tread softly watching Youtube videos as most that I've seen are done by folks who really need to keep their day jobs.  I tried watching a few, but the fat lady next door yelling at her kids, the wind blowing in the microphone and having to listen to everything the guy did since he reached puberty BEFORE getting to the task at hand was too much for me!

Seriously, LOTS of information on there that isn't accurate and for sure don't watch the videos about taking them apart and putting them back together.....HORRIBLE!

I use top quality re-useable gaskets in my kits.  Most others use the cheaper "skinned" back gaskets.  They stick like super glue after a short time in use so likely you'll have to get out the razor blades.

I can get you whatever you need and manufacturer of the best bushing install kit out there.  Shop is 740-397-2921, 7am-4pm M-F EST....tks....Cliff