Alright, got home and tried out the suggested adjustments. I ended up turning the mix screws out 1.75 turns from where they were last night, and turned the throttle screw .5 turn in. This is probably the best that it's idled yet, but the vacuum is still a bit lower and bouncing around more than I'd like.

I threw the air cleaner on and drove it around the block..it still has *slight detonation, and I noticed when I shut it down it didn't want to restart (acting like it's still too advanced on timing)

so..with that I think I'm gonna just walk away for a few..and figure out a different plan of attack.

 

I have to say, I'm not clear how you're thinking &/or digesting the notion of adjustments to the A/F mixture screw(s). There is no "set point" e.g. number of turns to the A/F mixture screws which is uniform to any &/or all carburetors. You just don't set the A/F mixture screws based upon some conceived notion of number of turns. I think you're outwitting yourself here.

First, every single Rochester Q-Jet was "specifically" designed for a particular engine. They are NOT interchangeable among various 350 engines, 400 engines, 455 engines, etc. The are & they were designed for very specific engine applications.

If you do not have a wide band sensor, you have only two options to make appropriate A/F mixture adjustments. By & far the simplest and most accurate is usage of a vacuum gauge.

When adjusting the A/F mixture screws it is NOT important to note the number of turns. What is important is to adjust the A/F mixture screw(s) one at a time to the highest achievable vacuum. That's it - done deal. Nothing more - nothing less. Lose the notion of number of turns . You're "dialing in" A/F mixture ratio you're not dialing in number of turns of the screw(s). So, hook up your gauge when you tune your A/F mixture screws - you're putting the cart ahead of the horse thinking number of turns has any significance. It's the highest achievable vacuum you're after.

Second, you can most generally very closely approximate the highest achievable vacuum by "listening" to engine RPM as you adjust each A/F mixture screw(s). Generally, you adjust each A/F mixture screw until the RPM increases then fall off. You want the point where the engine achieves its highest RPM without falling off. Do this for both A/F mixture screws one at a time. This is the old-school (nearly never fails) method. Vacuum gauge is the preferred method. The absolute best method is using a wide band O2 sensor (which you don't have installed).

 

Well, let me follow that up by clarifying. Yes, you can make/tune a Rochester Q-Jet from another engine specific to the needs of another engine - but you cannot do it out of the box. It must be calibrated for the engine it is sitting on - specifically the engine it is sitting on.

 

Correct, I know its not a number of turn setting, I was simply stating how much I'd moved it since where things were last night. It did seem to help settle the gauge out, but didn't seem to consistently improve the vacuum. My priority has been to get it to run/idle consistently first..which I think at this point has been relatively accomplished. That too leads to me to the point of just stepping away and going at the tuning instability from a different direction.

I had thought about how the more I turn the screws out, the more consistent the gauge got..but i also know that the best way to get it dialed in is with the wideband for sure. I think if I don't break down and buy one for this situation, I'll still go ahead and buy one for the garage.

 

It's unfortunate (nerve racking) you're having this issue. Lots of great engine experts/enthusiasts helping you. Of course, I'd prefer to have an engine on a dyno after achieving a solid tune-up, but putting it on a dyno is most likely where you'll gain the most information at this point in time.

Regarding your comment on tuning:

Consider the basics of engine performance as it relates to vacuum which may seed a thought.

Engine basics of performance regarding a tune-up are ALWAYS followed in chronological order:

(1) Set DWELL
(2) Set TIMING
(3) Set A/F Mixture Ratio

Noteworthy is this. The above process is top-to-bottom. TIMING does not affect DWELL. A/F Mixture Ratio does not affect TIMING and A/F Mixture Ratio does not affect DWELL.

The best way to get the CARBURETOR A/F mixture ratio dialed in is with a wide band. But, I think you should be clear on your understanding of something - you must FIRST have an established vacuum before you can Set A/F mixture ratio. At this point, from everything I've read, you don't have satisfactory/sufficient vacuum to set/establish A/F Mixture Ratio via wide-band, vacuum gauge or old-school RPM increase. Bottom line, you need to find some vacuum.

 

Brother, can you video or photo the vacuum gauge for us?

It's also worth noting the old saw, 90% of carburetor problems are electrical, in other words, are the points and coil and condenser ok?

I have a car, had it mixed way lean, because the ignition was fubar. Now it's much better after a tuneup, but that matters to the carb, I mean.

 

yes, and I kept trying to upload it here but kept forgetting. This was taken this afternoon, before I drove it around.

As far as finding the vacuum, I'm at a loss without tearing it down, honestly. No leaks have been found, so the only thing (if there are any) would be internal. I took a quick glance at the intake/head mating surface just in passing..I didnt see a drastic angle, but then again thought about how if they were off at the top, I'd think I could have found a leak by now.

 

I likely missed it trying to read numerous threads/posts.

What's the compression reading from each cylinder?

 

Disclaimer: I have not performed a compression test since degreeing the cam

 

To rule out an internal vacuum leak, pull the pcv valve out of the valve cover and the breather tube out of the other valve cover. Plug the grommet on each valve cover with your thumbs with the engine running for about 10 to 15 seconds. When you slowly remove one thumb there should be a noticeable puff of crankcase pressure. If you feel suction instead of pressure you have a vacuum leak on the underside of the intake.

 

Noted.

 

An even easier way to check for an internal vacuum leak, is to remove the oil filler cap while the engine is running and spray some "carb cleaner" into the tube. if the intake is sucking in on the bottom of the gasket, the idle will pick right up. I've found many intake leaks that way. Quick and easy. Another thing that you may need to do to be able to back out your idle screw to a more tolerable point is to drill an 1/8" hole in each of your primary throttle plates. This allows enough air in at idle to keep the engine running, without uncovering the transition slots in the carburetor. W31s came from the factory that way.

 

You do realize the pcv valve will pick up the vapors also.

 

those are sad number, both on the huge difference and being way to low.

do another test to see if anything changed

 

I'm hoping I can get out there one day over the weekend and just check off a bunch of things. I did pull the cap as it was also suggested the hanging idle could be interference. Not entirely sure what I'm looking at, other than some surface rust I didn't expect to see.

Im to the point where simple thoughts say its still not getting enough fuel across the board based on how its acting and past experiences, but if there's a vacuum leak, a compression issue, or anything more than they can address on the dyno then it may just be time to figure out whats next.

NOTE:: back to the compression numbers, those are cold. Not sure if that'd make a difference, but I do remember at the time I'd not fired the car up for a couple days prior to.

 

oh jeez,, every day is April fools day with you.

the differences between sides may be because you did it cold and the lifters had bled down over a few days,, I didn’t know that before, or this time. by the time you got to the other bank they were pumped up…I’m guessing here because you always throw curve *****

do it cold again like you did before, in the same order per cylinder, then do a proper hot test.

 

That makes sense, I never really thought about that.

 

This thread began w/ a supposed detonation issue although difficult to determine by the initial posts in the thread. At the end of the day you are producing essentially no vacuum at engine idle. Your compression is not "miles" off the radar.

It cannot be stated enough you tune engine performance in ONLY one manner:

(1) Set DWELL;
(2) Set TIMING;
(3) Set A/F mixture ratio

I'd likely throw your dwell meter in the trash. I have repeatedly viewed both your vacuum gauge test and the little bit you displayed w/ the dwell meter.

Bothersome/Troublesome areas to note:

(1) You need to learn how to perform the vacuum test accurately;
(2) The vacuum gauge needle needs to read STEADY. Your vacuum needle is not only (a) bouncing all around [it is [b]NOT steady]; (b) it is EXTREMELY low at a supposed 8"Hg (again, it is NOT steady); and, (3) what I can view on your dwell meter demonstrates dwell needle is all over the place. The dwell meter needle should be STEADY. It looks like the dwell is incorrect, as well. I'd likely throw that dwell meter in the trash. Dwell meters require a zero calibration. I don't want to steer this conversation about the disparity of various dwell meters, but the readings I see displayed on that dwell meter are seriously off the mark. Borrow someone's known good working dwell meter or buy another one.
(3) There is a high likelihood you aren't close to providing the correct dwell on this engine. If you can't provide the correct dwell you can't provide the correct timing and if you can't provide the correct timing you cannot create sufficient vacuum on the induction (intake) stroke of this engine.

A wide band analyzer allows you to optimally adjust your A/F mixture ratio - much as the vacuum gauge allows you to make this adjustment w/ less accuracy but you first have to have manifold vacuum - for which you have NONE.

You don't need to take this car for a dyno (another has rightfully already mentioned this) - what you do need is to take this car to a mechanic who knows how to set dwell & set timing with professional working equipment. I think you're chasing your tail here. Unless you like to spend countless hours (maybe $$) varying off on several roads to find a vacuum leak which you've stated apparently doesn't exist get some professional help w/ professional equipment. I've said it as have others, there is no dyno machine anywhere going to fix your issue.

Get someone (anyone) to properly tune the performance of this engine because what I'm viewing is off the map on the very basics of engine performance tuning.

Look, YouTube has tons of vacuum testing videos. See if you can find ONE which DOES NOT demonstrate a rock steady vacuum gauge needle. The needle has to be steady. Find numerous videos measuring dwell. You see any dwell meters bouncing around like yours? No. Your equipment or your understanding is wavering. Take your car to someone who has professional equipment or buy some new known good working equipment. I'm suspecting your dwell & your timing are far off the mark.

If you find you cannot set dwell accurately (with a steady needle) which specifically affects your timing, then suspect the IGN system is questionable:

Your points could be/likely are floating. The contact points field gap must close and open precisely. This is HIGHLY critical to providing the correct field to the primary side of the IGN coil.
When is the last time you checked and adjusted contact points gap w/ accurate equipment? This is crucial.
When is the last time you changed the contact points condenser? A critical piece of equipment to prevent stray/runaway arcing and create a solid field collapse.
When is the last time the IGN coil was replaced &/or tested?

Distributor cam lobes might possibly be terribly worn.

Get the engine tuned up by a professional, buy a new dwell meter or find a dwell meter which is working correctly. I don't like what I can see on basic engine performance tuning.

 

Alright, so I went out before work as curiosity got the best of me and checked to see how the mix screws were on the carb. To start with, evidently they were not even. I am way too meticulous when it comes to making sure the same adjustment is made to both, so I'm not entirely sure how they got off, unless it wasn't correct to begin with. I doubt it would've been sent uneven, but the box did look like it rolled down a flight of stairs, so there's no telling what may or may not have moved and I didn't verify from the start.

So, the DS screw was 6.625 turns from bottom, the PS was 6 turns. I reset them both at 6.5 turns out (verifying both sides twice to ensure I didn't screw up. With that being said, I'm going to work to get some time this weekend and just run all sorts of tests.

A: cold compression test to compare against previous numbers
B: while running, I'm going to verify vacuum gauge now that both screws are set correctly in hopes it is not bouncing anymore. Also 'may' back the initial timing down a bit, but will determine whether to mess with that after a test drive.
C: while running, will spray carb cleaner down oil fill tube as mentioned previous to attempt to find any noticeable change in RPM signifying internal vacuum leak.
D: Once shut down, will perform a hot compression test.

From there, that should answer a few questions for sure, but also I believe our next step is dyno. I'm not sure what rod/jet combo is in it, and (understandably so) John doesn't want someone tinkering with the internals of the carb without verifying its not an ignition issue first. I would just like to know so I can come prepared if everything checks out with the ignition on the dyno. It has been documented by many that the person who restored the distributor is suspect when it comes to setting them up. Verified when I checked dwell and noticed it was incorrect. I do know I am well beyond my level of know-how, and will be the first to admit that. While the best way to learn is to do, sometimes it's easier to do when you have someone physically with you to teach, rather than leaving it up to interpretation from a forum/manual/video/etc. Not a dig, simply a fact. I can justify A, B & D, but in finding C, it then creates an issue with one of the other variables. Some of which, I'm sure are self-induced..but again, I'm over my head at this point.

This shouldn't be this complicated. I've built an engine before, that would run circles around this one and had no issues tuning it. Just because its a BB, just because its an Olds engine..its still an internal combustion engine that requires the same things to work. I honestly think had we just treated this engine as we did the other and paid for machining to be done, and did all assembly ourselves, there wouldn't have been an issue. Trying to figure out where these variables lie is just getting a bit defeating. Especially knowing I intentionally paid people to avoid this kind of problem.

 

The meter I have is a dwell/tach, set to tach. The Dwell is solid. I have used it to verify and correct dwell already. The reason the needle moved is (I believe) the same reason the vacuum gauge was moving..the engine is sputtering.

I was typing it all out as you posted, but long story short the mix screws were NOT even as I expected they were. I know my adjustments were even, but I did not verify prior to first turn that they were from the start. I reset them this morning, and that will be one of the many things to check once I get some time. I also didn't think about how much it was detonating before sending the carb off-to check the plugs to make sure the gaps were still correct. That too could possibly lead to the stutter I'm sure. I can't speak to the shaft itself, but the internals of the distributor are new as of spring 2022. The rust seen in there is a bit concerning, but I will clean and apply dielectric grease to ensure its smooth.

I have never disputed the need for a wideband, just simply have stated I need to get it to where I can get it in the ballpark so we're not spending half of our time at the dyno chasing our tails. I understand the vacuum reading is extremely low. That has been THE constant throughout this entire time. I have exhausted anything external, and the local professionals insist the low vacuum is due to the cam being so large (this is why the local pro's don't seem to line up with what is seen online).

 

I watched the dwell meter in your video. It's not reading correctly. It should not demonstrate the amount of variance it is displaying. Dwell refers to the closed period of the contact points (points are fully closed together) it's not an average of opening and closing it specifically represents the duration in which the primary side of the ignition coil is being charged. I'm not convinced dwell is set accurately. Points floating? Condenser? IGN coil input/output? You should have a steady reading.

Yeah, back to vacuum. Maybe you didn't completely understand. Adjusting A/F mixture screws to a "set" number of turns so each (L & R) match each other is futile. You adjust each individually irrespective to number of turns. Think about this. Why have two A/F mixture screws if they both are supposed to be the exact same?

Additionally, no adjustments to either of the A/F mixture screws is going to have any affect on increasing your vacuum from 8"Hg to a minimum of 15"Hg. Sorry, you need a vacuum first to provide any benefit in making fine-tuning adjustments to A/F mixture. Your throttle body plate is nearly closed at idle, correct? I mean barely a crack is all it needs.

 

Two ways to go here:

1) Proceed on the assumption that, as stated previously, that engine with that cam should pull a lot more than 8" Hg, and find yourself a new professional who can effectively diagnose, repair and tune an engine. These guys are just using the cam to cover their own incompetence. Or:

2) Believe what those guys are telling you and install a milder cam. The one you have is likely a little much for your engine anyway.

 

I don't have it switched to dwell, it's switched to tach. I do not have a video showing the dwell reading but it does not fluctuate.

I understand there is no set number on the screws, I am just under the interpretation that the screws have to match. Maybe that's my previous experience with Holleys though.

I agree the A/F won't get me to 15"..but if it'll steady the vacuum and put me at 8-9..thats pretty much where I was with the previous carburetor.

The throttle screw was turned in a good ways, just to get it to run. I understand there's the mod about the hole in the plates to allow you to stay off the transfer slots, but then again..that gets back to the vacuum leak that I can't find.

 

If you had a wide band installed BEFORE you got there, you’d be that much ahead of the game, instead of wasting time as you mentioned.
Just a thought.
And 8” is low for sure. But I can tell you, I’ve had multiple customers install that same cam in other 400ci engines and none of them responded the same way your has. Just saying.

 

Yes, you definitely need to have a wide band installed BEFORE you head to the dyno. You should do the dyno install now since the guy(s) on the dyno aren't going to provide a ton of useful info w/o a wide band installed. Embarrassing (if not a waste of time) to head to a dyno shop only to be asked to return when you have the wide band installed - or, you're paying them to install it for you - plan to make another appointment. Sorta your choice, I guess.

 

Wideband ordered. Gonna take the bung to the hardware store when it comes in for a plug, then contact the local exhaust shop to see if they'll weld it into place. Gonna need to figure out wiring and mounting considering it'll be temporary (my plan is to keep it more as a tool for the garage than a permanent fixture in the car).

 

You're right, it shouldn't be this complicated. People managed to get these engines to run well before widebands were invented.

Sudden thought: timing issue. This is only sort of a joke -- we're all on the same page that the distributor is CCW on these engines, right?

Naw, I guess that wouldn't explain the compression numbers or the vacuum issue. Nevermind.

 

I have no idea how engines were tuned before the wide band came along…I’m truly stumped.

or,,,how points were set without a dwell meter.

 

Feeler gauges, hate those damn things, lol. My van runs like a raped ape though, after a recent tuneup.

 

Got home and had a bit of time before dinner was ready, so I went out and fired the car up to see if resetting the mix screws helped the stutter. Short answer, no. Once it warmed up, I did bust out the carb cleaner and sprayed all around the intake, carb, and down the oil fil tube as referenced in a previous post. I didnt notice any change in RPM, outside of the changes when it would stumble. I took it out for a drive and it seemed a bit more peppy, but coming back did have that same slight detonation. I went to put the tach away before driving it and found my thermometer..it seemed like cyl 1 & 8 were cooler than the rest (shooting above the exhaust port on the head, same spot for each cylinder) though I'm not sure that's related to anything.

I did call the dyno shop this afternoon while at work, to just get a feel for their availability. In talking with them, we discussed the vacuum concern, to which he said he has a guy there that he would like to look at the car and try to find a leak before putting it on the dyno (makes sense).

So, hopefully this weekend I can perform the cold & hot compression tests, then wire in the wideband (and find someone to weld in the bung) and we'll send it down there for them to find the vacuum leak assuming there is one.

 

Checking vacuum:
You connected direct to an intake manifold port?
Connected direct to carburetor manifold port?
Connected w/ a “T” into an existing manifold vacuum hose?
Brakes have no issues, good pedal, travel & braking distance?
Transmission shift points no issues with shifting? Checked rubber vacuum hose from metal pipe to rubber hose at Transmission Modulator?

 

At one point, I unhooked every vacuum line coming off of the engine and capped them, aside from the one hooked to the gauge and it made no change. I then moved from port to port making sure it wasn't an issue with the one Id been using..to no change. I have used different vacuum gauges altogether, no change.

Brakes have been better than they are now, but that was with the Jet carb, 18° initial timing pulling 9" of vacuum (steady).

 

You visually and physically checked rubber hose from modulator metal line to rubber vacuum hose into trans modulator?

 

The port from the intake that goes to the modulator is my primary go-to, so whenever I'm checking..9 times out of 10 there isn't any vacuum going to the modulator. The hose between modulator and steel line is a bit small for the modulator, but its in there. I don't understand why, but the modulator port and the steel line are two different sizes..so I put the smaller sized hose on to ensure nothing dumb would happen.

 

Run away, just run away!!!

 

WTF does that mean?
I don’t think it could be said any better.