New '74 CS owner doing tune up

CadillacGreen

CadillacGreen

Well-Known Member
Messages
244
Reaction score
22
Hi,

I am a fairly new CS owner that is attempting a tune up on my dual Zenith carb 3.0 CS with AT. I have worked on lots of old cars in the past, but am a bit stumped and am hoping for some input from more experienced CS owners on my issues.

Car was exhibiting low idle problems at first, idling around 500 and normally dying at stop lights with A/C going. Before I touched the carb settings (being familiar with WCFB's not Zeniths), I felt it best to perform a tuneup, etc.

Pulled the plugs and have definite fouling out of the plugs. No ash, just black, sooty and, in one instance, the smell of gasoline. Both 1-5 were like this, 6 appeared reasonably ok. I should also mention the gaps on the plugs were around 34 and am a bit concerned about that as engine was rebuilt approx. 4000 miles ago by Autohaus Exec in Burlingame, CA. It appears as if the carb may be running too rich.

So I went and had the carbs rebuilt by a local vintage import shop. When I got it back, I went ahead and replaced the plugs. The coupe seemed to run better, but still having issues. I replaced the points, which were pitted, with a new set and gapped to 16. At this point, I hooked up the dwell and got a reading of 25, which is, obviously, lower than normal. I shortened the gap and eventually got the dwell sitting at 36, but this made the point gap around 12, which, to me, is WAY too low.

I then took it for a drive without adjusting the timing to see what difference the new points made. The car appears to be bogging down going from start to around 20 MPH (e.g. worse than at 16) so I went ahead and reset them to 16. I should remark that I haven't touched the timing yet because I didn't want to until I was positive about this dwell issue. Dwell reads 25 again with the regapping to 16.

Anyhow, I checked the coil and it appears to be fine and I have checked all the wires and they appear to be fine in terms of firing regularly so I would assume the cap and rotor are within reason.

I turned up the idle to 950RPMS with the dist. vacuums capped as well.

I should say that I live in Las Vegas and today it is over 100 so I am not sure what, if any, fuel issues could crop up at these higher temps.

I did notice yesterday that, shortly after starting the car, it felt like I was getting vapor lock almost immediately as the car died and I had to crank several times and floor it to get fuel flowing.

I am really trying to get a handle on how much of this fuel or ignition. FWIW, I do have receipts for work done on this car back to the late 1970's/early 1980's. I am the third owner.

Any thoughts?

Thanks in advance!
 
Last edited:
First, make sure you don't have vacuum leaks. If it is running rich I doubt this is the case.

The two biggest problems with the Zeniths are:

1. Synchronizing them. If they are out of sync you can get all of the problems you described. Synchronising involves: float match, choke match, front back throttle stops, linkage balance, idle mixture balance. Did your shop fully balance them?
2. As they age the float level will tend to go up and the car will run rich. You can normally diagnose this by looking for fuel dripping from the primary venturis at idle. Getting the float levels right after rebuilding requires deliberate testing. It is adjusted by shimming the float valved. If the floats are high you will get many issues and if they are mismatched they will cause the engine to run rough, especially at lower speeds when the seconaries are still closed. Did your shop check this?

If you set the points you must re-time the car before assuming anything. The dwell angle does change the timing, actually by a fair amount. If the timing is too retarded the engine will be sluggish, if it is to far advanced you can get pinging and even backfiring out the carbs.

The feeling of vapor lock could come from many sources. I doubt it is vapor lock unless you have an electric fuel pump mounted to high or in the engine bay; the stock mechanical pump is pretty reliable. I would tend to think your timing is retarded, your vacuum lines are not hooked up or backwards, or maybe your accelerator pumps aren't working well -- do you see a stream of fuel in the primary venturis when manually pushing the throttle?

Personally I would make sure the carbs are static sync'd:
1. Disconnect common linkage from each carb.
2. Bottom the individual primary throttle plates with individual screws (springs on them)
3. Turn the idle mixture screws (located in the primary side base plate) to the bottom counting the turns on each carb. Average the number of turns and back them both out this number (probably 2.5-4 turns).
4. Connect the central linkages back to the carbs and back them down so that the individual throttles are bottom (this will require fiddling with the central linkage and the little adjustable links to each carb.). The goal is to get both throttle plates to start moving at exactly the same time with the central linkage.
5. Set the central linkage adjust screw so that the both throttles are just beginning to open and give it an extra turn or two. Sometimes it is necessary to bend the stop plate the central adjust screw is in to get the range of adjustment needed
6. Once you start the engine again you will need to use you ear to finish balancing. Some of us old timers use a rubber hose in our ear to listen and the smart guy will use a two vacuum gauges.
- Start with fine tuning the linkages
- Then adjust the idle with the central screw
- Next work on the mixtures screws (1/4 turn at a time until best idle and then add 1/4th turn to slightly richen mixture). They should be keep at the same number of turns unless you notice a big different front and rear
- Set the timing
- Last go back and reset idle (after timing, if far off, you may want to work the mixtures again)

I'm sure others here will do things differently but this basic approach usually works for me.

Personally I recommend investing in an electronic ignition. This removes all dwell problems and most distributor problems. I have a Crane unit which cost about $100 and it is imple to install. Once you get such a system installed and working you only need to re-time the engine when the timing chain stretches, basically never.

Good luck!
 
Hi,

Thanks so much for the quick reply. I will do as suggested. I have run a Pertronix in the past on a 440 Dodge and it worked fine, at least it was still working when I sold it. An electronic ignition is on the list of "to get" items.

I guess my biggest question at first is why the dwell is so low compared to what I think I should be seeing. The manual states 36-41 degrees and I am only at 25. Once I gapped it down to 36 degrees, I was about .012 and that seems way out of whack compared to .016. I could see .014 or .015, but .012 seems just too low. Should I gap it to the dwell of 36-42 degrees, then mess with the carbs, then set the timing or would you suggest I make sure the carbs are sync'ed first and then do the dwell again and set the timing afterwards together?

In the past, with other cars, I have always set the points, checked the dwell and then timed it, but I was concerned with how far off the gap is on this one, hence my question.

Thanks!
 
Last edited:
Also,

I am getting some backfire through the carb when throttle is applied every once in a while.

Just an FYI as I sort this out.
 
CadillacGreen said:
Also,

I am getting some backfire through the carb when throttle is applied every once in a while.

Just an FYI as I sort this out.
Click to expand...

This pretty much means the timing is too far advanced.
I guess my biggest question at first is why the dwell is so low compared to what I think I should be seeing. The manual states 36-41 degrees and I am only at 25. Once I gapped it down to 36 degrees, I was about .012 and that seems way out of whack compared to .016. I could see .014 or .015, but .012 seems just too low. Should I gap it to the dwell of 36-42 degrees, then mess with the carbs, then set the timing or would you suggest I make sure the carbs are sync'ed first and then do the dwell again and set the timing afterwards together?
Click to expand...

As for the dwell it is hard to say. To be honest, back in my shop days I used a dwell meter sometimes but generally relied on a feeler gauge. As long as the points are opening and closing you will be able to make the car run. I suspect your low gap is probably due to a worn distributor lobes and/or worn distributor shaft bushings. These are pretty common problems with older Bosch distributors. If you think about it, if the shaft bushings are worn the points will tend to push the cam away but when the cam is spinning it will tend to center itself and effectively increase the gap. In your case, perhaps by 0.003. I suggest that when you have the points at 0.012 you grab the cam and push it in the direction to open the points; I'll bet if you measure like this your gap will be about 0.018-0.020. Having a worn shaft is generally not a big problem but it will often cause idle and low speed roughness. It can also fool you when gapping the points.

My distributor is pretty much worn out and I could have picked up a new/rebuilt one but I opted for the optical pickup / electronic module since I am not one of the "keep it original" types. Because the optical slits are radial distributor slop doesn't matter much.
 
Hi,

Yeah, I am used to just using a feeler gauge in the past on my other old cars. That's why I was concerned on the dwell. I will check the shaft for wear and verify that way.

I will let everyone know how the carb synching goes, but need to talk to the shop first to verify what they did themselves.

Thanks for everything so far.
 
OK,

I checked the distributor and there is very little play side to side in the shaft. I continued to work with dwell and gapping and got it set to .014 and 36 degrees, which is within spec. The timing on the car seemed far advanced, as was suggested and I spent quite a while looking for the mysterious ball until I realized that the ball is not to be found on a '74 AT tranny, but rather a long post coming off the starter ring (the manual does state this, but the translation is a tad ambiguous). Anyhow, I plugged the vacuums and increased the idle to 1700 and reset the timing to be correct. Car runs much better now.

I still need to sync the carbs and the plate that holds the vertical idle screw on the dual linkage seems to be a bit high as I can only increase rpms to just barely 1700 without it bottoming out.

So, next step is going to sync the carbs one by one and then probably adjust the plate on the manifold if need be at that point.

No more backfire through the carb and the dwell and timing are correct, so things are looking up.

Will report back on the syncing once the temp drops before 112 again.

Thanks so far for all the help!
 
Took it out for a spin last night, temp about 102, but starting to cool off. Car drove great for the first 10 minutes or so down to the local strip mall. Right before we parked, I noticed the car started to sputter like it was having vapor lock. Car died as I pulled into the parking spot.

Upon leaving, car sputtered and seem to have fuel problems. Cleared out after revving the motor a bit and continued to the next store.

At the next store, the 8 Amp fuse blew for the choke, gauges, etc. Swapped out fuse, disconnected power source for choke wires and continued home, noticing that car would barely stay running at idle. It looks like the cleaner was touching one front carb side choke wire and shorting, going to put a new heat shrink tube on it tonight and recheck all wires in the choke series from main power source (where I disconnected) to end of the line.

I am wondering if I have a pinhole fuel line leak somewhere that is allowing air into the lines and vapor locking the carbs or if this syncing, which I am planning for the next cool day, will do the trick.

Also concerned that coil might be causing low spark situation when hot and am trying to determine correct coil to purchase if needed (I had a VW years ago that would run fine until coil was hot and then sputter out, eventually swapped the coil and problem disappeared).

The current coil is a Bosch black with red/orange labels on it. Part number is 0221119017. I called Bosch and they told me this coil has been replaced by 022111902174U. I am assuming the 74U is not needed as I can easily find the 0221119021, but not with the 74U attached as a suffix.

However, this also appears to be known as Bosch 00010, which is NOT the same as the 00012 "Blue" nor the 00013 "Red" that is the subject of so much debate.

I do NOT have an external ballast resistor present, but I DO have a clear plastic sheathed wire on the positive side of the coil that looks to be the infamous "resistance wire" that BMW started using in 1974 (my car is Sept. or Oct. 1974 IIRC).

If I am reading everything correctly, this "resistance wire" replaces the ballast resistor used in earlier cars.

As such, the PN# shown by many websites is 00013, which looks to be the "Red" coil, but I am wondering if anyone here has used the silver 0221119021 74U (which appears to be AKA 00010). It is listed for later model Bavs and 3.0S models. I am assuming the "Red" version is just a "hotter spark" version and the one Bosch gave me is the OEM spec'ed one.

Thoughts, comments, concerns?
 
I can't help with the resistance wire topic but the ballast is simply a resistor so it could be.

On the loss of power it could be vapor lock and it could be ignition. I had a problem with a defective condensor (cap) on the distributor; it was shorting the points to the distributor case when it got hot with the same symptom.

If you suspect vapor lock you can check for fuel in the floats when it happens by manually lifting the accelerator pump (you have to pop the air cleaner box to do this). Can you pump the gas peddle to get it to run? At your high temps vapor lock can be an issue but I would look for a crimped fuel line in before the pump (could even be in the trunk). Similarly a pin hole in the line before the pump could do this. Also, if you have a fuel filter in the line before the fuel pump they can increase the possibility of vapor lock - this got me last summer so I put an electric pump in the trunk.

You might want to go ahead and replace the fuel pump if you don't know it's age. The diaphragms can fail. They are readily available but pricey for some reason.

On the coil, it really isn't very critical for a "driver" car, they all will do the job. I am running a Bosch Red with a ballast and a Crane ignition. The slightly hotter spark doesn't seem to help or hurt; kind of like iridium plugs - marketing hype. If you are racing or using MSD it might be a different story

You might also install a heavy gauge ground wire from the distributor clamp bolt to the chassis. I haven't noticed these on E9's but my old E3 did have one. I doubt this is an issue but you do need a good engine to chassis ground; normally from the firewall to the starter area.
 
OK,

Just an update, the fuel pump appeared to be the culprit. Ordered a new Pierburg ($90.00 plus shipping) from an online vendor and the car no longer seems to stall out and runs smoothly. Being an Automatic, I still have RPM's that are a bit low in Drive at idle with the A/C compressor running. I read on here about fix for that beyond turning up the idle more so we'll see. Being in Vegas, the A/C is on a lot so I need to do something.

Still have to get the chokes working, but the car seems much more powerful and reliable now.

Thanks for all your help!
 
Low idle with A/C on

With your 1974--do you have the Bosch compressor or the earlier York type?
The York creates more drag especially in the A/T CS, whereas the Bosch is much smoother with less drag. Have a look--perhaps an upgrade would be in order to better handle your Las Vegas temps.
 
You must log in or register to reply here.
Back
Top