Setting timing - erratic vacuum reading

[jbooth35]

I’m trying to set up timing and carb using these instructions as they’ve been suggested before and seem solid. Vacuum Engine Timing | MILEPOSTS Garage (Tech Tips)
[URL]http://tvmoparclub.com/files/tech/Mopar%20Timing.pdf[/URL]
Car seems to drive great but the too lean smell is killing me. I’m using the vacuum port that goes to the brake booster and the gauge bounces wildly. Suggestions? I’m enjoying driving it but just want to get this running even better. I see a jump on the timing light reading too. Makes it hard to set everything.

 

[jbooth35]

They carburetor adjustment screws seem to have zero effect, so I took them out to examine them…. How does this thing even run.

 

[CBODY67]

A "too lean smell"??? I never have experienced that, BUT have experienced a "too rich" smell. Generally, you don't smell lean, even when the mixture is lean enough to cause "lean misfire" as you go down the road toward minimizing CO emissions.

The base timing should not be affected by intake manifold vacuum, period. It's a totally analog situation. DO ensure that the place you put the timing light signal pickup is at a place on the plug wire where it is as distant as it can be from another plug wire, to ensure that it's only getting the desired signal. Find a good tutorial on using a vacuum gauge to diagnose engine situations, circa 1960 or earlier. When I tried those things, in the late 1960s, I did not get the results I wanted so I got a timing light and dwell tach as soon as I could afford them. MUCH better results.

DO understand that there are pressure pulses in the intake manifold runners. Which is why the needle is a blur within a range of values on the gauge. Place the vac gauge's line to a place where you can get a smoother signal, as in at the carb base or on the choke pull-off vac port (full manifold vacuum rather than ported vacuum). IF you look into the bottom of the gauge, where the vac line to it would be attached, you'll see an insert with a small hole in it. That restriction is there to dampen the needle's movements, as a baffle of sorts.

Personally, I never could get the vac level at idle to match what others claimed it should be, although the car ran fine and clean at idle at the spec idle speed. Another reason I went to an electronic tach and such.

Just some thoughts,
CBODY67

 

[jbooth35]

A "too lean smell"??? I never have experienced that, BUT have experienced a "too rich" smell. Generally, you don't smell lean, even when the mixture is lean enough to cause "lean misfire" as you go down the road toward minimizing CO emissions.

The base timing should not be affected by intake manifold vacuum, period. It's a totally analog situation. DO ensure that the place you put the timing light signal pickup is at a place on the plug wire where it is as distant as it can be from another plug wire, to ensure that it's only getting the desired signal. Find a good tutorial on using a vacuum gauge to diagnose engine situations, circa 1960 or earlier. When I tried those things, in the late 1960s, I did not get the results I wanted so I got a timing light and dwell tach as soon as I could afford them. MUCH better results.

DO understand that there are pressure pulses in the intake manifold runners. Which is why the needle is a blur within a range of values on the gauge. Place the vac gauge's line to a place where you can get a smoother signal, as in at the carb base or on the choke pull-off vac port (full manifold vacuum rather than ported vacuum). IF you look into the bottom of the gauge, where the vac line to it would be attached, you'll see an insert with a small hole in it. That restriction is there to dampen the needle's movements, as a baffle of sorts.

Personally, I never could get the vac level at idle to match what others claimed it should be, although the car ran fine and clean at idle at the spec idle speed. Another reason I went to an electronic tach and such.

Just some thoughts,
CBODY67

Thank you for your thoughtful response. I meant “too rich” smell, as my wife doesn’t want to ride in the car since the fumes are pretty bad. I thought it was just the oil burning off, but have determined it is a rich running car smell. There is a small hose running just under the port feeding the brakes vacuum. I assume it goes to the vents. I may try using that port, but I don’t easily see any other options. Seems like that hose is another that I should replace as it is very hard near the engine.

 

[CBODY67]

When you pull the engine oil dipstick, what does the oil smell like? Similar "hydrocarbon" smell? Any dark smoke from the tail pipe? Does the smell clear out when the rpms get past about 1500rpm?

Getting the idle mixture optimized at "lean best idle", at the spec rpm, can minimize the smell greatly, by observation, from my experiences.

Looks like a Carter AFB? There should be a vac port on the carb base, at the front, as "choke vac port", PCV, and "distributor vac advance/ported vacuum", as I recall.

CBODY67

 

[Turboomni]

Why not rebuild your carb and get new idle mix screws. If it were me depending how the carb is otherwise, I would consider buying a new one for piece of mind. There is a great outfit advertised here and their specialty is rebuilding carbs. Woodruff I think.

 

[jbooth35]

When you pull the engine oil dipstick, what does the oil smell like? Similar "hydrocarbon" smell? Any dark smoke from the tail pipe? Does the smell clear out when the rpms get past about 1500rpm?

Getting the idle mixture optimized at "lean best idle", at the spec rpm, can minimize the smell greatly, by observation, from my experiences.

Looks like a Carter AFB? There should be a vac port on the carb base, at the front, as "choke vac port", PCV, and "distributor vac advance/ported vacuum", as I recall.

CBODY67

I see these 3 ports. One too the dizzy, one to pvc, the last back to air horn on the carb. I was thinking these were all ported as I had the same erratic reading when using the port to the Distributer.

 

[jbooth35]

Why not rebuild your carb and get new idle mix screws. If it were me depending how the carb is otherwise, I would consider buying a new one for piece of mind. There is a great outfit advertised here and their specialty is rebuilding carbs. Woodruff I think.

I think I will purchase a new carburetor so I can drive the car and make a trip to Youngstown to have Dana look it over. I did rebuild the carb but never actually touched the screws as the kit didn’t require it. That one adjustment screw seems like it has a piece of metal wire jammed on the end.. I’m guessing some is screwed up. Maybe someone can guess what is wrong with it. I’m thinking a AVS2 would be the best new car choice?

 

[CBODY67]

Try using the port that runs the choke's vac pull-off, as that should be straight manifold vacuum from a more stable source (meaning, not just ONE intake manifold runner). The distributor port should be ported vac, with only a few inches of vacuum at hot base idle, but much more vacuum as you put the rpm closer to 1500spm. In other words, find ONE vacu port that is full manifold vacuum and has a much more stable needle, if that even exists.

At hot base idle, is the flow out of the tail pipe smooth or does it have "skips" in it? Like a miss on one cyl?

Just some thoughts,
CBODY67

 

[jbooth35]

Picked up an AVS2 (it'll take a little while to get the carter repaired) and everything is much smoother, vacuum sitting even around 18. Had to pick up an adapter to move the throttle and kickdown linkage a bit further out, but now the air cleaner base doesn't fit with the new carb. It is always something. Can anyone recommend an air cleaner base that'll work? TY.

 

[CBODY67]

For 1968, Chrysler went to the "Holley-size" air cleaner base hole size. In the mean time, any 4bbl air cleaner on the aftermarket should fit, as long as it will clear the carb's choke items.

To use your existing air cleaner, you just need the base plate only from a 1968+ 4bbl air cleaner, as in 1968 and later. OR you can get a repro 1968 Road Runner air cleaner and use only the base, which makes the whole affair and incognito open element air cleaner. Same filter size as you now have, just that the edge of the base only extends TO the edge of the filter element, not to the edge of the air cleaenr top part.

For 1969, Chrysler went to the more modern style with a removable top plate, rather than a removable top "upside-down cup".

Enjoy!
CBODY67

 

[jbooth35]

Ah thanks. I want to keep the original 426 air cleaner so I guess I’ll have to hunt for a new/old base for 68+. There is someone selling a 13” base on eBay for $50. Would like to find the original source and save some $.

 

[jbooth35]

 

[jbooth35]

Here is a link to a 13" base on ebay that appears like it would work. Found some cheaper in 14" that I may be able to get away with given the room, but may restrict air flow more than desired.

MOPAR, DODGE , PLYMOUTH, 13” AIR CLEANER BASE ONLY. 340 .360. 400, 413 ,426,440 | eBay

 

[CBODY67]

Here is a link to a 13" base on ebay that appears like it would work. Found some cheaper in 14" that I may be able to get away with given the room, but may restrict air flow more than desired.

MOPAR, DODGE , PLYMOUTH, 13” AIR CLEANER BASE ONLY. 340 .360. 400, 413 ,426,440 | eBay

That base is the base for the aftermarket, generic version of the Corvette open air cleaner unit, which has been painted black. It also sits one inch higher than the OEM Corvette base, after we measured one one night for comparison.

At least the seller is accurate about the fact that it's an aftermarket base.

FWIW,
CBODY67

 

[jbooth35]

Back in business. My son designed and 3D printed a spacer that allowed me to use original air cleaner.

 

[Luke Pokrajac]

Given that "jumping" needle on your vacuum gauge...I'd suspect valve issues somewhere...burnt valve, bad guides, etc. Vacuum reading on a 383/440 with standard cam should be around 18-19" of vacuum with no needle movement...rock steady at idle.

 

[jbooth35]

Given that "jumping" needle on your vacuum gauge...I'd suspect valve issues somewhere...burnt valve, bad guides, etc. Vacuum reading on a 383/440 with standard cam should be around 18-19" of vacuum with no needle movement...rock steady at idle.

That’s what I was thinking too, but the car actually ran pretty good. Vacuum is steady after switching carbs to the AVS2 and using the manifold port on the new carb.

 

[Luke Pokrajac]

That’s what I was thinking too, but the car actually ran pretty good. Vacuum is steady after switching carbs to the AVS2 and using the manifold port on the new carb.

That's great! I actually gained 1" of vacuum on my 383 after changing to new 440 source heads. My car ran great with a bit of valvetrain noise on old 906 heads. After pulling them I had 2 exhaust valves that were down in the seat pretty far. I suspect that I have some worn valve guides also... All to be expected at 124K.