Good Initial Timing and Too much Total Timing Problem. Seeking guidance to minimize total timing. 1969 Swinger 340 4 Gear

[Cubzy]

I have a 1969 Dart Swinger 340 4 Speed. Recently purchased and trying to uncover and rectify a couple performance gremlins.

Have a little bit of background how to check timing. Motor was warmed and idle set to 700rpm. I disconnected the ported vacuum advance and plugged carb port to prevent vacuum leak. Set timing light to spark plug wire one and tach wire to coil negative terminal.

Initial idle timing is 12deg BTDC. This seems reasonable but feel free to comment.

Ported vacuum advance line was connected to the distributor and rpm increased to 3000rpm where timing increased from 12 to 57deg BTDC. I’m sure timing should have maxed out around 36deg BTDC. Looking for guidance what I need to do to rectify this.

Known items. Discovered today during testing spark plug wires on cylinders 5 and 7 are both intermittently shorting to the hooked header pipe. I ordered replacement 8mm wires today with Wire socks.

I have hesitation off idle currently and under hard acceleration it really stops pulling around 2500rpm. At around 2500-4000rpm I can see what looks like smoke coming from tailpipes in rear view mirror. But no smoke or visible smoke at idle. Only higher rpm. Looking at spark plug tips they are white and not golden brown. I assume misfires and timing is most likely linked to the tailpipe smoke. The motor was professionally rebuilt 3 years ago with limited runtime. Standard deglazed bore with new rings. Almost certain it’s not burning oil in the chambers.

No sign that the Harmonic Balancer has slipped. I have an Accel Dustributor. Upgraded to Mopar orange electronic ignition. Seeking help what to look for in distributor to reduce total mechanical timing, vacuum canister, springs, weights etc.

Thanks in advance.

 

[RustyRatRod]

With the vacuum can connected, 57 is perfectly acceptable. You don't include the vacuum advance when measuring initial timing. The total timing usually ends up between 32 and 36 degrees. That's initial plus mechanical. If you need to limit the total mechanical advance, it's time to disassemble the distributor, weld up and file the governor slots to the specific width to give you the advance you need.

 

[Cubzy]

With the vacuum can connected, 57 is perfectly acceptable. You don't include the vacuum advance when measuring initial timing. The total timing usually ends up between 32 and 36 degrees. That's initial plus mechanical. If you need to limit the total mechanical advance, it's time to disassemble the distributor, weld up and file the governor slots to the specific width to give you the advance you need.

Hi. Are you saying with the vacuum hose connected to the distributor pot that 57 degrees at 3000rpm is okay? I thought this should be 32-36 degrees?

 

[RustyRatRod]

Hi. Are you saying with the vacuum hose connected to the distributor pot that 57 degrees at 3000rpm is okay? I thought this should be 32-36 degrees?

Yes. It's fine. The 32-36 degrees is without the vacuum can connected, just like I said the first time.

 

[Cubzy]

Yes. It's fine. The 32-36 degrees is without the vacuum can connected, just like I said the first time.

Okay so just that I’m clear. I should keep carb vacuum hose disconnected and rev to 3000rpm. This should then be 32-36deg and after hooking up to distributor pot it should be 57deg at 3000rpm. What are those two terms called? I might have to search a video as I’m now confused.

 

[TT5.9mag]

“All in” timing is initial plus mechanical with some kind of curve that references RPM. vacuum advance is added on top of all in timing usually for cruise economy and the rate it comes in, as well as when it starts coming in are adjustable.

 

[RustyRatRod]

Okay so just that I’m clear. I should keep carb vacuum hose disconnected and rev to 3000rpm. This should then be 32-36deg and after hooking up to distributor pot it should be 57deg at 3000rpm. What are those two terms called? I might have to search a video as I’m now confused.

Correct. You also need to plug off the hose going to the distributor while you're checking timing or it will leak vacuum and possibly throw off your measurements.

 

[69FBCuda]

Did you check timing at 3000rpm with the vacuum advance disconected?

 

[66fyssh]

Initial Advance - engine at idle and vacuum advance plugged

"all-in" - vacuum advance still plugged, increase engine RPM until timing stops increasing. This is where you want 32-36ish. I'll add, this is the combination of initial plus mechanical advance from the weights in the distributor.

Then when you add vacuum advance it can shoot up into the 50's.

 

[69FBCuda]

Initial Advance - engine at idle and vacuum advance plugged

"all-in" - vacuum advance still plugged, increase engine RPM until timing stops increasing. This is where you want 32-36ish. I'll add, this is the combination of initial plus mechanical advance from the weights in the distributor.

Then when you add vacuum advance it can shoot up into the 50's.

This clarifys the process greatly.

Thanks

 

[Cubzy]

Did you check timing at 3000rpm with the vacuum advance

Initial Advance - engine at idle and vacuum advance plugged

"all-in" - vacuum advance still plugged, increase engine RPM until timing stops increasing. This is where you want 32-36ish. I'll add, this is the combination of initial plus mechanical advance from the weights in the distributor.

Then when you add vacuum advance it can shoot up into the 50's.

Thank you. This makes sense now. I will test this out again to confirm the mechanical advance. Suspect it’s going to come in at 57deg minus 12deg and be around 45deg if my math is correct. Still maybe to much mechanical advance?

 

[RustyRatRod]

I'll also add this. The timing curve isn't the same across the board. It is very combination dependent. In other words, all the figures talked about here will get you on the playing field. But you will need to further experiment with it to narrow it down more.

 

[66fyssh]

RRR is right on.

My 5.9 Magnum likes 20⁰ initial. I use an FBO advance limiting plate set at 14⁰ for an "all in" of 34⁰.

 

[Cubzy]

RRR is right on.

My 5.9 Magnum likes 20⁰ initial. I use an FBO advance limiting plate set at 14⁰ for an "all in" of 34⁰.

Shouldn’t initial timing(12 in my case)plus mechanical timing(haven’t tested this yet)=all in timing(57 in my case) 12+mechanical timing=57deg. Therefore my mechanical timing is 45deg which would be the mechanical timing. This sounds like way to much? What am I missing?

 

[Dartfreak75]

Shouldn’t initial timing(12 in my case)plus mechanical timing(haven’t tested this yet)=all in timing(57 in my case) 12+mechanical timing=57deg. Therefore my mechanical timing is 45deg which would be the mechanical timing. This sounds like way to much? What am I missing?

What you are missing is that you are including the vacuum advance! Your total timing is your initial plus the mechanical advance in the distributor. Let's just say 20 degree. So 20 plus your 12 initial is 32. Now you have the vacuum advance adding even more. So 32 plus 25 in the vacuum equals 57. You have two timing advance situations going on. The vacuum advance works off you ported vacuum so under load the vacuum dropps and your timing will go back to your total without the can. That's why you have to check timing with and without the vacuum can hooked up. Hope that helps

 

[Dartfreak75]

Here is a video I made. A while back it may help explain it better.

 

[66fyssh]

It's just words.

You want to limit initial plus mechanical to be under about 36. That'll help keep detonation in check.

When adding in vacuum advance, it just ends up where it ends up.

 

[RustyRatRod]

Shouldn’t initial timing(12 in my case)plus mechanical timing(haven’t tested this yet)=all in timing(57 in my case) 12+mechanical timing=57deg. Therefore my mechanical timing is 45deg which would be the mechanical timing. This sounds like way to much? What am I missing?

You DO NOT INCLUDE VACUUM ADVANCE speaking about timing. It is whatever it is when you plug the vacuum can in, UNLESS you have an adjustable vacuum can and then you can use that to tailor the vacuum advance to come in at different vacuum levels. Total timing = initial idle timing plus the mechanical advance in the distributor and DOES NOT INCLUDE the vacuum advance. The vacuum advance is ON TOP OF the total. "MOST" vacuum advance cans pull in about 20 degrees of timing, so if you're at 57 now, you are probably "around" 37 degrees total.

 

[Mattax]

Terms Related to Timing

Initial or base timing: Timing at an rpm with no advance added.
Normally on a stock engine timing at idle is the baseline. Idle is usually 500 - 650 rpm (pre-smog), or 600 - 700 rpm smog era.
Hot rodded and race engines requires some trial and error tuning to get the idle speeds down anywhere close to 700 rpm.
When you are measuring timing at idle it is critical to note the rpm. Timing at 800 or 900 rpm will likely be base timing plus some advance unless the spring tension is increased. Don't worry about it. Just write down the rpm.

Mechanical Advance: Degrees added by the distributor's weights moving outward with rpm. Usually just called advance.

Total Timing: Initial timing plus the maximum mechanical advance. With hot rods and race engines, sometimes the idle timing is very unstable, especially early in the tuning process. For that reason, a high rpm timing measurement is a better reference. For example, mopar performance instructions suggest measuring at 2800 rpm.

Main Purpose of Spark Timing

Mechanical or Centrifical Advance:
Compensates for the reduced amount of time (miliseconds) available for the burn as rpm increases. Because engine efficiency decreases burn time as rpms climb the rate of advance is not always propertional to rpm. A 'low performance' 318 usually has good lower rpm efficiency, but does not gain as much efficiency with increasing rpm. A 'high performance engine' is usually the opossite.

Vacuum Advance:

Vacuum advance is in addition to the initial timing and the mechanical advance.
Removing and plugging the vacuum advance hose (golf tee works well) is the standard procedure when measuring timing.
_____________________________________________________________________________________________________________________________


With vacuum advance connected 57* at 3000 rpm is on the high side but in the ballpark . Factory would be closer to 50*

Your '69 4 speed was originally setup to reduce emissions at idle and while coasting. It came with a distributor setup with a long and fast primary advance curve to compensate for the idle emissions. IF your car is setup with that distributor, or a distributor with similar advance, then initial has to be set lower.

More about this the next post

 

[Mattax]

Emissions & Timing.

Chrysler's answer to reduce excessive HC and CO was to make idle fuel mixtures leaner and at the same time retard the timing at idle. Reducing the initial timing put more heat into the cylinder wall (burn completes while the piston is further down the hole) at idle. To make up for the loss in power, idle speed was bumped up - especially needed with automatic transmissions.

The 340 was released in '68; all came with CAP (Clean Air Package) AFAIK.
So lets look at timing for a 273 4bbl to see how these idle settings in the CAP package were compensated for in the distributor advance.

By 1800 rpm the timing is essentially the same in both.

Your 340 probably has a distributor advance intended for initial timing of TDC or 5* but we don't know (unless you have the original distributor).
So you need to measure and plot the timing from as low of rpm as it will run, to at least 2000 rpm, preferably to 3000.
Then, if and only if it has a curve shaped like above, you set a baseline that will be ballpark:
1. Set the timing so from 1800 to 3000 rpm so its close to factory.
2. If, and only if, it has a long primary advance like the CAP 273, you can try connecting the vacuum advance to a manifold vacuum source.
3. Modify the advance governer by welding the inside of the slots and use the ported vac source for vacuum advance.


Here's the '69 340 timing for a 4-speed graphed.

My opinion, and its only my opinion, is the upper rpm timing is conservative. Even for street use (long trip with engine fully heat soaked) the engine might like a bit more advance assuming high octane fuel is available. Mopar may have done this on purpose in 68-69, knowing that mechanics might reset the inital a little higher if the specific engine and local conditions allowed.

 

[Mattax]

At around 2500-4000rpm I can see what looks like smoke coming from tailpipes in rear view mirror.

Under hard acceleration, it could be excess HC (unburned fuel) and/or NOx. An observer may be able to tell you based on color and smell.
Look at the spark plug porcelain for small specks that might be aluminum. That would indicate detonation under hevy load even if you didn't hear the rattle or ping.

Get the idle and centrifical timing figured out. Then you can work on air fuel mixture. Then you can tweak the timing and retweak the AFR as many times and ways you are willing to investigate to find improvements.
My suggestions for a procedure to Tune for Performance.

And for your carb, this may be helpful

How to read carb calibration chart?

I’ve learned a lot from this thread. Hopefully sometime this week I can order a few parts and find some time to piddle with it. I’ll come back in here and post what I do. Thanks guys. I think the metering rods are about 12 bucks and a set of Springs is around $9 if I'm not mistaking.. Remember...

www.forabodiesonly.com

 

[Mattax]

Just noticed you wrote you have an Accel distributor. I have no idea what type of advance mechanism is in it. You'll have to post some pictures, and more than befoer you will have to measure and plot the timing to know what the advance curve looks like.

 

[Dartfreak75]

Terms Related to Timing

Initial or base timing: Timing at an rpm with no advance added.
Normally on a stock engine timing at idle is the baseline. Idle is usually 500 - 650 rpm (pre-smog), or 600 - 700 rpm smog era.
Hot rodded and race engines requires some trial and error tuning to get the idle speeds down anywhere close to 700 rpm.
When you are measuring timing at idle it is critical to note the rpm. Timing at 800 or 900 rpm will likely be base timing plus some advance unless the spring tension is increased. Don't worry about it. Just write down the rpm.

Mechanical Advance: Degrees added by the distributor's weights moving outward with rpm. Usually just called advance.

Total Timing: Initial timing plus the maximum mechanical advance. With hot rods and race engines, sometimes the idle timing is very unstable, especially early in the tuning process. For that reason, a high rpm timing measurement is a better reference. For example, mopar performance instructions suggest measuring at 2800 rpm.

Main Purpose of Spark Timing
View attachment 1716259195View attachment 1715447028

Mechanical or Centrifical Advance:
Compensates for the reduced amount of time (miliseconds) available for the burn as rpm increases. Because engine efficiency decreases burn time as rpms climb the rate of advance is not always propertional to rpm. A 'low performance' 318 usually has good lower rpm efficiency, but does not gain as much efficiency with increasing rpm. A 'high performance engine' is usually the opossite.

Vacuum Advance:
View attachment 1716259196

Vacuum advance is in addition to the initial timing and the mechanical advance.
Removing and plugging the vacuum advance hose (golf tee works well) is the standard procedure when measuring timing.
_____________________________________________________________________________________________________________________________


With vacuum advance connected 57* at 3000 rpm is on the high side but in the ballpark . Factory would be closer to 50*

Your '69 4 speed was originally setup to reduce emissions at idle and while coasting. It came with a distributor setup with a long and fast primary advance curve to compensate for the idle emissions. IF your car is setup with that distributor, or a distributor with similar advance, then initial has to be set lower.

More about both of this the next post

This is a great explanation! Thanks!

 

[halifaxhops]

OK how do you see the 57? Dial back timing light? Digitals are great dial backs are usually off.

 

[Cubzy]

OK how do you see the 57? Dial back timing light? Digitals are great dial backs are usually off.

Yes it’s a digital light with the variable push button adjuster by Innova. Are these susceptible to error?