Setting Ignition Timing and adjusting mixture strength - Help Please

[John P]

Hi,

I’m continuing to try to improve the rough running of my Ulsteroid which has a mildly tuned 2-bearing coil engine. (Oversized inlet valves, Ruby head, flattened cam followers and a 1 ¼” SU Carb).

It has a centrifugal advance DK4A distributor which I suspect is part of the trouble but before stripping it down I wanted to eliminate any timing or mixture settings. The trouble is I’m not sure if distributor wear or wrong timing is masking an incorrect mixture setting.

I initially set the timing to TDC static and the car starts easily and runs reasonably OK but is very rattly at low speeds improving once you’re up to 30 MPH.

As I understand it the auto-advance provides a maximum of 16° so with the static timing at TDC this is presumably the maximum advance.

On-line I’ve seen recommendations that maximum advance should be between 22° and 27° so presumably I need to set the static timing to around 6° but is this correct? I have tried adjusting it “By Ear” but quite significant rotation of the distributor body doesn’t seem to make much difference.

I’m hoping to get the timing “right” so that I can move on to the mixture as currently I can’t reach a point where lifting the dashpot causes the tickover speed to rise and then fall back which is what I believe is the correct procedure.

Any advice would be appreciated,
John.

[andrew34ruby]

Are you setting the timing 'by ear' with the car stationary? I suggest you drive the car on the flat and up a hill, see how it goes. Then change the timing and drive it again. You should be able to 'home-in' on a position that goes fastest but also smoothest. I have done this with my seven, but there are others on here with much more seven experience than me.

As for the mixture, what colour are the spark plugs after a good run?

[Reckless Rat]

Setting the timing static at TDC will allow the engine to run, but it's probably not advancing enough at higher revs. Assuming that your dizzy is in good order and the bob weights and springs are working correctly, a static timing set up should be at around 1 1/4" BTDC, measured on the flywheel. However, it does seem to be a thing with Austin Sevens that the best way to fine tune the timing is out on the road as already stated. Ideally you should advance the ignition until the crank starts to rumble, and then back it off a bit.

If your dizzy is tired, you may never get it to run right.

On the circumference of the flywheel (if you can see it) is a scribed line marked 1/4 which when vertical corresponds to TDC. Rotate the flywheel for 1 1/4" (clockwise if you're looking at the clutch) and then set the static timing with the points just opening (use a test lamp). That should be not far off IMHO.

[John Cornforth]

Hi John P

My engine setup is not dissimilar. Two bearing (phoenix) crank, Late Ruby head and 1 1/8 inch SU on an ally "log" style manifold with repro nippy exhaust.

I found that timing marks added to the camshaft pulley work well, together with a small ally fixed pointer. I use a Xenon timing light with inductive "clothes peg" pickup. If you have timing scatter from gear train or dizzy spindle wear, you really need to sort that before going further. The timing lighs will soon show how steady things are.

As you say, a new DK4A has an advance of 16 crank degrees. Austin used to advise a few degrees of static advance for the HC head, this varied a little over the years with different handbooks. So the max total advance would have been perhaps 20 to 23 degrees. I have a suspicion that the squish turbulence imparted by the HC head means that less advance is needed than might otherwise be the case.

As you dial in more advance, the peak combustion pressure (and noise/harshness) increases. What you actually want is an increase in average combustion pressure and therefore torque. The latter is not quite so affected by timing, and there is a case for backing off the advance so that the torque is slighly reduced, in exchange for a more noticeable reduction in peak pressure. This is maybe particularly the case with a 2 bearing setup, where the added pressure of a HC head will exacerbate crank whip and harshness. You will notice this mostly around the 2000 to 2200 RPM resonance which annoyingly is around 30 mph. Why they went to 3 bearings I suppose.

Turning to the SU setup, all the official publications make the (unstated) assumption that the needle is one which the manufacturers have chosen for that exact engine setup, based on hours of bench testing. You will be able to set the idling mixture by jet nut adjustment, but this has less and less effect as the needle rises during driving at medium and high power outputs. Any need you have for mixture adjustment in the range you actually use when driving is only possible by swapping needles based on trial and error/rolling road. To be honest, the engine is fairly tolerant of a slightly too rich mixture, the only downside is fuel cost which isn't quite so much of an issue for a low annual mileage.

I have never had much luck reading plug colours on a seven. Maybe it's modern fuel, maybe it's than any colour is quickly obscured by a short period of sooty idle. You could always try the "plug chop" method (look it up) but it always seemed too much faff to me.

[John Cornforth]

Hi again

It is (or should be) well known that the earlier Ruby handbooks erroneously still gave the timing settings as for the earlier Manual distributor models, i.e. 1 1/4 to 2 (one and a quarter to two) inches which corresponds to 14 to 23 degrees. The manual models were set at full advance.

The later versions of the Ruby handbook called for 1/2 (half) an inch, which corresponds to 5.5 degrees static advance.

Sorry Rekkers, I have to take issue with your recommendation !

[Bob Culver]

Auto advance distributors are often a problem. May not be correct type, wrong or stretched springs and often very worn. The holes in the limiter plate often much enlarged. 27 deg full advance comes from the racer boys pursuing astronomic revs far beyond the top speed of a Ruby. The 1 1/4 static setting is near operating advance for manual advance models. For road cars where things happen slowly I  much favour manual advance. If curious can rig a mower control to operate as override. The minimum advance for full power, as judged by performance not noise, is the ideal.
The simple cheap old style spark powerd timing lights were useful for checking excessive slow speed advance, full advance, wander, scatter etc but awkward on the cam pulley 
Note the recommendation in early Ruby book is wrong and was a carry over from the manual model.
The Williams Specials book recommended  (for fast driven cars) 1 7/8 inch.full advance.. Fuels have changed; some reckon this makes adifference, some not.
If can find a suitable long thread the advance can be twisted to full and locked with a washer on top of shaft so can determine approx full actual advance.

[Malcolm Parker]

It is always very difficult to make adjustments when you are altering two variables at the same time.  I would set the jet of the SU carburettor about 1/32" below the bridge, generally about 8 flats of the hexagonal adjusting nut.  Use either an EB (Mini) or AN (Morris 1000) needle, both of these are known to suit an Austin 7.
Using a test lamp, adjust the distributor so that the points are just opening when the engine is at TDC.   Fire up the engine and advance the timing by turning the distributor until the idling speed rises without the engine sounding rough.
If you can't get the engine running smoothly, I would suspect the late Ruby head.  Many engines, especially if they are a bit worn, run roughly on the late head. Perhaps you could borrow an earlier head to see if it improves things?

[John Mason]

When messing with carburettors it is important to have all the other things correct before starting on the carb. Check and adjust if necessary both valve and ignition timing.

John Mason.

[John P]

Thanks for all the advice.

I'm going to add a timing pointer adjacent to the camshaft pulley so that I can use a timing light to both see if distributor wear is making the timing vary and then set the timing.

I guess I will need to paint some marks on the rim of the pulley, presumably at least one for TDC to ease the initial static setting and then another at say 22 degrees BTDC and use the strobe to match this mark with the pointer with this second mark at maximum advance.   (Unfortunately my timing light doesn't have the facility to set a variable BTDC). 

As the pulley is relatively small these marks will be fairly close to each other and also need to be very accurately so how have others done it?

John.

[John Cornforth]

Hi John P

The pulley rim is 108 mm (4 1/4 inches) in diameter and represents 720 engine degrees, so 10 degrees is 4.7 mm and 22 degrees is 10.4 mm.

I made a small filed notch mark with a tiny blob of white paint on either side for contrast

I set TDC by using a dial gauge clamped to the cylinder head with a rod down the spark plug hole. Best to set the TDC point midway between two points slightly either side of TDC