Author Topic: Everybody should check their ignition timing!!!  (Read 30701 times)

ScottRT

  • Guest
Everybody should check their ignition timing!!!
« on: March 21, 2009, 11:12:08 PM »
One thing every mini owner with classic Lucas points-type distributors should check is their distributors advance. I don't feel enough people understand just how important this is for power and economy. So... about that dizzy:

Does it work? Where is it at idle? Does it advance to 32 ~ 33 degrees Before TDC when "all in"?

Lotsa owners probably say "my car runs fine", but these dizzy's do get old and the springs get weak, and you should check it out.

Why should I check?: Having spark timing that lags (is retarded)from what the engine wants can easily cost you 25% in power and economy, yet still appear to run smoothly. Retarded timing also makes and engine start harder and run hotter.

How do I check it?:

-- You need a timing light and a tach, preferably. But first things first.
 -- Warm up your engine, and set your idle for 900 rpm. These cars will idle at lower speeds if the carbs are in good shape, but the water pump is very inefficient at lower rpms, and your ignition light will probably be on, so set idle at 900 to 1000 rpm.
-- Disconnect the vacuum advance tubing from the dizzy and plug the end of it during testing. When done, don't forget to hook the vacuum line back up. All street cars can benefit from vacuum advance. More economy will be realised when cruising.
-- Check the timing. Typically somewhere about 10 degrees before TDC is what you should find at idle. Slowly rev the motor up until your get maximum advance, or "all in". Did it make it to 33 degrees, or close to it? At what rpm did things reach 'all in"? Warmed up 1275 and big bore engines generally like all the advance in before 4000 rpm. Smaller bore engines like the timing to advance a little slower to avoid ping...maybe "all in" at 5000 rpm.

If you're not geting results like outlined above, you should have things checked out. A common problem is that the 2 small distributor advance springs get weak, and allow a good portion of the mechanical advance to come in while still only at idle speed. So what happens is people set the idle advance to 10 degrees BTDC, and wonder why they only have 22 or 25 degrees when"all in", and why the dizzy achieves "all in" at only 2400rpm.

It's important for a stable idle that no advance comes in until speeds above idle.

I went thru a few springs until I found a pair that allowed my advance to begin at just above 1000 rpm, and went "all in" at 3750 rpm. My 25D Dizzy has 12 degrees of mechanical distributor advance (24 crankshaft degrees), so I set my idle timing at 10 degrees, and have 34 degrees when I'm all in. SO far the engine loves if, but if it wants to ping during hot weather, I will retard it a couple degrees at a time till it's happy again.

A properly timed engine will happily rev-up. If your engine seems to run out of breath at 4000 rpm it could very well be the timing that's holding it back!!

A word of caution.. Try to find the proper specs for your engines timing requirements. If you have a custom motor, check the popular tuner books for advice on what to try for timing figures. Each engine type has its own perfect advance curve, and different dizzys have different amounts of advance that they throw in. I am merely trying to give enough insight that you can take a quick look to see if your engine is in the ballpark. I know there are ALOT of owners that don't know if they are or not. This is free HP and MPG to be had.

Scott T.
« Last Edit: March 28, 2009, 07:20:27 PM by ScottRT »

Offline 94touring

Re: Everybody should check thier ignition timing!!!
« Reply #1 on: March 22, 2009, 12:51:41 AM »
Very nice write up, this is what I like to see!

Offline MD-IN-UK

Re: Everybody should check their ignition timing!!!
« Reply #2 on: March 25, 2009, 01:17:44 PM »
Copied and pasted for referance. Thank you for such a well written piece.
THE BITTERNESS OF POOR QUALITY REMAINS LONG AFTER THE SWEETNESS OF LOW PRICE IS FORGOTTEN

Offline xcc_rider

Re: Everybody should check their ignition timing!!!
« Reply #3 on: March 28, 2009, 08:12:54 AM »
Not bad advice as I was one of the "it runs fine" guys. Since a PO put the flywheel on wrong I didn't have timing marks anywhere to go by so I procrastinated for a year or two. I finally got a hold of Doug Lawson and he worked me through finding TDC using a dial indicator, making a pointer and marking my vibration dampener for TDC, -5, -10 and -15 deg. It's amazing when you find out you had 38 deg advance on your engine without the vacuum advance engaged. (yes it will run like that) I've worked it down to 18 deg adv and there's much more power and lower operating temps in the summer. I've still got to lower it down to spec but there's other priorities to work on for now. 

So check it when you buy it...   dan

Offline 94touring

Re: Everybody should check their ignition timing!!!
« Reply #4 on: March 28, 2009, 10:25:00 AM »
I use to just turn the dizzy till it "ran fine".  It is amazing how much better the engine will run when its done properly. 

Offline notabmw

Re: Everybody should check their ignition timing!!!
« Reply #5 on: May 15, 2009, 09:51:38 AM »
I took today off and am going to check mine now

Offline MEhinger

Re: Everybody should check their ignition timing!!!
« Reply #6 on: May 15, 2009, 12:34:51 PM »
Great write-up and thanks. It does beg the question of where you go to get a selection of springs to get the results needed.

Offline notabmw

Re: Everybody should check their ignition timing!!!
« Reply #7 on: May 16, 2009, 09:44:23 AM »
Checked mine yesterday.  Here is what I got:

10 deg @ 900-1000 RPM

29 deg @ 4000 RPM

32 deg @ 5000 RPM

I had a mis-fire problem under heavy load.. 4th gear - foot to the floor.. It was farting & puking at about 4K rpm..
Turned out to be the coil... There was a crack where the wire plugs in.. hidden under the rubber boot.  Changed out with a 3 ohm flame thrower.. now she pulls like a train again.. :)

Offline deanwilhite

Re: Everybody should check their ignition timing!!!
« Reply #8 on: September 18, 2013, 08:48:29 PM »
This would be better if you started out assuming the reader knows squat.

Pretend I've never done this job and give me more details. Particularly what I'm looking for.

Where should the white lines line up? Top point on the jagged edged part/Bottom? What do the jagged edges represent? 1 degree or 10.

Offline John Gervais

  • A Really Swell Guy
  • 1380cc
  • *****
  • Posts: 685
  • Total likes: 23
  • Karma: 0
    • Copenhagen, Denmark
Re: Everybody should check their ignition timing!!!
« Reply #9 on: July 26, 2015, 07:59:48 PM »
I used set my ignition timing by increasing the engine rpm to 2000 and advancing the ignition until the rpms stopped rising, then retarding the ignition until the rpms drop by 250 rpm and clamping the dizzy then returning the idle speed to 1000.  It worked fine, for the most part.

But - now that I've got gauges, I use a vacuum gauge (either the one in the car or under the bonnet and holding a hand-held one) and a downloaded .jpg image scanned from a 1960's vacuum gauge instruction sheet... 

In my opinion, the vacuum gauge is super valuable and frequently overlooked.

Here are the relevant pages:

Hmmm, size matters...

Ok, the nuts and bolts of using the vacuum gauge:

Setting Ignition Timing by using a Vacuum Gauge

1.   Warm engine to normal operating temperature
2.   Leave the vacuum advance unit (if fitted) connected
3.   Ensure that the idle speed is fast enough so that the ignition warning lamp is 'off' - adjust if necessary - 1000 rpm is usually sufficient.
4.   Connect a vacuum gauge to the intake manifold vacuum take-off; many carb spacers have one, if you don't have one on yours, it's nice to have. 
5.   Note the vacuum reading.
6.   RICHEN the air/fuel mixture slightly - the previously noted vacuum reading should drop slightly and remain steady.  This eliminates erratic vacuum gauge readings due to lean misfire.
7.   Loosen the dizzy clamp and if you've got a 25D4 distributor, adjust the vernier wheel to a central position.
8.   Retard the ignition by turning the distributor counter- clockwise slowly and watch the vacuum gauge needle drop slightly.
9.   Advance the ignition timing by slowly turning the distributor body clockwise until the highest vacuum gauge reading is achieved and the vacuum gauge needle begins to 'flicker' or 'kick'.
10.   Retard the ignition timing slightly to achieve the highest STEADY/STABLE vacuum gauge reading.
11.   Retard the ignition timing further, just enough to drop the vacuum gauge reading an additional 3/4" Hg.
12.   Tighten the distributor clamp.
13.   Re-adjust the carburettor idle speed.
14.   Re-adjust the air/fuel mixture.

That's it -

« Last Edit: July 26, 2015, 08:29:14 PM by John Gervais »
- Pave the Bay -

Offline Dmulder

Re: Everybody should check their ignition timing!!!
« Reply #10 on: September 19, 2015, 02:17:33 PM »
what if I don't have a tach?  How do I go about doing this project without one?
"In like a lamb, Out like a lion."

Offline 94touring

Re: Everybody should check their ignition timing!!!
« Reply #11 on: September 19, 2015, 03:05:54 PM »
what if I don't have a tach?  How do I go about doing this project without one?

I had an old junk tach in my pile of parts.  I bet you could get a cheap one at an auto parts store as well. 

Offline MPlayle

Re: Everybody should check their ignition timing!!!
« Reply #12 on: September 19, 2015, 04:30:55 PM »
Advanced Auto parts and Autozone both seem to carry some basic tachometers under $50.  I would recommend getting an 8000 rpm tach - that will give it some margin at the top as a basic road car can rev very near 6000 rpm.

Offline Flyinace2000

Re: Everybody should check their ignition timing!!!
« Reply #13 on: October 11, 2017, 11:51:21 AM »
I've noticed that my throttle response is a bit hit or miss.  Last night i re-checked my timing, it was a bit off so i got it back to 8 BTDC.  One question I had is how stable should that mark be?  It would jump ahead (down a few notches) every second or so.  I would say it was stable for about 80% of the time.  Another thing i noticed is that vacuume advanced was way to sensitive and with very little throttle it would go full advance to 30'ish BTDC.  So that probably needs replacing.  Are these 2 issue or just one?

Offline BruceK

Re: Everybody should check their ignition timing!!!
« Reply #14 on: October 11, 2017, 09:00:45 PM »
I dunno.   My car has done the same thing.  I wasn't sure if the occasional timing light bounce was just a function of low tech equipment.   But perhaps someone more knowledgeable will comment?
« Last Edit: October 11, 2017, 09:17:57 PM by BruceK »
1988 Austin Mini
2002 MINI Cooper S
2007 Triumph Bonneville