Tuning SQ4 by ear

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Tuning SQ4 by ear

Postby adrian.hannam » Sun Aug 23, 2020 9:13 am

Seeking advice. I meticulously timed my Mk1 ignition at TDC on #1. I am now doing road tests. 15 miles so far, and next step is re-tension the head at 50 miles. Beyond that I would like to know more about optimising the ignition timing. After setting the ignition with a timing disk, I am hesitant to now play with the timing. I understand that after marking the staring point, you move the distributor this way or that until you get the best result. Not being experienced at multi cylinders, I am looking for some shared wisdom as I really don't think I have a good ear for engines. What is the best result? Plug colour? Easier starting? Best cruising? Bit of gut feel? I have mostly been doing slow running, which so far is ok, but short runs at 50mph are a little uninspiring. Also, silly question but Is the fastener you loosen to move the distributor for this test the vertical set screw or the horizontal clamp bolt and how much to move it? Thanks, Adrian.
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Re: Tuning SQ4 by ear

Postby Bob.Murphy » Sun Aug 23, 2020 10:35 pm


Its a long time since I had a 4G (or a car with a distributor for that matter) but normally the horizontal clamp plate stays locked onto the distributor body, the vertical locking bolt is loosened and the slot in the clamp plate (plus distributor) moved below it. A marker pen is used to mark the start and finish positions so that you can return to the starting point if it didn't improve.

This sounds easy, but actually you may have to slacken both clamp bolts, hold the distributor firm (no movement) and adjust the clamp plate so that there is some available adjustment in the slot before you start.

How much movement per adjustment ??? Small amounts only (i.e. half the width of the vertical lock bolt's stem). Only adjust one thing at a time (i.e. timing or carb) or you won't know where you are ;) .

How to judge the result ??? I would start by advancing the timing a bit, if you overdo it there will be pinking - which is bad. If you over retard it the exhaust pipes may turn blue - which is worse and less easy to fix :roll: .

Aim for smooth running, clean acceleration, no hesitation at speed and decent fuel consumption and plug colour. If you achieve all of this . . . Tell us how :lol: .

Good luck.

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Re: Tuning SQ4 by ear

Postby Gui.dorey » Mon Aug 24, 2020 1:55 pm


I just went through that, so here’s how I did it. I have no claim on being perfectly correct, it’s just how I went about it.

After the initial timing, I marked the distributor with a sharpie to have a reference - see picture, you’ll see my markings in blue. Btw, that bolt you see is the one that you need to loosen to turn the distributor.

I then went for several rides for the final adjustments. You must bring the engine to it’s operating temperature, which for me takes about 5 miles, and I try not to go faster than about 70km/h. I know she’s fully warmed up when my oil pressure gauge starts to drop.

Then look for a good stretch of empty straight road where you can ride back and forth in peace. I take her up the gears to 80-90 km/h and see how she sounds and feels - engine smoothness, how she pulls, acceleration, and how the engine sounds. You’ll soon pick up on what to listen to and what you feel. Then stop and loosen that bolt and turn the distributor a little bit in one direction - I’m talking about maybe a mm from that initial marking you made. Then go again for a run down the road. You’ll soon start noticing the difference and that something is not running so well as before. That’s the point where you stop and turn the distributor back to the point where you felt the best performance.

A few points from my experiences. When you advance the distrib. you’ll notice an increase in rpms and it actually sounds better. And I so I thought I was going in the right direction, but soon I noticed that during the run down the road my vibrations were worse, the engine sounded rougher and the acceleration was worse. AND there was never a sign of a ping, so you can’t go by that. In the end I actually had the best performance by retarding an increment from my starting position! Although when I was adjusting the dist. and listening to the idle it actually sounded worse as if the engine was struggling and wanting to die, but this was just because before it was too advanced and the idle was racing. I had to do a slight adjustment to the idle screw and now I know that idle is the correct one.

Buuuut, before all this I had to do several rides to get the idle mixture adjusted properly and get used to how she was running. So my advice is to first do a couple hundred miles to let her settle down and get everything else a bit bedded in, torque down the head a few times and for you to get a reference on how she runs before trying to play with the distributor. Unless it’s completely off it shouldn’t hurt anything.

BTW I never really looked at the plugs to try to read the ign advance. At least I don’t really think I can read them in that regard. For me reading the plugs was always more of an indication for the mixture (rich/lean).

Best of luck and let us know how you get on. I’m also still learning.


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