Learning to Tune

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Originally Posted by marting

Hi Dan
The engine doesn't need to hunt as such. What you are really looking for is the sweet spot where the idle is the smoothest (generally also the fastest). Try winding the mixture screw in until you hear the engine revs start to slow and then wind the screw out about 1/3 to 1/2 a turn. This should be close to the correct mixture, and the engine should be happiest here. Check by continuing to wind the screw out, the engine revs should change (slow) again within at most another full turn.
Also this needs to be done with the engine at normal operating temperatures.
Cheers, Martin

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The above info is just what I was looking for, so rather than just thank the post - I thank you in person. :)

Made some progress tonight, with Killer dropping by to lend assistance. So - firstly set the gap. I turned the engine over with the hand crank, until we hit TDC...my flywheel has been marked for this purpose, so we align the marking with the white triangle indicator seen through the flywheel viewing cover....now we could set the gap using feeler gauges (mine had closed up to 6 thou) so we sorted that to about 15 thou....all you need is a flat end and phillips screwdriver. Gap set. Right, now....attach the 5W bulb to set timing the next task....positive to low tension connector, negative to earth....turn the dissy, and finally the bulb starts a glowin as the points just open - timing set correctly.....so I tightened that darned distributor nut.....so she's all good. Sounded so sweet when we fired her up.

Armed with your info above, Martin, I have no fear and will attempt to set my carby tomorrow night!

My plan is to make an instructional video of the entire procedure for everyone's benefit.....Maybe all of this is common knowledge, but if it helps even a single extra soul, then it'll be worth it.....and we can drink beer! The vid will feature the who's who of Land Rover madness....the good knight, Killer, S3 ute et al - so stay tuned for that extravaganza. :)

SLOW Inc's first feature epic. Will post an official workshop day for those wishing to be extras.

Would I be right to think that dwell angle will vary with rpm? Maybe decrease with increasing rpm? The reason I ask was because I was going to ask if anyone had measured a 2 litre spread bore dwell angle when the gap was set correctly, but then I pondered that the angle would vary between engines dependant on their actual idle rpm.

Is this right?

PS - doing some further research, I realise it's wrong. The Dwell angle should be the same for any given engine, at any rpm, when the gap is set correctly. Anyone have a figure for the 2 litre spread bore engine? Somewhere around 50 degrees? Or shall I just inform the world tomorrow.....

Hi Dan
Thanks, I am glad I could help.
Dwell angle for a 4 cylinder should be 52 degrees regardless of engine type, displacement etc.
The dwell angle represents the degrees of distributor shaft rotation the points are closed. The remaining 38 degrees (360 degrees divided into 4 lobes = 90 degrees 52 + 38 = 90) are taken up with the opening, open and closing action of the points. By setting the timing you are setting the point at which the points open in the ignition cycle, and consequently send spark to the plug.
Setting the points gap sets the dwell angle. You are right; the dwell angle should remain steady. Worn distributor shaft bushes will cause the dwell angle to alter because the shaft will not be running true.
Cheers, Martin

Quote:

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Originally Posted by marting

Hi Dan
Thanks, I am glad I could help.
Dwell angle for a 4 cylinder should be 52 degrees regardless of engine type, displacement etc.
The dwell angle represents the degrees of distributor shaft rotation the points are closed. The remaining 38 degrees (360 degrees divided into 4 lobes = 90 degrees 52 + 38 = 90) are taken up with the opening, open and closing action of the points. By setting the timing you are setting the point at which the points open in the ignition cycle, and consequently send spark to the plug.
Setting the points gap sets the dwell angle. You are right; the dwell angle should remain steady. Worn distributor shaft bushes will cause the dwell angle to alter because the shaft will not be running true.
Cheers, Martin

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Wow - that is great information Martin.....so the Dwell angle will be 52 degrees for any 4 cylinder engine? I'm interested to hear that because it had been suggested that I set my gap with feelers, then measure the angle, write it down, and from then on set my gap using my multimeter, guided by the angle deduced as just put.....sort of suggesting that this angle would be some unknown, only revealed by taking the measurement after setting the gap correctly with feelers...but 52 degrees is 52 degrees!

Next question - if the gap can vary between 14-16 thou, how many degrees will this equate to, +/- from the theoretical 52 degrees?

Maybe that was the original point....a 14 thou gap, a 15 thou gap, and a 16 thou gap - all within tolerance, would have slightly different dwell angles, right?

a tip I was given many years ago when setting points is......stick a piece of paper between the points rotate the engine til they close than drag out the paper.........this removes the oil/grease film that was on you hands and feeler gauge that may have ended up between the points

Quote:

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Originally Posted by weeds

a tip I was given many years ago when setting points is......stick a piece of paper between the points rotate the engine til they close than drag out the paper.........this removes the oil/grease film that was on you hands and feeler gauge that may have ended up between the points

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I'll do that tonight too! Thanks.

Small bottle of fluorescent "poster" paint preferably bright orange (bottle will last 30 yrs!), fine paint brush .. (from a kid's paint set). Use to mark TDC on pulley and reference point on engine cover. Inductive zenon timing light (SCheap $60), vacuum test gauge to connect to intake manifold, tach-dwell meter pref analogue one so you can watch the behaviour of the needle rather than a jumble of changing digits e.g. Dwell Tachometer | eBay

Read also Ignition Timing - Les Bengtson it's very informative, gives detailed instruction on both static (test lamp) and dynamic (timing light) timing and applies to the Land Rover engine as much as to the old MG under discussion

Re carby: . You can set the idle screw watching the tach (0-1000rpm range) and vac gauge and listening all at once and get a pretty accurate position for it. A small dab of Loctite (can't remember the exact one) on the idle screw thread once it's set will keep it in position.

To successfully set the carby, first make sure the vacuum advance tube is firmly attached to the base of the carby or wherever and also to the distributor otherwise you'll get air sucked into the manifold leaning the mixture.

Set the throttle idle adjustment screw to the correct idle speed. which means you need to get the timing set correctly first. Then as you screw the idle mixture screw in 'slowly', you are leaning the mix and the engine will begin to run a little rough. If you keep going the engine will stop.
Take note of the position of the screw at the point where you notice it beginning to slow and run rough.

Then slowly screw outwards thereby making the mixture richer. The revs will pick up but as you continue the mix will become over rich, the revs will again begin to drop off and instead of a steady beat, it will "hunt" as it does when you put on too much choke.. brrrm ...brrrm...brrrm instead of an even bom bom bom bom etc:eek:;)
Note position of screw. Now turn screw back the other way so that it's in the mid-point between the extremes.

Now use the tach and throttle adjustment screw to set idle at correct speed as necessary.

It's "real" mechanics stuff ---enjoy it!!:D

See also http://www.aulro.com/afvb/technical-...l-motor-2.html

Inc. found a reference back in 2006 that the dwell was 60 deg for the Series 1 engine...
cheers

Always 52 degrees - or around 60 +/- 2 degrees for Series engine? Probably time to go and find out for myself....

Definitely not always 52 deg. That may be a reasonable theoretical number to get started but not in practice...

My "little black book" "Hawk tune up guide" Published in 1975 has tune up specs for most USA/European/ Asian vehicles . E.g MG variants 1963-72 listed as 60 deg dwell; Toyota corolla/corona 52deg; Rover 2000TC, 2000 auto 1965-70 60 deg; Triumph Sptifire 1971-72 4 cyl Mk4 42 deg; VW various 197172 1600cc 44-50 deg etc
It all depends on the state of tune, as well as the electrical characteristics of the coil etc
cheers