Timing with (Gunson) Tachostrobe

[Colin]

Team:- 

For years I've owned - but never used - a Gunson's Tachostrobe. Always looked a bit of a faff really, when, as an every day use car, I'd previously have had to get things up and running same day. So I timed the old girl manually.

I recently checked the timing (for one reason & another) again, manually - thinking once all seems confirmed as well, I might use the Zenon Tachostrobe which I never have previously.

I thought I'd Internet/YouTube the thing first.

Whilst I haven't yet used it - I came across the info attached below . . . which was news to me.

"Converting an early model of engine to run on UNLEADED PETROL entails RETARDING the
ignition timing to a new setting recommended by the vehicle manufacturer." (source - a Gunson leaflet).

My car has a Kipping unleaded head. Has had for years.

It is a high compression 1147cc engine. The recommended timing is given a 15 degs BTDC. And I've always kept it at that.

Never noticed any particular problems at that setting; I have never changed the timing to accommodate unleaded fuel, let alone now even more Methanol is part of the fuel mix at the pumps.

In this advice it was recommended one contacts the manufacturer for revised timing settings under unleaded fuel use - see pic. (let alone, as I mentioned, extra Methanol as 'standard'.

Does anyone know; 

a) how accurate such an opinion is about the use of unleaded?

b) what the correct retardation should therefore be (I contacted a medium but couldn't get through to Triumph)?

c) if and how today's methanol percentages might further change said timing - further retardation, or has Methanol no further effect to the existing situation?

Best,

C.

 

[johny]

I think the Triumph advice still holds:

With all engine settings correct accelerate in 4th on the flat with engine up to temperature and the pinking should stop as you reach 2000rpm. If the pinking is still present after this point you have to increase fuel octane OR back off timing. I choose do the first with an additive but each to their own.... 

[JohnD]

What's your compression ratio, Johnny?   I build mine with a CR of 10.5:1, and yes, in the spring old petrol may pink a bit.   But it never pinks on fresh  Shell V-Power, 99 octane.

John

[johny]

Just standard but I run it on 95 with a bit of Millers VSP to liven it up...

[Clive]

Call me pernickety, but it is ethanol, not methanol, that is being added.

But that is irrelevent, as ethanol has no effect on octane (well, the actual answer is complex, but e10 95 is the same octane as e0 95)

As for the drop in octane from the old stuff when the car was new, that may require a change. But then again, your distributor probably has wear and slightly stretched springs, you compression may not be as oroginal and so on. So he "best" answer is to keep advancing ignition until you get a little pinking under load, then back off a tiny amount.

 

[Pete Lewis]

if she doesnt pink  dont doanything 

you can run at factory settings with  most 97+  E5 fuels 

and retard a few degrees to use 95 E10  stops the pinking but reduces power and can increase the heat generated 

if it pinks on open road cruise acceleration then a lower advancing Vac unit can help 

Pete

 

[dougbgt6]

Colin,

You can best set the timing by ear, warm up the engine and slacken the dizzy clamp. Turn the dizzy until the revs start to drop, stop. Turn the dizzy the other way and the revs start to rise. When they stop rising you have reached the plateau, stop, turn the dizzy back a gnats. Tighten the clamp go for a drive. If it pinks retard a bit more. Repeat until it doesn't pink. 

The problem is these cars were designed to run on 5 star petrol which is no longer generally available, modern fuels are lower octane so if you're running on 99 or 95 your BTDC is going to be different. My GT6 I think was 13 degrees, if I remember correctly, but it's much less than that now, but I don't know what it is because I do it by ear. (Or vacuum)

The problem with strobe is slackness in the system means you think it's right, but it isn't. 

Vacuum. I have vacuum gauge, I turn the dizzy till maximum vacuum then back one bar. This is satisfyingly identical to doing it by ear.

Doug

 

 

[Colin]

I can't say I've heard her pinking in 35 years driving her. Dist was changed (can't recall why) and so is not 'old' original. 

Alwayschanged down (up!) when necessary rather than bang the big ends out!

It was an idle query really, but . .   

[Colin]

Doug - interesting concept! Never thought of doing it that way! 

[Clive]

1 minute ago, Colin said:

Doug - interesting concept! Never thought of doing it that way! 

Not ideal.

With my mappable ignition, best idle is at 28 degrees, but needs to retard to 15 ish for acceleration at lower rpm. A distributor can't do that hence setting idle by the pinking check. At a guess, "all in" timing (no vac) for 95 octane on a spit would be about 30 degrees. How it gets there depends on the baseplate and springs, all can be played with to get improvements, as can the vac advance capsule.

[dougbgt6]

3 minutes ago, clive said:

Not ideal.

Why? As said it's the same as doing it by ear. 

Doug

[Colin]

I guess I've raised this as I aim to change to elec ign (have kit - just don't understand it all well enough yet!) and thought; if the timing's right on points setting, a straightforward don't-move-a-thing as far as the dizzy is concerned should be alright.

Then I saw retard the timing thing, if using unleaded.

Do I need retarding?!? 🤣

[Clive]

21 minutes ago, dougbgt6 said:

Why? As said it's the same as doing it by ear. 

Doug

My explanation should cover it. But yes, setting timing at idle is fine if that is all the car runs at, but that assumes (ie no chance) that the mechanical advance is mapped to the engine. When new they were reasonable, but after 50 years, they will be way off. And new ones are very variable in terms of the advance curve (distributor doc and other specialists will be fine, but the sub £100 new ones? forget it)

Using the (edge of pinking" method, you are setting the timing for the engine when being driven. 

As a comparison, think of carb needles. You can get a decent idle with any needle, but once off idle it will be wrong. 

[Clive]

1 minute ago, Colin said:

I guess I've raised this as I aim to change to elec ign (have kit - just don't understand it all well enough yet!) and thought; if the timing's right on points setting, a straightforward don't-move-a-thing as far as the dizzy is concerned should be alright.

Then I saw retard the timing thing, if using unleaded.

Do I need retarding?!? 🤣

No, but fitting electronic ignition will almost certainly affect the timing, so it will need resetting. If no pinking, you are not too advanced (but may not be using enough advance)

[Colin]

Seems to me, most of you are saying 15 degs BTDC is actually not enough for actual driving conditions . . . on a small single solex carb engine of 1147cc . . . ??!?

[Pete Lewis]

from the original specifications of 1960s lots has changed  things will need a bit of a twiddle 

as Clive says fitting an electronic to replace the points its imperative you check the timing 

what make are you fitting ???

I have not ever found a  kit that replicates the position of the points  and can be miles different to what you remove 

all engines are different in how much advance they need to get  the bang right varies on so many things  

eg a 1200 herald is 15   a mk3 spit is  6   1600/2ltr vitesse 10    

fuel used to be 101 ron now its 95/97   it all comes down to strobes ears vac gauges   and a test run to get the optimum

Pete

[dougbgt6]

4 minutes ago, clive said:

My explanation should cover it.

I doesn't else I shouldn't have asked.

6 minutes ago, clive said:

Using the (edge of pinking" method, you are setting the timing for the engine when being driven. 

Not quite sure what that means, do you mean, I AM setting the timing for the engine when being driven or, I should be setting etc? 

7 minutes ago, clive said:

s a comparison, think of carb needles. You can get a decent idle with any needle, but once off idle it will be wrong. 

Yes indeed, but without your sophisticate mappable system the rest of us have to do the best we can with what we've got and that's by ear or vacuum.

Doug

[Colin]

Er, Pete - it's the Clubs'.

In garage atm. 

Will they differ?

[Pete Lewis]

being a petronix/aldon yes it will need to be reset  its all down to where the unit fits and where the magnetic triggers are fitted   

none match the points    sorry you must re time it 

Pete

[Colin]

Static (or with strobe) setting to manual data demands BTDC white marked dot in c'shaft pulley (I replicate on pulley flange top).

I could then mark with the oldskool degree chart 15 BTDC - in yellow maybe.

When changed to elec ign, could I confirm 15 degs BTDC with zenon strobe?

I feel I'm playing Devil's advocate here & should stick to static timing methods (gunson points/volt meter or 12V bulb) 

[Colin]

Lumenition Magnetronic . .   

[Pete Lewis]

the only spec is 15 deg  static   ie no advance taking place so bulb  will work  a strobe must be used at a slow idle    with vac disconnected 

if you want to do a full advance curve you need the test data in the WSM  and note most dizzy tests are done decelerating which you may find odd

youre tacho strob will give you engine speed and without looking it up a max of 30deg at 3000 would be par for the coarse 

Pete

[Colin]

 Cheers  Pete.

All interesting stuff.

It's not going in till my more electrically competent bro gets back off hol! 😁

[Pete Lewis]

3 minutes ago, Colin said:

Lumenition Magnetronic . . 

same applies you are changing all the guts that give youre coil a trigger  there are none that i have come across that  time as  the same as your points 

you must check and adjust ,   once fitted   fit and forget  but after fitting CHECK IT  do not assume 

Pete

[Colin]

Hokey cokey. Thanks, Pete - everyone! 😉😃