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Have to keep retarding ignition timing


daverclasper
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Hi. I do about 2/3 hundred miles of slow city driving, then go on trip every 8 weeks, or so, Often motorway, The car will then pink on harder acceleration and climbing gradients. I retard the timing 5/10 clicks on the vernier and ok. Then the same thing will  thing will happen after a couple of hundred miles. Pinking, then retarding.

Why might this be please.?.

Dave

Edited by daverclasper
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Hello Dave,

My first questions are:

1- how old is your dizzy and vacuum advance unit if you have the latter ??

2- do you run with points or electronic ignition

3- what RON grade of fuel do you use

Regards.

Richard.

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Are you still on points? You can sometimes get this if they're eroding, usually due to a failed condenser, or possibly the fixing bolt is loose. The gap gradually opens up, leading to smaller dwell and more advance. (It is also possible for the gap to close, due to wear or loose fixing, which increases dwell and retards the ignition.)

The city driving will lead to some coking up, which does encourage knock when next driven hard, but I wouldn't expect to keep needing to retard it - once should be enough.

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10 hours ago, poppyman said:

Unless the advance vacuum unit is sticking?

Actually... more likely the centrifugal advance. I have had them stick a few times - the upper shaft runs directly on the inner (lower) shaft and if not sufficiently regularly lubricated it gets stiff. Give it some high revs and the advance mechanism can operate... but the fairly weak spring return doesn't and you end up very advanced at lower revs.

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That's a good shout. My PI distributor did that sometimes, then randomly released itself, though that mainly showed up as a very variable idle, which got blamed on the throttle bodies and crappy linkages for a long time. It was only when it was struggling to start (wanted to run backwards) and the timing gun showed 30 degrees btdc at idle the penny dropped.

 

Nick

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Hi and thanks for all your input.

Hope all this lot may be relevant and not too boring

Went for another run out yesterday for about 10 miles on A roads. Pinking again on higher revs and under load on gradients. Retarded on the vernier for return journey (5 clicks and then another 5 as was still pinking a bit) only done about 50 miles, since I last knocked it back.

Car starts ok from cold and when warm just a quick flick of the starter.

I use tesco 99 RON all the time.

Vacuum advance moving point plates when pipe is sucked and holding vacuum.

Outer shaft has what feels like about 4 thou side movement (did have electronic ignition on car ages ago and couldn't notice any difference in how it ran compared to points).

Checked points. contacts good and gap still correct (last adjusted a few thou miles ago).

Outer shaft moves anti clock wise and returns, though not quite all the way (about 1mm short of rotational movement when looking down at the cams, if this makes sense). Have always kept it lubed with a few drops of oil down the top. Maybe centrifugal springs a bit weak?.

The rotor arm key is a bit worn, so the arm will turn a bit on the shaft, though is not loose as such, and arm appears to stay in the same position (has been a reliable arm, so reluctant to change it).

No strobe gun to see whats happening at different revs, though will get one if useful?.

I could strip dizzy down and see if any wear anywhere else, if that's useful?.

Cheers, Dave  

 

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Just the pinking. Assumed it was timing related.  Dizzy clamp is not loose by the way.

About 1 and 3/4" depth of 20/50 engine oil in each dashpot. Correct disc thingies that secure the carb diaphrams (the lighter ones for Vit Mk1 2 litre).

Don't know if the springs are doing their job (if I can find out what the correct length should be and measure mine, would this be useful).

Mixture looks ok, going off plug colour (apart from one plug that looks as if it running a bit weaker, as mentioned in a previous thread, though that was no 6 cylinder, which is now looking ok and No 1 cylinder now looking a bit weak !).

I do have a quite a chunky generic vacuum/pressure gauge. though not sure if this would be suitable. I have the original breather valve plumbed between the rocker cover and top of inlet manifold arrangement.

Thanks, Dave   

Edited by daverclasper
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Thanks Pete. This has got me thinking. The rocker cover gasket is tired and broke in a couple of places (no oil leaks, as there is quite a bit of suction when you put your hand over the filler neck).

Also the rubber seal on the filler cap has split (not sure if this can replaced easily as the cap looks like it doesn't come apart easily?).

The hose's for the PCV valve are also tired and could well be leaking a bit.

Could all these be upsetting things. I don't quite understand manifold vacuum and what it does, I don't think it's mentioned in my collection of car maintenance books.

Cheers, Dave 

Edited by daverclasper
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they measure the suction between the engine inlet valves and the throttle plates , open the taps an this drops close the taps it rises, 

idle gives around 18-20 inhg,   foot to the floor 0-5inhg.  cruise  10 -12 ish   the idea is cruis with as high a reading as possible to get best economy

 this takes all the fun away. but these gauges give a good idea of engine settings

once mixture and idle are about right you can advance up to 21 , to get the best , down hill taps shut  readings go higher around 30 ish

some have green and red zones on to guide the right foot !!

you do need to crimp or restrict the feed pipe to stop intake pulses wagging the needles about  bit of metal pipe squashed down till a steady needle will work well

just another gadget to worry about !!!

 

Pete 

 

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20 minutes ago, daverclasper said:

Thanks Pete. Do you think those issues I mentioned in my last post could be causing the pinking please?.

Unlikely, although if they're contributing to oil ingress into the manifold then it might encourage coking up in the cylinders, which will encourage pinking.

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any air in from the breather system will have some upset on the mixture  settings 

but the PRV should stay closed till any pressure is detected  from the breather ,  so downstream of the prv  should be sealed fully 

if the rocker zone is poorly sealed then the prv probably doesnt open much  

having said that if theres deficiencies in the breathing and you had odd running problems well they need a sort out to eliminate them from the symptoms

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