Ignition Timing

[kevinw]

The story so far:

Cleaned the damper (behind the pulley), so I can now see the "before" and "after" vernier marks. Did the "Tippex" trick, putting a mark at 10 degrees btdc
Started engine and allowed to warm up properly, confirmed the idle speed at about 750 - 800 rpm (it is an auto, so the idle needs to be just a little bit faster)
The points have been recently changed and set using a dwell meter.
Checked the timing with the strobe. Miles out, at least 15 degrees advance, so it should have been pinking like mad. The car has only done a gebuine and verifiable 55000 miles and I hae what I think is the comlete service history, so failry sure the engine has never been to bits and put back together incorrectly.
Adjusted the timing, went for a run around "the test track"

What a difference! The idle is a bit lumpy - I need to have another go at setting the mixture as I think it is too rich still, but when running, it sounds like (dare I say it) a BMW. No pinking, but it is tricky to make it labour being an auto and lots of power.

Curiously, the strange noise I had that started after the semi-sports exhaust had been fitted has now stopped.

Kevin

[Alan Chatterton]

Does your car have vacuum advance fitted (small pipe from dizzy to inlet manifold?)

If so, remember you need to set the timing with the vacuum pipe removed, which could explain the 15deg reading..............

[kevinw]

Yes - runs off the front carb. I didn't think it made any difference at idle speed (but then, I know very little about petrol engines)

Doesn't make any difference though, either with the vacuum advance connected, disconnected at the carb end and waving in free space (ie at atmospheric pressure) or plugged with my finger over the end of the tube.

Kevin

[Alan Chatterton]

It should at tickover..... thats what it for!!

At high vacuum (ie light throttle settings or no throttle) it should advance the timing significantly.

This is why you need to do the timing with this disconnected.

Try sucking the end of the hose (with it connected to the end of the dizzy) with the timing light on it, if no movement then this is siezed in the dizzy and needs sorting..........

[sorbs]

I tried sucking on my vacuum pipe until I went cross eyed, no visible change in the timing.

I ordered a replacement from Chris Witor and it was just the same, it can be operated by hand and is not seized but there is no way that you could operate it by sucking it on the pipe, your lungs would bleed first. My mate and his Mum both had a go too then I tried the one on my mate's 2000, none of us could suck hard enough to operate the mechanisms. The spring inside is pretty strong.

[Umquat]

Maybe this is where my timing is going wrong possibly... I dont see any change either when my car is at tickover with the pipe removed or connected. I'll check the airflow from the carb and see whether there sufficient suction at tickover to actually move the diaphragm or not. I suppose the airpipe might be holed but I've checked it before and not seen anything

Regards

Gavin

[kevinw]

I tried pulling the pipe off at the carb end and putting my finger over the end of the spigot - the vacuum can be felt, but it is miniscule. I've also done the same on an exhauster (vacuum pump) on a large diesel of the sort fitted to busses and that would try to pull your skin off!

Kevin

[Umquat]

Glad I'm not the only one! To borrow a Clarksonism it's about as effective as an asthmatic gerbil sucking through a straw!

Running twin Stromberg CD150's i think

[Mike Stevens]

Distributor vacuum test. I'm pretty sure that if you remove the cap and then suck on the pipe, you should see the base plate move inside the distributor. I'm afraid that I don't agree that you can't suck enough - at tickover you'll only get a few inches water gauge - it aint that much.

I think I may go and give it a try! I happen to have an early PI distributor on the bench!

Oh yes, you should remove the vacuum pipe when doing dynamic timing.

In terms of setting, my views are that the factory settings were fine at the time, but modern fuels are so different to fuels then that the original setting may not be correct. I've tended to go by the Alan method - keep advancing it until it pinks then back it off. Yes, I know this is a bit empirical, but as long as you don't labour the engine and be sensible, you shouldn't really have any problems. And I run on just unleaded with no additives. Well no, not me, the car!

Cheers,
Mike.


Cheers,
Mike.

[kevinw]

Probably the same carbs on mine as our cars are more or less the same age -Strombergs of the sort that need the expensive allen key to adjust through the dashpot rather than from underneath. Without having a really close look, it seems to me that the vacuum spigot is on the atmosphere side of the throttle butterflies. Car runs at low throttle setting and high, driving like a hooligan and doing full throttle acceleration it runs fine; trying to make it "pink" fails, so, I'm more confused than ever! Yes, I know, it doesn't take much

Kevin