worn distributor

[tdafforn]

hi All,
My Elan is wired up so that I can either use a conventional distributor with Aldon ignitor or a crank sensor triggering a coilpack via a megasquirt ECU.
Anyhow the difference is rather startling.
since having the car I have had slight hesitation when picking up from low revs when I open the throttle rapidly.
With the MS ECU it has entirely disappeared.
in addition to the this the idle is smoother.
What hasn't changed is the top end and cruising which is pretty similar
my question is (apart from the obvious, that the MS ECU system is much more accurate) why is the distributor system fluffing on take off from low revs..?
Any thoughts..?
I ask because at some point I may remove the ECU for another project and I'd like to sort the problem with the distributor system..
Cheers
Tim

[paddy]

I've got an Aldon TC103 distirbutor and ignitor. I did this to solve erratic timing (when viewed with a strobe) with the previously fitted distributor, which also required new timing chain to solve. I now get a rock-steady timing mark under the strobe at all engine speeds. (Incidentally the situation with the new distributor and conventional points was very nearly as good, so it's not really down to the ignitor.)

When I first timed it, it was based on the workshop manual spec wtih 10 degrees static which gave something like 17 degrees at 1000 rpm and around 34 degrees maximum. At this setting, the engine was extremely tractable from around 1500 rpm and you could put your foot down with no hesitation.

Then I read a post from Rohan saying that the max advance shouldn't really go beyond something like 28 degrees for unleaded fuel and a road-tune engine. (Standard head, SE cams and Webers.) I retarded the timing by a few degrees so it maxed out at about 30 degrees, and (subjectively) the performance at 5000 rpm upwards was improved.

Now, however, tractability at low revs is much worse and it's annoying driving it in traffic or anywhere where you have to stop. Beating other cars away from the lights requires an embarrasing high revs + lots of cluch which isn't the effortless impression you'd rather give. I've decided to put it back to how it was, but not got around to it.

So, my conclusion is simply that there is too much advance in the Aldon distributor for a road engine, and there must be a more suitable curve. I guess your ECU has such a curve.

I'm sure others have lots more experience with fiddling with this kind of thing, but I don't believe much or all of it is down to more accurate/consistent timing from the ECU.

Paddy

[tdafforn]

ECU currently has the same ignition curve programmed into it as the dizzy graph in the wilkins book..
Although it is only 10 degrees at idle (600 rpm).
as you'll see from my other post, i mistakenly dropped this to 8 degrees last week (trying to sort out a trigger issue I had) and got a backfire that snapped a tooth on my starter (doh!)
I guess I could use the ECU to play with the timing curves and then see if I could get a new dizzy made up to match as close as possible?

Tim

[gerrym]

"Programmed the same as the Miles Wilkins Book"

Mechanical distributors are compromise timing devices limited by what can be achieved with weights, springs, counter springs, vacuum (whilst allowing for friction and wear).

Some aftermarket ECUs allow for idle stabilisation via ignition advance. Most OEM ECUs use this as well. Check the instruction manual for your ECU and see whether it has this feature - and whether it's been enabled in the software.

This should give you all the advantages of steady idle without compromising throttle transition.

Regards

Gerry

[tdafforn]

I think with the megasquirt you just set the advance at really low (ie towards stall) revs so that it forces the revs up...

[paddy]

(Sorry to hijack the thread) I just re-timed it and it's not as rock-steady as I remember it, after about 3000 miles. Is it possible that the timing chain needs re-tensioning after that time? The distributor is the same age and I can't believe it's worn. I don't want to lift the cam cover unnecessarily. Is there a safe but "blind" procedure for tensioning the chain (eg tension it until the variance in the timing disappears and then back off a bit)?

Paddy

[gerrym]

Tim, re the idle stabilisation, this uses dynamic advance. Not the same as as just advancing the idle on a static basis. If your ECU has this feature, it will definitely mention this in the manual. If not, then it probably doesn't have this feature.

Regards

Gerry

[zarelan]

Paddy,

I went through the same dilemma with my Aldon TC-103 Distributor and Ignitor 2 years ago. It eliminated the erratic idle, the stumble at low revs and gave much smother acceleration. The TC-103 has a very different curve to the original Lotus spec. It advances earlier and to a higher total value. I was concerned about engine detonation so I retarded the static timing to 6 deg to keep to total advance below 30 deg, but just as you have reported, the car becomes very unresponsive at low revs. So I put the static advance back to 10 deg, and that's how it has been since. I don't hear any pinking at high revs, so I guess my Sprint engine can take the increased advance without any probs.....

--Antonio

[neilsjuke]

Check that the rotor has no movement in the shaft mounting some of the new overseas replacements are a poor fit .
Neil

[Shiny_kit]

I fitted an edis/megajolt kit to my mgb and it made a big difference - idle was much better, starting it was much easier, smoother running etc.

The spark from the coil pack is much bigger, and it's timed more accurately - my old dizzy had 92k worth of wear in it, and it's so easy to tweak the mapping. I was wondering about converting the +2 but I think if I do change it I will go for a 1-2-3 or something a bit more traditional looking.

[bast0n]

I run an Aldon distributor with a Bosch rotor arm,(that knocks the Chinese Lucas jobber into a cocked hat), and my timing is as specified. Sprint spec engine. I have found it superb, BUT, I have spent simply ages getting the carb balance and mixtures spot on as these seem to have more influence on smooth running at low revs,(mine pulls in top smoothly from below 1500 if you are smooth), and gives oodles of power higher up.

Hope that this helps.

David - who is not growing up too quickly..........

[paddy]

(Sorry to hijack the thread) I just re-timed it and it's not as rock-steady as I remember it, after about 3000 miles.

Just to follow up on this:

The ignition timing was uneven with about 4 degrees (at the crank) of scatter. I checked the timing chain adjustment today, and the total movement between the cam sprockets was 14.5mm. I adjusted it back to spec (12.5mm), which took about 3/4 of a turn on the adjuster screw, and magically the scatter disappeared, timing back to being rock steady as before. The engine idles much more evenly again. So it doesn't take much to upset it, and accurate measurement is quite critical.

I'll keep an eye on it - perhaps the chain will keep stretching at this rate, or perhaps it was just "bedding in".

Paddy