SU carb and Vac advance logic.

[wookie]

I guess some must use the scatter gun approach and just change expensive parts

Yup, seen this first hand where I used to work, mind you even sending the computer diagnostics output back to the head of UK technical support doesn't always stop them telling you to replace components that logically can't be causing the problem but since it was still under warranty why care.

I also remember having to change the language on diagnostic kit to Italian so you could change some settings as it wouldn't store the change if you did it in English, wtf....

 

[Chris Stevens]

Yup, seen this first hand where I used to work, mind you even sending the computer diagnostics output back to the head of UK technical support doesn't always stop them telling you to replace components that logically can't be causing the problem but since it was still under warranty why care.

I also remember having to change the language on diagnostic kit to Italian so you could change some settings as it wouldn't store the change if you did it in English, wtf....

What about when its out of warranty? I guess they would change parts just the same...................

 

[MrFluffy]

You can test this theory yourself. Disconnect the vacumn advance and drive it and record the afr's on your wideband at various rpm. Then advance timing by 5deg and repeat, if the afr changes between static setting alteration at given rpm points it does.
Timing does affect afr reading slightly though, because if the propogation time to fully burn the mixture isnt correct you get unburnt mixture out the exhaust with a non optimal setting which affects the reading. It doesn't change the actual AFR however as thats a fixed ratio, only fool the sensor a little by the presence of more gases for the sensor to see. You need to measure with a 5 gas analyser to see the true ratio in these cases accurately which is why the emissions testing is 5 gas.

I've just fitted a accuspark stealth electronic ign unit to my 101, it sits inside the distributer and goes where the points are. You still keep your vacumn unit and dizzy etc as stock, but there's no more points gap. It runs off the original power fed to the points & coil. Theyre about 25 quid on ebay and it took me about 30 mins to fit. I noticed idle improvement immediately on start up, I lost a small occasional sneeze when idling.
The megajolt or edis setup is another option. Just throwing the accuspark into the mix as its so cheap and easy to do.

 

[cardiffrob]

Thanks. In the absence of a written down answer I will have to do it experimentally and also find a suitable RVC revcounter. Next stop....Scrapyard!

Can you keep the points in the dissy with that Stealth kit? On the MGC I found a lot of spark scatter with Optronic due to the lack of points allowing the timing cam to rattle loose rather than being held tight by the heel of the points. After that I used a 22D6 (Big Jag engines) because they have longer bearings and hold the dwell and timing a LOT better.

 

[MrFluffy]

No, not on my install. The answer is to make sure your bearings are in good shape, which mine are.
before :-

After

 

[MrFluffy]

EDIS/megajolt off a toothed wheel on the crank eliminates the whole distributer drivetrain from the equation if you want to take that route and I run a megasquirt injection and spark setup on my bike with individual 5v logic signal coils, one per plug. I just used the stealth unit on the 101 as I'm not wanting to get too deep into changing the engine right now but just wanted electronic ign for the ease of starting and general lower maintenance they bring to the table. Doddle to fit, instant result, cheap as chips and will do for now.

The 101 has a rover v8 with a lucas 35d8 distributor if thats of use to know.I think your jag dizzy is a 22D6, which accuspark etc all have the same kits for.
Curious about how you use a 6 cylinder distributer on a 4cylinder engine, is it just a different rotor cap? Here's a short list of common distributers from the period if it helps.

• • 4-cylinder Lucas (22D4, 23D4 and 25D4) - 3LUC4-25D
• 4-cylinder Lucas (43D4, 45D4) - 3LUC4-45D
  
  
  
  • 6-cylinder Lucas (22D6 and 25D6) - 3LUC6-22D
  • 6-cylinder Lucas (45D6) - 3LUC6-45D
  • 8-cylinder Lucas (35D8 with single points) - 3LUC8-35D

 

[cardiffrob]

4 and 6 cyl 22/23/25D distributors use the same body and drive shaft so you can basically pull all the top end and springs off of one and stuff it on the other type. The MGC, being a 6-banger, was an easy one to convert to a 22D4.
I played about with plug gaps today to see what was possible, just for personal interest. I have one of the Intermotor/Lucas Sports coils and NGK BPR6ES plugs plus some BR5ES and I got well past 35 thou gaps without being able to 'detect' any difference in the behaviour of the engine. Would I be right in assuming that the dissy points will suffer if the plug firing voltage goes up? Also, can plug voltages/sparks cause physical injury to maybe heart tissue? I took one heck of a blast from our Mondeo last year.

 

[MrFluffy]

CDI and modern ignitions can absolutely kill you, its a known risk around mechanics I would hope. Same with a magento based ignition. I have a bike with a mallory sprintmag on it, I'm always extra careful round that, its not the voltage with a mag, its the duration of the spark event as it collapses into the plug. This makes a mag suited better to producing a sustained spark and its output rises as rpm rises so the spark gets stronger. Thats why if you wander round a top fuel car pits you'll see dual mags until relatively recently on the top flight cars.

I have no idea how a large gap would affect the life of a set of points, I would have thought that any extra load would have affected the coil itself rather than the LT circuit, since its just acting as a way to sink the magnetic flux stored in the coil by the LT circuit. There comes a point that too large a gap means the plug has too much resistance/impedance for voltage the coil produces on its secondary to sink HT into it and then you get a misfire. This is particulary likely during high rpm use when you might not notice, cold starting etc and if it does this, its more likely to foul.
I've not played much with gaps, I tend to set them to what the oem recommended and if its a extreme case just rely on having a stronger ignition to cope with higher cylinder pressures etc, but there's probably some tiny gain to be had from it, when I get my dyno set up I might have a play.

 

[cardiffrob]

I have a confession to make. When you said you had a Rover V8 in your 101 I thought you had a very fast old Peugeot. Duh! Clearly this medication is still affecting the stupid section of my noggin. Turns out that a Peugeot 101 is actually a Moped so I was probably thinking of a 104. I then Googled 101 V8 and it all made sense.

 

[Chris Stevens]

CDI and modern ignitions can absolutely kill you, its a known risk around mechanics I would hope. Same with a magento based ignition. I have a bike with a mallory sprintmag on it, I'm always extra careful round that, its not the voltage with a mag, its the duration of the spark event as it collapses into the plug. This makes a mag suited better to producing a sustained spark and its output rises as rpm rises so the spark gets stronger. Thats why if you wander round a top fuel car pits you'll see dual mags until relatively recently on the top flight cars.

I have no idea how a large gap would affect the life of a set of points, I would have thought that any extra load would have affected the coil itself rather than the LT circuit, since its just acting as a way to sink the magnetic flux stored in the coil by the LT circuit. There comes a point that too large a gap means the plug has too much resistance/impedance for voltage the coil produces on its secondary to sink HT into it and then you get a misfire. This is particulary likely during high rpm use when you might not notice, cold starting etc and if it does this, its more likely to foul.
I've not played much with gaps, I tend to set them to what the oem recommended and if its a extreme case just rely on having a stronger ignition to cope with higher cylinder pressures etc, but there's probably some tiny gain to be had from it, when I get my dyno set up I might have a play.

Not many modern day cars or bikes using CDI ignitions nowadays, as spark duration not long enough for complete combustion on lean burn engines. Most are inductive, which has longer spark duration, but lower peak KV at the gap.

 

[piman]

Hello Rob,

"I'd like to get to grips with vac advance theory if I can."

It's not really that complicated. Tune the fuelling to run weak at the mid range then adjust the timing with a vacuum advance module. It just takes lots of dynamometer time to get it right. It's only applicable to a road car, not for competition as it's both uneccesary and reduces power.

Alec