ignition timing /stalling

[malminor]

I fitted a 1275 type crank pulley as part of an alternator change on my 1098 engine. I have a timing light but I am not sure how to use on a minor.
I have new points etc, the advance and retard is working under vacuum.
the car has recently began stalling when slowing down for lights etc.
I am not familiar with SU carbs yet, though I have a colour tune kit if it's of any use. I run with NGK plugs lead fuel additive.

[biker_bits]

If the problem started after replacing the pulley it may well be a coincedence. Pulley should not affect timing.
Timing marks on Minor are on the crank pulley (a notch) and the static part (three v-shaped pointers) of it is below that pulley.
To check with strobe timing light you need to connect the strobe to No1 plug lead, pass the cable under the engine (rear of dynamo/alternator, so it does not get caught in the pulleys), so that the strobe light would reach the timing marks.
Not sure what differences are between standard and 1273 pulleys though - will timing mark still be the same as standard Minor?
Some SU info: http://www.xkclub.com/tech013.htm
Carb would be my favourite in this case - may well need a clean out of the float bowl and blow through the main jet. One crude but effective way (worked for me when I got stuck) is to remove air cleaner, rev the car up and cover the air intake of the carb. This will suck through any muck that may be stuck in the main jet. Still, it is not a replacement for a carb clean out.
To check filter bowl. Find where fuel pipe connects to the carb - that is the float chamber top. Remove 3 screws securing it and gently lift it off. Any muck, rust and water in the bottom of the bowl?

[Alec]

Hello Mal,

it could just be that the idle speed is too slow? Simple checks first.

Another check is to remove the air cleaner and insert a finger into the intake and lift the piston. You should feel some resistance, release and it should slowly drop and come to rest with a distinct 'click'. If it does not the jet needs centring.
S.U.'s generally do not suffer with blockages of the main (and only) jet.

Alec

[MoggyTech]

The Minor is a bit unusual WRT the way the clutch works. When the clutch is pressed, it actually reduces the engine revs slightly due to the drag of the release bearing on the clutch plate. I suspect it is a combination of slightly low tickover speed, mixture, timing.

You can use the lifting pin on the carb to set the mixture. Lifting the piston 0.8mm you should get a slight increase in revs, or no change in revs. If the revs drop, the mixture is too weak. Colourtune isn't really much use, as you will get a blue flame over too wide a mixture range at idle with the SU carb.

Also check for inlet air leak, carb float level too low, blocked air filter, fan belt too tight.

There is also a very small chance the crank thrust washers got distorted when you fitted the crank pulley, if you over tightened the pulley dog nut.

[dunketh]

I am not familiar with SU carbs yet, though I have a colour tune kit if it's of any use.

Nope. I have one and its never been any use.

There are numerous online guides to SU tuning but in my experience I found using an exhaust analyser was the best way.
I then adjusted the carb until the CO reading was around 2.5 - 3 which is what its supposed to be. Voila, fuelling sorted.
Any garage or mobile '£35 Krypton Tune' chap should be able to sort it, save you the bother.

Why did you change the pulley during an alternator conversion? Did you just fancy a pulley with the damper?

[Alec]

Hello Moggytech,

"Colourtune isn't really much use, as you will get a blue flame over too wide a mixture range at idle with the SU carb."

Sorry, I have to disagree there, although any oil burning gives the indication of an over rich mixture.

"There is also a very small chance the crank thrust washers got distorted when you fitted the crank pulley, if you over tightened the pulley dog nut."

I can't understand that given that the thrust bearings are in the centre main bearing area?

Alec

[MoggyTech]

I can't understand that given that the thrust bearings are in the centre main bearing area?

Yes it's very unlikely, but I have seen this on a spridget engine. The crank got pulled forward and distorted the thrust washers, resulting in a very tight crank rotation.

Re the Colourtune thing. I have one, but also have an exhaust gas analyser, and have found that I get blue colourtune flame at idle, anywhere between 1.5% to 8.5% Co gas content. Using the lifting pin method, the Co is around the 5.5% at idle (slightly rich), but that's kinder on the valves anyway.

[Alec]

Hello MT,

ther had to be something else wrong for that to happen, there is not normally anything in the cam sprocket area\timing cover to 'pull the crank forward nad if it did that would also bind?

Colourtune colours are not just a simple blue but a variation and require a pale blue for correct combustion. Certainly, like many instruments it is down to use and interpretation. The exhaust gas analiser falls down with multiple carburettor applications.

Alec

[Mogwai]

The 1275 crank pully will fit ok but one thing to check is the position of the timing mark notch as the earlier ones will be the same as the minor with the timing marks at the botom but later ones (A+) had the timing marks near the top of the pully so would be in the wrong place. but would be easy to cut a notch in the pully in the same place as the original one

[bmcecosse]

The crank certainly can't be pulled forwrad vy tightening the damper bolt! So that's a Red Herring. Colour tune is useless - because at best it can only tell you an approximation of the idle mixture - and realistically - how long does the engine spend idling ! Plug colour tests are the only way (unless ex gas analyser on RR) to tell if overall mixture is correct. For stalling etc - first just pick up the idle speed - the alternator takes power at idle speed (the dynamo did not) and so drags the engine down slightly.

[Alec]

Hello BMCE,

it seems I am the only one on this thread that likes Colour tunes!.

And, as you well know, with a correctly specified S.U. (which is easily checked on a standard car), if the idle is correct then all else up the range will be.
There is a lot of merit in plug colour and gas analysers especially on a rolling road but they do have their limitations with multi carburettor engines. Ideally, plug reading should be done at various speeds under load and the engine switched off at that point. How many do it that way?

back to Colour tunes, I find them useful on my Injection Triumph as a check (I use three of them, saving up for six:-)

Alec

[Orkney]

Your not alone Alec i like them too, trouble is ive lost mine

[aupickup]

i like mine as well

[bmcecosse]

Waste of money in my opinion - And SU were clever enough to include a simple test device (the lift pin) in the carb to let you set the idle mix correctly. I agree - plug tests at many speeds/loads - but an overall plug test after a good hard run will give a good approximation of the running mix.

[MoggyTech]

it seems I am the only one on this thread that likes Colour tunes!.

Hi Alec,

I still own and use a colourtune plug. For certain applications I still find it very usefull.