Hiccups

[silloyd]

Reset mixture - in fiddling I had made it slightly rich but not desperately so. Smoothed things ever so slightly but still have the mis-fire.

No. 4 exhaust (Valve eight) was a bit off so reset that and checked the others...no improvement.

No broken springs, plenty of oil on the rockers and no particular amounts of gunge:
[frame][/frame]

[Straw clutching]
Could it be the carb not allowing the engine to idle properly? The float bowl is full and only has 'dust' in the bottom, the fuel filter on the pump is clear. I always understood the HS2 carb to be pretty tolerant but could there be damage to one of the more sensitive parts, e.g. the needle, that is upsetting fuel flow at low revs but is less significant at higher revs?
[/Straw clutching]

[bmcecosse]

No, occasional miss is down to ignition. Can't remember - but have you tried a new set of plugs ? I have seen for sale (but not used) little translucent tubes that fit on the plug tops and you can see the spark..... Maybe worth a set so you can see which plugs are not getting a spark........

[silloyd]

Does feel electrical but I'm running out of ideas.

I've seen those widgets too but wasn't sure if they were a bit useless ('snake oil' territory). Anyhow I used a Colortune yesterday to actually see what was going on inside. I tried it on cylinders 1 & 2 and the random misses on both are visible but the cause still eludes me.

• power is getting to the coil (14v) - I have tried bypassing the ignition circuit with a direct feed from the battery;
• coil seems OK - I get the same results from both that I've tried.
• loom supply from coil to dizzy seems OK - temporarily bypassed the loom wire from the coil to the dizzy;
• dizzy appears to be OK - no obvious cracks in the cap, changed the dizzy cap, changed the condenser, changed the rotor, internal earth strap seems to be sound;
• plug leads seem OK - swapped the plug leads but this happens on more than one cylinder;
• plugs seem OK - swapped the NGK plugs for some brand new Champions but again the miss happens on more than one cylinder';
• engine earth seems OK - I have tried a temporary jump lead from engine block to battery.

Clearly something is not right still.

[bmcecosse]

The little tubes are indeed 'snake oil territory' - but at least you found a 'use' for the otherwise useless colortune - it's told you/us that the problem is general, not just in any one cylinder. Must admit - you seem to have covered pretty much everything. The 'tubes' would show if there is a good reliable spark on each plug - the colortune just shows us that the 'flame' is failing sometimes. Could it be that the carb is flooding over (fuel too high/float valve leaking) and it periodically floods the engine, extinguishing the flame.... I wonder if you temporarily disconnect the fuel pump while the engine is idling (20 seconds) - does the engine idle smoothly then?

[silloyd]

The fact that the problem lies across all cylinders suggests to me that the cause is most likely one of the common components and therefore I've effectively eliminated from the equation the HT leads to the plugs and the plugs themselves.

The battery is, of course, part of the common circuit but it gives good voltage and holds a charge, even after much cranking, so I've ruled that out as well.

That leaves the LT circuit to the coil, the coil, the LT circuit to the dizzy, the HT lead to the dizzy, the dizzy itself (including: cap, internal earth, points and condenser) and the earth from the block.

Out of those common elements, I have replaced or bypassed everything. Things that have been bypassed with wire I think I can be confident that the temporary replacements are sound.

However when it comes to the coil, dizzy cap, 'King' HT lead, condenser and points...there's no assurance that any of my spares, even new ones, are not faulty, e.g. I have three new condensers but all three could be duff!! So the process of elimination is not assured or foolproof (as fools are far too clever!)

I'll give the float bowl idea a bash later - thanks for the continued suggestions

Have to say this is hacking me off a bit now

[katy]

Take a good look at the distributor, especially the top bushing. If it's worn excessively the shaft could be wandering about erratically. Also check all the rest of the inards to be sure that they're all OK. I know that you said the unit was "pretty new", but that doesn't mean that there couldn't be problems w/it.

[silloyd]

When I said the dizzy was pretty new, I meant that it (Accuspark 45D) was brand new about 200-300 miles ago, sorry if I didn't make that clear.

However, you are right that it being new doesn't mean it works properly There doesn't appear to be any lateral play at the cam but I think I will remove it and check/lubricate anyway...after I've tried BMC's float suggestion. Another for the list of checks!

[silloyd]

Temporarily disconnecting the fuel pump while the engine was idling didn't help.

Dizzy next...

[silloyd]

Dizzy looks to be fine, no extraneous play or wear. As I had it out (Fnarr! Fnarr!) I re-checked the internal earth strap, lubricated the plates and checked the vacuum advance.

On the points the pivot (that the plastic cam follower rotates on) was very stiff, making me wonder whether they were sticking open periodically, so I swapped them (again) for a third set that move freely but it didn't help.

The 'snake oil' spark plug thingies are beckoning me ..... ...no, don't let me get seduced...

[bmcecosse]

Do you have another dizzy you can try - even an old one?

[silloyd]

I still have the 25D but its vacuum advance doesn't work (that's why I changed it). I guess I could give that a bash...

[bmcecosse]

Try it - just to see if the 'missing' is still there.

[silloyd]

Old 25D, points and condenser (everything else constant) gives the same result, which suggests that I can eliminate the dizzy(?).

So, does that point to a carb related problem??

The float bowl height is OK according the the workshop manual, the float needle valve works correctly and we've established that fuel over-supply is not the problem. So:

1. Jet worn?
2. Jet needle bent/worn?
3. Jet not centred?
4. Butterfly loose?
5. Vacuum loss between the carb and the manifold, e.g. cream crackered gasket?
   (Vacuum adv. pipe ends are new and sealing, pipe to rocker appears to be sealed well - both are clear and working and blocking either/both temporarily raises the revs but doesn't cure the problem)

Carb strip?

[bmcecosse]

Can't see it being the carb - and yes you have certainly elominated the dizzy - and presumably the HT leads too? Is there ANYTHING on the Ignition side that has not been swapped at some point? HT King lead perhaps - I believe you have swapped the coil at some point -although of course 'It's never etc...' ? Have you watched the engine running with the rocker cover off - to see if any of the valves are sluggish at closing?

[silloyd]

I'm sure that I have swapped/bypassed everything on the electrical side but I think I will step through them again, just in case.

Will try looking at the valves later.

[silloyd]

I repeated the following:

1. put the 45D back in;
2. bypassed the ignition switch connection by connecting between battery and coil +ve;
3. bypassed connection between coil -ve and dizzy;
4. checked voltage at coil +ve: ~16.5v (is that right?);
5. checked for loose electrical connections: none spotted;
6. checked connection between coil and dizzy;
7. measured resistance of HT leads: all around 5kohms.

Didn't get as far as swapping coil...again.

Also ran the engine for a short while with the rocker cover off: no obvious sluggish/sticking valves...just a lot of oil spatter around the engine bay now

[bmcecosse]

16.5 is very high - should be no more than 14 volts - but there may be a 'local' effect at the coil (due to inductance etc) - so check the volts at the battery. Could also be inaccurate voltmeter - what does it read with engine stopped - and say side lights on (just to knock the peak off the charge). I have to say - you've pretty much got me stumped!! Just about the only thing left to consider is manky petrol - is it years old - possibly contaminated ? You would need to rig up a temporary suction line from the pump inlet to a can of fresh petrol to see if that helps.......

[silloyd]

I have the luxury of two digital multimeters (don't ask ) and they read within 0.04V of each other.

I went back and checked and I must have mis-read the meter or have been thinking of something else (I'm clearly losing the plot ) as I'm now getting about 13.8V from the battery (engine off) and about 12.6V with it running. However, I have spotted something else.....

When testing the voltage my ear was close(ish) to the control box and I could hear a faint (gzzt) crackling noise from it. On opening it up I found that the missing coincides with a series of small sparks from the contacts on the left (nearest the wing). Could this be causing interruption of the supply to the coil and therefore loss of spark or is this more likely to be as an effect of the engine faltering?


BTW, the petrol is not old or to the best of my knowledge manky and the tank was topped up with two fresh gallons of Sainsbury's finest unleaded only last week.

[bmcecosse]

That's better - I assume you mean 13.8 running and 12.6 off......... So - to test that theory - take the leads off the dynamo and run the engine!

[silloyd]

Sorry, yes 12.6 off and 13.8 running.

Tried without the Dynamo and engine still misses.

Now for a little penance...forgive my father Issigonis for I have sinned, I gave the 'snake oil' man my £6 and he gave me four spark plug whatsits. I connected them between my HT leads and plugs and they lit up the engine compartment with a strange and hypnotic, pulsing orange glow...Ooooh! ...and they showed a nice regular spark on all cylinders with no obvious missed firing cycles so it's not electrical then! (That's three hail Minis and a couple of Ave Marinas by my reckoning)

Has to be mechanical or fuel then innit!?!?


P.S. thinking of leaving the 'snake oil' plug thingies in as they are completely mesmorising!!