Not the average misfire - SOLVED

[MarkyB]

loads of spares, testing parts is easy

Swap exhausts then.

[simmitc]

The saga continues New head fitted. Absolutely no difference. Still the wretched misfire persists. Exhaust swap next...

[mike.perry]

The only thing you have not swapped is the chassis number plate!!

[simmitc]

Almost right. I changed a tyre, and that's cured it Only joking

[horologiumwatches]

Given all the things that you have already checked, my money would be on a collapsed sciencer internals causing a restriction and poor back pressure. Put your palm over the tail pipe. You should feel a certain amount of pressure. I think you have tried everything else. The only other thing I can suggest is that you try a brand new coil. I have experienced coil failure that only occurs under load when hot, took an age to find!

[John.n]

have you tried a new dizzy cap or whole dizzy?
Regards,
John

[bmcecosse]

It's 'NEVER' the coil......

[horologiumwatches]

It's 'NEVER' the coil......

Well this was. Im assuming I am just missing the sarcasm in your post on the internet.......

[lambrettalad]

no thats his tag line on this site ,you will soon get used to it ,he knows his stuff

[bmcecosse]

When I say 'never' - just sometimes, it IS the coil - but honestly, they are extremely reliable pieces of kit and very very rarely fail - and when they do, it all or nothing...... This refers to original coils - modern replacements are hopeless, and often incorrectly specified.....and can fail - sometimes within days/weeks... I just hate to see folks wasting money on new coils whenever the engine develops a wee stutter! It can also be the coil connections - always worth checking/tightening. And is the coil connected right way round?

[katy]

At one time I had a '63 VW beetle that developed a high speed miss. Turned out that one of the spark plug wires came loose on the plug, it ran fine at lower speeds but when revved up the draft from the cooling air would lift the wire up on the plug so that it couldn't fire, slow the engine down and the wire would drop back into place and the plug would commence firing.

[simmitc]

Oh how I wish it was something simple like that. To re-cap: All igniiton components changed several times, including swapping with another Minor - the fault stays with the original car. There is plenty of gust from the exhaust, but I have ordered a new one to try. Will report back after fitting...

Thanks for all the suggestions, after the exhaust, I'll be left with only the block, but (a) I hope that it doesn't get to that and (b) the symptoms just aren't right for a block.

[katy]

Have you checked for vacuum leaks? Especially around the intake manifold and carb.

[simmitc]

Very good thought - that was the first place I went, and the original vacuum unit was faulty, but swapped (and since, the whole dizzy too). Manifold swapped. tube swapped, carb swapped. Each time the fault remains with the original car whilst the old part works perfectly on the other car!

[bmcecosse]

I suggested worn camshaft a while back - have you checked any of the lifts? And the cam timing? Checked?? You say you ran a direct feed to the coil - but what about the wire from coil to dizzy? Try a jumper cable there.

[simmitc]

Well, there were some excellent suggestions, but I think that I'd already tried them all. We all missed one thing, and I just can't believe that I was so stupid as to ignore the possibility In my defence, I've never known this component cause these symptoms before, and nobody else suggested it either. So, after changing all the ignition and fuel parts previously listed, making a special fuel tank, testing the bores with oil, stripping the original head and fitting a new one, using a new manifold and getting a new exhaust; and all-in-all fiddling for many hours over a couple of months and spending a few hundred pounds; the ultimate answer took less than a minute to fit and cost about £4: the air filter. Although looking OK, it clearly had something seriously wrong with it. We learn something every day, and I shall now add that to my list of things to check for a misfire.

[bmcecosse]

Crikey.....must have been almost completely choked solid..... Does the breather tube spew oil all over it?? The HS 2 with the direct breather feed into the carb is much better in this respect.

[simmitc]

It's an HS2 setup, there is no feed into the filter apart from nice fresh air. As I say, it looked OK - I've certainly seen a lot worse that still perform OK; it was just a process of saying "what haven't I changed" and doing the Sherlock Holmes of "after eliminating... whatever is left...".

[bmcecosse]

Well done finding it!

[lambrettalad]

Well done ,so your persistence paid off