midget misfire 1275

[chard]

Hi

warm engine, under load, gentle acceleration, low gear 2000-2500 rpm, the engine stutters (just once) and then pulls ok?

Does this point to anything obvious to look at 1st? or should I just start with the points and work through the ignition?
Could it be the vacuum advance for instance and how do I check this?

[SB - Nigel]

chard said:

Hi

warm engine, under load, gentle acceleration, low gear 2000-2500 rpm, the engine stutters (just once) and then pulls ok?

Does this point to anything obvious to look at 1st? or should I just start with the points and work through the ignition?
Could it be the vacuum advance for instance and how do I check this?

Hi again

Hopefully someone with knowledge will be along soon - but the good thing about these old cars is that they are quite simple so it'll either be

petrol = carbs or pump - carbs or their set up more likely here (?)

or

electric = as you say - I'd start at pionts here, still on points and it's aways worth checking condition of dissy cap, rotor arm, leads and plugs anyway

BTW if you ever get the car feeling sluggish for no aparrent reason then think of coil

[minimoog]

Cliche has it that there are very few Spridget running problems that don't lead back to a dodgy condensor

[Robert060379]

Sometimes the Diafram in the vacume advance perishes with age. Get a MG Metro Turbo top end a 1380 big bore kit.

[MG Mark]

What the vacuum advance actually does is explained in the last post here: http://www.pistonheads.com/gassing/topic.asp?h=0&a...

So if it was a problem in that respect, it should happen all of the time, not just under load when warm. If you wish to check the vacuum advance, remove the distributor cap, disconnect the vacuum pipe from the manifold and suck hard - you should see movement of the arm connected to the diaphragm, but if not it may be because you are not sucking hard enough......

Nine times out of ten a problem in that area is based on an electrical issue, and the symptoms you highlight point to the condenser as the most likely source - generally, they fail gradually, and as they do, the effect is a weaker spark - when the engine is under load and warm...

Basically what it does is that the field induced by the coil collapses when the points open, but that induces a current in the primary coil as well - not very much, but it's enough to erode/burn the points. The condenser prevents the points from arcing and prevents coil insulation breakdown by limiting the rate of voltage rise at the points.

Bottom line is replace the condenser and the points, and see what effect that has before going further.

MG Mark




MG Mark