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MG Midget and Sprite Technical - starter problem 1275

Chaps...this isn't a wind up, please read on...
I am experiencing "odd " starting characteristics with my '66 Midget.
Fully charged battery, checked with voltmeter and hydrometer, all six cells spot on.
First start of the day...very sluggish turnover...until I pull off the white/black lead from coil to dissy after which the engine spins like it's going to do a somersault. Put wire back and sluggish again.
The engine WILL eventually fire up.
..but what the fudge has this problem with the satrter to do with the LT circuit...or am I missing something blindingly obvious? Many thanks for anyone with an idea!
Cheers, Dave
David Cox

Starting on full advance? Just a guess. Do you have vac advance on your dissy? Is it stuck?
Greybeard

or broken an advance spring in the dizzy--
Could also be a seized or sticky mechanical advance, do you oil the felt pad under the rotor button ever--
If you take the cap off, and just twist the rotor button to check if it's still spring loaded or sticking
William Revit

thanks for your thoughts, chaps, but the engine runs absolutely fine once it's started...pulls well in all gears etc etc....It's this first start of the day turning-over problem that I'd like to understand. Why, when the coil is in the circuit, does the starter motor work so sluggishly?
Dave
David Cox

Because it is trying to start with to much advance.
When you disconect the coil the timing is not a relevant factor.

The engine can then still run fine an restart easy when warm
O K

I don't think it's a timing issue. Too much advance would surely cause piston slap as the mixture detonates on the "up" compression cycle [thus working against the starter motor's efforts to turn the engine]and there is no hint of this...and in any case the engine runs fine when it HAS started....Timing problems would also be present for every start as well, which is not the case.
I'll put it down to a dodgy earth in the SM...I'll change it tomorrow. Either that or the Prince of Darkness has infected the circuit with Goblins.
Dave
David Cox

Why not try retarding it for one morning and see what happens.
It is free and reversed within a couple of minutes
O K

Got to be too much advance at cranking speed. Check it with a timing light while cranking. That there are no symptoms of too much advance when running indicates there may be an issue with the advance mechanism that is preventing any further advance once running - broken spring as per Willy's post, seized or sticky cam, etc.
Time to look inside and see what's happening.
Paul Walbran

Could it be a dodgy starter solenoid? I had problems with mine a few years ago. When the engine was cold the starter barely turned over, but found that if I (carefully!) shorted the large solenoid terminals with a spanner, the starter flew round. I managed to spray some switch cleaner into the solenoid and it's been fine since......

Edit: meant to say that maybe disconnecting the ht coil is allowing sufficiently more voltage for the solenoid to 'click' on
J Smith

...just to put this thread to bed...
spent a happy hour or two yesterday dismantling the entire starter circuit and cleaning up every last contact point. New solenoid and a refurbished starter motor [from my own bench] and all is good. Bottom line: the SM earth bush holders were loose on their rivets..not conducive to carrying a cold cranking current of however many amps it is. Also, the armature end float turned out to be out-of-spec [Lucas give this at 10 thou max] which would have added to general noisiness of engagement. [Moral of the story: refurbish your own SM...all the bits are readily available!]
Thanks to those who chipped in. Dave.
David Cox

This thread was discussed between 05/09/2019 and 07/09/2019

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