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MG Midget and Sprite Technical - Misfire

So my 1500 is misfiring.

I think its fuel related... ie carbs

It badly misfires when I touch the throttle... constant revs and deceleration is fine.

Any smart ideas where to start?
C L Carter

hi, "most fuel problems are electrical problems" have you points or electronic ign. ? id try the basic electrics first. plugs,points cond cap leads.
regards bob.
trebor

Hi.
Will it start easily without choke?
Does it feel like its going to stall as you press firmly on the throttle.?
Then clear itself and run smooth?
!"Flat spot"!
If you press throttle gently do the rev rise smoother?
Has the fault just happened or has it been gradually getting worse?
Make sure a throttle screw hasnt worked loose,or the big nut/jet adjuster underneath hasnt stuck on!
As suggested,also check plugs and points gap,cap,leads and that the dizzy is tight and hasnt slipped round!
Have you done any work to,or replaced parts on it recently?
That should keep you busy till lunchtime!!
Let us know what you find!

Dave
Pilkie

I'm with Bob start with the very basics onwards - and any new parts just added or adjustments just made
Nigel Atkins

Do the initial diagnosis from the comfort of the driver's seat!

Does the rev counter needle go wild when it is misfiring? = LV electrical fault.
If not, then the chances are its fuel related.

When driving and it misfires, does pulling the choke out for a moment make it better, or worse? If better, then it is a weak fuel mixture, likely caused by low fuel level in the float chamber (fuel pump not keeping up, maybe a split pump diaphragm?) or a fuel blockage (maybe in the pipe from float chamber to the jet)

If pulling the choke out makes it run worse, then it is flooding at the carb or maybe the choke is sticking open.

Do you have a lazy cylinder? With the engine running pull each plug lead off in turn. If the fault is on one cylinder then removing that lead will not make it run worse. And it is not likely to be fuel related. Swap the plug from the lazy cylinder with another. Does the fault move as well in which case it is the plug. If no, then it is the HT lead or dizzy cap. Or possibly a valve issue but do other checks before you come to that conclusion.
Guy W

I went through most of the diagnostics you've suggested already. So I went back to basics. It was the points (which were new 2 months ago) - the rivet of one of the contacts had come very very loose and was rattling all over the place... I can't believe she was running at all to be honest. - Good as new now.

On this note, does anyone know where to buy decent points and condensors? The ones from the mgoc seem to last a few months and pack up!
C L Carter

I've put this many times and no doubt you've passed your nose over it, eyes rolling, lips tutting

Distributor Doctor - http://www.distributordoctor.com/

don't change a working condenser, despite what some think (including MGOC Spares it seems) it's not part of the service schedule nor is replacing points at service - consult your Driver's Handbook for the necessary info :)
Nigel Atkins

hi. i dont know the makes but all my points on my 65 midget were red.i always had trouble with these. more recently i bought some from a different shop local to me and they were brown. they seem to have lasted longer so far.
bob.
trebor

Bob,
follow the link on my last post for more info

'red' rotor arms highlighted the problems 5,6,7? years ago and probably before that, or perhaps it was points, I can't remember, then there's the condensers ...
Nigel Atkins

Looking through my spares (trying to downsize again)

I've got a NOS Lucas CS1 set of points(kwickfit type) you can have.

Post an e mail address for response and I'll pop them in the post.

R.
richard boobier

While I agree that most fuel problems are electrical (are they ever!) with this symptom if the misfire is a gasp rather than a BANG BANG misfire I'd be checking the carb dampers in the dashposts have the right amount of oil before diving into the electrics. Or indeed that the plungers are both done up and haven't unwound themselves as occasionally happens.

And if all was right there, then I'd dive into the electrics ...
Paul Walbran

Ooh thanks Richard - carter dot christan at g mail dot com
C L Carter

Paul,
it was newly fitted CB points, probably poorly made - >> It was the points (which were new 2 months ago) - the rivet of one of the contacts had come very very loose and was rattling all over the place...<<
Nigel Atkins

Christian,

Will drop an e mail later after supper.
You are in luck again - found a hens tooth !
NOS Lucas condenser C1 DCB01 - so will pop that in the bag also.

R.

richard boobier

Smack in a simon BBC set with a decent rotor (the one supplied is just so so
Alex G Matla

Ha! Thanks Nigel :-) Hope my kids don't read this or they'l add AND READ to the DECREASED ABILITY TO THINK AND REMEMBER sign they've posted on the wall over my seat at the dinner table ....
Paul Walbran

Paul,
you want to write on the other side of the sign for them 'yes and try finding your names in my will' and just smile every time you see the face of the sign
Nigel Atkins

Hehe, good plan, I love it. Fortunately all said here is in jest, quite a lot of which happens around said dinner table :-)
Paul Walbran

Paul,
something like that is always a good test of humour, you seem the decent sort so I'm sure you wont leave them in debt - well not too much anyway :)
Nigel Atkins

This thread was discussed between 02/02/2013 and 06/02/2013

MG Midget and Sprite Technical index

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