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MG Midget and Sprite Technical - 1275 missing

A friend has a 1275 that suddenly start to miss badly. He/she had the distributor and plug leads and spark plugs replaced but it made no difference. I just dropped by and set the timing, points but still ran like a hairy goat. There is an exhaust blow, engine pipe but no other leaks that I could hear. When the air cleaners were off if the air inlet was blocked with my hand the revs. rose, same on both carbs. but it only revs. on the front carb. when linkage is operated.(leakage between the carbs. disconnected).
I noticed that the new plug leads are breaking down, which was evident when I pulled to leads off to see if the engine change with one lead off. (Ouch!)
The back carb. does not seem to be working so next week I will try compression test and replace the leads with ones I have.
The car was going well and just started breaking down so maybe carb. out of synchronisation? Do damage to rear cylinders?
Any comments appreciated.
Col.
C Pearce

Col, dirt in the back carb preventing fuel reaching the jet would be my first check.
Out of sync carb's won't cause damage, it'll just run like a hairy goat lol...

best of....
MGmike
M McAndrew

I had a quick check of the back carby but from that quick look it looked clean.I did noticed there was excess fuel around the front carb. How can I see if fuel is getting to the jet(fuel bowl was full and needle was seating correctly).
Gives me something to think about untill I get back to the car. It is a couple of miles out of town.
Col
C Pearce

Col,
If there is dirt in the jet of the rear carb, you won't necessarily see it. It will lurk down in the jet tube, pushed down further by the carb needle when at rest and washed up into the jet orifice when the throttle is opened and the piston and jet rises. You can clean the jet by removing it and rinsing through with petrol, but FRM posted a neat and quick method on another thread recently:

" Remove the air filters, hold the throttle linkage to about 4000rpm, and choke each carb solidly with your hand; remove hand before engine dies, let it recover speed. Do the other carb, repeat a few times. This will suck any water or most dirt right through the jets"

If this doesn't cure it, I would do a compression test. She may have a burnt or sticking valve on #3 or #4
Guy Weller

Have you pulled the plug wires to see if the miss is just on a single cylinder? Could be a blown head gasket between 3/4.
Trevor Jessie

Thanks for all comments. FRM method won't work as the any throttle opening other than just above idle causes it to stall. Looks like the next step is pull the needle and clean., after is try a different distributor cap and plug leads.
Thanks, Col
C Pearce

Up date. Replaced distributor cap and leads, still running rough..
Tuned carbs
Checked timing
Looks like manifold leak so Fridays job.
More updates to follow.
Col.
C Pearce

A lot of duff rotor arms about.
Remove dizzy cap. Using lead from coil hold near brass on rotor and flick ignitiion. If you get a spark the rotor is duff and earthing down the dizzy spindle.
Alan
Alan Anstead

Thanks Alan I will try that too.
Col
C Pearce

some places sell 'red' rotor arms I'm not sure if they're all made at the same place but he's a good source - Distributor Doctor - http://www.distributordoctor.com/red-rotor-arms.html

also remember the order of checking/adjustment (tappets,) CB points, plugs, timing, mixture

and modern CB points can be poorly made so are faulty after fitting plus they may need readjusting again after some miles of use

buy NOS CB points from a reliable source like Dissy Dr

also - check the points are installed correctly - see the appropriate page in the Driver's Handbook
Nigel Atkins

This thread was discussed between 23/02/2013 and 27/02/2013

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