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MG MGB Technical - Engine missing

My 1971 1800 mgb roadster has developed an instant loss of power on normal driving and recovers almost as fast. It has been intermittant and getting worse. I have changed the ignition dash switch, the coil, plug leads and now am about to change the condenser in the distributor. It has the original distributor. If anyone has had similar problems or have some suggestions it would be much appreciated. I have owned the car for 12+ yeras and did the original restoration, so I can vouch for the rebuild etc
Thanks Ian Denton, Australia

Ian. Ignition or fuel? If ignition related (low tension circuit), the tach will drop to zero when the engine quits or show erratic fluctuations as the power comes on and off. If not, check out the fuel pump.

If it seems to be a low tension circuit problem, do not forget the ground wire between the points plate and the distributor body. Many of these are getting old and may have some broken strands--especially after 38 years of use.

Your original distributor is, most probably, a Lucas 25D4, but it may have been something other than that if you have one of the made in Australia cars. I have little knowledge of them except from comments people have made over the years. It would be interesting to know what dizzy you have and what the specification number is.

Les Bengtson

For what its worth, I had similar problems a while ago and I traced it directly to the points gap. I bought a dwell meter, which I found to be a boon for checking the points and its more accurate than just relying on a feeler gauge to check the gap. You check the dwell with the engine running and without having to take the dizzy cap off. Its very simple and very quick.

Could be a dodgy (weak) connection involving the Brown wire
down below at the Starter Solenoid.

Daniel Wong

This reminds me of an apparently genuine Quantas maintenance sheet. The pilot reported "Number 3 engine missing". The mechanics response was "Engine found on right wing after brief search". There are many others, see

If the tach is still recording engine revs when power has been lost it could be HT problems as well as fuel.

Fuel won't generally cause an instant loss of power, as the float chamber run down the effect on power is gradual, and usually one carb empties slightly before the other which also makes for a gradual power loss i.e. firing on 2 instead of 4. The diagnostic for that is to turn off the ignition the instant it happens, bring to car to a halt, and listen carefully to the fuel pump (assuming it is an SU and not some after-market types) as you turn on the ignition again. If the pump chatters away then it was fuel i.e. pump or its connections. If you get nothing from the pump, or maybe just one click but the car starts and drives away normally, then it wasn't fuel, so if the tach *was* still registering then it is probably HT.
Paul Hunt

This thread was discussed between 14/07/2009 and 16/07/2009

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