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MG Car Repair/1978 MG Roadster Ignition Timing


QUESTION: I have a 1978 MG Roadster high compression and its doing my nut in, its on twin SU HIF 4 carbs and all i want to do is find out what the correct ignition timing is and how it should be done because i have tried every mortal way suggested and i still don't think its right,first the timing marks are on the front pulley at the top on the left as you look into the engine what degrees are these set at is it 2 degrees or 5 degrees increments.
then should the vacuum pipe be disconnected ? and second what RPM should the engine be running at to set up the timing.
I have had the car out last summer and it went great but,and there the story begins.
I don't like anything on my vehicles that i don't understand this car has had a small fortune spent on it and looks as if it has just come out of show room top and bottom, so please can you send me in the right direction before i go around the bend.

ANSWER: Hi Tom.  I assume you have a UK specification MGB.  This is important, because the USA and California specification cars are both different from UK cars.  

The timing marks are the 5 points (with 4 notches in between them).  They are at 20, 15, 10, 5, and 0 degrees before TDC.  

Timing must be set with the vacuum pipe disconnected from the distributor.  I need the engine number to be sure if your car is a 1977-78 car or a 1978-80 car.  They have different timing.

---------- FOLLOW-UP ----------

Yes it is a uk spec
Engine N/O 18v-27566

I assume that the full engine number is 18V893-27566.

Your timing should be set at 13 degrees with the engine speed steady at 1,500 rpm.  Then speed the engine to 2,000 rpm and verify that the timing has increased to between 20 and 24 degrees.  Finally, re-connect the vacuum pipe and set the tickover to 850 rpm.

If you have access to a dwell meter, then it would also be a good idea to check the dwell angle, which should be about 51 degrees (somewhere in the range 46 to 56 degrees).  This is more accurate than setting the points gap with a feeler gauge.

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Barrie Jones


MG Sports Cars from 1949 to 1980 - Including MGB, MGBGT V8, TF1500, TF, TD and modern Midgets. I also specialise in SU carburettors, Lucas wiring, suspension, steering & brakes.


I have owned my 1955 TF1500 since 1966. Technical specialist for the TD and TF with the MG Car Club T Register. Also owned 20 MGBs and currently own an MGBGT V8. Written 3 books on MGs and produced a DVD on how to strip and rebuild the TD/TF gearbox.

MG Car Club.

Barrie's Notes on the 1953-55 MG TF (author). /=====/ Barrie's Notes on the MGB (author). /=====/ Barrie's Notes on the MGB GT V8 (author). /=====/ The Essential Buyer's Guide to the MG TD, TF and TF1500. (author)

M Phil, C Eng, BSc (Eng).

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