Morris 970 Cooper 'S' - Tuning by AG Classic Car Tuning
The above is a MK1 Morris Cooper 'S' 970cc. For those who know these cars they have a near square bore to stroke ratio, which ultimately means they are a high rpm little motor and regularly run at over 7,000rpm.
The above engine build is by 'https://www.craftedclassics.co.uk/' as one of the UK very best engine building specialists for the classic A and A+ engines.
On my arrival the brief given was that it was a devil to start...it would sometimes stall at junctions etc and engine rpms would often fluctuate ....ie some days run at 1300rpm at idle, some days ready to stall at 800rpm or less.
First clue lets take a look at the spark plugs....Dark, shiny ceramic. Not the cleanest burn I'd ever seen!! More investigation required.
So on the 970 Cooper 'S'.....I went on to check the static ignition timing, points gap (Later checked by dwell angle meter), jet heights, needle profile, needle insertion position into H4 SU piston.....and of course replaced the Spark plugs provisionally with new NGK BP6ES to help burn off any similar dark residues in the combustion chamber/piston crowns. (Plugs gap set to 0.026").
Below two pic show the post 'tuning' difference in spark plug burn colour with a slightly hotter running plug
(left -NGK BP6ES versus Right - NGK BP8ES).......I'd probably settle on an NGK BP7ES overall for this vehicle, maybe??
Now time to get stuck into those beautiful Twin H4 SU Carbs. Knowing that this engine also had an up-rated camshaft thought to be in the region of 266 to 286 (exact profile not known)...this needed to be considered when checking how potentially suitable the needle profile was. #CT profile is after all a pretty rich profile as originally determined via dyno tuning.
The profile was a good fit however the piston rise was too quick for the AUC8103 dampers to form the correct venturi enrichment using standard SU damper oil. Hence the damper dimensions were checked (all good) and then the oil was replaced with a 60/20w......and proven by exhaust gas analysis to be just right for this application.
Ignition timing at idle, and resultant mechanical ignition advance curve.
Let's firstly clarify that this 970 Cooper 'S' engine was still running an original Lucas 23D4, which means no vacuum advance and it was still on 32 oz contact breaker points...set to 0.012". But more importantly giving approx 60.0 deg +/- 1 deg points dwell angle.
Initially found to be approx 5 deg BTDC at idle....fully advanced at approx 19 deg BTDC. Together with the BP8ES plugs, this explains all the symptoms as originally described by the owner.
The mechanical ignition advance range of this distributor was very much like an Aldon Red (6 to 7 deg distributor advance...12 to 14 deg at the crank). Hence to achieve the key start...driving...mid/upper...and upper ignition timing, required the ignition timing at idle to be quite advanced. (Details of which are held by myself of course).
The outcome once fuelling was tuned and ignition timing set correctly.....back to being a little flyer again!!