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Car Forum / MINI / July 2004Could timing be the problem
I have just fitted a branch to my 1977 1100 mini clubman, however in order to get an increase in power i had to advance the timing drasticaly. The specifications require the timing to be set at 12 degrees BTDC at the moment it is advanced passed 15 deg BTDC, as a result fuel consumption has increased drastically. After fitting the branch should I need to adjust any other settings i.e. ignition timing,plug gap etc since I want to bring timing back to specified setting. With the standard manifold the car was running fine just that I thought I could improve efficiency by fitting a branch and freeflow. And Elvis was sitting next to Clubman in the spaceship, which I thought was kinda weird, but then they turned to me and said: > I have just fitted a branch to my 1977 1100 mini clubman, however in order > to get an increase in power i had to advance the timing drasticaly. The [quoted text clipped - 6 lines] > just that I thought I could improve efficiency by fitting a branch and > freeflow. This is pretty much a classic problem. Fitting the new manfold has increased airflow through the engine, and now you're running a weak mixture. A weak mixture burns much more slowly, and produces much less power. Advancing the ignition timing partially compensates for the slow burning mixture, and recovers some of the lost power, as you've found. In the long term, a weak mixture will seriously overheat the combustion chambers, and lead to all kinds of component damage. You need a new carb needle with a fuel delivery profile that matches the engine's new air consumption. The only real way to determine which profile you need is a session at a good rolling road dyno shop that understands SU carbs. > You need a new carb needle with a fuel delivery profile that matches the > engine's new air consumption. The only real way to determine which > profile you need is a session at a good rolling road dyno shop that > understands SU carbs. OR you could visit www.minifinity.com where you can download a very useful piece of shareware called WinSU. This can give you an idea of the different needles that may be used in the varied world of the SU carb. You put in your carburettor, air inlet (i.e. what sort of air filter you are running, such as standard, K&N etc), and exhaust info and the program will suggest a more suitable needle. At at least ?50 an hour, rolling roads are nice but very expensive, especially if you have other engine issues which may extend your time at the garage. By the way please join us at Minifinity for further useful advice and the occasional top tip! HTH Karen >> You need a new carb needle with a fuel delivery profile that matches >> the engine's new air consumption. The only real way to determine [quoted text clipped - 7 lines] > filter you are running, such as standard, K&N etc), and exhaust info > and the program will suggest a more suitable needle. WinSU is just a guide, a quite good guide, but a guide none the less. Nice shamless plug for your forum - but it's from www.winsu.co.uk :) > >> You need a new carb needle with a fuel delivery profile that matches > >> the engine's new air consumption. The only real way to determine [quoted text clipped - 11 lines] > > Nice shamless plug for your forum - but it's from www.winsu.co.uk :) Thanks for the correction, Karen You NEED a new needle for the carb. Try e-mailing minisport and they'll find you the correct one for the job. You'll probably need AAU or AAF needle. Minisport use the AAF needle in their stage 1 and beleive me they probably know what they're talking about. Just got mine from their on Thursday just gone and it was ?8ish but they will post, total cost would be around ?10ish depending where you live. > I have just fitted a branch to my 1977 1100 mini clubman, however in order > to get an increase in power i had to advance the timing drasticaly. The [quoted text clipped - 6 lines] > just that I thought I could improve efficiency by fitting a branch and > freeflow.
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