QuestionHi Barrie,
I have a 1968 MGB with the GF engine and twin 1 1/2" SU carburetors. When filling the dashpots with engine oil, how high a level should I fill them to? Also, what symptoms would the car exhibit if the oil level in the dashpots was too low?
Finally, can you recommend a book that covers the basics of SU carburetors?
Thank you in advance!
Regards,
Dan
AnswerHi Dan. The MGB uses the same oil in the engine, gearbox, and carburetter dampers. If you live in a hot climate, then use 20W/50 but if you live in a cold climate then use 10W/40. In Alaska you might need 5W/30.
Look inside the hole where the damper goes. There is a metal tube about 3/8 diameter. This is the dashpot. Fill this tube until nearly full, maybe 1/4 of an inch from the top. When you insert the damper, a little oil should overflow and lubricate the outside of the dashpot. This should be done once a month if you use your car regularly.
The dampers in the dashpots slow the rise of the pistons inside the carbs when you snap the throttle open. This produces a temporarily rich mixture, necessary for smooth acceleration. When the oil is low, the pistons rise too quickly, and you feel it as a hesitation (or flat spot).
I have written a booklet on the MGB. It is called: Barrie's Notes - Maintaining an MGB in the 21st Century. There are 8 pages on the SU carburetter, and the book is available from the MG Car Club in the UK. If you need more information, I recommend the Haynes book #0299 entitled SU Carburettors (see www.haynes.co.uk).
