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MG MGA - carb pussle feed back

After a lot of aggro., the Riley twin SU spit back problem has been sorted ! For the record it was a combination
of faults. Rebuilding the SUs was 50% plus improvement, though I couldn't see anything drastically wrong inside them. Reinststing the water circulation through the inlet manifold also showed an improvement as the engine got hotter. But it was still not possible to get a good feel for the mixture settings, ie., lifting the pistons did not do much and a check with colour tune showed a fairly rich mixture. Got to be an internal problem ? Out with the pressure pac chemical spray used to clean the gum up inlet problems on boxer engined Subarus. Five minutes later a clean running engine and a 100% result. The car has not been run much for the last couple of years, use it or loose it perhaps.
Thanks for all the helpfull comments Sean
S Sherry

OK, not an MG forum topic, but, you've got my attention with the "gum up inlet problems on boxer engine Subarus". I just happen to have one but have not seen this issue. What is this problem and what is the spray you use to correct it?

G T Foster

I am not sure of what Sean is referring to, but I often use a spray to clean Mass Air Flow sensors (MAF) on modern cars. The MAF is typically a hot wire (electrical resistance wire) which measures air flow through the inlet manifold. It gets clogged with the re-circulated crankcase vapour and gives a false reading to the engine computer. The spray is similar to carburetter cleaner.

M F Anderson


Just some more info on the MAF cleaner.
It is available in the USA from:

Also see attached image.

Sorry about the non-MGA content.


M F Anderson

K & N filters KILL hot wire airflow meters. The mixture of oily dust in bad news. DO NOT USE ONE if your car has a hotwire type AFM.
Mick the AFM is in front of the recirced air or they would all die quickly. Clean DRY air is all they should see. Chang air filters often in these cars.
R J Brown

This thread was discussed between 19/06/2009 and 20/06/2009

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.