Mini Magazine - - Tech -

Q I’ve just re­placed the head gas­ket on my 1991 City. When I had the head off I lapped in the valves and re­placed the

seals as you do. Any­way couldn’t help but no­tice my ex­haust valves had a white de­posit. I as­sume this means it’s run­ning lean and cook­ing the valves? Josh Hag­ger A A white de­posit cer­tainly sug­gests it is run­ning a lit­tle lean, or may fea­si­bly be just poor qual­ity fuel. The most com­mon cause of lean run­ning is fit­ting a re­place­ment air fil­ter, chang­ing the stan­dard plas­tic cased type with an af­ter­mar­ket pan­cake or cone type. Th­ese gen­er­ally flow a great deal more air than the stan­dard setup, par­tic­u­larly at cruis­ing speeds. Way too many folks fit th­ese fil­ters then try to cor­rect the fu­elling by sim­ply ad­just­ing the jet. This is not the way to do it. It re­ally needs to be checked and set up prop­erly on a rolling road, as in­vari­ably a dif­fer­ent fuel me­ter­ing nee­dle is re­quired. Jet height ad­just­ment should be kept to an ab­so­lute min­i­mum just to tweak idle mix­ture, not to ad­just over­all fu­elling. We have seen some jets that have been wound down to try and get the en­gine to run af­ter fit­ting one of th­ese pan­cake/cone type fil­ters that they are some 5/8-inch down the jet tube! That’s way too much. If in doubt, get the car set up by an ex­pe­ri­enced tuner on a rolling road. The ini­tial cost could save you from big bills in the long run.

Your air fil­ter should be set up pro­fes­sion­ally.

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