WITHOUT VACUUM PIPE REVS INCRESED
Discussion
I have just bought a 1000cc mayfair. Tinkering as you do plugs points timing etc when i noticed that on idle the revs picked up when i removed the vacuum pipe from the dizzy. Is this correct would have thought the other way as now making a weak mixture as i did not cover the pipe with my finger. covering the pipe made the revs fall again. Anything wrong do you think ?
Ok then, it's probably running rich then, the reason i asked is that the stage one kits do run rich at idle anyway so this can happen.
To give a basic check, make sure everything is connected and undo the carburettor damper top with the engine running, if you lift the carb piston about a couple of mm whilst it's running the engine speed should raise a little then drop if the mixture is about right, if it cuts out or drops straight away then it's a little weak, if it rises and stays risen while you hold it up then it's too rich.
To weaken off or richen up the mixture adjust the carburettor jet mounting underneath the carburettor, but only little by little, a half turn makes a lot of difference screwing it in weakens, and out richens, after each adjustment do the carb top back up and give the engine a little rev and once it has settled to idle recheck again by lifting the carb piston.
I usually run mine a little weak, just get it to the setting then turn weaken off a quarter turn, and I do roughly 15000 miles a year with no problems.
If for any reason you're unsure, find a friendly MOT station and ask them to check the emissions at idle and set it to around 3.5% CO content at idle speed.
Hope this helps
To give a basic check, make sure everything is connected and undo the carburettor damper top with the engine running, if you lift the carb piston about a couple of mm whilst it's running the engine speed should raise a little then drop if the mixture is about right, if it cuts out or drops straight away then it's a little weak, if it rises and stays risen while you hold it up then it's too rich.
To weaken off or richen up the mixture adjust the carburettor jet mounting underneath the carburettor, but only little by little, a half turn makes a lot of difference screwing it in weakens, and out richens, after each adjustment do the carb top back up and give the engine a little rev and once it has settled to idle recheck again by lifting the carb piston.
I usually run mine a little weak, just get it to the setting then turn weaken off a quarter turn, and I do roughly 15000 miles a year with no problems.
If for any reason you're unsure, find a friendly MOT station and ask them to check the emissions at idle and set it to around 3.5% CO content at idle speed.
Hope this helps
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