Technical Mixture screw 28IMB

[JonPiz]

Good evening! As a general rule of thumb, how many turns does the mixture screw have to be screwed out

 

[smart51]

2 turns minimum, 3 turns maximum. If you need to turn it out more, you need a larger jet. If you need to turn it in more, you need a smaller jet.

 

[Toshi 975]

Initial setting should be 1 1/2 turns out

 

[the hobbler]

Initial setting should be 1 1/2 turns out

I agree totally with what "Smart51" and "Toshi" have said, but it is not just a matter of "turn it out 1-1/2 turns and all should be well". It is a balance of both the 'idle-speed' screw AND the 'mixture screw". To start from scratch, GENTLY turn the mixture screw fully in, and then out 2 turns. Turn the 'idle-speed' screw out to the point that it is not in contact with the butterfly lever, and then turn it in until it is JUST making contact, and then another 2-1/2 turns. This SHOULD give you quite a fast idle speed; if it doesn't, turn the 'idle-speed' screw in just a little bit more. When the engine has warmed-up, and you no longer needing to use the choke, screw the MIXTURE screw in until the engine begins to run a little bit roughly, and then turn the mixture screw out GENTLY until the idle has smoothed out again. The, turn the idle speed down a little, and repeat the proceedure with the mixture screw. Continue doing this, a little bit at a time, until you have an idle speed of about 900rpm, (which will be indicated by the fact that the ignition light is just flickering) and a smooth idle speed. If you have a standard carburettor and have not played around with the jets, there is a very good chance that you will not need to swap jets and that adjustment (as described) will give you a nice smooth (for a 2-cylinder engine) idle speed.

 

[JonPiz]

I agree totally with what "Smart51" and "Toshi" have said, but it is not just a matter of "turn it out 1-1/2 turns and all should be well". It is a balance of both the 'idle-speed' screw AND the 'mixture screw". To start from scratch, GENTLY turn the mixture screw fully in, and then out 2 turns. Turn the 'idle-speed' screw out to the point that it is not in contact with the butterfly lever, and then turn it in until it is JUST making contact, and then another 2-1/2 turns. This SHOULD give you quite a fast idle speed; if it doesn't, turn the 'idle-speed' screw in just a little bit more. When the engine has warmed-up, and you no longer needing to use the choke, screw the MIXTURE screw in until the engine begins to run a little bit roughly, and then turn the mixture screw out GENTLY until the idle has smoothed out again. The, turn the idle speed down a little, and repeat the proceedure with the mixture screw. Continue doing this, a little bit at a time, until you have an idle speed of about 900rpm, (which will be indicated by the fact that the ignition light is just flickering) and a smooth idle speed. If you have a standard carburettor and have not played around with the jets, there is a very good chance that you will not need to swap jets and that adjustment (as described) will give you a nice smooth (for a 2-cylinder engine) idle speed.

Thank you, that’s my job next weekend sorted