Airbox sealing afffect on mixture?

[UKAndy]

During my investigations into why my 1978 GS750E was running rich I noticed the seal between the air filter housing and the airbox was missing. I have replaced the seal and also added foam seals to the end plates. I replaced the boots recently so my airbox is now as close to original build as possible.

My question is how do you think this would affect the mixture, would it be leaner or richer?

An air leak in the air intake usually would lead to a leaner mixture but as this is a leak on the inside of the airbox. My thoughts were that it will not make any significant difference except it may give a better balanced airflow as more air would flow through the filter.

Andy

[Steve]

It's not just that there will be more air through the filter, it's more like all the air that moves through there, moves through pre-planned passages. Air that enters past seals can disturb the airflow and the turbulence at the intake of the carb is what causes the problems. This will indirectly affect the mixture because of all the differences in apparent airflow with all the turbulence.

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[UKAndy]

Thanks for the input. The results showed a leaner mixture across all 4 cylinders, checking the plugs one cylinder is now running a little lean and the others are perfect colour. I will have to back off one of my pilot fuel screws another 1/8th of the turn.

[Nessism]

Thanks for the input. The results showed a leaner mixture across all 4 cylinders, checking the plugs one cylinder is now running a little lean and the others are perfect colour. I will have to back off one of my pilot fuel screws another 1/8th of the turn.

Where are the pilot fuel screws now? Most bikes run best with the screws between 3/4 - 7/8 turn open and the air screws between 1.5-2.0. And if the intake path has openings such as at the boots, that will lean the mixture.

[UKAndy]

The pilot fuel screws are all set 1/2 turn out from lightly seated. Currently my no. 2 cylinder plug is white i.e. lean and the others are all a chocolate brown. My air screws are at 1 turn out. I gave the bike a few miles of low throttle running after sealing the airbox to see what affect it would make. I am going try backing no. 2 fuel screw 1/4 turn to see if gives similar results to the others. I tried 3/4 on all before and it was very rich.