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 Posted: Mar 2, 2021 04:33PM
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"......to advance the spark timing at low engine speeds to improve the fuel economy at low rpm...."

Not strictly true .... At low rpm you're not going to improve fuel consumption much because you're not using much anyway.

The vacuum advance really comes into play at cruising speed on non city roads.  The extra advance allows you to cruise at 60 odd mph with much less throttle than you would need without it.  There is real benefit at much more than what you might consider to be low speed running.  With my 1330 I found fuel consumption at 70 mph reduces by around 30%.

Cheers, Ian

 Posted: Mar 2, 2021 07:17AM
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BTW. Its vacuum suction to advance the spark timing at low engine speeds to improve the fuel economy at low rpm. At high rpm there's no vacuum in the intake system, so the spark advance reverts to what you set on the distributer. What setting did you choose for your 998?

 Posted: Mar 2, 2021 02:28AM
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US
Thanks!

"A gentleman does not motor about after dark".  Joseph Lucas (1834-1902)

 

 Posted: Mar 1, 2021 08:50PM
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Use the "nipple" next to the throttle plate. 

 Posted: Mar 1, 2021 06:55PM
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998 - HS4 SU - 123 Distributor

"A gentleman does not motor about after dark".  Joseph Lucas (1834-1902)

 

 Posted: Mar 1, 2021 05:18PM
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Which engine, which carb, which distributor?

 Posted: Mar 1, 2021 02:55PM
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US
Does the vacuum pipe connect the distributor to the carb and if it does, why, and which nipple on the carb do I use?

"A gentleman does not motor about after dark".  Joseph Lucas (1834-1902)