Peter Delaney
GT40s Supporter
Pete - sorry for the thread drift, but it seems relevant to your interest in the vacuum gauges & tuning.
Trevor, I see where you are coming from - perfect 90deg setting at WOT should translate to a perfect idle setting. However, I doubt that I have a perfect set of TB's / spindles / butterflies / linkages !
As mentioned previously, the only problems I have had are related to throttle positions near idle - specifically, fast openings off idle (most often when blipping the pedal on down-changes - the odd cough & spit, & sometimes some backfire). When Steve does his magic with the vacuum gauge or rubber tube (getting the butterflies all synched at idle & just of idle), the problems disappear - for a while. In good or bad idle tune, the engine has always run clean & strong at part or full throttle.
This all lead me to think that the culprit was the fact that the butterflies get slightly out of synch at idle over time (non-perfect linkages, heat cycling, vibration, etc).
So I reckon that tiny variations between butterfly positions equate to significant % differences in air-flow between TB's at closed/near-closed throttle, but at WOT, the % differences are much less noticable - hence the problems at near-idle & the lack of problems at WOT.
Does any of that make sense ?
Kind Regards,
Peter D.
Trevor, I see where you are coming from - perfect 90deg setting at WOT should translate to a perfect idle setting. However, I doubt that I have a perfect set of TB's / spindles / butterflies / linkages !
As mentioned previously, the only problems I have had are related to throttle positions near idle - specifically, fast openings off idle (most often when blipping the pedal on down-changes - the odd cough & spit, & sometimes some backfire). When Steve does his magic with the vacuum gauge or rubber tube (getting the butterflies all synched at idle & just of idle), the problems disappear - for a while. In good or bad idle tune, the engine has always run clean & strong at part or full throttle.
This all lead me to think that the culprit was the fact that the butterflies get slightly out of synch at idle over time (non-perfect linkages, heat cycling, vibration, etc).
So I reckon that tiny variations between butterfly positions equate to significant % differences in air-flow between TB's at closed/near-closed throttle, but at WOT, the % differences are much less noticable - hence the problems at near-idle & the lack of problems at WOT.
Does any of that make sense ?
Kind Regards,
Peter D.