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19 minutes ago, Graham said:

Cant really see any description as Ebay is having serious problems at the moment.


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1 minute ago, stuart said:

Cant really see any description as Ebay is having serious problems at the moment.


Description reads;



A ShackTune Metering Unit Vacuum Dump Kit...

The Lucas Pi system is great most of the time...
Until you add a camshaft with too much overlap between the inlet and exhaust valves.
The overlap on the valves causes a huge jump in the amount of vacuum presented to the MU.
This high vacuum normally occurs around 4000 rpm as the exhaust scavenging becomes efficient.
As a consequence,  just when you need full fuel the MU is tricked in to leaning the mixture out....
This can be so bad that it effectively stops the engine accelarating any further.

The ShackTune dump kit is the remedy. 
It controls the vacuum presented to the MU by monitoring rpm and triggering a bypass solonoid.
Once triggered the vac to the engine is blocked and the MU is vented to atmosphere through a sintered brass filter.
The control box is configurable to your desired rpm point, and also different cylinder counts.. so 4, 6 or 8 cylinder..

The control box also acts as an accurate Tacho as the cuurent rpm is always displayed. 

The control box should not be mounted in the engine bay..
The control box does not need an additional relay..
The control box switches the earth on and off, so the pos side of the valve needs a 12v ignition feed..
The solonoid valve is to be mounted just above the MU with the supplied rubber pipe..
The kit does not come with any additional wiring..
The kit does come with instructions on wiring the control box..

The wiring is relatively simple..
Control box-
Black to earth
Red to ignition Positive
Grey to ign coil Negative
Blue to the black wire on the valve.
Black to Blue wire on control box
Red to ignition fed Positive

Warning----- On the control box, Do not connect any wire to positive, other than Red... or you will blow the electronics and destroy it...

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I fail to understand what it does.

A MU supplies MORE fuel with reduced vacuum, so am I missing something?


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If i understand this right..... the unit will tellnthe MU to supply max fuel at above the set revs

For racing this might work for max power

but how will the engine ever slow down again?

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As I read it, it effectively tells the metering unit to go to full throttle when you are accelerating at part throttle, once you get past a selected rpm.

I assume that once the rpm drops below the set point it switches off the solenoid again.

Two problems I can see with this.

1, thrash it round to the red line and the metering unit will stay full rich even with the throttle shut until the rpm drops below the set point. Sounds like an invite for bore wash.

2, If letting the engine revs build under a relatively light throttle, it will go full rich once it gets past the set rpm. Imagine sitting with the engine in neutral and revving it, or something like an autosolo where you might have high rpm at light throttle going around the cones. A very light throttle opening would be needed to get to 4000rpm, but then it would suddenly go full rich. Cue the clouds of black fuel smoke.

I could understand it working if it had a MAP sensor and could link rpm and vacuum. It could be used to trim out part throttle weak spots, but rpm alone won't work any better than the Lucas metering unit does on vacuum alone.

I would have thought a simpler solution would be to give it more throttle when approaching the flat spot


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