5 replies to this topic

[pig on the wing]

Any one know what diameter the vacuum pipe is or what size T piece will fit...

Thanks

[KernowCooper]

its micro bore not sure of the size but you can get one here http://www.minispare...|Back to search

[pig on the wing]

I need a T piece to attach a vacum guage, they come in 4,5,6mm when I search for them

[gazza82]

I'd personally leave the dizzy pipe as is and fut a sandwich plate with adaptor to carb mounting. Gauge needs larger diameter pipe.

[dklawson]

You said you are tapping into a vacuum source for a gauge and asked about the size of the vacuum pipe.  I assume you are talking about the pipe/tube going from the carb to distributor.  If that is your plan, that is not where the vacuum gauge connects.

 

The carb to distributor tubing is typically "ported" vacuum which means it is measuring the pressure drop in the carb venturi.  That is not what the gauge is intended to measure.  Vacuum gauges connect to the intake manifold to sense manifold vacuum.  All the articles and tune-up information you find that refers to idling at 17-20" of Hg is based on manifold vacuum, not ported vacuum.

 

There are several ways to tap into manifold vacuum.  You can use a T in the brake servo hose (if a servo is fitted AND if the servo check valve is on the servo, not on the manifold).  If no servo is fitted, there is often a plug on the intake manifold that can be replaced with a hose connector for the vacuum gauge.  However, the easiest and cleanest method of connecting the gauge to the manifold vacuum is with a new carb spacer with a nipple port built in.  These are available from some of the main retailers.  For example, the item linked below is available from Mini Spares.

 

http://www.minispare...=350/MFA446.jpg

 

[pig on the wing]

Thanks very much