22 replies to this topic

[stormintrooper]

some people mentioned piping into the servo line, how did people do this as the pipe would end up being too big for the gauge end?

[dklawson]

On my installation I fitted a brass "T" in the brake servo line. The "T" then 'steps down' to the hose I used for the vacuum gauge. This can be as clean or as dirty as you want to make it. You could always make your own adapter by using a brass hose splice/coupling and drilling and tapping it's mid-point to accept a small barbed fitting like you would use on fish tank air lines. The tapped joint could be soldered together if you are using brass or glued with gasket sealant if you are using plastic.

[E23TFD]

Holly thread resurrection Batman!

Been reading up and came across this but after any other guidance.

Have a 92cooper converted from SPI to HiF44 carb, now my feeling is it needs a good rolling road tune up as only done around 80miles in two years.

Starts up and idles lovely and choke not needed for particularly long. Vacuum gauge reads in the sweet spot but drops right off on acceleration but returns straight back when at constant speed. Oil and water fine ie no cross contamination. Oil pressure looks good as well.

Will be start of next season before it goes to the rolling road but anything to look at over the garage months then happy for more mini based knowledge on vacuum oddities.

Shows the search works!!

Edited by E23TFD, 25 October 2020 - 08:08 PM.

[Ethel]

Not sure what you're asking. The accelerator pedal controls the throttle, which controls the amount of fuel/air mix reaching the engine.

 

If the throttle is set to hold a particular road speed, it's allowing the engine just enough fuel to produce the power required. As long as you're not at maximum speed, then less than a full cylinder's worth of air is required to burn it properly. That's achieved with reduced manifold pressure: same volume but lower density.

 

So a vacuum gauge is a direct measure of engine efficiency as more power from less fuel requires less air & thus less manifold pressure (or high vacuum).

 

Now when you put your foot to the floor, the throttle is wide open and the carburettor's task is just to provide the right amount of fuel for the air going in to the unrestricted engine. The gauge will register closer to atmospheric pressure, any drop in pressure is down to inefficiency in the induction system.

[E23TFD]

Thanks for the reply Ethel. My ramblings were basically are my readings normal for this engine and if not from experience what does this point to.

Should the vacuum gauge always remain constant and not swing down during acceleration?

[GraemeC]

What you describe sounds perfectly normal - high vacuum at tickover and cruise (throttle closed or only partly open), low vacuum when accelerating (large throttle opening).

[E23TFD]

Appreciate that, reading online starts to suggest head gasket issue hence the fluid check detail and normal running.

Thanks both

[timmy850]

At 100% throttle you should be pretty close to zero vacuum.