G'Day Matt,
Inlet manifold should be under vacuum so will not blow bubbles. Thats how you check exhaust and BBQ gas cylinders are not leaking - with soapy water (not matches)
I would think if wd40 is getting in in sufficient quantity watch the exhaust for white smoke. (Popemobile?)
I did have a problem with regularly chewing up the large bore manifold gasgets and getting air leaks when it fractured. I was told the material they are made out of is (insert unflattering comment). Lucky for me I still had the machined grooves in the head for the locating rings and was able to use the standard, ordinary, plain, regular metalised manifold gasget and no problems since. That was 3 years ago and have not even had to re-tighten the (brass) nuts. They ARE brass arn't they?

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Over 1,000,000Km, but now my retirement restoration project

yep, brass manifold nuts.


OK, I know i'm a bit on the stoopid side, but I'm still not sure how to check for vacuum leaks? I might just try the wd40 and see what happens.

cheers
Matt

Matt,
I think the trick is to use the long thin plastic tube (straw thing) nozzle extension and give it a good blast where the manifold bolts to the head. Though I must confess I have not bought a can for ages, so do not know if they still supply the plastic tube that fits into the spray nozzle. If you don't have this bit then I think the exercise would be pointless.

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Over 1,000,000Km, but now my retirement restoration project

Gotcha.

Yep the real wd40 still comes with the tube.

So I watch for the revs to rise if there is a leak right?

Hmmm, all depends on me able to get it started again I suppose

Matt

you will notice the revs rise to about 2k for as long as you spray.

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Have you double checked the ignition timing? that can cause funny things to happen. I usually fit the dizzy slightly lose after putting an engine back in and put it a bit retarded then after starting it, you advance it until the idle goes highest then back it off a bit.