elementary manifold vacuum question

[Stowe, Ted-SEA]

I have a question for the collective. I think I have forgotten vacuum 101. I
am trying to make sure everything is hunky dory before I strap my gm
throttle body onto my car.I have a 77 mgb 1800 cc.

this has siamesed intake and exhaust ports unfortunately.

when it is cold and I hook up a vacuum gage to the intake manifold, at about
600 rpm the needle fluctuates between 15-19 inches. meaning that the needle
itself is nearly invisible I can see the trend. if I pinch the hose to the
gauge, I can dampen down the 'pulses' and get it to stay steady. at higher
rpms this effect goes away completely.

as it warms up ,at 1000 rpm, it will fluctuate between 16-18 and eventually
just settle down to a buzz at about 17+.

the engine runs fine and idles fine by all appearances, no shaking or
anything.

I have no idea if the cam is stock or not.

I remember that one is supposed to actually restrict the vacuum line to
resolve this issue, I am just wondering if this sounds like word valve
guides or seals.

I don't know if the gm 1800 cc I have this from had this type of issue and I
am wondering how this would affect the sensors on the throttle body/ECU. I
don't seem to remember this as an issue on other engines.


thanks for all the great support btw.

Ted Stowe