MGB: Vacuum leak

Two issues; very high idle speed and rough running with commensurate lack of power.

For the rough running, I want to check for a vacuum leak. Chilton's says to attach the vacuum gauge to the intake manifold "beyond the throttle plate". Newbie question; just exactly where IS the throttle plate?

Second question regarding high speed idle; there is an idle speed screw located just in front of the carb, but turning it hasn't done a darn thing. I know, I know, I'm supposed to do it in a particular way to adjust it correctly and I will do so eventually but shouldn't turning it at least have some sort of impact? I will note that the engine may not have been fully warmed up yet (it was late in the day, so will do it again today), so might that have been the cause?

you will have to identify your car year (at least!) and any mods from stock before gaining any useful insight.

Avatar shows a RB car? ZS single carb?
From that I can only tell you the throttle plate (aka butterfly valve) is in throat of carb.
Like Mac said, more info is needed.
RS

Generally looking for vacuum leaks we use a high tech tool. A can of spray carb cleaner with the plastic straw.

Spray stuff while the engine running and look for a change. The intake manifold at the center of the engine where it is impossible to get a wrench is a good possibility. Check anyplace where there can be a vacuum. Carbs,manifled, hoses. etc. The throttle plate is the plate that moves with the accelerator pedal you can see it with the air cleaner off. (see how it works).

A vacuum gage is hooked up to any carb/manifold port where there is vacuum at idle. Not rocket science.

What car and carb do you have?

Make sure the throtle cable isn't too tight. It can hold carb throttle plate partially open and make impossible to lowere idle speed.

Glenn

Sorry hit button twice

Thanks for the advice, gents; I have the original single ZS carb. It continues to idle at high speed and I think it is likely related to an air/vacuum leak somewhere. I will look for it with the carb cleaner can.

Incidentally, I found the third screw for the choke laying in the rail directly underneath the carb and put it in and cinched it up, tightening the choke to the carb sufficiently. I think this might also have contributed to exposing the fast idle problem.

Well, it appears to be a stuck EGR valve. Anyone have any experience un-sticking them, or does it simply need replacement?

My mechanic told me to pinch off the hose when it is idling fast and, if no change, then the EGR valve is stuck. Does that sound accurate to you guys?

Dunno 'bout the egr valve, but I don't figger how a vacuum gauge can detect a vacuum leak.

How can you tell if the vacuum is steady but a touch low, it 'aint just a worn engine?

EGR valves are replacement items.