Vacuum at idle and idle speed RPM

[mbflemingkf]

I had a buddy of mine over yesterday and we were hooking up and setting my rebuilt carb. He has a vacuum gauge but we were getting a zero vacuum reading at idle.  As soon as you gave it some gas, the vacuum went up but nothing at idle.  Any idea what's up?  On my 54, we hooked the vacuum gauge to the line up at the vacuum advance (disconnected the line at the vacuum advance).

Also, what RPM do you set the idel speed adjustment on a 54 K w/Hydramatic?  One book I have says 425-450 but I've also had other opinions.

Thanks.

[Fid]

Mike, my 1955 Motor's Manual says idle speed with a Hydramatic should be set at 450 rpm. It should be 500 for manual shift. Regarding the vacuum, there is actually more vacuum at lower RPMs which is the opposite of what you'd think. I know it's amuzing when driving a car with vacuum wipers, as you speed up, the wipers slow down, push in the clutch to shift, the wipers go crazy, let out the clutch after the shift and they slow to a crawl. The wipers are almost useless when you're in overdrive (can you say "Rain-Ex"?). I couldn't find any specs on the vacuum but look at this way - at least you can't say your new carb sucks!

[mbflemingkf]

Thanks, Lowell for the idle speed reference. That's helpful.   Your 2nd response on the idle speed make no sense at all and isn't consistent with what the vacuum gauge was saying but I do appreciate the input, nonetheless!!  Maybe it will stir some other comment!!

[stroker70]

Hi Mike, when you check idle vacuum,the gauge needs to be connected to ported vacuum at the intake manifold. ported vacuum is anyware below the carburetor base plate. Vacuum from this source will be highest at idle and drop off to nothing as the throttle is increased, and then go to a positive pressure if you are superchaged provided the pressure box is installed. checking vacuum at the carburetor will be zero at idle and increase as the trottle is opened and that is why distributor advance diaphrams are connected at that area.  Hope that helps.  PS     Ported vacuum can increase as the throttle is opened and this a problem on a non supercharged engine. It typically happens when the exhaust system is plugged up.

Chris

[mbflemingkf]

Chris, on a supercharged 54 Kaiser engine, where would I get the ported vacuum pick up?  Any ideas?  I didn't know any place else to pull it from.  Thanks.

[stroker70]

Mike, I looked at my Dragons engine and I don't see any vacuum port anyware on the intake manifold. It appears a vacuum gauge is useless on a 226. Who would a thunk it?

Chris