You know, my instinct says that you might have a problem with one or more of
the vac loads. We have heard of vac boosters on the power brakes failing and
letting the vac pressure drop. I have to wonder if you are suffering for
something along this line.

I am not sure, but I think the test for this is to unplug all vac loads in
the system, and block them off. See what the vac is, then plug each in one
at a time and see where the vac drops.






"Rich Hampel" <RhmpL33@nospam.net> wrote in message
news:180120051536111216%RhmpL33@nospam.net...
> "problem" performance continues in a rebuilt 2.8L GM .....
> Engine now has 4000 miles on it and still has relatively low manifold
> vacuum. Vacuum is running 14-15 in hg. at idle and should be a few
> inches MORE vac. to adequately run all the vacuum controls: Brake
> booster, heater controls, dist. vacuum advance, *power piston* (2SE
> carb), etc.
>
> I checked and checked for manifold leaks, reset the damn manifold
> gaskets three times.... etc.
> Im pretty damn sure the problem is the engine 'mechanicals' .
> Compression is 130 psig all cylinders
> Mechanical valve timing has been degreed, and verified OK.
> Ignition timing perfect - both by vacuum gauge (max rpm less 1/2" hg.)
> and by accurate degreeing + timing light. --- both methods equate to
> the same EXACT timing advance.
> NO leaking vacuum hoses or controls.
> If I remove a vac. hose from the manifold port the engine
> **increases*** rpm --- which tells me I dont have a leak.
> Poor vacuum causes power piston in carb to lift 'early' (for over-rich
> mixture) - if I manually hold power piston / metering rod and remove a
> manifold vac hose = same rpm increase.
>
> Engine was broken in with 20 weight straight weight non-detergent oil.
>
> Im about ready to dump a half can of cleanser down the carb to scuff
> the cylinder walls in desparation and run the valve lifters with ZERO
> lash ......
>
> Your sage advice would be appreciated. I need another 2-3 inches of
> vacuum to make all the vac. controls, brake booster and power piston-ed
> carb. to operate properly. Any advice of why this damn engine is
> running 'short' by about 2-3 inches hg. of vacuum and what to do about
> it would be VEEEEEEEERRRRRRRRRRYYYYYYYYY much appreciated.
>
> ;-)