'89 vacuum questions

[zoe60]

This could be a long question. My B6 Weber powered Festy has always suffered from low vacuum. It runs at about 16 inches and jiggles about 1 inch constantly. If I snap the throttle it goes nearly to zero and then goes to about 24. If I do a cranking test it goes to 10 and snaps back to zero at the same rate that the engine is rotating. The car runs real good. Always has a little bit of a rough idle but nothing objectionable. Now the really odd thing. It had the same problem with the original B3 with the factory carb, an Aspire B3 with the factory carb, then slightly higher vacuum but same jiggling needle when I went to the Weber, and now the B6 with a Weber. The only thing common to all engines is the intake manifold and the disty. I never tried the cranking test on the previous 2 engines. I wonder if some other people with carbed cars could check their vacuum and let me know if this is normal? Or give some insight as to what may be causing this. I would sure appreciate it. Could it be that These engines with carbs just naturally have low vacuum? I know the gauge is good cause my other car is a steady 20. Not that big of a deal. Ive been driving it that way for years. I just get a hankering to figure it out sometimes. Compression test is acceptable. Thanks!

[WmWatt]

The vacuum on my carburetted engine dropped after I "inspected" the vacuum hoses by pulling and pushing on then to see if any were loose. I guess one is now.

The jiggling may be dirty spark plugs or ignition wires, ie missing.

[zoe60]

What is your normal level? I have always wondered what it should be on these engines. I only have mine to compare to. So strange that it has done the exact same thing with 3 different engines and 2 different carbs. Of course the first engine was shot.

[william]

jumping vacuum some times is the result of one cylinder being low on compression and making the gage fluctuate when the low compression cylinder is moving down.
a compression test may tell you what's going on.

[zoe60]

I think compression is pretty good. Maybe kind of low but even. #1 160, #2 160, #3 hair over 160, #4 barely under 160. I've never done a leak down test. I would really like to know how many inches somebody elses carbed car pulls for comparison. I always thought that 16 inches is too low. Whenever I read one of those vacuum troubleshooting lists it seems like it would be ignition. I'm at 12 degrees advanced, cleaned and gapped plugs, New wires. It has an aftermarket ignition system. I should be getting a max MPG cam from Matt Dickmeyer soon, maybe that will help. The car is giving me no problems, I'm just trying to figure this out.

[WmWatt]

Mine is 185-187 dry at 120k km (about 72k mi)

[zoe60]

Well thanks for checking Wm. I figured my compression was low but at least its even. I don't think 160 is considered terrible. At least it's even. The car does run great, pulls pretty hard and never consumes a drop of oil so I'm OK with it for now. Wonder what your vacuum gauge reads when you test it? Ballpark figure would be nice.

[zoom zoom]

I've had a vacuum gauge on a couple and I can't get them over 16 at idle, some people supposedly have engines that are around 18 at idle, but....i haven't seen it for myself. I reworked a head with a 3 way valve job stem seals, and a .02" shave and it never went over 16 at idle.. I remember one time having one at 18 idle, but it would ping under load so I had to set it back.

all of mine are EFI cars.

[zoe60]

Wow! Thanks a lot. That's what I wanted to hear. Sounds like I'm pretty normal for once! I should be getting my max MPG cam next week and I will let everyone know if the vacuum improves and what gains in MPG of course. Thanks again zoomzoom, and Mr. Watt too.

[WmWatt]

Vacuum on my car is 21. Checked today.
Look for hose leaks?
So long as it's in the green zone on the guage it should be good.