Vacuum weirdness, 20Hg then 14-15Hg?? Steady (1 Viewer)

[Dizzy]

pull the vac line to the distributor and plug the barb on the carb or VSV.

 

[Pighead]

Exit at a point where there is a leak. I guess theoretically if there is a leak at athe manifold or other vacuum line, smoke would exit at that point. Basically just blow smoke into the intake.

With the engine off, I assume?

Booster is new. Could be distributor; how do I check to see that diaphragm is bad?

Disconnect vacuum line from dizzy, put another vacuum line (a clean one) to the diaphragm nipple, with dizzy cap off, suck on vac line and see if points plate moves

 

[81fj40]

Yes, engine off. Ok, going to pull out the vacuum pump and test the choke breaker choke diaphragm, dizzy and little plastic valve thingies.

 

[81fj40]

Vacuum tested the 2 choke diaphragms on the carb and the dizzy diaphragm; all held vacuum.

 

[81fj40]

Going to test vcv's next.

 

[65swb45]

Vacuum will not drop 5” from a small leak, only a large one. ‘Large’ as in brake booster, PCV hose, EGR hose, cracked manifold. And it will definitely change the idle. I find it impossible to believe the idle did not change.

I once had a precipitous drop in idle according to my vacuum gauge where the sound of the engine did not change. It was one of my more methodical days, and it only took me a couple of minutes to consider the possibility that the guage was fault. Bought a new one and confirmed that was the culprit.

 

[81fj40]

Yeah, dont know. Absent checking all the lines, etc, I will probably pull the manifolds off and inspect. Maybe have them machined and put in a new gasket. I find it hard to believe that would be the culprit given they are new (10 yrs old but less than 100 miles on them) and so is the gasket.

It all happened from one day to the next. Its not the booster, I checked that. So something changed dramatically, and quickly. Just dont really know what that is yet.

All will be revealed at some point I guess.

 

[Pighead]

Yeah, dont know. Absent checking all the lines, etc, I will probably pull the manifolds off and inspect. Maybe have them machined and put in a new gasket. I find it hard to believe that would be the culprit given they are new (10 yrs old but less than 100 miles on them) and so is the gasket.

Y'know, sometimes, albeit not very often, but sometimes, Mark A. has a clue about what he's talking about. And, your engine looks fairly well sorted. It might just be a little cheaper and easier to check the accuracy of that vacuum reading with another gauge, either bought or borrowed. If not just to save yourself some wrenching, potentially, but to be able to say something along the lines of "Wrong again old man, keep your half-baked ideas to yourself".

 

[81fj40]

Definitely going to pursue all the low hanging fruit and picking up another vacuum gauge tomorrow. Appreciate all the insights, I know it will get figured out at some point. This is fun! Or else i wouldnt have a cruiser

 

[DougAustinTx]

You didn't change the position of the idle screw did you? If you opened the butterfly even a little, it will have a dramatic effect on vacuum at idle.

 

[81fj40]

Ok, so far I found that the VCV under the air cleaner on the passenger side has failed. VCV on drivers side is functional. It's a start! Really stoked I found something to fix!

 

[81fj40]

Finally got the replacement VCV and plumbed it up, back into the green on the vacuum gauge at 18Hg. Probably a little leak somewhere; however happy that this expensive (albeit vital) piece of plastic took care of the issue.