Question for vacuum schematic gurus

[Panoscopic]

OK, I took the carb off to replace the power valve. Once the carb was off, I could really see the mess that many of the vacuum hoses were in. In trying to unravel the mystery of all the hoses, I discovered two "orphaned" hoses and a strange bypass.

Seems that the PO unhooked and plugged the original hose that fed the advance on the distributor from the HDC CTO. Then, he ran a hose directly from the distributor to the vacuum source on the left side (from front) of the carb. The hose that orginally used that source went to the spark CTO, which was just left hanging there.

I'm guessing that putting all this back to normal could likely slove many of the problems of rough idle that I have been experiencing.

What bothers me, is why was this done? The PO had all the work done my a local "professional" shop. Somebody who did this must at least have some idea of what they were doing? Any ideas?

[Gawdzilla.]

on my carb (without smog crud) that's the ported vacuum (and the right one for dist advance)- sounds like they were just trying to bypass stuff (maybe trying to cure the rough idle problem?)

[Joe Guilbeau]

Just fix it and move on...

[letank]

best guess would be a defective CTO switch, like open all the time to both ported and manifold vacuum, which would mess up diagnostics.

especially on later years.. you have a few of those thermostatic valves....

cheers

Michel

[Panoscopic]

Michel: Thats what I'm thinking - the CTO was open, and this is an easy fix. However, it appears the reason for all this is so that when the engine is cold, the vac advance is over-ridden so you would get a better idle when cold. My guess is that the mechanic was looking at the engine when it was cold, saw no vac coming to the advance and said "hale, I know how to fix this..."

[Panoscopic]

Originally posted by Joe Guilbeau:
Just fix it and move on...I plan to, its just that I am very methodical, especially when it comes to something I am just beginning to understand. I want to know why it was done because there can be only two reasons:

1) The mechanic did not understand this stuff and just overrode it without looking at the implications.
2) There was some other legitimate reasons - other components that failed - like the CTOs

[Ernzo]

I have seen where 'mechanics' have re-routed hoses in order to help the unit smog. Since mechanic' does not really know or care to know about the GW cto/vacuum hose web, he simply hot wires them in the old fashioned way.

Cto failure is somewhat easy to TS. I means they override the vacuum until the water heats up then allow vacuum to pas (more or less). They are also cheap and there is a great chart posted here that REALLY helps.

[letank]

CTO are an easy fix... but it is still 3 X $25.... after a while it adds.....

the easy fix is to have the engine at operating temp and go from there to check vacuum readings....

the chart is very useful..... it avoids paying the high dealer cost

cheers

Michel