help identifying unknown vac hose!

[5t341tH]

Hi guys. I just picked up my 78 620 about 2 weeks ago and it has been a blast cleaning it out and making it nice. I was going through the engine today and I noticed a loose hose towards the right side of the engine bay. It seems to be a vacuum hose that goes into the carburetor. If I plug it up, the idle rpm drops. I notice no difference in drivability but I do want to know where it goes and what it does. Any input would be awesome. Thanks

 

heres a oic(u guys like this word?)

 

[flatbed620]

If you don't see any open ports to plug it into, look on the underside of the air cleaner, several attach under there.  where does the other end go to?  I will look at mine tomorrow to see if I can trace it.

[5t341tH]

Would be most grateful. Thanks 

[Recon716]

I think that's the line that connects to the distributor? Not certain though.

[datzenmike]

Vacuum advance is a metal line with only 3-4" of hose on the dizzy end.

 

California?? I see it is.

 

That hose is most likely to the vacuum switch on the inner driver's fender used for shutting off the idle fuel  by shutting off the idle cut solenoid under high vacuum when decelerating. Think about it, when decelerating, the carb is at idle and supplying fuel that isn't used and going right out the exhaust pipe. This is an ingenious system to save a small amount of fuel otherwise wasted. It does not work if the transmission is out of gear or the clutch pedal depressed or it would stall.

[5t341tH]

thanks for the input guys. i found out where it goes.

[datzenmike]

The red circle is the CAC valve and yes there should be a small host from the intake to it. There should be a small hose to that thing just to the right of your red circle as well.

[5t341tH]

thanks datzenmike! of course you would be chocked full of information

[5t341tH]

Hello all! It's been a while but I need some help again. I had this truck running for a couple years now. I installed a weber carb and now the time has come for SMOG. So I need some help reconnecting some unknown vacuum hoses I am unsure of.

 

So nipples 1, 2, 3. I am not sure where these go.

 

The green lines show what I assume is the correct routing. The right green line comes from the charcoal canister purge line. The left green line goes to the manifold nipple. Am I correct in my assumptions?

 

[datzenmike]

1 and 2 are for the altitude compensator. Look on the air filter housing for a sliding lever marked L and H. It's possible that you don't have this and these two pipes would just be capped.

 

3 is from the BCDD but my FSM (and my 78) does not have the hose.

[5t341tH]

Thanks Mike. So the altitude compensator on my air filter housing has been connected together. So it's a single hose bridging them together. I assume I can bridge the nipples together? And 3 can be capped off I hope? I hope the smog place won't give me crap about it

[datzenmike]

My diagram doesn't help much but I think the front hose from the carb goes to the low altitude side.

[5t341tH]

Thanks for the tips mike. I got it all hooked up and running. While this carb was out of the car, I did a total rebuild on it myself. Used a whole rebuild kit. Although I'm having the same issue with it when it was originally on there before my weber. Accelerating from idle, it stutters a bit before picking up. This stutter is slight and happens with small throttle applications. After that initial stutter, it runs great. This is repeatable every time. What could it be? If it WOT the pedal, there is no hesitation. It only happens if I drive it casually. Could it be a bad jet?