What to do with vacuum lines when windshield off?

I figured plugging it was the correct thing, but saw a reference in another thread to it maybe being better to leave it open? Is all the vacuum from the fuel pump, or is there also manifold vacuum? I don't have a top for the jeep, so wipers are not a concern at this point, but some day I'd like to rebuild the motors and get the system working for the gee-wiz factor. I have noticed I can hear a vacuum leak from the drivers side motor when running, is this a normal bypass type deal, or do I have cracked hoses?

I guess in summary, two questions: Do I plug or leave open when removing windshield frame, and if I want to semi-long term bypass the system, what is the best method?

Thanks!

 

I would plug the line. I don't believe your engine is gonna run right with it open to atmosphere. If it's open it's gonna mess up you air/ fuel ratio. Before I got my wipers working, I couldn't get my carb tuned right with it open. basically it's just a big vacuum leak. HTH

 

Thanks, that's what I originally thought...not to mention I definitely don't like the aspect of sucking raw air into the engine. Funny thing is, the carb seems to be tuned quite well, runs like a sewing machine once it's warmed up. Can't wait to finally get tags on it and go cruise around.

 

What's the rational behind leaving the fuel pump line open? Would that not invite dust and grime into that mechanism? Not calling you out, just trying to get a grasp on it all. thanks!

 

a simple plastic check valve in the hose somewhere solves the problem no matter what the vacuum source is.

 

"The wiper vac and the eng vac are separate, at least off the fuel pump I had on mine."

- Mine have always had both the engine and pump vacuum in same line, to supplement each other.


"a simple plastic check valve in the hose somewhere solves the problem no matter what the vacuum source is."

- How so? It seems to me that would prevent vacuum reaching the wipers even when connected.



My M38A1 (military cousin to the CJ5) has a simple manual on/off vacuum switch mounted on the left side of the dash, in the vacuum hose just where the hose emerges. This would allow for removing the W/s and shutting off the open line.

 

"To prevent the pump from "sucking" and not being able to discharge..."

I'm not getting this. Surely the normal situation with the wipers off is the same as a closed vacuum line? And in the stock set-up, the vacuum pump "discharges" to the intake manifold continuously, whether "sucking" an open or closed wiper valve. It is a vacuum - there is never anything to discharge, unless air is being drawn through the operating wiper mechanism.

Am I missing something?

 

because a check valve works by letting air go in one direction only.

 

As I said, "unless air is being drawn through the operating wiper mechanism."

But the normal state is wipers off, and no air movement. So why would we need to have an open line when the wiper tube is disconnected?

 

"because a check valve works by letting air go in one direction only."

Of course. So if it is in-line with the normal suction flow, it accomplishes nothing. If placed against the flow, it would prevent the wipers from ever working at all. I still don't see the point.

 

I'm curious about this also and I see both your points. I went through this same dilemma thinking "you wouldn't want to block the air flow because it may strain the booster (vacuum pump on lower half of fuel pump)".

I personally blocked mine (m38a1) because there is a tee fitting with a .040 opening to the atmosphere to vent the distributor so air will enter the booster even if the wiper line is blocked. On the CJ models I'm not sure if there is an additional vent like I'm describing. Without looking at the extra pump I have I imagine there may be a spring loaded bypass in the booster??

There is very knowledgeable guy online named Wes who advised me to block mine so I did. He could explain it better.

 

I used to work on packaging machines with vacuum pumps. They all have a discharge, they wouldn't work without one! Where would the air go that you are pulling out. It's just like a water pump, they pull a vacuum to get the water to the impeller to pump out the discharge. No discharge, no water coming in to the pump. If a vacuum pump keeps a vacuum for long it will over heat and burn up. Now, I have seen pumps with a relief valve that would open if a certain amount of vacuum was pulled to save the pump if something happened. Those were some strong springs in those valves!

 

block it. Mine idles high & presumably rich when the wipers are disconnected. I plan on putting a small ball valve inline, behind the dash.