Holy moly. Yes I believe there is one in the manual, either Clymer or Haynes, but it will not be an easy thing to do if all yours are missing. I replaced all the vacuum lines on mine, but the original lines, or what was left of them, were still there, and I did it one line at the time. I believe the small lines (there is a total of 10 feet of those, I bought 10 feet, and has 2 inches left over) are actually supposed to be 4mm, but I used 5/32" from Autozone, and it worked fine. I will see if I can find a diagram somewhere. There are 10 pieces of vacuum line, 4 T fittings, and 2 plugs just on the PBL/PBR sensor system.
MINE ARE STILL ON THE BIKE BUT T HAS BEEN SITTING FOR OVER 4 YEARS JUST WANTED TO REPLACE THE LINES THE BIKE ISN'T RUNNING RIGHT AND I WAS TOLD IT COULD BE THE VACCUM LINES JUST WANTED SA DIAGRAM SO I WOULDN'T MAKE A MISTAKE OR MISS ANY OF THEM THANKS
Boy are you in luck. Yes it is a good idea to replace them, but don't take them all off at once. Get about 10 feet of vacuum line, and a pair of sharp wire cutters. Remove one piece at the time, cut a new piece, same length or a tiny bit longer, and replace it. Expect it to take a while, but it will be 10 times easier to do it that way than to try and replace them after removing everything first, other than for someone who has a LOT of experience with the LTD.
You will be able to get to all the small stuff by only removing the fake tank and air filter housing. But be aware that there are some larger hoses under the air chamber (that big aluminum box with the plastic cover that the air filter assembly sits on) that you cannot get to without removing the whole thing, air chamber, throttle bodies, manifolds, etc. It was a couple of those that gave me so much trouble with my fuel injection. You can get the whole unit out the left side by removing fuel injectors, the fittings at the top of the fuel injectors, the aluminum elbows the bottom of the fuel injectors fit into, and the manifolds underneath those. You will need to disconnect the red hoses from the elbows, the vacuum hose from the air valve to the air chamber, and a vacuum hose to something called an anti backfire valve, which mine no longer has. You will also need to remove the 4 metal pipes that go to each corner of the cylinder heads, slide the unit about halfway out the left, then disconnect the throttle cables and unplug the throttle position sensor.
Not really difficult, but VERY time consuming. I just did it. I would wait on that, and see how it runs first. If you decide you need to go ahead with it, repost. There are a lot of small details involved, which I wrote down as I took it apart and put it back.
That is a good diagram of the underside of the air chamber, which I recently had off. You can't see stuff to good in the diagram, and even less on the bike with the air chanber in place. Here is what I did, and what I had problems with. I posted a link above, click on the picture to make it bigger.
The parts I circled in red are nothing but an emissions device, and serve NO purpose. I removed the box in the middle, and all 4 of the hoses that go to the metal pipes. For right now, I simply put vacuum caps (3/8") on the ends of the 4 metal tubes, until I can figure out how to cap off the holes in the head. Where I circled in blue is where I put the vacuum caps. I also used a much smaller vacuum cap on the 4 way cross fitting when I removed the line to the antibackfire valve. You also have to plug up a hole in the bottom of the air chamber, I used Permatex gas and oil resistant silicone. Again, nothing circled in red has anything to do with the way the bike runs, and getting rid of it makes a whole lot more room under there, which I needed when I improvised my repairs.
The parts I circled in green, that have the red hoses connected to them, are the reed valves, and are what caused me so much trouble. These are required to make the bike run, and they are very poorly designed. The valves themselves were fine, but the fittings connect to them with a short rubber hose, WHICH IS PART OF THE VALVE ASSEMBLY, and cannot be replaced separately. Mine were rotted and cracked and created a severe vacuum leak, which made a chirping sound while the engine was running, as the reed valves opened and closed. I ordered some more used valves, but wouldn't you know it, the rubber part was rotted on those too. So I had to reconfigure the whole system, find another way to attach the hoses to the valves, which meant relocating the hoses, and adding some fittings. It took me nearly 3 weeks to finish, but I am confident I will not have any more problems with it. Despite the fact that what I made is not exactly the same as stock, and changed both the length and inside diameter of some of the hoses and fittings, it works perfectly. With the way I did it, there was no room for the parts circled in red, and as I said, they serve no purpose, in fact the exhaust will run cooler without it. It is an air injection system, designed to inject air into the exhaust, like "smog" pumps used to do on '70s cars. I have removed similar systems from several bikes, with absolutely no problems.
If you do find a problem with the rubber part of the reed valves, it is not a hopeless situation. I can put together some pictures, drawings, and a description of what I did. Hopefully you don't have this problem.