Petcock question

Hey all, I picked up a 1982 xj750 Maxim a few months ago to rebuild as a first motorcycle and also a high school graduation project. This website has been fantastic through the process. The P,O, was three quarters of the way through a carb rebuild and about to start rebuilding the petcock so both parts came unattached to the bike. I figured out the carbs ok but now that I wanna fire it up to see if it runs, I realized that I have no idea what the second and smaller nozzle on the petcock runs to. I figured that the larger one runs to the carbs but I could be wrong on that too. Could someone please throw me a bone?

 

That should be the vacuum line if I'm not mistaken, and it goes to right above the number two carb from the petc0ck. Larger one goes to the center and down low into the carbs to a connection down in there, should be fairly easy to locate. good luck!

 

Thanks a bunch macros!

 

By the way Joos, petcock should flow fuel in the pri setting with no vacuum. Should flow fuel in the on or res setting ONLY with vacuum.

 

The smaller spigot is the vacuum switch for the petcock. It is attached to the #3 intake nipple (carb #3 is the static unit that all other carbs are synced to). The larger spigot is the main fuel line that will feed fuel to a fuel rail "T" located between carbs 1 and 2. Be sure to use fuel rated line and install clamps.
As mentioned by pbthoe, the fuel should not flow in the ON position unless a vacuum signal is applied to the small spigot. Any drips indicate the need for an overhaul.

 

petcock tech: http://xjbikes.com/Forums/viewtopic/t=25058.html

One clarification:

The vacuum line connects to the #3 intake manifold on the 650/750s; it connects to #2 on the 550s.

 

Dammit, those proprietary 550's got me again, lol.

 

YOU were correct; FOR A 550.

And you would think it doesn't matter, and it probably shouldn't, on the earlier bikes. However, one of the later "XJ family" series, I forget if it's the XJ600 or the Seca II, has different jetting on ONLY the #2 carb (where the vacuum line connects.) The only reason I can see for that would be the vacuum connection.

Gotta remember something here: The 550/600s (the chain driven XJs) while being the same "family" of bikes, have a great many subtle (and therefore not obvious) differences between them and the shaft-driven XJs. (As well as between themselves, the 550 Seca and Max have different frames.)

Which is not to say the shaft-driven XJs are "all the same" either; look for instance at the different varieties of front brakes fitted to the 650/750/900s-- there are at least 3 or 4 (or more?) different types of calipers used, different sized rotors with different offsets, etc. And that's just front brakes.

Gotta be careful when passing along tech advice that it actually applies to the bike being discussed.

 

Don't feel alone macros, Fitz hands me my lunch on this regularly. But he is right, we need to get our ducks in a row before we offer advise. It defeats the purpose of this fine forum to pass out bad info (I could use a spoonful of that).

 

Thanks all for the help. Invariably, once I hooked up the fuel and vacuum lines, another problem sprang up so off to battle that. Gotta love thirty year old bikes that sit for five or six years...

 

Thanks guys! I should have said it goes to the nipple without a boot on it above one of the carbs, lol, maybe that would have worked, but I got the message and will be careful about the advice I offer!

Mac

 

How about for twenty or more? Been there...

There's a solution, you know. Take charge of your process. Right now the bike is running the show, not you.

Read this; and think about it... http://xjbikes.com/Forums/viewtopic/t=24010.html

Trust me, once you take charge, it's a lot less frustrating.

 

Fitz-
Thanks for your advice, that's a great way of looking at the project and a solid starting block. My previous post was a *poor* attempt at humor, didn't mean to set anyone off.

 

No offense taken, let's beat this thing so you can write about your success!