Introduction and a few Questions

[Rogue21]

Greetings Everyone,

I have been reading lots of good information from this website for many months now, bought an XS back in November, became a member at the start of this year, and this is my first post! (I hope I am posting this in the correct location)

I have this internal desire to work on machines and really admired what people have done with their 650s, and I knew it was the right motorcycle for me. I bought a 78 xs650 (miles and history are pretty much unknown), its in pretty rough shape and needs a lot of work. When I bought the bike, the owner swore that it was a runner, but a dead battery must be the reason why the thing wouldnt kick over. I had driven 2.5 hours and an ice storm was coming so I was under a time crunch. I bought the bike for bottom dollar in hopes that I could get it started. Fast forward to now, the bike currently runs, but not perfectly. I have just a few questions if anyone can help me out.

Things I have done: Cleaned the carbs. Just got the carb rebuild kits in the mail and will be putting in all the new parts soon. Timing chain adjustment and valvle adjustment are complete. Cleaned the advance timing unit and installed new springs.

I can get the the bike to kick over and idle pretty good, but it likes to backfire (through the exhaust i think) every once in a while when i rev the engine. Also, when I rev the engine, the revs like to 'stick' a little bit, they wont come down right away. Is the advance timing unit supposed to snap back right away? Even tho i put the new springs in it seems like it is sticky (and when the bike is running the ATU wont close right away..maybe that is due to the revs sticking?). If I rev the engine too fast (a quick and sharp twist) the engine chokes out and dies on me.

Sorry this is so long, but one more thing. What is the purpose of the vaccum petcock that goes from the tank to the intake manifolds? and what is the purpose of the breather tubes that run from the top of the engine to the air boxes? Whats the benefit/harm to just closing these lines off and not worrying about them? Thanks for all the help!

 

[Grinder]

Here is a video on what the advance should be doing. If it's sticking you may have to pull the rod out and regrease it.

 

[retiredgentleman]

You should click on the "Tech" section at the top of this page and read the "Maintenance and General Troubleshooting" sub sections. There is lots of good info in there to help you get started.

 

[XSLeo]

Getting the advancer rod and the bushings in the cam clean and fresh grease will help. If not and your new springs came from Mike's they may be a bit long. On one spring, mark it so you can tell which spring is which, Clip the loop off one end and bend the first turn of the spring up for a loop. This make the spring pull a bit harder. If it's still a bit sluggish clip the other spring. Usaully just one spring is all you need to clip.
On the rebuild kits the needle and neddle jet are often a generic set. If the numbers match what is in your carbs they will work. If the numbers are different they might not work.
If they are different then use whats in your carbs.
The float needle and it's seat may have a different number but they should work ok.
On the petcock there is a vaccum line that when the engine starts the engine vaccum opens the valve so fuel flows to the carbs. If they are working right they are nice. you don't have to turn them on and off all the time.
The problem is that after 30+ years the vaccum part fails and can let fuel flow when it shouldn't or suck fuel in through the vaccum line.
Mike's has a replacement for them without the vaccum part.
As the pistons move down in the cylinders pressure builds up in the crankcase. As the pressure builds up it needs to be vented or the seals can blow out, use more oil, run poorly. With the breather installed as the pistons move down the air flows up the camchain tunnel into the head. From there it gets pushed down and out through the breather box out the tubes to the air.
Like most old cars vented there crankcases out to the air.
On the later models the EPA said thats a no-no, so they ran them into the air boxes and got returned to the engine.
If you run the stock air boxes leave them hooked up that way. If you run a pod filter you can remove the tee and put a small filter in the hose. This way as the pistons move up and draw air back inthe engine , dirt and such won't be pulled in too.
Just a thought, if you have the idle set a bit high it, the idle may be slow to return. Un synced carbs can slow the return to idle. An air leak somewhere can lean out on side and slow the return to idle.

 

[XSLeo]

Wecome to the board. Almost forgot that. Glad your here.