'81 xs400

Josh

XS650 Member
Messages
6
Reaction score
0
Points
1
First off I'd like to say "howzit" from sunny Hawaii and I look forward to what this forum has to offer!

Anywho, I have an '81 xs400 (as the title states) and have a general question about cleaning the carbs. The bike currently runs fairly well but only with the choke completely out. The guy who I bought the bike from said that it hasn't had a tune up in approximately 5,000 miles (currently has 12,000 miles) and has been sitting in storage for about three months. Should I take the time to completely rebuild them or "chance it" with some light work. I have read the other post relating to this question and haven't pulled the bowls off yet but I at least wanted to hear what others had to say who are much more experienced than I am in this area.

Thanks in advance for your info!
p.s. I also have an '81 650!
 
Hey Josh, Welcome to the forum!

Sounds like a classic case of clogged pilot jets. The choke on most Yamahas is actually a fuel enrichening circuit and is giving the bike the extra fuel it needs since the pilots are restricted or clogged. I would pull the carburetors and remove the bowls to get a look at how bad they are. Pull the pilot jets and spray some carb cleaner through them and then compressed air. If everything else in the carbs looks clean, that might do the trick. Let us know what you find!
 
So after tearing the bike apart for a thorough cleaning it turns out the pilot jets were indeed a little clogged and the bowls looked pretty nasty too. I cleaned everything meticulously and then moved on to air. I found a stock airfilter from '81 almost completely clogged and no air filter in the other...wow. Also the threads for the spark plug looks to be misthreaded on the head and that really concerns me. Is there anything I can do to fix that? Other than that the bike runs REALLY nice and I'm REALLY pleased after four hours of work!
 
Last edited:
Good work on the carbs!

About the stripped spark plug threads. How bad are they? If just the first few threads are cross-threaded and it's making it hard to get the plug started on the right threads, you might want to look into using a back-tap. I never used one but they sound interesting.

http://www.back-tap.com/

http://www.jegs.com/i/JEGS/555/80595/10002/-1&parentProductId=954483

If they are really bad you might want to use a helicoil or timesert.

I had a helicoil put in a cylinder head on a 4 cylinder and it worked fine. I pulled the head and a machine shop did the work since they were already testing it for cracks and to make sure it wasn't warped (had a blown head gasket).

You might want to do some reading about the pros and cons of helicoil as some people will advise against it. Also some people will say you need to pull the head and others will say you can do it with it still in place

http://www.popularmechanics.com/automotive/how_to/4212608.html

http://www.timesert.com/

Do a google search for Spark Plug Hole Repair or Spark Plug Thread Repair.

Let us know how it goes!
 
I'll look into the back-tap a bit more before I take action with this. At the moment I just don't want to deal with it because it seems to be just fine but come time for the next tune-up I'll have to deal with it. Sigh...
 
Hey there. i'd say you wont know until you look, its a good sign if both carbs hold gas but if thier both suspicious, you really gotta get in there to look and measure. Start with the bowls and the jets in the bowls, if the're all varnishy and stinky, chances are the rest of the carbs are too. Do each one seperatly so theres no mix up of parts. Theres a detailed pdf on this site about carbs. Good luck!
 
Back
Top