heylawnguy Posted March 30, 2009 Share Posted March 30, 2009 Hey their guys. I am new to motorcyles, In fact I dont even have a bike license yet, and I am looking for an old xs 400 or xs 650 for a starter bike. Anyways I went to go look at a nice 81 xs 400 special today, and the bike was in pretty decent condition for its age. However the owner said that he rode it all last season and it ran fine, but after he took it out of winter storage it starting fine but was running really rough. He said it has a serious lack of power compared to last year and now it keeps stalling. Anyways I started it up and it sounded like it was idling fine, when I reved the motor it sounded strong, but then when I put my hand on the exhuast pipes, you could feel one side getting warmer but the other side stayed cold. After about ten minutes the one side was so hot you could no longer touch it, but the other side was still pretty cold. I could still wrap my bare hand around the pipe near the top by the cylinder. I also noticed that the exhuast opening on the end of the pipe on side that was warm had a nice brown color and was dry. The side that stayed cold looked wet and had oil around the outside including a little puddle on the inside lip. You could feel exhuast comming out of the pipe but nothing compared to the good side. Any ideas or suggestions on what the problem could be? The bike is exactly what I have been looking for, but being new to motorcycles I dont want to take a chance on it without some research. As the saying goes "A fool and his money are soon parted" THANKS Link to comment Share on other sites More sharing options...
KFunk Posted March 30, 2009 Share Posted March 30, 2009 If you look back thru the forum, you'll see there's several threads about xs400's starting up and only running on one cylinder, and often taking a while of warming up before the second cylinder kicks in. It's usually due to clogged passages inside the carb for that cylinder. A very thorough cleaning/rebuilding of the carbs may take care of it. I haven't gotten mine quite working on both yet at first, but I'm new. It still takes me a while to warm mine up and like 50 feet of riding before the left cylinder kicks in, then I'm good to go all day. Link to comment Share on other sites More sharing options...
GaSo Posted March 30, 2009 Share Posted March 30, 2009 could be a bunch of different things, but all fairly easily correctable. first thing you'll want to do is completely clean the carbs, top to bottom. then, make sure the floats are set to the correct height. finally, if the pilot screws are shot, you'll probably want to replace those with new screws. oh, and then balance the carbs so that both are pulling the same amount of air in, operating synchronously. here's what I had to do to my 81 XS400 Special II to get her running this spring (again one where the previous owner had it running reasonably well teh previous year). I had the same problem, where it didn't have much power and only wanted to run on one cylinder: replace an o-ring on the butterfly valve rod to fix air leaking in and making the right cylinder run lean / bike only want to run on choke when cold. ($10) clean both carbs with shop air (90 PSI). (free) replace battery. ($$$) replace pilot screws (combined with float levels, fixed left cylinder not wanting to fire at idle / general performance). ($15) adjust float levels. (free) synch carbs. ($5 for some hose and ATF fluid, had the yardstick) ...which is why I recommended those things Link to comment Share on other sites More sharing options...
heylawnguy Posted March 31, 2009 Author Share Posted March 31, 2009 Thanks for the info guys. Do you think the fact that it looked like the muffler on the dead cylinder side was wet and had a little oil puddle on the inside would be a serious concern? I offered the owner about half of what he was asking for it to take it as is and he declined. So we agreed that he would take it to a mechanic and get it running properly first and then I will go back and buy the bike for closer to the asking price. Hopefully he will stick to our agreement and call me when the bike is fixed and not just try and sell it to someone else without fixing it. It was a pretty nice bike with a vintage flair to it., and it seems to be hard to find one with the wire wheels like this one has. It does show some wear and tear with a little bit of rust on the frame and a dinged up rear fender, but overall not bad for a 28 year old bike for the price. Looks it it would be a great first motorcycle to get my license with. Anything else I should look for on these bikes? How much compression should it have in each cylinder minimum? Well until I get some sort of xs I will just have to dream about it and play around with my 2003 yamaha 49cc BWS (Zuma) scooter. Link to comment Share on other sites More sharing options...
Recommended Posts