Stalling Issue

[xs650newb]

Hello all,
This is my first post to the forum.

I picked up a 1981 XS650 Special a couple of weeks ago that was non-running. I paid $650 for it. I ordered carburetor rebuild kits from MikesXS and I got the bike to fire right up, however, it was running rough, which I expected because the mufflers had several holes that were quite large.

I have cut off the mufflers and I am currently running open drag pipes. In addition to this I am using MikesXS Performance pod filters.

With this setup and stock jetting I can get the bike to idle (very loudly), however, I have NO power at low rpm. When I open up the throttle the bike will general sputter and die.

Obviously I need to rejet. I ordered the Heiden Tuning kits from MikesXS and I plan on installing that tomorrow. I am going to go with the 145 Main and 45 Pilot. How does this sound? In addition I am going to install the adjustable needle. Is it truly necessary to drill out the vacuum slide? I would like to avoid any permanent changes. ALso, I have been told the air screw should be backed out 3 turns from seated, as opposed to the factory 1.5 turns. How does this sound?

Finally, I just installed tonight an adjustable washer that goes into the exhaust pipe which can be controlled, to add some back pressure. I will try to ride the bike again tomorrow before I rejet, but I am sure I will still have to rejet.

Adam

Oh, is it possible to rejet without removing the carburetor from the bike?

 

[gggGary]

Get it running well with what you have before you start changing. It is unlikely that the stock jetting on a BS34 Or any XS650 carb is so far off that it doesn't run reasonably well. As an example I just brought a 79 back from the dead. Cheap pods and a 2 into one with no baffle and holes all over. It ran fine on stock jetting, I could feel it stumble lean at WFO going up a hill. Pulled the plugs and they were on the light side of tan. Warned new owner that jetting would have to be dealt with after he got his chosen exhaust installed. Your question about changing jetting without unmounting the carb is a pretty good clue that you have not got the carbs clean yet. Sounds like an issue with the pilot jet or passages. The carb guide details everything you need to know.
http://www.amckayltd.com/carbguide.pdf download it, print it, read it till your eyes bleed.
A single short cut or I don't have the tool to do that will result in a crap running bike. Short version get it running then mess with jetting, adding a new variable to an existing problem NEVER helps. Rejetting requires endless patience. There is NO quick fix jet kit. Good luck or more correctly; I hope you take the time to get a good running bike, it's worth it.
Oh and welcome to the forum, we love pictures and an intro.

 

[xs650newb]

I have already cleaned the carbs. I took them off the bike, did a complete dissassembly and clean and reinstalled with new rebuild kits. Perhaps I need to check other things like valves, static timing, etc, because other than a carb cleaning and bench sync I have not done much.


Adam

 

[gggGary]

Yes set cam chain and valves. Static timing on an 81 is pretty much set in stone. You may have overhauled but something was missed.Sorry, it happens to me too. Did you check for throttle shaft play, change throttle shaft seals? Do the carb cleaner arround the intakes and throttle shafts test. Fuel level by float height and checked with clear tubes. New o-rings in the float valves? One thing I do on BS34s is bump the taper jet up with a couple of tiny washers. Many use the Canadian taper jet mod. Do an on bike synch, the homemade manometer works great I hear, I have gauges or I'd build one myself. Get volt meter on it, be sure she is charging. You always need to check for worn brushes on an XS650. I like to do a compression test, to test is to know.

 

[5twins]

Yes, you can change jets with the carbs mounted if you have the proper stubby tools. I use these Craftsman knurled bit holders and metric sized screwdriver insert bits that fit the jet slots exactly .....

http://www.sears.com/shc/s/p_10153_...3c&srccode=cii_10043468&cpncode=00-19968263-2

I get the metric sized screwdriver tips here .....

http://www.wihatools.com/700seri/710serie.htm

The use of improperly fitting tools on the soft jet heads is just asking for trouble. Of course, you already did that when you sawed your mufflers off, lol.

 

[littlebill31]

Read up on the carb guide gggGary linked. It's a must. Before you start with the adjustable needles and main jet get it to idle. The pilot jet does this, which is idle to 1/4 throttle. Changing your main will not make it idle nor build up rpm's. Wrong circuit. These carbs work off of throttle position, not engine speed. So 1/4 to 3/4 is the jet needle and 3/4 to full is the main. All these circuits overlap, so if you can't get it to even rev above an idle to 1/4 throttle then don't worry about the needle and main.
You need to adjust, as Gary said, the cam chain tensioner, valve lash, then carbs in that order. You have a TCI, so timing is n/a. Check for leaks as well around the intake boots. The mix screw runs best at about 3 turns out. The best thing to do is get the bike running great before you start changing things. I have the stock jet needle and needle jet. It runs perfect, so I have no reason to change it. Is the o-ring and washer still in the mix screw? What condition is the o-ring?