newb with some questions

[AceofSpades]

Hi, everyone, I am a newb with a mildly modded 75 XS650. The bike is mostly stock and I am having a few issues.
I have open pipes, pods and thats about it. The biggest problem is that when idling, it only fires the left cylinder. as you tip into the throttle, the right cyllinder begins to fire and the bike really takes off. I have not adjusted the carbs at all. I put in fresh plugs and got no improvment. Is this more carb or coil related? I have an 81 XS650 for parts and was planning to use the electronic ignition, but was hoping to get it running good on points first and converting to electronic over the coming winter.

Any help and/or suggestions are greatly appreciated.


Thanks,
Chris

 

[bloodthirstysystem]

test for spark - take off the right side plug wire, stick it on an old plug and bend the ground straight out. rest it next to the motor and start the bike. you should see a blue spark about 10mm long jumping from the electrode to the engine case. if you see it go to the carbs.

most likely it is a plugged circut in the carb. take them off and clean

 

[AceofSpades]

I get spark, and when I tip in about 25% throttle, both cylinders fire and the bike pull like mad.

 

[bloodthirstysystem]

time to rebuild the carbs.

read this whole article.. it's worth the time
http://www.amckayltd.com/carbguide.pdf

 

[5twins]

It may be as simple as the idle speeds being out of sync. The right carb may be turned down too low and if too low, that carb will be effectively shut off at idle. Try turning the idle speed up on that carb.

 

[AceofSpades]

ok will try..... any idea how I should be jetting the carbs? will only run 92 or better octane gas.

 

[5twins]

No one can say for sure exactly what your jetting will need to be. Every one of these bikes seems to respond a little differently to mods. Testing is really the only way to find what's right for your machine. That being said, the usual requirements are one or 2 up on the pilots and one to maybe 3 or 4 up on the mains. Here's a chart I made up with the stock jetting specs for the various years. Compare what's in your carbs now to what was stock for your year. Many of these bikes have been changed already by P.O.s .....

Since you should already have a rather large pilot in there (#45), you probably only need one size up on that. Your stock 127.5 main was one of the smaller sizes used during the model run so you may need a 2 or 3 size increase on that. As you increase the size of the main, it will eventually make the upper midrange too rich and cause a stumble. When that happens, you'll need to lean (lower) the needle. Until you start leaning the needle, the stock pilot is sometimes still OK. Once you fool with that needle setting though, besides leaning the upper midrange, it will lean the lower portion and the upper part of the idle circuit as well. Then the larger pilot is usually required.