no spark troubleshooting help please?

branson

branson

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Hello y'all. Just got a 1980 xs 400 sg in non running condition. I have fuel and air but no spark in either cylinder. The left hand plug wire is broken. I pulled on it very lightly and the boot seperated frome the wire. I'm wondering if the common cause of the other cylinder not functioning is coil related? Its a cdi system and I know lil to nothing about them but thought it might have two capacitors and one bad plug might hinder the other cylinder's ability to spark by damaging the coil. Any help advice or trouble shooting guides would be appreciated. Oh I almost forgot to mention the battery is fully charged and new. All other electrical systems function fine.
 
I'm not entirely sure if the 80 XS400 uses the same ignition as the XS650, if so then it's a TCI not a CDI. If it is simular to the XS650 the coil is a single primary with dual outputs. When the coils fires current flows out one plug wire to the plug, jumps the gap to the engine, travels across the the engine to the other side, jumps the gap across the plug, to the wire, back to the coil.
The plug caps just screw on the wire, cut the insulation back on the wire about 1/8 inch. Now spread the inner wires out so they point outward in a starburst pattern. Now screw the cap back on. This will fix the connection, Do it to the other side too.
Now if the wires are damaged where they hook into the coil, then you might need a new coil. Most stock coils have the wires as part of the coil.
You can test for battery voltage at the coils, should be at or very near battery voltage. If no or low voltage you need to figure out why. No voltage = no spark.
You also need the check voltage at the TCI box. No voltage here and the TCI won't work so no spark.
If you get spark after fixing the plug caps then the ignition is working. Are the plugs new? Are they getting wet with gas? Are the air filters clean?
Do you have a repair manual? I think there are links to some in the XS400 TECH section.
Might be a good thing to read all the tech section.
Leo
 
my bad i think it is a tci not a cdi system the plugs are newish but worked when i had spark the boot issue is on the side opposit the plug where it meets the wire on the left hand cylinder only i can literally pull the wire out of the boot while the boots still on the plug i have air n fuel in both cylinders so no worries there
 
You should have two separate coils on that bike. My '80 does and so did my son's '81. It would be strange for both coils to be bad at the same time. I would suspect another cause.
 
Well I have reacquired spark but still can't get it to run. I suspect plugged carbs at this point. Its been sitting for too long and I've got a pretty crusty tank =( fuel still pours outta. The pepcock like nobodies bussiness but it just won't fire.
 
Do you have an oil can with the pump lever? I have one I use to test engines. Clean out or get a new one, fill with gas. Remove plugs, put two squirts in each cylinder. Reinstall plugs, try starting. This gas should get the bike to fire and run for a few seconds. If it does then your ignition is ok, the carbs need cleaning.
This manual is geared more toward the XS650 BS38 and BS34 carbs But the XS400 carbs are very simular.
www.amckayltd.com/carbguide.pdf
There are many tiny passages inside the carbs that need to be extremely clean before they work right.
Leo
 
I used a syringe to put a shot of gas in each cylinder. No boom. Positive spark. No aitbox though. I found two in a box of parts that the bike came with. It seems that the previous owners version of maintainence was to remove whatever broke and throw it in the box. I have good spark and recharged the battery. Ill try the shot process again. I think he put the rubber on the pepcock backwards. The holes are always open. Is that backwards?
 
Petcock backward? Holes always open? Any picks so we could see your deal?:)
 
I don't have any pics or a camera unfortunately. But since my floats n everything are pristine and I just unneccessarily tore down polished and reassemble my carb ill just set it to pri or try it on the other settings. If it works great. If it doesn't oh well. I figured out why I kept feeling like an idiot the whole time. When I checked for spark I did it with the plug just off the cooling fins. Bhen I tried it with the threads touching no more fire. Same thing on both sides. At least the last owner did the same thing. He sold it to me with two extra coils an extrra condensor an extra ignitor box an two extra carbs. All because he had two cracked boots. I spent five thirty two and wouldn't ya know it: its alive!
 

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