Spark problem HELP!!!!

[XSIvan]

Hi guys,I am new to this forum as well new to xs650 machine. I just got 1983 XS650 bobber wana be. The bike is in bad condition,starts with no problem,idles fine,but the spark is cutting off at 4000rpm??? What could be the problem??? I put new plugs,did the test on the coil primary and secondary,I tested the pick up coil for resistance and checked ok. Anyone please????

 

[XSLeo]

This may sound a bit goofy but is the charging system working right? The TCI ignition is very voltage sensitive. If your charging system isn't doing very well the battery voltage gets low and strange things happen. Your symptoms may be a result of this low voltage.
Easy to test, remove the seat, hook a meter to the battery, start the bike, What's the battery voltage at idle?, what's the voltage at 2500 rpms?, what's the voltage at 5000 rpms?
Oh Welcome to our little forum.
Leo

 

[gggGary]

After you do what Leo suggests;
See the charging system guide in tech if it ain't charging right.
If the charging is OK put a timing light on it and watch your advance curve between idle and 3K is it advancing?
Yeah, Welcome aboard.

 

[XSIvan]

Thanks for answering guys.Charging system is fine,new reg/rec,new coil and wires,the advancer is advancing. Soooo???? How about that transistor inside the TCI unit???

 

[gggGary]

So are you using an in line spark gap to see the spark go out or does the motor lose power for unknown reasons at 4K?

4000 RPM is about where the slides come up (diaphragms, holes, tears) and the bike starts to go on the mains (size, dirt etc.)
As always set cam chain tension, and valves, then check carbs, ignition etc.
Spray carb cleaner looking for air leaks by intake manifolds throttle shafts etc.

 

[XSIvan]

Carbs are nicely cleaned I checed the diaphragms everything is good. And yes I use in line spark tester and at 4K there is intermit spark brake off that you can clearly see. This bike is driving me crazyyy I am thinking maybe is the pick up coli??? But when I check the pick up for resistance it was good.

 

[gggGary]

Fire it up and test run in the dark. look for wayward high voltage by the coil. I am going to guess the coil/wires are going bad. A high RPM short is not uncommon. and a new aftermarket coil, wires, and caps are seldom a bad investment.

 

[TwoManyXS1Bs]

We had some members here that tracked similar problems to vibration-induced intermittant connections; like in ign switch, kill switch, connectors, ...etc.

 

[XSLeo]

On the TCI box often it has loose solder joints. Many get fixed by just resoldering all the solder joints on the TCI board. Try this first. While you are doing this look at all the components on the board. Do any look burnt? If so replacing the burnt parts may fix it.
If you find any burnt parts post up a pic showing the part. I'm sure someone can tell you what the parts is.
Searching this board for TCI box fixes, igniter box fixes or something similar will find a lot of threads on TCI repair.
Leo

 

[XSIvan]

Thank for all your help guys. The TCI box looks fine no burned parts nice soldering joints. I even try another TCI box and solder new transistor and no luck. Only thing that i didnt change is the pick up coil and the harness.

 

[Dennis]

try a new magnet on the rotor

 

[Tomterrific]

One more thang. Pod filters? Some pods are not constructed well for the CV carbs. Remove pods and test ride.

Tom