Diagnosing XS850 no start

[code3cody]

Hey all.

I picked up a new to me 1980 XS850 and am having some difficulty tracking down a tough / no start issue with it. A little background on the bike: bought it as a ''kind of'' runner. It has a new set of Mikuni RS carbs on it, which have never been run as the previous owner couldn't find a throttle cable that worked for the application. The starter button was stuck in so e-start doesn't work but I was able to start it briefly with the kick start and it did idle for a few seconds. It appears to be in fantastic shape otherwise (looks brand new still), so I picked it up for $500 and took it home.

Since bringing it home, I have adapted a throttle cable to work however I have only been able to get it to start once since. When it started, it ran fairly well. It would rev and idle relatively well although a little finicky. It was very difficult to start it from cold at that time, but once running seemed to run fine. Have not been able to get it to start since. Plugs are new and all the plug wires and caps are in good condition.

I believe I am chasing down an ignition issue as the bike will not start with ether directed in the cylinders though the spark plug hole or through the carbs.

I have visualized spark when cranking however it appears quite weak. I have measured the following with my multimeter:

Resistance at primary on coils of 3.1ohm on all 3.
Resistance at secondary #1 13.67ohm, #2 13.34ohm, #3 14.31ohm.

I am getting 0 volts going into coils 1 and 3 however 2 is getting somewhere around 7ish when the key is on but not cranking.
When cranking the bike I'm only getting 0.5-0.8 volts going into the 1 and 3 coils.

So my question is what voltage should I be getting into the coils with the key on and not cranking the bike, and why am I not seeing any voltage going into 2 out of the 3? Is this an ignition module that needs replacing? Is there a way to test the ignition module with my multimeter? If this is all normal, what is a good direction to start looking instead. I hope its okay to post this in a 650 forum, there doesn't seem to be much out there for the 850s otherwise.

Thanks for the help.

 

[650Skull]

Can't help you much.

This site has a lot of info in the 750/850 triple. Well worth downloading what you need. Who knows when this could be lost

http://xs850.minek.com/

Biker.net
http://www.biker.net/triple_parts_index.html

 

[Signal]

Your coil primary and secondary resistances are near enough within spec.
You must use a known good battery when testing for a fault like this, batteries can read 12V but collapse dramatically under load.
The following is assuming you are using a good battery.
After a quick look at a diagram the red white to the coils goes through the kill switch. Testing the red white at the coils to ground I think you should have 12V. I would unplug the coils to do this test to stop the TCI upsetting your result.
With this type of ignition power goes through the coil and is switched to ground by the TCI unit.
A corroded kill switch or connection anywhere in the supply or return circuit will cause a voltage drop.

This is an XS 650 site but there are a few of us here who have Triples and there are other bikes in restore threads as well. Nice carbs cost more than you paid for the bike, nice one. I have a set to go on my bike and I am using a motion pro push pull throttle, you need push pull as a safety thing.

 

[750triples]

Hey all.

I picked up a new to me 1980 XS850 and am having some difficulty tracking down a tough / no start issue with it. A little background on the bike: bought it as a ''kind of'' runner. It has a new set of Mikuni RS carbs on it, which have never been run as the previous owner couldn't find a throttle cable that worked for the application. The starter button was stuck in so e-start doesn't work but I was able to start it briefly with the kick start and it did idle for a few seconds. It appears to be in fantastic shape otherwise (looks brand new still), so I picked it up for $500 and took it home.

Since bringing it home, I have adapted a throttle cable to work however I have only been able to get it to start once since. When it started, it ran fairly well. It would rev and idle relatively well although a little finicky. It was very difficult to start it from cold at that time, but once running seemed to run fine. Have not been able to get it to start since. Plugs are new and all the plug wires and caps are in good condition.

I believe I am chasing down an ignition issue as the bike will not start with ether directed in the cylinders though the spark plug hole or through the carbs.

I have visualized spark when cranking however it appears quite weak. I have measured the following with my multimeter:

Resistance at primary on coils of 3.1ohm on all 3.
Resistance at secondary #1 13.67ohm, #2 13.34ohm, #3 14.31ohm.

I am getting 0 volts going into coils 1 and 3 however 2 is getting somewhere around 7ish when the key is on but not cranking.
When cranking the bike I'm only getting 0.5-0.8 volts going into the 1 and 3 coils.

So my question is what voltage should I be getting into the coils with the key on and not cranking the bike, and why am I not seeing any voltage going into 2 out of the 3? Is this an ignition module that needs replacing? Is there a way to test the ignition module with my multimeter? If this is all normal, what is a good direction to start looking instead. I hope its okay to post this in a 650 forum, there doesn't seem to be much out there for the 850s otherwise.

Thanks for the help.

I have an XS750, voltage dips quite a bit under load from the starter, even with a good battery. I normally have mine hooked up to a booster when I'm at home tuning the carbs. Do the oil, neutral, tach and speedo lights dim when you crank the bike? when you get it running and rev the engine do the lights get brighter? if the lights are dimming/brightening you will need a stronger power source than just the motorcycle battery to test your spark.

 

[Jan_P]

Oopsss you have another carburetor thread .
But please check how much the voltage drops It can be an old battery .To weak for effective start.

I dont know this bike but some bikes have a function for cutting power to lights and so at startup.
Kick starter is good.