Photos from Sam Rk's post

Hey guys, update on the FJ problems. Took the tank off and checked the spark plugs. They're heavily fouled with a soft black soot. If I'm not mistaken, that indicates rich running, not lean running. That'd almost conclusively narrow it down to an ignition/weak spark issue. What's the tolerance on the ignition coil for the 87? And would it show when cold, even if the bike only has issues when warm? Thanks for all the help guys!

25 comments
  • its a fuel starvation problem then bud . its getting enough fuel when it sits and then because the flow is restricted its becoming more and more starved until it eventuallty cant run . get those carbs off and give them a clean , check the fuel tank breather hole .(open the cap and run it) and check the fuel pipes and tap .

  • I thought that thick black soot on the plugs means it's running too rich? If it's leaning out to the severity required, wouldn't the plugs look baked? Plus, bringing it back to idle and letting it idle doesn't improve the behavior. It just continues to worsen until I let the bike sit for hours on end.

  • And what is the spark like ?

  • No idea. Should I ground the plug and hit the starter? Plus, it's kinda hard to test given the way its behaving. (Only having issues when hot, with extended running)

  • Would it be a definitive test if I do it on a cold engine?

  • yeah see dont put the plugs anywhere near the holes . If they are flooding there`ll be gas shoot out of there an the plugs will ignite it . ....put them well away from the holes and just see how strong the spark it .

  • Not got a mouse moved into the airbox have you. They like building nests storing nuts places like that.

  • Iwas then thinking that mate . weird or what !! I was then about to type check the airbox for mice i swear ..lol

  • Nope already checked. Air box is clean.

  • David, spark is weak as all get out, and that's with iridium plugs. Should throw a nice strong ark, right? I'll take some video.

  • Spark is super weak, even when cold. Battery voltage showed 11.5 with the lights on. The video was taken from 6 inches to a foot away from the plug. This is with NGK iridium plugs. Tried an old B8HS just to see if it'd spark another plug. Didn't even throw a spark. (Posting video separately, because Facebook)

  • Check the voltage at the coils, if it is more than 1/2 volt below the voltage at the battery, clean all of the electrocal connections between the two. I have had very good results installing a relay to power the ignition system. This site has a great how-to for installing the relay.

    http://www.wgcarbs.com/index.p hp/using-joomla/extensions/com ponents/content-component/arti cle-categories/89-coils

  • Low battery?

  • Possibly, but I'd like to think not. The battery is brand new.

  • Less than six months on it.

  • Try charging it, could be battery, or rectifier, or stator

  • Start leaning it out..... Coils are probably just fine.

  • Why would fuel-air be a problem in a sudden failure issue? It literally ran perfectly since I bought it. It sat in the garage for two days (pretty normal), and started having issues the following morning. I've taken it up and down in elevation, ridden it in 95 degree weather all the way to 25 degree weather with no ill effects.

  • Update: some funkiness with the voltage. When put to the battery, the multimeter took a while to register the full voltage, rather than the instant reading that I'm used to. Coils also came out to ~9.5 volts left and .05 (!?) right. Given that, I don't even now how it starts at all

  • That is very low voltage at the coils. Clean up the connections and do the power relay!

  • I was just looking at the plugs. Are your muffler pipes sooty and wet on the end after running ? If it is to rich (flooding) it can cause the same problem. Check your oil also for gas ? I still think it is a carb problem. On the voltage problem have you cleaned up the start / kill switch ? Inspect and clean the red connector coming from the altenator located left side by the battery. Unplug it and take a look. Old electrical system requires a good going through. with the bike running have you checked the charging voltage ? Your battery resting in good shape should be around 12.7 volts and running you should see at least 13.8 to 14.8 volts. No more than 15 volts.

  • +1 on that. Get some emery cloth and clean all of the connections. After 30 years they get a bit gummed up. Start from the battery and work out. Also how good is your battery. If it is not giving the full amount of power these bikes will play up. Anything less than perfect and the gremlins creep in.

  • Also get yourself a Haynes Manual. I would be lost without mine.

  • First of all check the spark cups-wires connection. It could have oxide between. Simply cut 1 cm from the wires and connect everything again

  • After, fit a coil relay to improve the voltage. You can find the electrical scheme and how to do it in my web www.fj1200.info ENGINE section