engine dying

[bigbore2]

I just resynched carbs and rode bike long enough to know things were working good, but during the synch of my carbs, the #2 cylinder had gone out. I cleaned the plug and that got it running long enough to resynch and test engine. Now bike just won't run unless its revved up the 4 or 5 grand and it has no power. It is also missing a lot. I felt all the pipes and #2 pipe was much cooler than the others but not cold. Is this a coil problem or igniter problem? How do I diagnose this?

[yamaha fj rider]

Sounds like plugged pilot jets and maybe a plugged idle mixture screws circuit. Hope this helps? 

Kurt     

[bigbore2]

Or a crimped fuel line.  Just another reason to go to pods instead of the airbox. I will need to be more careful when putting my tank back on.      I still do have the issue with the #2 cylinder not firing all the time . After reading another post here about coils, I am going to switch the 1-4 and 2-3 coils to see if the problem moves with the switch.
Had my coils tested and they looked fine, although they were not hot.  Thanx to whomever put my post here from general maintenance. Owe you a beer.  yamahafjrider. I did not mention carbs just rebuilt and everything clean in there.

[bigbore2]

Cannot switch stock coils because the 2-3 coil has too short of a spark plug wire length to reach both the 1 and 4 cylinders.  I guess I have to rely on the bench test for now and see how it runs.

[Pat Conlon]

Make sure the coil is toasty warm before you test. Take a hair dryer and heat that puppy up.

[bigbore2]

A hot coil may show a problem where a cold one doesn't?  I have been driving it and no sign of a problem yet.

[Pat Conlon]

yep, that's why the shop manual says to bench test the coils warm....

I'm not saying that your problem is with the coil. My bet is that is carb related.

[Dan Filetti]

A hot coil may show a problem where a cold one doesn't?  I have been driving it and no sign of a problem yet.

Yup, I had a coil that would only miss-behave when I sat at a light for too long on a warm or hot day.  It tuned out to be the engine heat, radiating up onto it that caused the issue.  As long as I was moving, and/ or only sat for short periods of time, the problem never occurred.    It would only start happening, then get worse and worse the longer I sat stationary with the motor running.  For me, the engine would cough first every 20 seconds, after sitting there initially for say 30-45 seconds.  Then after perhaps a minute or two of this the frequency of the coughing would become enough to stall the engine if I did not feed it some throttle.  I put a timing light on it on and it became crystal clear this was my problem.  I replaced the coil and it worked flawlessly from there on out.

Prior to this I had been through the carbs thinking this was the issue, I wished I had tested the coils first. Although it's not a bad thing to go through the carbs, this is an easy 15 minute test that will eliminate or identify the coils as the culprit assuming you can reproduce the symptom in your garage.  The carbs on the other-hand, are somewhat more involved.

All that said, this sure does sound like plugged idle jet on #2, if it was a coil you'd be dropping two cylinders.

Dan

[yamaha fj rider]

If it was a coil problem it should not start working at higher rpm's unless maybe a bad connection but that is a stretch. I still think pilot jet or mixture circuit plugged. Hope this helps. 

Kurt

[andyb]

It could do so if there was a severe vibration sorta thing going on, which would be appropriate if he's trying to fix the synch.  More likely it'd be just crazy intermittent though.

Never bother with a synch on a rack of carbs that could possibly be dirty.  Waste of time.  Start with things as good as you can get them, it makes it more rewarding when you're done. 

[yamaha fj rider]

andyb is right trying to synch dirty carbs   . andy would this only effect the #2 cylinder if it was a coil problem? 

Kurt

[bigbore2]

Carbs are clean and just rebuilt.  Started right up after re-installing them.  Runs great now that I synched carbs, however I synched them when engine not hot, but plan to recheck after engine/carbs up to operating temp.  Engine starts immediately when cold, don't need to use choke.  Really runs great and has not acted up now for a week or so.  I had a crimped fuel line, that was the last problem and the reason I started this post. I am still learning about this bike as I have only put on maybe 300 miles or so. Speedo out in San Diego getting fixed.   Will need to bench test coils warm/hot. My heat gun ought to do the trick as long as I don't get to close and only use the lowest setting.