odd idle problem

[Alexander Dzikiewicz]

hello all, i hope you are all enjoying this new beautiful site.
my 87 fz750 has a very strange mis-fire. basically at idle the bike is running off the 2 center cylinders which is fed by the ignition coil on the right side of the bike, but as the bike REVS up the left ignition coil begins to work. i tested this by disconnecting the left coil (which idle stayed the same) and reved up and the bike ran like sh*t, but when the coil was plugged in the and reved to higher rpm up the bike ran mint, I belive the coil is fine becasue to my understanding a coil should either work or not work im leaning toward a decay in the wires, but how the heck to u detach the wire from the coil on these bikes?

thank you

[Graham Beale]

Have you checked the HT wires at the plug cap end? They corrode & come loose with age. I was able to unscrew all 4 of my caps, chop out the corrosion & screw the caps back on. Threads in the caps can be corroded too. Don’t think they will be failing at the coil end as they are sealed but if the seal has broke down you can possibly do the same thing?
Also check the 2 wires & plug that go to the offending coil.

[Alexander Dzikiewicz]

yeah you were right i went and bounght new spark plug tubes and it solved my problem, BUT NOW, after the bike has warmed up a lilttle bit i will be sitting at idel around 900rpm and the bike will shoot up to 2100 ish rpm and just sit there i would turn down my idle control screw but how could it temperarly idle at 900rpm then all the way up to 2100rpm?

[Graham Beale]

Does it do this every time you start the bike? If it’s been laid up for a while without being started regularly then I would try some fresh fuel. If it still has erratic idle then I would check for air leaks by spraying WD40 or similar around the air box rubbers & listen for a change in idle speed. If it still plays up I would be tempted to strip the carbs & clean all the jets.

[#1 FZ]

Ditto on what Graham said… today I pulled my carbs and the pilot jets were plugged. It ran on choke only and would not rev (old gas). Now with new plugs/clean carbs and fresh fuel it revs great but doesnt idle perfectly off choke. I am going to have the carbs checked again by a cycle mechanic friend of mine to verify that I didn’t miss anything….my bike sat for quite a while contributing to my dilemma.

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