Hi all , just had my bike dyno'd and all fueling set up, the dyno operator says it runs perfect until it gets hot then starts to misfire like its running on two cylinders.if he lets it cool down and starts it again it runs sweet until warm. I have an idea what it is just wondering if their is anything specific to the fzr that could cause this ?

That's odd, I can't think of anything. Unless he ran it up to temp then did a power run up to 12.5k rpm when the bike would restrict if it doesn't have an M-Box on it, (the speedo runs off the front wheel and would be at 0)

I had a problem with the YZF 750 engine last year, running NGK plugs supplied by PO.
one cylinder dropped after initial 20 ish miles. Returned to normal after 5 mins. stopping.
would reoccur every 5/10 minutes or so once hot.
Replacing the offending plug sorted it
Apparently there are a good few "snide " NGK plugs out there !

If its dropping 2 cylinders ; is it the same coil ?

How are you circumventing the speedo drive (if speedo fitted) restriction.?

If the restriction circuit is still operational ; how are you emulating speedo operation ?

M-max box or cordless drill to speedo cable ?

It runs fine when cold , I ran it right up to temp last night and no problem so it must be going down under load , as said above I am thinking a coil

Ride it and see if you can get a misfire before you change the coils.

Sounds like coil to me,Seen it often coil ok untill it gets hot,Then breaks down.

Sounds like coil to me,Seen it often coil ok untill it gets hot,Then breaks down.
Said that twice

The ignition is supposed to be derestricted (race bike) so it has no speedo or speedo drive, if it was still restricted it would do it when cold aswell wouldn't it ?

Stretch85 wrote:The ignition is supposed to be derestricted (race bike) so it has no speedo or speedo drive, if it was still restricted it would do it when cold aswell wouldn't it ?

Yes it would; but until you informed us of its status, the previous questions and suggestions were very relevant.

The restriction would come in at 12.5k rpm if it's there.

If the bike's had the carbs set up and then breaks up on 1 cyl I'd look at HT lead, plug cap, and plug. If it's 2 on the same coil then obviously that coil or the electrics going to it. Run the bike up to where the symptom start then maybe swap the coils and repeat. If you replace them then think about using some Dyna Coils / leads etc