FZ600 wont go over 5000

[alan_g]

Hi everybody,

I'm new here, been a yamaha lover since my 1971 DT175 that I got in 1980. (still in my garage!)

Anybody out there help me, I'm stumped. Just rebuilt my FZ600 after 10 years in pieces in the corner of the workshop (not the engine)

Rides fine, starts, idles,pulls, perfect up to 5000. try to go over, coughs, severe hesitation, wont rev higher.

Makes no difference if its low gear acceleration, or creeping up in top on the dual carriageway.

Tank's been dipped/zinc plated, so no rust. petcock already rebuilt, checked out again all ok.

Plugged the vacuum for the petcock, then ran it up with the tank off, big funnel full of petrol, air filters off.

got her up to about 6500, mist spray a little easy start, and she revs up to the red 10000.

Same test after stripping the carbs twice. second time adjusted float height (about 1mm out)

Still no difference.

Sprayed easy start on the inlet rubbers when running, to check for air leaks - non found.

Plugs new from rebuild. Colour seems ok (only done about 80 miles though)

Coils check out on the multimeter to what the Haynes manual says, get the note change(and electric shock!) when you pull each plug lead off.

Can the CDI develop a fault that only affects high revs? (Personally never known this)

Any one got any ideas?

[Airhead]

Beats me Alan could be the CDI but I wonder if you can find one cheaply to test? I would go with an ignition issue or perhaps carb diaphragms but havent got any experience of this so it's a bit of a guess really.

[KirriePete]

I'm inclined to think carb diaphragms - after 10 years sitting they will likely have gone off, either perished and developed tiny leaks or gone stiff. Either way, they won't be generating enough lift to bring the mains into play, which would give you the symptoms you describe.

If you need new ones, try NRP.

You're welcome.