Flat Spot

[Dcock]

Right so after blasting it half way back from poole bike night tonight my 1998 fzs600 developed a problem. As i was trying to blast it past my mates fz1 my bike lost power and now will not rev past 7k unless i hold the throttle back for a good 5 seconds and then finally revs past it but with very little power. It feels liek a very bad flat spot. Also it seems to happen lower down the rev range if i'm in the lower gears. I feels as if it looses power at the point when the engine used to start pulling hard. I'm wondering whether it's running lean as i had the fan come on for the first time today also the carb rubbers are cracked, but i sprayed wd40 on them and the idle did not change.

Any ideas?

Thanks, Dan.

[Punkstig]

tonight my 1998 fzs600 developed a problem. As i was trying to blast it past my mates fz1

You sure your mate didn't twist his throttle at this point?  :lol


How old is the air filter?


Are all cylinders firing- once engine is warmed up spray wd40 or similar onto exhaust headers, does the liquid evaporate at the same time on each exhaust?


Check plug caps, run it in the garage or at night and see if there's sparks arcing to the engine case.
Plug caps can be pulled off and spray inside with wd40/ contact cleaner, ends can be trimmed off the ends of the HT leads and threaded back onto caps.

[Dead Eye]

Sounds like the same problem reported by a few others. Almost worth checking out some of the stutter threads

If this is a new problem then I'd say the fuelling probably isn't the issue. Look in to the electronics and potentially the regulator as it was an issue for Mr red98... it only took him nearly 18 months to finally get it sorted :|

[Dcock]

cheers for the replies. I had a look at reds thread (Not quite all 40 odd pages though) How do i check the regulator? Also could spark plugs cause this?

[darrsi]

Hold on a minute, spraying WD40 on cracked rubbers at idle is a hell of a lot different to giving the bike a handful of throttle.
I was gonna say air anyway, but this sounds exactly like what my bike was doing when my inlet rubber was folded in half on refitting and letting air in.
As soon as i tried to overtake it just bogged down, but was "okayish" when riding normally.
My money's definitely on the rubbers from your description! 


As a possible temporary fix, and also as a fault finder, i would try filling the cracks with silicon or something similar and see if it stops it from bogging down.

[Dead Eye]

Unfortunately there are just sooo many faults that can cause this problem At least we seem to be rooting out the most common and exotic ones

[red98]

try the easy things first.......how old are the plugs ?...inlet rubbers are very thick if the cracks are small that wont be the problem  .....can be filled with silicon but will need to remove to do a good job.....as already suggested ,check air filter,we do like a K+N filters on here   

[darrsi]

I was thinking more of the airbox rubbers rather than the inlet rubbers, they're not that thick.

[red98]

I was thinking more of the airbox rubbers rather than the inlet rubbers, they're not that thick.

ah yes.....very flexable and i have seen the problem you had with folding in before...never seen these crack though,the flexabilty probably helps 

[HarryHornby]

Check air filter, check spark plugs and think about replacing the plug caps if they look really old..... just my two pence worth 

[Dcock]

UPDATE: Today i decided to check the air filter, pretty clean. so i moved onto the carb to head rubbers. I took each one off had a look and even though they are cracked real bad on the outside, it has not penetrated all the way through. Back on they went. I then took the carbs off and holy shite the float bowls were full of rust. So i cleaned all the float bowls and all the jets (we have a blanker mid jet that fooled me into thinking it was blocked for a while) and then had a look at the diaphragms and lubed up the slides. I also decided to reset all the air/fuel mixtures screws as the idle was bad beforehand. That was a mistake as one of the screws just snapped off. So i had to cut a slit in it to be able to turn it... anyway that sorted i put it all back together with a new fuel filter and now it runs perfect again. So i'm guessing it was blocked up carbs or something carb related. Just a side note, two days beforehand i put in a small amount of carb/injector cleaner in with my fuel. I wonder whether this had a part to play?

Cheers for the help.

[darrsi]

Nice work, glad you sorted it out quickly 

[Punkstig]

Sounds like the cleaner loosened some gunk and blocked it up!

[red98]

nice work.....glad its sorted