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'98 FZS 600 Misfire


Janie
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My '98 FZS 600 has developed a bit of a strange misfire. From cold it starts, runs and pulls just fine. After just a couple of miles if you crack the throttle open suddenly it loses a cylinder. Backing the throttle off brings the cylinder back online. If you then roll the throttle on gently it will accelerate as clean as a whistle all the way up to silly revs and speeds (Honest officer, I was just trying to trace a fault :fingerwave: )

Changed the plugs just incase I'd got one breaking down under pressure but to no avail. Re-calibrated the TPS because that was out and the problem seemed to go away for a little while but now it's back with avengance. Had the tops off all of the carbs to check for damaged diaphragms or bent needles. The bike was rejetted when the stainless race system was fitted but the problem exists whether I've got my standard can or race can on so gawd knows.

Any suggestions would be greatly received.

Thanks

Janie

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First thing I would do is try draining the carb floatbowls incase you have water or dirt in the bowls and when you crack open the throttle it's drawing water/dirt into the jets. Tony.

Cheers Tony, I'll try that tomorrow :thumb:

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Guest MaD.VeZ

Just a thought, but with the fault being there with sudden acceleration, could it be a lack of electricity i.e a poor battery or other electrical issue. Just a guess mind as I'm not familiar with the bike.

Vez.

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Just a thought, but with the fault being there with sudden acceleration, could it be a lack of electricity i.e a poor battery or other electrical issue. Just a guess mind as I'm not familiar with the bike.

Vez.

I wondered that myself but the bike has a brand new battery on it and the charging system is pushing 13+volts into it when the engine is running. My fella has gone over the entire ignition system with a multimeter checking resistances, continuinty etc and looking for faulty wiring but found everything to be in perfect order. The only real anomaly was the resistance in the plug caps. This is quoted in the manual as 10K-Ohms @20c. We got figures ranging from 9.1 to 12.4. or there abouts. Not sure if this would have a discernable effect on the spark or whether the values are within tolerance for the bike as no +/- figures were given in the manual.

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I wondered that myself but the bike has a brand new battery on it and the charging system is pushing 13+volts into it when the engine is running. My fella has gone over the entire ignition system with a multimeter checking resistances, continuinty etc and looking for faulty wiring but found everything to be in perfect order. The only real anomaly was the resistance in the plug caps. This is quoted in the manual as 10K-Ohms @20c. We got figures ranging from 9.1 to 12.4. or there abouts. Not sure if this would have a discernable effect on the spark or whether the values are within tolerance for the bike as no +/- figures were given in the manual.

Which carb does the fuel tap vac line come from?, got a scottoiler?. Does that connect to the duff cyl. Small vac leak in there would kill snap throttle openings but would be fine nice and steady. May even stay hidden/ sealed till it gets warmed up? My suzuki did exactly what you are describing when one of the rubber caps for the vac take offs dissapeared. Never did figure where that went :huh: .

When was the last time the carbs were balanced?, thats a possible too while we are collectively scratching our heads.

Lastly is it always the SAME cyl that dies out or is it random.

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Janie you have pretty much done everything i can think of here :huh:

I would guess at the same but how would you know?

:lol: hop off, run along side the bike and see which burns your hand the least... :D

She may just be THAT good. B)

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Which carb does the fuel tap vac line come from?, got a scottoiler?. Does that connect to the duff cyl. Small vac leak in there would kill snap throttle openings but would be fine nice and steady. May even stay hidden/ sealed till it gets warmed up? My suzuki did exactly what you are describing when one of the rubber caps for the vac take offs dissapeared. Never did figure where that went :huh: .

When was the last time the carbs were balanced?, thats a possible too while we are collectively scratching our heads.

Lastly is it always the SAME cyl that dies out or is it random.

Right lets answer these one at a time

The bike doesn't have a vac tap on the tank, the carbs are fed via an electric fuel pump and there's no Scottoiler so the fault's not there. The carbs were balanced about 2 weeks ago when the fault reared it head.

I've been told by one or two people that an air leak might be the cause so when it decides to stop damn raining I'll have a look at that too. Someone also suggested that one of the sliders in one of the carbs might be sticking when i wack the throttle open. :shrug:

Have no idea which cylinder it is that dies but we've swapped the coils over just incase there was a fault there and the misfire feels the same whichever way we wire them up.

All these suggestions are really appreciated guys and I'll keep you posted as to what we find. :hug2:

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Janie, i dont suppose you have visual of the slides with the airbox open?

i know this would mean a tank removed but i'f all else fails and if it were me i would be watching the action of the slides if it were possible to see if any one of them is having a dicky fit (possible diaphragm issue) I know you checked them though so its a stab in the dark and would mean using a remote fuel supply. bloody awkward problems with four cylinder bikes eh?

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Janie, i dont suppose you have visual of the slides with the airbox open?

i know this would mean a tank removed but i'f all else fails and if it were me i would be watching the action of the slides if it were possible to see if any one of them is having a dicky fit (possible diaphragm issue) I know you checked them though so its a stab in the dark and would mean using a remote fuel supply. bloody awkward problems with four cylinder bikes eh?

Taking the tank off and rigging a remote fuel supply is no problem. 2 allen headed bolts, a fuel pipe and a multi plug for the fuel gauge and the it's off. I wondered about seeing the sliders moving myself so had a look in the Haynes manual to see what was involved in removing the airbox. The first sentence reads........ 1. Remove engine... I stopped reading at that point :lol:

I need to get this sorted soon as all this messing with oily bits is ruining my nails :rolleyes::lol:

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Taking the tank off and rigging a remote fuel supply is no problem. 2 allen headed bolts, a fuel pipe and a multi plug for the fuel gauge and the it's off. I wondered about seeing the sliders moving myself so had a look in the Haynes manual to see what was involved in removing the airbox. The first sentence reads........ 1. Remove engine... I stopped reading at that point :lol:

I need to get this sorted soon as all this messing with oily bits is ruining my nails :rolleyes::lol:

Cant you just remove the filter and see down to the slides, even using a mirror or one of those overgrown inspection mirrors (Dentist stylee)

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Big up to everyone who suggested stuff but special hugs go to the YPVS TONE massive :hail::D Drained the float bowls.... Went for a ride....... misfire gone. How chuffed am I :D :D :D

On my journey though I did discover that now it doesn't misfire when you whack the throttle open....the clutch slips instead :rolleyes: Ahh well, on with the overalls and out with the toolbox again. At least this is a straightforward job. :eusa_doh:

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Hi Janie

Glad to be of some help.I always think it's best to try the basics before delving into carbs as unless your carefull you can sometimes do more harm then good. Regarding the clutch slip do you know what oil is in the engine as you really want a 10w/40 motorcycle specific oil ( NOT car oil ) which has JASO-MA spec on the bottle and make sure you have 10 - 15mm of freeplay measured at the end of the clutch lever. Tony.

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Hi Janie

Glad to be of some help.I always think it's best to try the basics before delving into carbs as unless your carefull you can sometimes do more harm then good. Regarding the clutch slip do you know what oil is in the engine as you really want a 10w/40 motorcycle specific oil ( NOT car oil ) which has JASO-MA spec on the bottle and make sure you have 10 - 15mm of freeplay measured at the end of the clutch lever. Tony.

Hi Tone,

Yeah it's bike specific oil from my local bike shop and the freeplay at the lever end is set right.

I've had the bike for a number of years now and before that it was owned by a guy called Alan Dowds who at the time used to be road test editor for Ride magazine, and I've got various pictures of it being used and abused by members of the editorial staff. The fact the clutch has lasted this long is a minor miracle given the amount of time the bike spent on it's back wheel while under the "care" of the Magazine staff lol.

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Hi Janie

The only thing left is to get the clutch stripped and the clutch plates checked for wear and replaced as if its been used as a test bike the clutch has probably had a hard life. Doesn't Alan Dowds now write for Superbike magazine ? Tone.

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Hi Janie

The only thing left is to get the clutch stripped and the clutch plates checked for wear and replaced as if its been used as a test bike the clutch has probably had a hard life. Doesn't Alan Dowds now write for Superbike magazine ? Tone.

Got a new clutch on order from Fleabay so that'll be going in as soon as it arrives, and yes you're right, Alan is now deputy editor of Superbike magazine.

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Janie, i dont suppose you have visual of the slides with the airbox open?

i know this would mean a tank removed but i'f all else fails and if it were me i would be watching the action of the slides if it were possible to see if any one of them is having a dicky fit (possible diaphragm issue) I know you checked them though so its a stab in the dark and would mean using a remote fuel supply. bloody awkward problems with four cylinder bikes eh?

:huh:;):huh:;)

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