Temperamental 3rd cylinder

[e-a-m-o-n]

Hey guys, so the third cylinder on my FZX250 is giving me bit of trouble. most of the time the bikes running mint, but occasionally the 3rd cylinder cuts out, when i say ocasionaly im talking every 3 days give or take (bike is riden everyday). Sometimes it cuts while riding (warm engine) sometimes its dead from the get go. Funny thing is it comes back to life as suddenly as it goes, sometimes after a few minutes, sometimes after 30min or so of riding... Ive given the carbs a good clean out, adjusted the pilots back to stock position. changed the spark plugs, cleaned air filter. All the basics checked, but not sure what to check from here... any ideas?

[FJRider]

Check the plug lead at the coil. It may be earthing out between the coil and the plug.

It does sound like an electrical issue.

[Akzle]

damn. google paid off for figgy.

yurp. 'lectric issue.
intermittent problems are PITA. checking HT leads/spark would be a good start.

else could be dodgy capacitor on one of your CDIs. else dodgy sender/magneto assy.

how do you know it's 3rd cyl if it's happenin while you're riding?

running it in a dark garage will show up any shorts-to-ground off your HTs.

[jellywrestler]

do you know which cylinder it is? if so then try swapping around the coils and seeing if the fault stays on that cyl or moves to another.

[e-a-m-o-n]

Forgot to mention that most of the time its only the lower revs thats affected. Occasionally its dead over the whole rev range, but usually just from idle to 3000ish. Thats why i thought it probably wasnt electerical, but could be wrong.. Is there an easy way to check capacitors? and what do you mean by sender and magneto assay? Im a bit thick when it comes to electrics on bikes..

Cheers for quick replies too

[awayatc]

start with easy things first,then work your way down....
Check sparkplug lead first....?

[Akzle]

Forgot to mention that most of the time its only the lower revs thats affected. Occasionally its dead over the whole rev range, but usually just from idle to 3000ish. Thats why i thought it probably wasnt electerical, but could be wrong.. Is there an easy way to check capacitors? and what do you mean by sender and magneto assay? Im a bit thick when it comes to electrics on bikes..

Cheers for quick replies too

again. how have you verified it's cyl 3? test as per other guys suggestion.

capacitors can generally be checked with multimeter. but most oft' are sealed units. as my 1st post. HT leads is first check. visual of insulation/ boots, then run it in dark garage and watch for fireworks.

sender and magneto are what sends spark signal to CDIs. (like a dizzy in car) would more likely show up on two cyls/ same CDI, but possible if contacts are broken and would explain intermittency.

[e-a-m-o-n]

Ive checked the headers each time its happend and the third is always the one thats cooler. Stone cold if it happens on start up. Sweet will give all the leads a good check over in the morning

[mossy1200]

Sounds like a resistor spark plug failure. Get a set of plugs and get the bike shop to gap them for you and fit those first.

Temperamental 3rd wife issues sound like alot more trouble than you have going on.

[e-a-m-o-n]

[QUOTE=
Temperamental 3rd wife issues sound like alot more trouble than you have going on.[/QUOTE]

haha cant get your piston moving in her cylinder either aye? bugger...
Anyway... Got her all setup in a dark garage to check for HT sparks, went to start it aaaaaand HYDROLOCK!!! shit. So it definatly seems to me like its a fuel problem.. But what to do from here? Im to scared to start it again in case i bend a rod..

[Akzle]

i assume hydro lock something like vapour lock. but i'd find it highly unlikely, for no good reason whatsoe'er.

pull the plugs and turn it over by hand to clear the cyls.

as far as "fuel problem": that'd be a carb stripdown and cleanup there bud. pay attention to float condition and floaty-ness. and that their height-tab-setting-ey bits are all good.

if it was, in fact, hydro-locked, that'd suggest a priming hose had filled the cylinder while it was sitting...

-edit-
you're unlikely to bend a rod under tick over speeds.
if you have anything else that could leak into the head? fucked gasket? coolant?

[mossy1200]

haha cant get your piston moving in her cylinder either aye? bugger...
Anyway... Got her all setup in a dark garage to check for HT sparks, went to start it aaaaaand HYDROLOCK!!! shit. So it definatly seems to me like its a fuel problem.. But what to do from here? Im to scared to start it again in case i bend a rod..

Take sparkplug out. Turn it over pushing bike in 3rd to get most fuel out of cylinder.

Theres grit or dirt etc in the needle and seat above the float for that carb or floats stuck.

[e-a-m-o-n]

like said in the first post all the carbs have been thoroughly checked and blasted out. no grit or sticking floats. is it possible for the cyl to fill with enough fuel to hydrolock just from the spark not firing? doesnt seem likely to me. when you say gasket/coolant which gaskets do you mean? head?

[FruitLooPs]

No, it will never fill while the engine is running it will escape out past valves.

Vacuum operated petcock, or manual on/off/reserve? My GSXR750 had the same issue, only I did bend a rod :pinch:

Mine happened by attempting a bump start on a full load of fuel, I believe a diff cylinder fired first and came up on the liquid filled one. :facepalm: Be sure you've cleared the cylinder, get float valve looked at because its not shutting off the fuel flow. If its a vacuum operated and not set for prime, then you've got a fuelcock problem & the carb float valve to fix.

As for the cylinder dying issue, I've had the exact same thing too as it happens haha. In my case it was a 5k ohm resister NGK sparkboot, couldn't even get continuity across it so iono how it ran at all!

Make sure if you've got resistor sparkboots that the plugs are non resistor type or you may get reduced spark. Easy enough to check the spark boots and HT wire resistance with a multimeter - should be 5k or whatever is printed on them for the boots and you can find spec for lengths of HT lead on google or in a manual i'm sure. Also loose termination at the coil end, oxidised copper core in the HT leads etc.

It may just be the fuel getting into the cylinder is wet fouling the plug for periods and the high rpms might drag enough air across for it to fire up but fairly unlikely I think.

Get the known issue with the fuel delivery fixed, and further diagnose as required.

[DEATH_INC.]

My old fzr thou had the symptoms you mention, it was the needle valve. Too much wear in it, and it'd flood when left sitting and run on 3 when ya fired it up in the morning. Usually by halfway to work it'd pick it up and run on 4 again....

[e-a-m-o-n]

Cheers guys, got a full set of needles ordered, will let you know if that makes a difference.

Fruitloops- I do have a vague memory of the HT lead copper being a bit green when i changed a boot a while ago, do you rekon that that oxidization could cause the intermittent cut out? And when do i connect the multimeter to the spark boot to check resistance? when the bikes running or just with the key on? havent done much elec-trickery on bikes..

[Akzle]

Cheers guys, got a full set of needles ordered, will let you know if that makes a difference.

Fruitloops- I do have a vague memory of the HT lead copper being a bit green when i changed a boot a while ago, do you rekon that that oxidization could cause the intermittent cut out? And when do i connect the multimeter to the spark boot to check resistance? when the bikes running or just with the key on? havent done much elec-trickery on bikes..

:facepalm:

off bike. set to range that covers your 5ohm. (x1, x10) measure between boot (plug end) and cap (CDI end)
unlikely that the oxide would beggar the connection.


pop quiz though: what do you ever check the resistance of in a live circuit?

[e-a-m-o-n]

:facepalm:

off bike. set to range that covers your 5ohm. (x1, x10) measure between boot (plug end) and cap (CDI end)
unlikely that the oxide would beggar the connection.


pop quiz though: what do you ever check the resistance of in a live circuit?

wouldnt know mate. never checked a resistance.