1990 FZR250 misfiring

[Driftmonkey]

Picked up a bit of a mistreated 3LN FZR a few days ago. 1990 with 40,000kms Been fiddling with It for the past few days trying to sort it out but it starts misfiring REALLY badly at about 13,000rpm. Runs beautifully all the way up until this point. Doesn't do it as bad in higher gears.

Ran a tank of 98 with a fair amount of carb/injector cleaner through it, checked plugs, cleaned tank out, charged battery up, and done a tonne of tidying up cleaning around the bike but I am stumped. I've done a bit of searching and no one seems to come to a definitive answer and I don't have the means to go out and buy a few new coils tcis and new sets of carbs with no certainty the problem will be fixed.

TLDR; typical 'help thread', I need to know an elimination sort of process to pinpoint the problem.

[Driftmonkey]

EXUP is operating as it should as is the fuel pump.

[kiwi-on-wheels]

Check your earths, i had one break off on my cbr and it wouldnt rev over 10k. Also ran like s**t.

Might be worth running a couple of new earths?

[Driftmonkey]

Read somewhere while searching that spraying water on the extractors could give an indication of which cylinders are misfiring. So did that and the water dissipated instantly from cyl 1 and 2. 3 and 4 took a while with 3rd taken the longest. gunked up carbs not supplying enough fuel at top end? will sort some new earth's out on the mean time. Cheers for suggestion.

trying to avoid taking the carbs out cause I know there's going to be perished rubbers that'll need replacing all over the show.. why did I buy an old bike..

[FJRider]

Read somewhere while searching that spraying water on the extractors could give an indication of which cylinders are misfiring. So did that and the water dissipated instantly from cyl 1 and 2. 3 and 4 took a while with 3rd taken the longest. gunked up carbs not supplying enough fuel at top end? will sort some new earth's out on the mean time. Cheers for suggestion.

trying to avoid taking the carbs out cause I know there's going to be perished rubbers that'll need replacing all over the show.. why did I buy an old bike..

Rearrange the same plugs in different cylinders. Then do it again. If the observation follows the plugs ... :pinch:

[Driftmonkey]

Pretty much isolated the problem to cyl #3 and #4. Pulled leads from each cylinder and the bike died when 1 and 2 were pulled, bike ran still but noise changed a bit when 3 and 4 were pulled. Will get new plugs asap, least that'll cross one thing off the list.

[Driftmonkey]

https://www.youtube.com/watch?v=9QuLmZwvIJ0

[FJRider]

Pretty much isolated the problem to cyl #3 and #4. Pulled leads from each cylinder and the bike died when 1 and 2 were pulled, bike ran still but noise changed a bit when 3 and 4 were pulled. Will get new plugs asap, least that'll cross one thing off the list.

If you have two coils ... one will cover 1 - 3 ... the other 2 - 4. Possibly a short in the leads from 3 - 4. If it died with 1 & 2 pulled ... 1 & 2 were the good ones.

[Driftmonkey]

Got home later after work and decided i had enough of the misfiring. straight away pulled carbs out. Needles in carb 3 and 4 were blocked. Along with the 3rd spark plug being finger tight. :eek: Just in the process of putting back together crossing my finger and toes that it'll go now. Fair amount of junk in the carbs but it's cleaned out and it idles much better. Here's hoping. Tank and fairings left to put on

[Driftmonkey]

STOKED. :woohoo::scooter:

[mossy1200]

STROKED IT. :woohoo::scooter:

Good for you. Now get back to tuning your bike.

[Driftmonkey]

Good for you. Now get back to tuning your bike.

Hahaha, ya ya. All done now after sitting around for a good while with a grin on my face :woohoo: So I guess water on the extractors really DOES give you an idea of where to start looking for problems.
What blew my mind was that the carbs weren't even hard to take out. Was only a 2 hour job pulling fairings tank carbs cleaning reassembling and I'm no bike guru by ANY means.. clearly.


For everyone elses sake that might come across this thread (because there is so many bloody threads on this sort of shit but no one updates with a solution). My solution was a combination of things

Switch to 91 octane (was using 98 .. )
Remove carbs and clean needles
remove and clean sparkplugs
flush tank
disconnected, sanded surface and reconnected earths + added two more

[ducatilover]

If you have two coils ... one will cover 1 - 3 ... the other 2 - 4. Possibly a short in the leads from 3 - 4. If it died with 1 & 2 pulled ... 1 & 2 were the good ones.
Noooooo FJ, ya silly ol' bugger :girlfight: Cyls 1&4, cyls 2&3 are pairs.

STOKED. :woohoo::scooter:

Good to see you sorted it out.
Don't run it on 91 though.

[Driftmonkey]

Noooooo FJ, ya silly ol' bugger :girlfight: Cyls 1&4, cyls 2&3 are pairs.


Good to see you sorted it out.
Don't run it on 91 though.

So I should continue to use 98? I stopped by Botany Honda motorcycles for a little bit of advice and they said the highest octane rating out when my bike was made was 87 octane, and that I want to use a fuel as close to that as possible.. correct orrr :nono:

[ducatilover]

Our octane ratings are different to the ones used overseas. Japanese fuels are much higher quality. Hence why most 45hp 250s do not manage to make the 45hp they once did when they come to NZ.
I would run 98, it is more detonation resistant, and with a carboned up 250/4 pulling 18,000rpm, you need the best fuel you can get.

I would not listen to anyone who gives such fucking stupid advice.

[Driftmonkey]

Our octane ratings are different to the ones used overseas. Japanese fuels are much higher quality. Hence why most 45hp 250s do not manage to make the 45hp they once did when they come to NZ.
I would run 98, it is more detonation resistant, and with a carboned up 250/4 pulling 18,000rpm, you need the best fuel you can get.

I would not listen to anyone who gives such fucking stupid advice.

Hahahaha, that's so ironic. The only reason I went there is because I know I was talking to someone who worked on bikes all day (assumed they'd give real proper good advice). :weird: Back to 98 it is then I guess :niceone: Cheers for that yamahalover ! Much appreciated

[ducatilover]

Hahahaha, that's so ironic. The only reason I went there is because I know I was talking to someone who worked on bikes all day (assumed they'd give real proper good advice). :weird: Back to 98 it is then I guess :niceone: Cheers for that yamahalover ! Much appreciated
Not all of us mechanics give good advice
Chances are, mine is shit too :bleh:

[kiwi-on-wheels]

With some of the reports of "advice" given by botany honda, i'm stunned that they are still in business....

[ducatilover]

With some of the reports of "advice" given by botany honda, i'm stunned that they are still in business....

I wouldn't discount them. I have not really heard any other foolish advice from them, so as far as I am concerned it may be a one off and hopefully a bloke having a brain fart :cool:

[Driftmonkey]

My next issue has appeared on this terrible bike.. ring gear for the starter. When I turn the bike over sometimes the starter just spins freely without making the typical starter noise you get. I can see the starter motor easily and it's in a fairly accessible place but my question is.. how hard is it to replace and are the parts easy to find? Is it a case of just replacing the starter motor or is it more than that

[bogan]

My next issue has appeared on this terrible bike.. ring gear for the starter. When I turn the bike over sometimes the starter just spins freely without making the typical starter noise you get. I can see the starter motor easily and it's in a fairly accessible place but my question is.. how hard is it to replace and are the parts easy to find? Is it a case of just replacing the starter motor or is it more than that

Sounds like your sprag clutch might be buggered. Easy to replace, pull off engine side cover and a few bolts holding it on to a thing... It generally look just like a gear with two sets of teeth and a bulky inner bit iirc.

[Driftmonkey]

Currently on the hunt for one but... they don't seem to be easy to get a hold of? Do you have any links to a parts store or know of anywhere that could stock one? Or would second hand in good condition be good enough?

[ducatilover]

Yeah will be the sprag clutch. Pull it apart and see what's fucked on it first
I've seen a few smaller bikes get gummed up by using the wrong oil and sometimes a simple wee clean sorts 'em out

[Big Dog]

Currently on the hunt for one but... they don't seem to be easy to get a hold of? Do you have any links to a parts store or know of anywhere that could stock one? Or would second hand in good condition be good enough?

If your local dealer can't help try mrcycles.com.


Stupid phone / Tapatalk, apologies in advance.

[Driftmonkey]

So, gonna get to doing the sprag clutch. Am going to change oil and filter at the same time.. I've read that it's ok to use car 10w30 car oil in bikes as long as the oil doesn't have friction reducing additives otherwise the clutch will slip. Is this correct? I'm going to buy a 10w40 castrol or whatever the first thing I see when I walk into repco is

[Big Dog]

Putting car oil in is a pretty good way to get more mechanical experience but a pretty crappy way to look after your ride.
Stupid cheap auto do a cheap bike oil. But use bike oil.

Engine oil is for engines.
Transmission oil is for transmissions.
Motorcycle oil is for motorcycles.


The important difference being on a motorcycle the same oil is shared by the engine tranny and clutch.

Car motor oil will glaze out your clutch, gum up your transmission and cause it to wear prematurely.
Can also lead to blocked oil pathways inside your engine etc.

Don't do it. Putting car oil in your bike might save you a twenty now but sooner or later it will cost you hundreds if you are lucky. Your bike if you are not.


Stupid phone / Tapatalk, apologies in advance.

[Driftmonkey]

Putting car oil in is a pretty good way to get more mechanical experience but a pretty crappy way to look after your ride.
Stupid cheap auto do a cheap bike oil. But use bike oil.

Engine oil is for engines.
Transmission oil is for transmissions.
Motorcycle oil is for motorcycles.


The important difference being on a motorcycle the same oil is shared by the engine tranny and clutch.

Car motor oil will glaze out your clutch, gum up your transmission and cause it to wear prematurely.
Can also lead to blocked oil pathways inside your engine etc.

Don't do it. Putting car oil in your bike might save you a twenty now but sooner or later it will cost you hundreds if you are lucky. Your bike if you are not.


Stupid phone / Tapatalk, apologies in advance.

Yeah ended up with Castrol Activ 4T but never got around to doing the sprag. Tomorrow morning should be good. Hopefully I can get it sorted.. :sweatdrop

[ducatilover]

Oil just needs to be JASO MA rated for your clutch. JASO MB should be sweet too

[Driftmonkey]

Pulled engine cover off, found a few gears there... :shit:aaand, couldn't see anything out of the ordinary.. no gears were worn, no gears showed any signs of chips/cracks, no metal in the cover or near the cover. Just wiped everything down to give it a bit of a tidy and put back together. Still happens. Just sounds like the starter is spinning freely without grabbing onto anything, then it'll make a tonne of clunking and it'll catch on and then start up.. :weep: I need to learn how to play with bikes properly..

[Gadget1]

Pulled engine cover off, found a few gears there... :shit:aaand, couldn't see anything out of the ordinary.. no gears were worn, no gears showed any signs of chips/cracks, no metal in the cover or near the cover. Just wiped everything down to give it a bit of a tidy and put back together. Still happens. Just sounds like the starter is spinning freely without grabbing onto anything, then it'll make a tonne of clunking and it'll catch on and then start up.. :weep: I need to learn how to play with bikes properly..


Have a look at this to start (no pun intended) with:http://www.dansmc.com/electric_starters.htm

There's plenty of other info on motorcycle repairs on the rest of the site.

[Big Dog]

Pulled engine cover off, found a few gears there... :shit:aaand, couldn't see anything out of the ordinary.. no gears were worn, no gears showed any signs of chips/cracks, no metal in the cover or near the cover. Just wiped everything down to give it a bit of a tidy and put back together. Still happens. Just sounds like the starter is spinning freely without grabbing onto anything, then it'll make a tonne of clunking and it'll catch on and then start up.. :weep: I need to learn how to play with bikes properly..
Sounds like your starter solenoid to me.

To test try and reproduce the spinning sound, then tap the starter motor with a heavy object (I would use my trusty rubber mallet) if it suddenly engages there is your issue. If not and it slowly winds up you are not getting enough voltage to your starter.

Check your battery, connections etc.
Test any relays etc between battery box and starter.

I have never had this problem on a bike but had similar on a number of 20+ yo cars.
Always been the solenoid gummed up or burnt out or a faulty earth from the starter.

Is problem present when engine is already hot?


Stupid phone / Tapatalk, apologies in advance.

[ducatilover]

Sounds like your starter solenoid to me.

To test try and reproduce the spinning sound, then tap the starter motor with a heavy object (I would use my trusty rubber mallet) if it suddenly engages there is your issue. If not and it slowly winds up you are not getting enough voltage to your starter.

Check your battery, connections etc.
Test any relays etc between battery box and starter.

I have never had this problem on a bike but had similar on a number of 20+ yo cars.
Always been the solenoid gummed up or burnt out or a faulty earth from the starter.

Is problem present when engine is already hot?


Stupid phone / Tapatalk, apologies in advance. The starter doesn't have a throwout solenoid like a car though, it's a constant mesh system with a sprag clutch on a gear between the starter and flywheel usually.

[Big Dog]

The starter doesn't have a throwout solenoid like a car though, it's a constant mesh system with a sprag clutch on a gear between the starter and flywheel usually.

So most likely the starter taking to long to get up to speed?
(Assuming op is correct that everything looks good in the sprag clutch? And is in fact looking at the right part? )

Stupid phone / Tapatalk, apologies in advance.

[Steve Gauge]

my guess starter motor if it was solenoid (separate unit ) starter motor wouldn't engage .
Also with the back firing issue these bikes have big issues with cracking inlet rubbers .

[ducatilover]

So most likely the starter taking to long to get up to speed?
(Assuming op is correct that everything looks good in the sprag clutch? And is in fact looking at the right part? )

Stupid phone / Tapatalk, apologies in advance.

The sprag clutch is bolted on behind the flywheel, so one assumes the OP hasn't removed the flywheel yet.
I haven't yet seen a starter that doesn't spin fast enough to engage a sprag clutch yet, but I have seen plenty of worn roller/rotors and porked casings/races



And Steve Gauge is very much correct about the intake boots on these, or any older Jappa

[bogan]

The sprag clutch is bolted on behind the flywheel, so one assumes the OP hasn't removed the flywheel yet.
I haven't yet seen a starter that doesn't spin fast enough to engage a sprag clutch yet, but I have seen plenty of worn roller/rotors and porked casings/races



And Steve Gauge is very much correct about the intake boots on these, or any older Jappa

I don't think sprags even have an activation speed as such, just any torque in that one direction should be enough to engage em. On my busted vfr one I found it would engage correctly at the start, but then slip and disengage at higher rpm.

[ducatilover]

I don't think sprags even have an activation speed as such, just any torque in that one direction should be enough to engage em. On my busted vfr one I found it would engage correctly at the start, but then slip and disengage at higher rpm.

Yeah you can often make them engage at very low rpm until it hits compression stroke :spanking: