Running on 3 cylinders (Random cylinder at fault)

[Clanky]

Hello,

I've been chasing a frustrating issue with my bike's starting/idling. It's an FZR 400 but uses re-jetted FZR 600 carbs (this is not a mod but a standard factory set up) which is why I'm asking on this board for help. I have been experiencing occassional issues with the bike running on only three cylinders until it has warmed up after a couple of minutes and then it seems to be fine.

It began to be harder to start (I'm in the UK and the weather is warm/mild), strong cranking but it just wouldn't fire straight up and using the choke seemed to make this worse. If I gave it part throttle it would eventually catch and start to fire but the revs rose slowly to about 1000 rpm before finally going up in a sudden rush. I thought this may be due to just three cylinders firing properly and then the lazy one kicking in. After about a minute it was fine. However, the misfiring cylinder would change each time. Sometimes it was 1 or 4 and other times 2 or 3.

I have swapped over both sets of coils for spares and the same issues continue (I haven't tested the coils with a volmeter but it would be very unlucky for all the coils to be bad) All the leads and caps have been checked and look fine.

Plugs were new about a thousand miles ago. Pulled them out yesterday and they were very clean. 1,2, and 4 had no real colouring at all and 3 was a nice clean tan colour.

I have stripped and cleaned the carbs thoroughly twice now and all the jets and passages are clear and the jets are the correct stock sizes. Emulsion tubes show no obvious signs of ovalling. Fuel pump works fine.

The engine was a second hand replacement that I put in 1000 miles back and the valves were checked and all within spec.

Carb and air filter boots are sound so no obvious vacuum leaks.

Today I have reset the float heights to 24mm from 22mm and this has helped with the starting and it idles great when warmed up and it will now take use of the choke. Mixture screws 2 3/4 turns out. Carbs were re-synched afterwards with a vacuum gauge. However, I'm still getting a cold cylinder on initial start up and the randomness of which cylinder decides to play up is really confusing me. I'm completely out of ideas now. Any advice would be really appreciated.

[MaParkerColo]

Not an expert on this, but my first thought reading you post was coils, but you appear to have eliminated that. Which leads me to my suggestion. Could your TCI be failing? If I am remembering this correctly it is going to control the coils and how and when cylinders fire. I can't exactly envision how it could be failing such that the problem would move from cylinder to cylinder though, but it would be something to think about. If you could get a hold of a know good one you could just plug it in and see if your problem disappears.

Have you carefully cleaned all the connections in the circuit too? Poor connections at terminals have been the source of many peoples misery over the years especially on bikes that are almost 20 years old now.

Just something else to chase, but hopefully it helps,
Mark

[Clanky]

Thanks Mark,

I'll get a voltmeter and start testing the coils and TCI, I'm not very clued up on electronics but there's plenty of guides on the web to help. I did look at the connections and they were clean but I gave them a shot of electrical cleaner anyway. I've got a few days off coming up and I would like to get this fixed soon.

[DonTZ125]

The plugs fire in pairs, so if 3 cylinders are firing, the coils and TCI are good. You might have a bad plug or cap.

I realise you've cleaned your carbs, but it really sounds like either the pilot or starter jet on that cyl are fouled or otherwise damaged.

[Sooty]

Had a similar problem to this on my 600. Would only happen when cold, checked out the coils & plugs, replaced HT leads and caps, cleaned out the carbs and reset the float heights, did a compression test and still it was missing when cold. Once warm would run on all four and pull like a train. Finally one day it decided to run on only two cylinders from cold and wouldn't clear, suspected fouled plugs or failed coil and took the plugs out to check them (cylinders 2 & 3), laid them on the rocker cover and started the bike up. What I found was the plugs were fouled and there was oil coming out of the engine! Stripped the head off the engine to find the valve stem oil seals had gone. What was happening, when stood overnight, oil was seeping past the seals and dripping into the inlet tract. As soon as you started the engine the plugs were getting a unhealthy spray coating of oil and fouling. With only the oil weeping into the engine over time (probably 3 or 4 drops) there was no clouds of smoke when the engine was running as a clue and nothing to worry about when starting. Take your carbs off and look down the inlet tracts, if they are bright aluminium then it probably is not your valve seals. If there is discolouration (dirty oil stain) then chances are it will be your valve stem seals. On mine 1&4 were bright & shiny 2 & 3 were discoloured.

[Clanky]

Thanks for the tips everyone,

Sorry for the late reply but I've been distracted with work and house repairs. The bike still occassionally plays up but not so much lately. I can put up with it for now but I'll have another look over everything when I get the time. If I can confirm the fault I'll post it up.

Cheers

[HybridSport600]

The cdi unit is electrical, and usually when electrical fails, its just plain done.buy 4 cheap little inline bulb spark testers and put them on all for, look for spark. I would say from the info you gave , that I would suspect fuel/air mixture. You stated that it runs a little better with a float height adjustment from 22 to 24, you have actually lowered the the amount of fuel allowed into the bowl. which would say that it was getting too much... with it running better hence the use of the choke now.......I would take the floats out of all carbs and float them in a large boowl of water. Gas is heavier than water and will sink. If they are seeping gas into the float it will sit deeper in the water. With the weight of the float its self, you want to see about 3/4 of the float or more above the water line to be good. any less then remove it and shake it heavily right next to your ear and listen for liquid sloshing around inside. A bad float will actually flood it enough to kill the spark and can explain the cleaner plugs than the one that was good to be the tanish color. Let us know!

[LoneFizzer]

The cdi unit is electrical, and usually when electrical fails, its just plain done.buy 4 cheap little inline bulb spark testers and put them on all for, look for spark. I would say from the info you gave , that I would suspect fuel/air mixture. You stated that it runs a little better with a float height adjustment from 22 to 24, you have actually lowered the the amount of fuel allowed into the bowl. which would say that it was getting too much... with it running better hence the use of the choke now.......I would take the floats out of all carbs and float them in a large boowl of water. Gas is heavier than water and will sink. If they are seeping gas into the float it will sit deeper in the water. With the weight of the float its self, you want to see about 3/4 of the float or more above the water line to be good. any less then remove it and shake it heavily right next to your ear and listen for liquid sloshing around inside. A bad float will actually flood it enough to kill the spark and can explain the cleaner plugs than the one that was good to be the tanish color. Let us know!

The FZR has a TCI, not a CDI, Gas is actually lighter than water, thats why it floats on water. I do agree that floats can leak however that was common on old Brass floats, Plastic floats are far less likely to leak. The simplest and easiest way to test the floats for leakage is shake it near your ear, I doubt thats the fault tho. Don't waste your time putting them in water.

You could buy a Motion Pro Spark Tester, set it to 6mm. If you see a Strong Blue Spark on all 4 plug leads your ignition system is probably fine. Knowing how harsh the British weather can be on motorcycle electrics, you should if you haven't already, Inspect every connection from the battery upwards to the ignition system including the Solenoid, Ignition Switch, Pick Up Coil, TCI E.T.C. When you are sure your electrical system is fault free turn your attention to the carbs

Good luck

HS6 I admire your enthusiasm, however your inexperienced incorret advice only serves to make things more difficult for everyone including the OP

[HybridSport600]

A transistor Ignition unit applys with the same principal as a capcitor unti as well, its all based on an electronic circuit. and if it gets fried, sizled, toasted whatever you wish to call it, its still DOA, and will not work and then not work on osacion, it simply stops as the circuit has been broke. I actually have over 20years of exp, but everyone is entitled to thier opinion I guess...I agree with a brass float is more likely to leak down due to the brazed union of the two halfs, but fuel effects all materials differently and this includes "Plastic". The plastic ones are actually more likely to develope this condition due to the same chemical makeup (petroleum), And I have seen it happen on many different types of bikes including quads and snow machines. If it is stored in cold temps for a length of time and is cold enough the gas can freeze, and will split the floats. Simply that you have not expierence this condition Im guessing, does not make me inexpierenced nor a waste of this poster's time, but simply another possibility to cross off his list. Plastic floats are in fact a product of petrolium, as well as the gasoline used in our machines and will slowely deteriorate the longer exposed. if you knew anythng at all about gasoline and the chemistry of the different components and that they have different freezing temperatures per type and grade, the boiling point and the freezing point as well is different. Get gasoline cold enough and it will freeze. The actual freezing temperature will depend on subtle properties of its constituents.

[reelrazor]

A transistor Ignition unit applys with the same principal as a capcitor unti as well, its all based on an electronic circuit. and if it gets fried, sizled, toasted whatever you wish to call it, its still DOA, and will not work and then not work on osacion, it simply stops as the circuit has been broke. I actually have over 20years of exp, but everyone is entitled to thier opinion I guess...I agree with a brass float is more likely to leak down due to the brazed union of the two halfs, but fuel effects all materials differently and this includes "Plastic". The plastic ones are actually more likely to develope this condition due to the same chemical makeup (petroleum), And I have seen it happen on many different types of bikes including quads and snow machines. If it is stored in cold temps for a length of time and is cold enough the gas can freeze, and will split the floats. Simply that you have not expierence this condition Im guessing, does not make me inexpierenced nor a waste of this poster's time, but simply another possibility to cross off his list. Plastic floats are in fact a product of petrolium, as well as the gasoline used in our machines and will slowely deteriorate the longer exposed. if you knew anythng at all about gasoline and the chemistry of the different components and that they have different freezing temperatures per type and grade, the boiling point and the freezing point as well is different. Get gasoline cold enough and it will freeze. The actual freezing temperature will depend on subtle properties of its constituents.

Clanky, get your bike outa that -100°f blast chiller!

I have not experienced the condition where gasoline is heavier than dihydrogen monoxide. I HAVE experienced many many customer's fuel tanks with 'globules' of water at the bottom of the tank....and have repleced a number of fuel tanks that rusted at the seams at the bottom of the tank. Coincidence? I think not,

[LoneFizzer]

A transistor Ignition unit applys with the same principal as a capcitor unti as well, its all based on an electronic circuit. and if it gets fried, sizled, toasted whatever you wish to call it, its still DOA, and will not work and then not work on osacion, it simply stops as the circuit has been broke. I actually have over 20years of exp, but everyone is entitled to thier opinion I guess...I agree with a brass float is more likely to leak down due to the brazed union of the two halfs, but fuel effects all materials differently and this includes "Plastic". The plastic ones are actually more likely to develope this condition due to the same chemical makeup (petroleum), And I have seen it happen on many different types of bikes including quads and snow machines. If it is stored in cold temps for a length of time and is cold enough the gas can freeze, and will split the floats. Simply that you have not expierence this condition Im guessing, does not make me inexpierenced nor a waste of this poster's time, but simply another possibility to cross off his list. Plastic floats are in fact a product of petrolium, as well as the gasoline used in our machines and will slowely deteriorate the longer exposed. if you knew anythng at all about gasoline and the chemistry of the different components and that they have different freezing temperatures per type and grade, the boiling point and the freezing point as well is different. Get gasoline cold enough and it will freeze. The actual freezing temperature will depend on subtle properties of its constituents.

I agree that most intermittent faults are electrical, I disagree that on a four carb system a leaking float would cause intermittent faults on all 4 cylinders. Clanky is in Portsmouth UK so I doubt he nor his bike has ever experienced -100 F the freezing point of Gas/Petrol. From the original post I can tell that Clanky Knows his stuff, he probably even knew that Gas/Petrol was lighter than water.

[reelrazor]

Yes, back to topic..

Clanky, has this engine had a compression check?

Or better yet, a cylinder leakdown test?

Poor compression causes poor vacuum, which in turn causes poor/inconsistent carburetion.

Tight/leaky intake valves would be consistent with your poor performance/startup issues, that get better with engine heat. Luck of the draw comes into play when starting a multicylinder engine like this. Two or three random holes fire-they develop the heat which helps seal the valves(as well as draw the fuel which helps to act as a sealant)...the other cylinder(s) have to go along for the ride and at some point join the party.

[LoneFizzer]

Yes, back to topic..

Clanky, has this engine had a compression check?

Or better yet, a cylinder leakdown test?

Poor compression causes poor vacuum, which in turn causes poor/inconsistent carburetion.

Tight/leaky intake valves would be consistent with your poor performance/startup issues, that get better with engine heat. Luck of the draw comes into play when starting a multicylinder engine like this. Two or three random holes fire-they develop the heat which helps seal the valves(as well as draw the fuel which helps to act as a sealant)...the other cylinder(s) have to go along for the ride and at some point join the party.

Great advice, may I add that a weak spark wont fire up a cold cylinder, a weak spark will or can however fire up a warm cylinder. Think about battery voltage say 12V, when cranking it may drop to 10V. If you have poor connections anywhere leading to the ignition system you could have 10V max to the ignition system/coils, whilst cranking it could drop to 8V which equals poor starting, if the coils are supplied with a lower voltage than what they demand you get a weaker spark. A warm engine can run with a weak spark, a cold engine wont, also if the pick up coil is contaminated with water rust or any contaminates that can play havoc.

When living in a -100 f environment check your floats, your gas has frozen

[Clanky]

Thank you,

Lots of helpful advice and I do appreciate everyones input May be a while until I get a free weekend to crack on with things but I'll let you know how it goes.