Honda CBR 600 FX Mystery Mis-fire

[Pomeroy94]

Calling on all gurus!

Got a Honda CBR 600 FX 1999 with 20K - carb’d model (never buying a bike with carbs again)

Bought in February 2019 and run roughly 1K on it been fine since, started riding one day about a month ago and a misfire developed out of nowhere which also had it running completely lumpy like bunny hopping a car at low revs.

Had the carbs, jets and bored cleaned by a garage, plugs changed and also balanced at the same time. Compression test was fine so head and pistons are fine. Slight oil on the plug for 4 so changed and has been ok since. Ran ok for a week and then back to square one started lumpy as hell again at low revs.

1&2 are fine 3 is slow-er but only marginally, 4 was cold until revved and it pulled through but still hunting on idle - has started brightening and dimming the lights now which I didn’t notice before but I haven’t run it at night so now thinking Rectifier? Don’t know for sure and I’m bored of parts darts!!

Checked the air lines, vac lines and air pipe asst under the air box. Put a new OEM air filter in for good measure too. Also it had a new fuel pump just before I had it.

Now ready to set it on fire. Help!!

[Rubin215]

Do the standard electrical and charging tests; voltmeter across the battery terminals should give you around 12.5v with the ignition on but the engine not running, 13-14.5 with the engine running at a high tick-over (1500rpm).
Revving the engine higher should not make a difference to the voltage, if it does your regulator is knacked.

[Matt_E_Mulsion]

Ignition coil breaking down???

[Adam_W]

Matt_E_Mulsion said:

Ignition coil breaking down???

I was about to suggest coils and leads if it has them (they stick coils or is this too old?)

[Matt_E_Mulsion]

It could have two coils, each supplying a pair of cylinders.

[Pomeroy94]

Matt_E_Mulsion said:

Ignition coil breaking down???

Swapped coils and made no difference to the missing, 4 was still cold. Has ignition wires which run individual plugs to each coil stick

[Pomeroy94]

Rubin215 said:

Do the standard electrical and charging tests; voltmeter across the battery terminals should give you around 12.5v with the ignition on but the engine not running, 13-14.5 with the engine running at a high tick-over (1500rpm).
Revving the engine higher should not make a difference to the voltage, if it does your regulator is knacked.

Will give this a go, Thank you, so standard tick over no choke and then rev to see if any fluctuation on voltage?

[Pomeroy94]

Adam_W said:

Matt_E_Mulsion said:

Ignition coil breaking down???

I was about to suggest coils and leads if it has them (they stick coils or is this too old?)

4 coils each with individual plugs fed from a singular ignition wire. Swapped them but made no difference moved 3&4 to 1&2 and still cold on start for 4 and slow to warm on 3 so It’s some form of breakdown for supply to cylinder 4 but not internal which made me think electrical and it’s not the coil ( I assume from my swap test) so I would then guess supply to the coil but I’ve got voltage at the plug on the wire

[Matt_E_Mulsion]

Have you swapped the actual spark plugs???

[Pomeroy94]

Matt_E_Mulsion said:

Have you swapped the actual spark plugs???

I haven’t... only because they were changed 2 weeks ago & it was the same symptoms before hand I hadn’t really entertained the plugs being an issue, however I have been proved wrong many a time before lol

[dibblecorse]

It's not T57 DHY is it ?

[Pomeroy94]

dibblecorse said:

It's not T57 DHY is it ?

Nope, V Reg, I'll assume thats an old one of yours with the same issue? looking online this issue seems to plague the 95-00 Carb'd models with no one finding a real solution - well posting a solution I don't believe so many ended up scrapped because of it lol

[Pomeroy94]

Rubin215 said:

Do the standard electrical and charging tests; voltmeter across the battery terminals should give you around 12.5v with the ignition on but the engine not running, 13-14.5 with the engine running at a high tick-over (1500rpm).
Revving the engine higher should not make a difference to the voltage, if it does your regulator is knacked.

No good, its got consistent voltage on ignition live, tick over and with revs, was kind of hoping it would be fked so I at least knew what the problem was lol but alas, the bike is still fubar'd

[Matt_E_Mulsion]

If it's had new plugs then you can dis-count that. I just couldn't work out if you had renewed them or not.

[Pomeroy94]

Matt_E_Mulsion said:

If it's had new plugs then you can dis-count that. I just couldn't work out if you had renewed them or not.

Damn. Running out of diagnostic ideas lol

[Krikkit]

Could be a few things, I'd start with a crank sensor.

If you can't get very far with it I'd check the ECU for a dry joint on the circuit boards.

[Pomeroy94]

Krikkit said:

Could be a few things, I'd start with a crank sensor.

If you can't get very far with it I'd check the ECU for a dry joint on the circuit boards.

Any ideas off the top of your head where the crank sensor is on a FX before I go searching?

Do these have an ECU? I thought the CDI/ECU on this model was for the ignition barrel and ignition purpose only?

[Krikkit]

Pomeroy94 said:

Any ideas off the top of your head where the crank sensor is on a FX before I go searching?

Do these have an ECU? I thought the CDI/ECU on this model was for the ignition barrel and ignition purpose only?

I think, from a quick Google, it should be on the exhaust cam on the left-hand side of the bike. That's for a 2001 bike though, so a 99 might be slightly different. If not, I think it should be straight-forward to track down from the loom based on this:



Anything numbered isn't the sensor, so that only leaves a couple in the engine region. It could be crank or camshaft sensor.

I know the bike is an injection-only controlled machine, but it still needs a sensor to dictate the exact position of the engine for timing the spark.

Edited by Krikkit on Thursday 26th September 08:40

[Prof Prolapse]

"Parts darts", love it. It sounds like you've ruled out some fairly serious issues and they're simple bikes so don't worry too much, you will get there. It simply has to be Fuel/Air/Spark. Personally I'd not be too worried about sensors etc, just yet.

Not an expert but do have one of these bikes and have had it apart a lot... If you're confident the poor lighting is significant, I'd be staying with spark as you can test most of it with a voltmeter, and work methodically and not assume anything. Look at it as a list of things you need to know are working;

• Battery
• Plugs
• Coilpacks - Visual inspection of insulating rubbers. Resistance test. Swap around.
• Regulator - Hard to test. As above, voltage across ignition should be measured <13.5 and consistent across rev range, but sometimes failures can be intermittent. Given their high failure rate, I keep a known good one handy to test I bought for buttons on ebay (I'd not recommend running a cheap on on the bike long term however).
• Stator coil - There's a three pin plug easily accessible on your bike. Inspect it for signs of damage (they can produce high voltage in their death throws and melt) then unplug. There are three pins, each corresponds to a copper coil within the stator, you can test each of the coils very easily without removing anything. I've not done it in years but just youtube it for a guide.

The rectifier is located under the seat fixed to the frame with two slightly awkward bolts. Testing can be difficult, you can only really do a "diode" test to ensure things are flowing in the correct direction. Personally I have a spare cheap Chinese rectifier I use to know if it's failed (again).

You're not near Edinburgh are you?

[ssray]

Take the plugs out, check them and put them in different cylinders
Could quite easily be a plug