Honda CBR 600 FX 1999 hunting/surging/weird symptoms

[Pomeroy94]

Evening all,

I’ve got a Honda CBR 600 FX (carb version not FI), this is my first bike since February with 20k on the clock, been faultless for 1000miles on a hot day last weekend I went for a ride for about an hour and on the way home it stalled pulling away after what I can only describe as bogging down/lumpy behaviour.

Pulling away anything less than 1/2 throttle was lump lump lump and stall if you didn’t pin it then suddenly it would burst into life, once above 30mph and 4K revs it was ok again, started in first up to 30mph 4Krpm then by the time I was home it was 1st&2nd gear up to 4kRPM.

The lumpy behaviour is very sudden and on set, no other symptoms except a minor oil leak from the gear changer area - specific unknown not found it yet as haven’t cleaned it up to see where it originates.

Could this be carbs need jetting/balancing? If so why would they suddenly behave like this, I’ve not got any experience with carbs so I’m just drawing on car knowledge and trying to apply rationally.

Any pointers appreciated! I have planned to try and get it over to a mechanic late this week but just looking for an FYI type scenario where I may be able to DIY Repair.

[Sammo123]

My 2000 CBR600 FY carb model does exactly this! Two different garages couldn’t figure out what was wrong with it so it ended up getting parked in my garden and left. That was about 5 years ago!

[FredClogs]

There's a voltage regulator under the rear fairing, check that out.

[Pomeroy94]

Sammo123 said:

My 2000 CBR600 FY carb model does exactly this! Two different garages couldn’t figure out what was wrong with it so it ended up getting parked in my garden and left. That was about 5 years ago!

Christ... doesn’t instil confidence lol! I have read online about not the plugs but there’s a tip like a rail that the plugs sit below that has caused an issue previously.. what did the garages go through diagnosis wise? I suspect either dirt in carbs or carb issue but can’t be certain

[Pomeroy94]

FredClogs said:

There's a voltage regulator under the rear fairing, check that out.

Tested reg/rec in terms of output and all is well so far.. doesn’t mean it’s not faulty but from output it’s ok, reckon it could be throwing a spike?

[Sammo123]

Pomeroy94 said:

Christ... doesn’t instil confidence lol! I have read online about not the plugs but there’s a tip like a rail that the plugs sit below that has caused an issue previously.. what did the garages go through diagnosis wise? I suspect either dirt in carbs or carb issue but can’t be certain

It was such a long time ago I honestly can’t remember what was and wasn’t checked. They were both pretty thorough though. The issue made the bike nigh on impossible to ride hence me parking it up.

[FredClogs]

Pomeroy94 said:

FredClogs said:

There's a voltage regulator under the rear fairing, check that out.

Tested reg/rec in terms of output and all is well so far.. doesn’t mean it’s not faulty but from output it’s ok, reckon it could be throwing a spike?

I think they either work or they don't, I had mine for 4 years and it's the only thing I ever had to fix (until it went down the road), but I'd must have replaced it 2 or 3 times. similar symptoms, wouldn't tick over well and you had to gun it to get it to take off.

[Smiler.]

I had a similar issue with a VTR1000.
It turned out to be something blocking the air intake when at low speed.
Probably unrelated, but I thought it worth a mention.

[Pomeroy94]

FredClogs said:

Pomeroy94 said:

FredClogs said:

There's a voltage regulator under the rear fairing, check that out.

Tested reg/rec in terms of output and all is well so far.. doesn’t mean it’s not faulty but from output it’s ok, reckon it could be throwing a spike?

I think they either work or they don't, I had mine for 4 years and it's the only thing I ever had to fix (until it went down the road), but I'd must have replaced it 2 or 3 times. similar symptoms, wouldn't tick over well and you had to gun it to get it to take off.

Would charging issues also occur though? As battery has been fine so far, has gone 2 weeks with no use and started on the button first time?

[Pomeroy94]

Smiler. said:

I had a similar issue with a VTR1000.
It turned out to be something blocking the air intake when at low speed.
Probably unrelated, but I thought it worth a mention.

Cheers dude, worth a lock could be debris in the air intake system or filter I suppose or maybe even a vac leak on an air pipe?

[FredClogs]

Pomeroy94 said:

Would charging issues also occur though? As battery has been fine so far, has gone 2 weeks with no use and started on the button first time?

Yeah, you're right.

[Smiler.]

Pomeroy94 said:

Cheers dude, worth a lock could be debris in the air intake system or filter I suppose or maybe even a vac leak on an air pipe?

From what I remember, the issue with mine was a piece of plastic which had come loose & at low speed (thus low air flow), was enough to restrict air into the carbs. When above 30/40, it was held clear. I didn't fix it, the chaps where I got it serviced did, after some dyno time (which resulted in no issues).

[gavgavgav]

(this is the same engine set up as the hornet I think) Are the carbs sitting OK on the rubber tubes to the head/ are they split? I had something like this as there was an air leak that developed when the rubber tubes aged. Needed loads of throttle to add some fuel to all the extra air.

But it could be other factors if its air related, including the PAIR valve pipes (if you have that installed), or even one of the vac connections coming loose(especially if you've had the carbs balanced recently). It's all quite easy enough to check.

[Rubin215]

Start by changing the plugs, then try stripping and cleaning the carbs.

[CypSIdders]

Had similar problems with my carbed CBR600, it turned out to be a hair line crack in spark plug.
A new plug sorted it immediately!

[P46]

Had the same bike with very similar problem and turned out to be one of the coil sticks.

[Prof Prolapse]

Not an expert but I have had possibly the most unreliable one of these bikes ever made so had it apart more times than is actually normal. They're really simply easy to work on bikes and cheap parts exist, be patient and you'll get it sorted fairly easily.

Fuel/Air/Spark, that's what you're looking at but not necessarily the order, and we can only guess without seeing the bike.

Personally, and again this is a guesstimate, I'd be more inclined to look at the fueling. The easy one is that (as with the breathers which you should also check) the fuel line can get kinked, and another one I'm aware of is that the fuel pumps on these bikes can fail. When mine did, the symptoms were similar to what you describe, I can only speculate it went at all because the vacuum created meant it could mask the symptoms of a dying pump.

Testing the fuel pump, I recall anyway, was fairly straight forward (Google it). You can also just remove it, take the top off, and look at the contacts, they get worn and it's pretty obvious. You used to be able to get rebuild kits from Wemoto for about £12, or a chinese pattern pump for the same price. In all honesty I'd rebuild it if you can despite the additional time, as cheap fuel pumps are often not great longevity wise.

There's lots of stuff it could be however, that's just a hunch, just go for the easy stuff first before you start throwing parts at it.

ETA: As above, Plugs, breathers, battery, even coil packs (check resistance) are all good suggestions to check as well!

Edited by Prof Prolapse on Thursday 25th July 09:25

[mad4amanda]

check the nylon filters on the onside of the fuel tap if it has one once they start to break up they get everywhere and can cause issues like this and more is awful stuff to get out the tank too

[vtchequers]

Sammo123 said:

My 2000 CBR600 FY carb model does exactly this! Two different garages couldn’t figure out what was wrong with it so it ended up getting parked in my garden and left. That was about 5 years ago!

Still in your garden?

[Sammo123]

vtchequers said:

Still in your garden?

Yep, sitting on the path next to the house under a bike cover. I haven’t taken the cover off in at least two years which means I haven’t started it in at least two years.