Blowing black/brown smoke at high revs

[jigantor]

Hi all,

This is my first post about my first bike ('97 GS500E). I've searched the forums & the net a bit but haven't found an answer to this specific problem - many apologies if I'm covering old ground. Please feel free to direct me elsewhere if there's an answer I've missed.

MY issue is this: bought a second hand 1997 GS500E a couple of weeks ago. It seems to be in great condition, runs well, a couple of my more bike-savvy mates checked it out and gave it the thumbs up. However, I've noticed that if I pull the throttle hard, it blows a significant amount of black/brown smoke once it gets over about 9000rpm. The smoke stops if you hold the revs at that level or if the revs drop below about 9000. There is no smoking if you build the revs more gently, even up to the redline. There's no impact on performance (I didn't even realise it was happening until a mate riding behind me pointed it out).

I've got two questions:

1) is this something I should be concerned about?
2) if so, what should I do about it?

Thanks in advance,
Tim

PS From what I've read, black/brown smoke is burnt hydrocarbons which can be caused by various things, from air filters to fuel levels. However, most of what I've read seems to apply to producing smoke at all revs, not just at high revs after sharp throttle. I did read somewhere that black smoke at high revs can be caused by increased pressure blowing out built-up soot etc...not sure if that's the case?

[mister]

Not to answer your question specifically... or really at all... but *I* see no reason to go Full Throttle on the bike. Half throttle gives all the acceleration needed.

Does my bike blow dark smoke if I give it a boot full around 9k? Stuffed if I know. I'm sure it would... a fully open throttle with barely enough time to burn the fuel getting dumped into it, is sure to blow some crud out the back. But I don't need to use such throttle at such revs.

Of course, my riding is different so...

And oh... a pic of your bike please.

Michael

[ohgood]

And oh... a pic of your bike please.

Michael

2nd - pics !

the gs is supposed to blow richness at the top end like that. now, big time smokiness ? nah. it's just rich. ride and enjoy

[The Buddha]

My 89 with its increasing miles used to do this ... 25K+ miles on it at that time.
Exhaust soot collects in the pipe cos well ... it just does. Then the first rev up it blows all that crap off. Of course with time/age it will do it more and more, and spray water+oil+gas+soot out the exhaust a wee bit. Put yout hand behing it and it will be sprayed with fine droplets of it. Rub your hands together and smell it ... wakes you up better than coffee.
Cool.
Buddha.

[dauphinc]

One word: Seafoam. After engines get a few miles on them, they build up carbon. Some of that crud can be carbon blasting out. I did this to my dad's truck with 250K miles on it, and it quit blowing dark smoke. It's good to drive easy, but when you do, after a long time carbon builds up and gets gunked everywhere. If you get on it from time to time, it blasts this crud out. I just took my plugs out and poured seafoam down in the cylinders to clean them out- there was a good bit of gunk everywhere. Basically, a carbon treatment can help. If not that, the carbs could be running  a bit rich- but not noticeably if it's not sputtering. Brown smoke, from what I remember, is carbon buildups.
Just a thought.

[The Buddha]

Anything you put into the tank has the potential to get the crap out of the crap pockets in the tank - yes the famouns crap pockets strike again - and into the carbs. Aggressive cleaning I'd save for the carbs when they are in the washing trough.
Cool.
Buddha.

[centuryghost]

I'm just not sure why you are revving till 9k 

You are way past the powerband by then.

[ecpreston]

Half throttle gives all the acceleration needed.

I'm just not sure why you are revving till 9k 

worst. answers. ever.    

[centuryghost]

Half throttle gives all the acceleration needed.

I'm just not sure why you are revving till 9k 

worst. answers. ever.    

What do you have to add?

[ecpreston]

What do you have to add?

That's all, I'm not claiming any relevant contribution with that post either.  
But the bike is making just about peak HP at 9k, and shifting around 10k is pretty reasonable, so it certainly doesn't seem too silly that he might be up there. I think his bike has a problem, not his right wrist. However, without knowing if it's oil or fuel smoke, I don't know what the problem is.

[jigantor]

Thanks for the quick responses!

I'm actually very rarely up in those sorts of revs - I only noticed the problem when doing a fast takeoff to see how quickly it could move off the line (the answer? Plenty fast enough for my tastes) and my mate behind me got a faceful. Sounds like it's not a sign of imminent bike death, so I'll just keep an eye on it and see how it goes. I have discovered a (probably) unrelated thing with the fuel tank capacity though which I've put in a separate post.

Finally, as requested:





(cross posted on the 'Who are you' thread)

Cheers,
Tim

[mister]

Half throttle gives all the acceleration needed.

I'm just not sure why you are revving till 9k 

worst. answers. ever.    

Cool. I won something 

I never go full throttle and don't have any problems overtaking anything. Including B Double Trucks - that's a semi with two trailers - even when they are sitting on 100kph.

If you want to give full throttle. Go for it. maybe your bike even needs it to get there. I don't know. Whatever floats your boat.

Michael

[oramac]

Black smoke usually indicates a rich condition.  However, free reving the bike basically dumps fuel into the carbs and the unburnt fuel comes out as black smoke.  If the bike runs smoothly and you don't notice any hesitation or 'dead spots', then you should be fine.

Blue smoke would be a bigger concern...that would be oil. 

Usually the gs is a lean bike.  If you're blowing black smoke, yours may have been rejetted.  That's good.  Does it start up easily, or do you have to use a lot of choke.  If it starts up with little choke, especially when it's cool, then you've probably got a rejetted bike. 

No worries!

[dauphinc]

Well put, señor oramac.

[jigantor]

I hardly use the choke at all, even on (relatively) cool mornings - though given this is an Australian summer, a 'cool morning' is still around 15C  . Still, sounds like it's probably been rejetted.

Awesome!

[oramac]

After I rejetted my '99, I rarely used the choke, if ever.  Even on very cold mornings (at or below freezing), it would start with no hesitation.

Now my bike starts with no choke at all...ever.  But then, it's fuel injected.