Black sooty plugs

[ukjules]

I have always had black sooty plugs on my GS550E 1980 on Plugs 1,2,3 - 4 seems to always be ok.
this happens after a plug clean and say 100 miles.
It seems to make it idle perfectly i have to endure this.

One other point to note before comment is this:
I ride the bike like an old woman ! Hard to admit but 99% of the time I only do
6000 revs and at that build up slowly. I have never hammered it.
the bike is worth so much to me I dare not hurt the poor dear machine !
So bear that fact in mind when looking at the following stats :

Before head rebuild Detail: for last 3 years before current work below

Plug gap - 0.6-0.7
Valve clearances set
Timing spot on
Carbs balanced
Oil leaks around upper gaskets
ill fitting air box on carb intakes
Poor / not possible to idle
poor but adequate fitting exhaust pipes to head. (4 - 1 motad)

Mixture screw - Cy 1 2 3 4
Here I went down to 3/4 turn on Cy 1,2,3 but always 2 1/4 on 4.
It was then better for sure but would in no way idle.


After new cylinder and Head rebuild: a few months ago and current state.

Plug gap - 0.6-0.7
Valve clearances set
timing spot on
Carbs balanced
Valves lapped
New oil seals
Head skimmed
New gaskets (no oil leaks)
Slightly better fitting air box on carb intakes
Perfectly fitting exhaust to head (Same 4 - 1 motad)
runs like a dream - and will tickover perfectly

Mixture screw - Cy 1 2 3 4
2 2 2 1/4 2 1/4
Result - Cy 1,2,3 black / sooty
4 ok.
not done more tweaking that that at present but will depending on what people think.

So remember the bike now runs like a dream but has black sooty plugs as it always has done !

Is it a case of open the gad darned throttle more ?

Jules

[tkent02]

Open the throttle. Wind it out. Do it again and again.

We have had this conversation before. The 550 is designed to be run at high RPM. It doesn't even start to make it's real power until after about 7,000.
In 140,000 or so mies I have never ridden it without redlining it at least a few times. The throttle is wide open more often than not. Nothing has ever failed.

Remember it was designed this way, to make it's best power at high RPM. Running it as it was intended can't hurt it.

[Eli69]

valve seals maybe? are you burning oil?

[ukjules]

you are right we have had this conversation before.
It is at least the only advice i have not taken but only due to my ill informed concern to my bike.
My hand will not turn past 6000 revs but I will solve that issue.

I will do as you say this time and ride it hard .... ish and check the difference.
As it is going so so so well it absolutely has to be the slow riding that is the issue.
(not that it is an issue if i clan the plugs regularly)

Trust me on my old Honda Fireblade (now sold) i never had this slowness / low rev issue.
Only on bikes that matter.

will report on this supersonic increase in revs,

[ukjules]

New valve seals put in on the head rebuild.
(no difference on the plugs)

no oil leaks, no smoke out of exhaust now.

the constant is driving like an old woman though.

[uk gs nut]

Try a hotter range plug, if you have ngk 8 try 7 it may run slightly hotter and burn fuel more efficiently. Is your air filter clean and not over oiled ?.

[tkent02]

I just assumed you had B8ES plugs, are you using something different? Black and sooty is one thing, black and sooty enough to cause problems is another. Are the plugs loading up enough that it misfires?

Oil fouled would be shiny black, sooty is a fuel thing. How did you adjust the mixture screws? Is the needle and it's clip position stock? Perhaps someone jetted it for the pipe and got it too rich?

OK I read it again, #4 stays clean while the others soot up? What's different about #4? Same spark plugs?
As a tuning tool, what is your fuel consumption? You ride it gently, it should be over 50 mpg?

[trippivot]

a list of the things I can think of that make a black and sooty spark plug;

- poor quality of gasoline - water or additives in your fuel?

- short slow rides with too cold heat range of a spark plug - the spark plug needs to reach 550F degrees to self clean.

- not enough ignition timing advance

- excessive resistance in the resistor caps -- resistor spark plugs? double resisting

- needle jet slightly too rich.

- fuel not completely burning

riding slowly is fine but your spark plugs should be brown-ish and clean.

[John Park]

a list of the things I can think of that make a black and sooty spark plug;

- poor quality of gasoline - water or additives in your fuel?

- short slow rides with too cold heat range of a spark plug - the spark plug needs to reach 550F degrees to self clean.

- not enough ignition timing advance

- excessive resistance in the resistor caps -- resistor spark plugs? double resisting

- needle jet slightly too rich.

- fuel not completely burning

riding slowly is fine but your spark plugs should be brown-ish and clean.

I'd add float level to the list.

[uk gs nut]

+1 on float levels, and slight sticking of float valves. Any puddles or stains below bike when parked for some time ?

[ukjules]

I have had to get my notebook out again due to this ....

-spark plug type: NGK8 (I have never tried NGK7) does a ngk7 run slightly hotter then ?
-It is black / sooty (not oily ) and there is madly no problem at all (bar it getting sooty in a 100mile ride)
It goes like hell ! sounds brill , idles perfectly, no smoke.
- I am using poor quality petrol from Morrison's supermarket.
- petrol consumption- 45mpg (this is so approx but i reckon it is at least that)
- Timing spot on !
- air filter cleaned and re oiled 3 weeks ago. - no change
- no puddles leakage under bike or carbs
-ht leads all ok

Mixture settings:
Mixture/pilot screw - Cy 1 2 3 4
turns 2 2 2 1/4 2 1/4
Result - Cy 1,2,3 black / sooty
4 ok.

(I am yet to turn 1,2,3 down by 1/4 turns more)

Carbs:
All i have ever done with these is remove , dismantle and clean up.
note that the old engine setup (cylinder and head) gave exactly the same results - 1,2,3 sooty and 4 ok.

I have never checked the float level - due to ignorance and i remain ignorant on that subject
The needle jet has always been the same - never checked if they have been changed ...

This is almost a problem but not a problem at the same time.
I would like it running spot on though .....

[mrbill5491]

Try a hotter range plug, if you have ngk 8 try 7 it may run slightly hotter and burn fuel more efficiently. Is your air filter clean and not over oiled ?.

A higher heat range plug does not run hotter per say. What it does do is the longer ceramic electrode retains more heat to help burn off any left over deposits on the tip after combustion.

[tkent02]

I would like it running spot on though .....

Then open the throttle and wind it out!!
Chugging along is so hard on these engines! They are not designed for it.
It's not rocket science!

[mrbill5491]

Then open the throttle and wind it out!!
Chugging along is so hard on these engines! They are not designed for it.
It's not rocket science!

Yup, if you are lugging the bike in the higher gears, that could be contributing to the problem. Wind that engine out in the gears, not saying redline each time, though get it up in the rpm ranges. I typically shift around 6-7K most times.

[tkent02]

I can't imagine riding a 550 like that, it's just incredibly slow below 6,000 or so. How do you keep ahead of traffic? How do you go up hills? How do you stay awake?