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Sooty 4th Plug

  • Thread starter Thread starter anikmankar
  • Start date Start date
A

anikmankar

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The 4th plug seems quite sooty and comes off easily with wiping it genthly (no wire brush required). I am runnng the following...

- ) 4into1 - V&H
- ) K&N filter (stock type)

have checked the following
- Float height - all ok
- Air screw - set to bursen blue using colortune - The colour is all ok at idle (blue), flick (yellow) and steady RPM (Blue).
- Balanceed all carbs using vacumn (however a little difficult to get the 4th cylinder to sync). If sync'd at idle - high RPM goes for a toss and vice versa for Cyl 4
- Plugs : NGK iridium plugs...
- CArbs all cleaned - no leaks
- All the other plugs are nice and grey

I have not yet checked the valve clearance ....could this be the reason for it to soot ?


Model : 1981, GSX750 (Alias GS750E)

thanks
 
good spark

good spark

Spark is very good...The Plug is dry...no smoke from the exhaust but do smell fuel when the bike is running.
 
Have you checked to make sure that the choke slide is not hanging up on that carb? It could be valves. If things are getting too tight, you'll have less air on the intake stroke less exhaust getting out and thus be running rich.
 
Last edited:
Choke ok

Choke ok

The choke side is ok...The Idling is perfect ...response on throttle is also great...
 
valves ok

valves ok

Checked the valves - some were slightly off except the 4th cylinder.

Anyways got them all set ...rode the bike ...BUT the 4th one is still covered with Black Soot.

I interchanged the plug wires and coil - maybe be a bad coil. but still the plug is black.

When i tried to balance the carbs...noticed that I am unable to get the 4th cylinder to sync at idle - at high RPM 2500K , I am able to sync it but then the idle is going for a total toss. I usually leave the balance at 3000 K as that where i am when I ride

Would a Rich Carb cause this ? The colortune is showing all ok at idle (blue), Blip (Yellow) and steady High RPM (Blue)
 
I would think weak spark, but you already covered that. Maybe someone previous had been adjusting the carbs & tried to adj the #3 screwing up the baseline
 
baseline ?

baseline ?

What do you mean by up the baseline ?

cylinders 1,2,3 can be sync in line...the 4th shows a higher level on the vacumn gauge.
 
all in line

all in line

Have managed to sync (in line) with 3 - so now 1,2,3 are all in sync at all RPM's...the 4th goes for a toss.

At Idle : Cant adjust the 4th to be in line with the other 3 cylinders (or even the 3rd). The vacumn need for the 4th is aways about couple of PSI above the 3rd one. Adjusting it makes it worse.

At 2.5K : Increase the idle to 2.5 using the throttle cable screw - sync them all in line and then bring the idle down, but the bike runs like crap after it... plus I notice if i do that...the 4th one opens a little late from idle.
 
The first sync can be a pita. Bring four down to three and mess around with them. You'll see that one will affect the others.
Keep plugging at it. You'll get it.
Make sure a couple of fans are blowing on the headers.
 
4 remains there

4 remains there

I just cant get the 4th one down to level with 3rd.

If i back out the adjust screw completely it still remains a couple of PSI higher. The 4th cylinder needle is higher than the 3rd (and the rest) - I think indicate there is less vacumn.

IF i screw it in the difference between will increase and the 3rd level with also decrease hence effectivitly increasign the gap...hope not too confusing.
 
You need to lower the other two to lower the idle and bring four down.
 
not happening buddy - not happening.

I have tried all tricks ...

BTW - should the adjustment be done at idle or at cruise rpm (2.5 / 3 )?

from what i understand...

3 is fixed
1/2 - the link between these 2 will level my 1 and 2 carbs
3/4 - will level 3 and 4 (so this is step 2)
2/3 - will level 2 and 3 hence need to level 1 /2 first. and at this point since 3/4 are in sync and 1/2 are in sync...will sync all 4

correct ????


maybe i should back them all out and start all over again to sync..any specific order or the above is correct.

Thanks for your inputs////
 
Ive noticed the advice given here about syncronising carbs at a high tickover a few times & that confuses me :|

from the dynojet fault finding sheets i have the reccomendation is to sync at the lowest possable idle where you can get a reading, ive lost count of the times ive re balanced carbs for people who have not followed this simple rule, it can be a pain to do but works

so sync at a lowest tickover possable then pick the tickover up to normal & all should be well

Another point modern unleaded fuel usually gives a slightly black (but dry sooty) look to plugs & exhaust outlets so the old rules that worked with 4 star leaded fuel have changed slightly
 
thanks for the input...

only the 4th has the "sooty" problem

Regarding the sync...I have tried it at idle (lowest rpm)..the 4th just does not tick. The 4th still showed a higher vacumn that all the rest...
 
still not in sync

still not in sync

Well i tried to sync them all over again...back out all screws...

-) increase the rpm via the throttle stop screw.
-) sync'd 4 to 3 - no issues.there
-) reduced the RPM to idle
-) Synced 1 to 2 - had to increas the rpm to idle
-) 3 and 4 were will in sunc
-) Balanced 1&2 to 3&4 - 1,2,3 sync'd but 4 showd less vacumn (a little high on the needle)
-) Adjusted idle to 1K
-) Bike tick properly but the 4th one is still off by could of PSI's
-) Increase the RPM via throttle to 2. and2.5 - all needle show synd/

Unclear - why the 4th one is giving problem at idle. However, bike rides ok...no issues at crusing, pickup and idle.

BTW - 4th one is still dry sooty
 
4th opening a little late

4th opening a little late

Just realized ...while doing a visual check noticed the 4th link is opening an 1MM late. i.e. when i open the throttle slowly i can see the other 1,2,3 opening sligltly before the 4th.


I think i need to take the carbs out and do bench sync first.

WILL A RICH CARB CAUSE THE UNEVEN SYNC ON THE GAUGE ???
 
If the carbs are not jetted correctly or you need a valve adjustment the sync will be erratic.
 
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