Sooty 4th Plug

[tone]

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

[anikmankar]

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...

[anikmankar]

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

[anikmankar]

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 ???

[chef1366]

If the carbs are not jetted correctly or you need a valve adjustment the sync will be erratic.

[anikmankar]

Leaky carb...

I think the problem has been isolated. Check the float height on the 4th carb. There was a slight leak from the pin after it closed causing the carb to flood eventually after sometime. The drip was slow slow - that it didnt really flood the carb when the bike was off. Once the bike started and at idle or low RPM it flooded the carb.

Set the height again for this - about .5 mm more. Now no flooding. the carb is not sooting so far.

Did a manual carb bench and then with the gauges...At Idle (1000 RPM) the 4th gauge is off but at 1700 RPM all gauges are ok and synced. No issues on higher RPM also.

Looks like this has been sorted out. Now I have to just make sure my Timing is correct. I tried using the timing gun..its not picking a pulse. Will try and locate another gun which connects in series (instead using a battery and pulse).

Thanks guys..

[Steve]

First of all, many thanks for providing details on the bike and what has been done to it.

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)

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 ????

-) 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/

Nice to see that you might have this one licked, finally. \\/

However, there are a few things that need to be addressed:
1. Carb sync is the last thing to do in the adjustment sequence. Recommended sequence is valves, timing, carbs.
2. Factory manual says to do carb sync at 1500-2000 rpm. I usually do it at about 1200.
3. Yes, carb #3 is "fixed", all the others should be adjusted to match it, but the factory manual specifies adjusting #2 to match #3, then adjusting #1 to match #2&3, then adjust #4 to match the others. Note that on bikes with a crossover tube between exhausts 2&3, the vacuum reading should be about 1/2 cm lower than 1&4.
4. You keep mentioning PSI readings. Vacuum is measured in cm of mercury or inches of water. PSI is a pressure measurement. Are you using analog gauges (with needles) or liquid in columns? Either way, a lower vacuum reading indicates that cylinder is open a bit more than the others.


.

[anikmankar]

First of all, many thanks for providing details on the bike and what has been done to it.







Nice to see that you might have this one licked, finally. \\/

However, there are a few things that need to be addressed:
1. Carb sync is the last thing to do in the adjustment sequence. Recommended sequence is valves, timing, carbs.
2. Factory manual says to do carb sync at 1500-2000 rpm. I usually do it at about 1200.
3. Yes, carb #3 is "fixed", all the others should be adjusted to match it, but the factory manual specifies adjusting #2 to match #3, then adjusting #1 to match #2&3, then adjust #4 to match the others. Note that on bikes with a crossover tube between exhausts 2&3, the vacuum reading should be about 1/2 cm lower than 1&4.
4. You keep mentioning PSI readings. Vacuum is measured in cm of mercury or inches of water. PSI is a pressure measurement. Are you using analog gauges (with needles) or liquid in columns? Either way, a lower vacuum reading indicates that cylinder is open a bit more than the others.


.

1. Carb sync is the last thing to do in the adjustment sequence. Recommended sequence is valves, timing, carbs.
Mine is has CDI so will have to do carbs first
have done the Valves, CArbs, Timing - on the weekend.

2. Factory manual says to do carb sync at 1500-2000 rpm. I usually do it at about 1200.
The carbs got sync'd at 1700. At 1200 the needles were not getting in line

3. Yes, carb #3 is "fixed", all the others should be adjusted to match it, but the factory manual specifies adjusting #2 to match #3, then adjusting #1 to match #2&3, then adjust #4 to match the others. Note that on bikes with a crossover tube between exhausts 2&3, the vacuum reading should be about 1/2 cm lower than 1&4.
since I have 4-into-1. All the needle are set to be in line. I have done the setting slightly different. but the end result is same - I think

4. You keep mentioning PSI readings. Vacuum is measured in cm of mercury or inches of water. PSI is a pressure measurement. Are you using analog gauges (with needles) or liquid in columns? Either way, a lower vacuum reading indicates that cylinder is open a bit more than the others.
Good catch - you are right thats in CM's. Using Analog Guages

thanks