Topic: -Updated and found the problem- carb syncs telling me about other problems?

[xsmooth69x]

so im syncing my carb with sync gauges and cylinder #3 drops when throttle is applied.

this is the story.....fresh oil, bike is up to operating temperature and 2 fans are in front of the bike

i have the big idle screw about half way in and the slides all adjusted at the lowest RPM i can get it around 1200 rpm before the bike stalls and adjusted all the carbs so they are level blimping the throttle every time i screw the carbs to make sure everything lines up.

so all my carbs are lined up and the bike is idling great.

so then i decided to slowly roll on the throttle and all the carb pressure raise except carb #3 the needle starts dropping while all the other raise evenly.

i thought it might have been the gauge so i switch around the gauges and still the same thing.

my timing was set correctly before i stored the bike. Also how often does the timing need to be adjusted? and how does it get off if so?

all my air fuel mix screws are turned out 1.5 turns. i pulled the spark plugs and all of them where black so i decided to change all my air fuel screws to 1.25 turns.

bike only runs pure premium with no ethanol.

1) so what are the gauges trying to tell me if anything?

exhaust doesn't seem to be leaking on cylinder 3.

did a compression test with throttle all the way open and all the cylinders are around 120 psi......

carb boots are all perfect when i installed the carbs last. the bike was stored in my garage during the winter. full tank of gas w/ seafoam.

put about 50 miles on the bike so far.

[DJ_AX]

I'm just stabbing at it here...

cracked rubber?
Opens up with more vacuum...

[xsmooth69x]

I'm just stabbing at it here...

cracked rubber?
Opens up with more vacuum...

last time i put my carbs in they where mint.... guess ill shoot some wd40 or carb spray and see if something changes? is that how you test it again?

[lucky]

so im syncing my carb with sync gauges and cylinder #3 drops when throttle is applied.

this is the story.....fresh oil, bike is up to operating temperature and 2 fans are in front of the bike

i have the big idle screw about half way in and the slides all adjusted at the lowest RPM i can get it around 1200 rpm before the bike stalls and adjusted all the carbs so they are level blimping the throttle every time i screw the carbs to make sure everything lines up.

so all my carbs are lined up and the bike is idling great.

so then i decided to slowly roll on the throttle and all the carb pressure raise except carb #3 the needle starts dropping while all the other raise evenly.

i thought it might have been the gauge so i switch around the gauges and still the same thing.

my timing was set correctly before i stored the bike. Also how often does the timing need to be adjusted? and how does it get off if so?

all my air fuel mix screws are turned out 1.5 turns. i pulled the spark plugs and all of them where black so i decided to change all my air fuel screws to 1.25 turns.

bike only runs pure premium with no ethanol.

1) so what are the gauges trying to tell me if anything?

exhaust doesn't seem to be leaking on cylinder 3.

did a compression test with throttle all the way open and all the cylinders are around 120 psi......

carb boots are all perfect when i installed the carbs last. the bike was stored in my garage during the winter. full tank of gas w/ seafoam.

put about 50 miles on the bike so far.

Please tell us what year you have. Cheeeesssshhh!!

When you do your vacuum sync just use the "big" idle screw(the one that raises all the lifter arms) to keep the engine running.

IF the vacuum is dropping when you open the throttle it can mean that #3 exhaust pipe could be clogged up.

Do you have the tops of the carbs off to make adjustments?
No mention of that.

[xsmooth69x]

sorry its a 1975 cb550

i also have a kerker 4-1 exhaust with a cherry bomb glass pack in the back



ya the bike dosnt stall because i use that idle screw to keep it going. the reason i mentioned that is because from what i understand adjusting your carbs at the lowest RPM as possible give you the most accurate/precise

tops of the carbs off? the tank is off and i hook up an auxiliary fuel tank so i have space to work when fiddling with the screws

[TwoTired]

so im syncing my carb with sync gauges and cylinder #3 drops when throttle is applied.

so then i decided to slowly roll on the throttle and all the carb pressure raise except carb #3 the needle starts dropping while all the other raise evenly.

You are going to have make a better description.

Gauges read zero when the engine is stopped. (That's a calibration setting, as the actual pressure is 29.92 inches Hg at sea level).  The gauge indicates increasing numbers in vacuum > than 29.92 as the engine slowly increases speed.

Clearify if "dropping vacuum" means increasing numbers or numbers closer to zero on the gauge.

If I interpret your description one way, it means you have the #3 carb slide more open than others.  Another, interpretation is just the opposite.

Do make sure the valve adjusters aren't too tight.  In fact, if you are doing a carb sync ALL the 3000mile tune up items should be check and verified first.

all my air fuel mix screws are turned out 1.5 turns. i pulled the spark plugs and all of them where black so i decided to change all my air fuel screws to 1.25 turns.

The carbs on the 75 CB550 use air bleed screws for the pilot circuit. Turning inward enriches, outward leans, it's primary effect is on idle mixture and throttle twist response.  If the plugs are sooting because of slide needle position error, too large mains, or over use of the choke, the plugs will still soot even after tweaking the air screws.

[freeze]

Atmospheric pressure at sea level is 14.7 psi (zero on your gauges)....29.92 inches of Hg (mercury) is what is known as absolute vaccuum something you will never sea in the induction system of a motorcycle

[freeze]

From what I am understanding from your post, the vacuum is increasing as the throttle is applied on no. 3?
If so, I would suspect an issue with that carb, like maybe the slide isn't opening with the others. Pull the carb tops and make sure linkage is tight and watch as you open the throttle that each carb linkage moves in sync.

[crazypj]

Verify all service items (plugs, timing, valve adjustment)
Sounds like your not actually syncing carbs?
 You don't have 'pods' fitted?
High vacuum means slide is not lifting at same rate as the other 3
Need some pics of what your doing

[lucky]

With 4 into 1 exhaust the problem with #3 cylinder cannot be a clogged exhaust.

[TwoTired]

I'm not sure what you are trying to argue here.  But to make some technical corrections:

Atmospheric pressure at sea level is 14.7 psi (zero on your gauges)....29.92 inches of Hg (mercury) is what is known as absolute vaccuum

Not  really...
Definition: Absolute vacuum is a volume of space containing no matter.

...something you will never sea in the induction system of a motorcycle

You won't see an absolute vacuum anywhere on the planet.
You will see zero on the gauges when the engine is stopped.  They should be calibrated for whatever pressure exists at your location/elevation.

I believe his gauges are calibrated in inches of Hg, btw.  This would be a differential reading relative to atmospheric pressure.

[BobbyR]

i have the big idle screw about half way in and the slides all adjusted at the lowest RPM i can get it around 1200 rpm before the bike stalls and adjusted all the carbs so they are level blimping the throttle every time i screw the carbs to make sure everything lines up.

so all my carbs are lined up and the bike is idling great.

so then i decided to slowly roll on the throttle and all the carb pressure raise except carb #3 the needle starts dropping while all the other raise evenly.

i thought it might have been the gauge so i switch around the gauges and still the same thing.

my timing was set correctly before i stored the bike. Also how often does the timing need to be adjusted? and how does it get off if so?

all my air fuel mix screws are turned out 1.5 turns. i pulled the spark plugs and all of them where black so i decided to change all my air fuel screws to 1.25 turns.

I am sorry but this seems confusing which is causing all of these answers.

When synching carbs you are adjusting the height of the slides not the air screws. If you are using the air screws to even out the vacuum using is not a synch.  When you synch one carb is the reference carb, and you adjust the slide heights so that all the other carbs match the reference carbs. This means all the slides are not necessarily at the same height.   

[Vinhead1957]

I'm thinking synchronization is for idling and lines up all four for a smooth low volume fuel consumption. Everything vacuum wise is good! I'm thinking your main jet circuit is clogged. You could do a compression check on that cylinder to further investigate. Or drop the bowl and check the main jet

[lucky]

When doing a sync it IS to get the idle to be the same on all four carbs BUT....
How you do it is by adjusting height of the SLIDE not the mixture or idle screws. The slide controls the air at idle.

First make sure all four mixture screws are the same setting. LEAVE THEM ALONE.

Now get the engine running and idleing.
With the vacuum gauges connected to the vacuum ports look at the gauges.
Try to get them alll to read about 8-10lbs of vacuum at idle at 1000 RPM.

To do that you will need a 8mm wrench and and with the tops of carbs removed
Adjust #1,#3,and #4 so that they are the same as #2. Keep lowering the idle (BIG IDLE SCREW) until it is about 1000 RPM, and all of the vacuum gauges read about 8-10 lbs vacuum.


You are done.

[TwoTired]

To do that you will need a 8mm wrench and and with the tops of carbs removed
Adjust #1,#3,and #4 so that they are the same as #2. Keep lowering the idle (BIG IDLE SCREW) until it is about 1000 RPM, and all of the vacuum gauges read about 8-10 lbs vacuum.

For the 75 CB550, the carb tops do not need removal for vacuum sync.  The slide height adjusters are exposed in the connecting linkage.  In fact, all positions of the carbs can adjust individual slide height, ...which I do not recommend.  Pick the carb with the deepest vacuum reading (needle furthest from zero), declare it the master, and adjust the other carb's slide height to match the vacuum on the one which you have designated "master". Don't adjust the master's slide height at all.

Further, the indicated vacuum reading numbers don't matter much.  Of importance, is that they all read the same at end of the procedure, and they all track each other with whatever is done to twist grip.  Actual indicated number value is relatively unimportant. 

[lucky]

To do that you will need a 8mm wrench and and with the tops of carbs removed
Adjust #1,#3,and #4 so that they are the same as #2. Keep lowering the idle (BIG IDLE SCREW) until it is about 1000 RPM, and all of the vacuum gauges read about 8-10 lbs vacuum.

For the 75 CB550, the carb tops do not need removal for vacuum sync.  The slide height adjusters are exposed in the connecting linkage.  In fact, all positions of the carbs can adjust individual slide height, ...which I do not recommend.  Pick the carb with the deepest vacuum reading (needle furthest from zero), declare it the master, and adjust the other carb's slide height to match the vacuum on the one which you have designated "master". Don't adjust the master's slide height at all.

Further, the indicated vacuum reading numbers don't matter much.  Of importance, is that they all read the same at end of the procedure, and they all track each other with whatever is done to twist grip.  Actual indicated number value is relatively unimportant.

Thanks TWO TIRED. I forgot that it was a 550.

[BobbyR]

To do that you will need a 8mm wrench and and with the tops of carbs removed
Adjust #1,#3,and #4 so that they are the same as #2. Keep lowering the idle (BIG IDLE SCREW) until it is about 1000 RPM, and all of the vacuum gauges read about 8-10 lbs vacuum.

For the 75 CB550, the carb tops do not need removal for vacuum sync.  The slide height adjusters are exposed in the connecting linkage.  In fact, all positions of the carbs can adjust individual slide height, ...which I do not recommend.  Pick the carb with the deepest vacuum reading (needle furthest from zero), declare it the master, and adjust the other carb's slide height to match the vacuum on the one which you have designated "master". Don't adjust the master's slide height at all.

Further, the indicated vacuum reading numbers don't matter much.  Of importance, is that they all read the same at end of the procedure, and they all track each other with whatever is done to twist grip.  Actual indicated number value is relatively unimportant.

You have just heard from the Guru of the 550. No better info to be had.

[dusterdude]

Ot here but,how ya hangin lloyd!!!!!?

[MRieck]

You won't see an absolute vacuum anywhere on the planet.

Oh no....I guess you've never been to DC Loyd.

[TwoTired]

Ot here but,how ya hangin lloyd!!!!!?

I'm aging.  But, so far, it's better than the alternative.  I've learned to expect change with the future, as uncomfortable as that can be.

Murphy once told me I was a pessimist, btw.

I'm actively considering a new religion, if you are interested:
http://www.wikihow.com/Become-a-Full-Fledged-Curmudgeon

[TwoTired]

You won't see an absolute vacuum anywhere on the planet.

Oh no....I guess you've never been to DC Loyd.

I was there once in the mid 80's.  So, it's been awhile.  I recall thinking many areas were rather pretty, even pleasant. 
Are you saying all the gas bags have been repelled? 

[lucky]

so im syncing my carb with sync gauges and cylinder #3 drops when throttle is applied.

this is the story.....fresh oil, bike is up to operating temperature and 2 fans are in front of the bike

i have the big idle screw about half way in and the slides all adjusted at the lowest RPM i can get it around 1200 rpm before the bike stalls and adjusted all the carbs so they are level blimping the throttle every time i screw the carbs to make sure everything lines up.

so all my carbs are lined up and the bike is idling great.

so then i decided to slowly roll on the throttle and all the carb pressure raise except carb #3 the needle starts dropping while all the other raise evenly.

i thought it might have been the gauge so i switch around the gauges and still the same thing.

my timing was set correctly before i stored the bike. Also how often does the timing need to be adjusted? and how does it get off if so?

all my air fuel mix screws are turned out 1.5 turns. i pulled the spark plugs and all of them where black so i decided to change all my air fuel screws to 1.25 turns.

bike only runs pure premium with no ethanol.

1) so what are the gauges trying to tell me if anything?

exhaust doesn't seem to be leaking on cylinder 3.

did a compression test with throttle all the way open and all the cylinders are around 120 psi......

carb boots are all perfect when i installed the carbs last. the bike was stored in my garage during the winter. full tank of gas w/ seafoam.

put about 50 miles on the bike so far.

Syncing the carbs is the VERY LAST thing to do after all other issues are resolved.

[xsmooth69x]

wow ok sorry about my initial post i was super ADHD.

i was trying to say initially where all the things i did after i noticed the wierdness (ill get back to that)

i pulled the plugs to do a compression test thinking that cylinder 3 was letting go. 120psi with the throttle completely open. so then i noticed that my plugs where black (aka too rich). Please correct me if im wrong but i thought screwing in the idle screw all the way down means its practically cutting off the fuel (all air little gas). then when you back it out your releasing more fuel (more fuel with air) so what i did was screw the screw all the way in and backed it out 1.25 turn (originally 1.5 turns)

now i fixed the super richness and tested the compression on cylinder #3
---
also on a side note the carbs are completely stock. i have my E clip set one step up from the bottom; example

        ---------------/-x-/-/-/--

^ so if that was the needle the x is where the clip is out of the 5 positions

---

also from what i understand what the gauge reads dosnt really matter. you just watch the needles. i dont have a pro grade sych gauges its a fleabay set

---

so i took my carbs completely apart when i was building my bike. now everything is put back together except i have no reference on the position of the BIG idle screw should be before starting the sync.

initially i started screwing in the BIG idle screw until it barely started to lift the rack. carb sync'd the bike then noticed that when the bike got warm i had no range to unscrew the BIG idle screw to drop the idle to the point the BIG idle screw didnt even touch the rack.

^ that's the prologue ^

soooooooooooo this time i decided to re sync my carbs slowly moving the BIG idle screw and adjusting the carb sliders until the BIG idle screw is now in the middle where i have the ability to move the BIG idle screw in either direction to adjust the idle either way.

after everything was lined up at 1000-1200 rpm or right before the bike would stall out. (the most precise and accurate time to adjust the carbs from what ive read)



i designated cylinder #1 as the master. (sitting on the bike the carb all the way the left or the carb with the choke on it) then moving left to right while sitting on the bike adjusted 2 3 4 to match #1 (master)

so the bike is idling nice and smooth. then when i apply some gas and bring it up 3k-4k the gauge for cylinder #3 falls toward the starting position of the gauges before there is vacuum. the rest of the gauges raise in the opposite direction of the starting position of the gauges evenly together.

[xsmooth69x]

ok i just read another thread where twotired posted a cut out of a carb and i totally F'd up the air fuel screw

all the way in is all fuel

so originally with 1.5 turns, to lean it out i would turn it out 1.75 wouldnt i?

[xsmooth69x]

bump