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Carburetor adjustments

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Carburetor adjustments

Hoko
Is this the correct order for carb adjustments?
1)  Synchronize
2)  Adjust pilot screws to highest rpm's
3)  Set idle speed to 1000 rpm
4)  Set fast idle to 2750 rpm
5)  Accelerator pump adjustment
78 CB750F3 Super Sport
Austin, TX
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Re: Carburetor adjustments

Lucky 1
I would NOT do it that way.

Syncing the carbs is the last thing.
Syncing the carbs is adjusting the height of the slides and  that controls the idle speed of each carb.

The accelerator pump rod is not really adjustable like the book says.
Leave it alone. The book is wrong.
Leave the fast idle cam alone. No one ever messes with it.

Synchronize LAST
Adjust pilot screws all the exact same number of turns.
Set idle speed to  about 1000 rpm. When syncing

Make sure the accelerator pump and nozzles work correctly.


When the carbs are off of the bike remove all 4 mixture screws and make sure that all 4 "o" rings are in good condition and not mangled.
Put them back together with spring and washer .
O ring first ,then washer,then spring.


Make sure you do not throw away the fuel hoses between the accelerator pump nozzles on the carbs because they have brass restrictors inside the hose .
On a new adventure now.
A V Star 1100 adventure.
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Re: Carburetor adjustments

shinyribs
Administrator
I kinda disagree with Lucky....but I also agree.???

Baseline all your adjustments according to the FSM. Put them on the bike and sync them. They run so bad when they're outta sync I wouldn't even attempt to fine tune the idle mixture screws.

Just my $0.02 .
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Re: Carburetor adjustments

Lucky 1
I basically agree. They may need to be synced twice.
 Once just to get it in the ball park, and a final sync fine tune.
On a new adventure now.
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Re: Carburetor adjustments

Hoko
In reply to this post by shinyribs
shinyribs wrote
I kinda disagree with Lucky....but I also agree.???

Baseline all your adjustments according to the FSM. Put them on the bike and sync them. They run so bad when they're outta sync I wouldn't even attempt to fine tune the idle mixture screws.

Just my $0.02 .
So after it's sync'ed well and running evenly there's no need to fine tune with the pilot screws?
78 CB750F3 Super Sport
Austin, TX
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Re: Carburetor adjustments

Lucky 1
Do not touch the pilot screws after you set them.
Make sure they are all set the exact same number of turns.

Syncing is adjusting the height of the slides that control the amount of air.
You do not sync by adjusting mixture screws. Period.

The nuts and adjuster screw on the top of each carb are the adjustments for the syncing of the carbs.

You need to get a workshop manual.


If you adjusted a mixture screw AFTER you synced the carbs you would have to re do the syncing because you have changed the mixture. (The amount of gas during idle) Get it?
On a new adventure now.
A V Star 1100 adventure.
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Re: Carburetor adjustments

Hoko
Just wondering because the FSM says to adjust them out until I get the highest idle.
78 CB750F3 Super Sport
Austin, TX
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Re: Carburetor adjustments

Lucky 1
Yes I understand, but really the most important thing is that they are all the same.

You can do lean highest idle but it really just is a waste of time. Especially if the slides are off.
And they only have to be off by.007 thousandths to make a difference.
Then you will not know if it is lean because of the slides or the mixture screws. a mess.
Set the mixture screws and then just worry about the slide height, but moving both adjustment makes a mess.

IF it is a stock bike and the book says 1 turn  open you can play around with it all you want
But unless you have a better tach that the one on the bike you are just wasting time.
Sears sells a Dwell Tachometer that will help. About $40.00

But it is still fiddling around with adjustments of the mixture screw of 1/16 of a turn or less . Silly.

Just set them all to 1 full turn  or what the book says and leave them alone.
IF there is popping on decell of the engine when revved up in the shop, then you will need to richen those mixture screws. Try 1-1/4 turns but just set them all exactly the same. No popping.

On a new adventure now.
A V Star 1100 adventure.
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Re: Carburetor adjustments

Hoko
Sounds like a good deal on that shop tach, I'll get that.  I've got all the pilot screws set 1 3/4 turns out per the FSM so I'll just leave them there.  All carbs are bench sync'ed as close as I can get them.  I just have to get a set of vacuum guages, clean the tank, replace hoses, etc and start it up.  Thx!
78 CB750F3 Super Sport
Austin, TX
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Re: Carburetor adjustments

Lucky 1
Yes, a good set of vacuum gauges is a must have with these CB750 engines.
On a new adventure now.
A V Star 1100 adventure.
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