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shadow trike said:
I want to sync my carbs for my 06 shadow aero 750 does anyone have the specs for this?

Thanks
Specs?? there isn't really any specs so to speak. The idea in sync'in them is to "Balance" them. A manometer meters the vacuum (pressure if you like) between the carburetor and the cylinder. So what you want is for ALL the cylinders to be equal.
MarKC
 

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The only spec you need is idle speed.
As you adjust each carb, the idle will change slightly.
You'll adjust a carb, adjust the idle, adjust the carb, adjust the idle...

Just keep doing this until the carbs are as close to equal as you can get
them and the idle is at spec. I believe most late model idle is 1200+/- 100 RPM.
 

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litnin said:
The only spec you need is idle speed.
As you adjust each carb, the idle will change slightly.
You'll adjust a carb, adjust the idle, adjust the carb, adjust the idle...

Just keep doing this until the carbs are as close to equal as you can get
them and the idle is at spec. I believe most late model idle is 1200+/- 100 RPM.
Good point! but if your bike don't have a tach, or you don't have one to check the idle then you'll have to set the idle by ear,
high enough to not sound like its about die,
not to high that it sounds like its running way.
MarkC
 

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MarkC said:
Good point! but if your bike don't have a tach, or you don't have one to check the idle then you'll have to set the idle by ear,
high enough to not sound like its about die,
not to high that it sounds like its running way.
MarkC
That's easy. Get a small piece of copper flexible copper wire.
Take one of the plug wires off, wrap the copper wire around the plug tip,
and stick the plug boot back on.
Start the engine. Go over to the side of the bike where the wire is sticking out.
Take a look at your watch, and when the second hand gets to 00, grab
hold of the wire and start counting. Every time you jump and twitch,
that's one revolution.

:lol: :lol: :lol: :lol: :lol:


{{{Disclaimer: Do not actually try this at home. It was a poor attempt at humor and doing this will cause electric shock!!!}}}
 

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jeeper78 said:
So synching the carbs consists of just adjusting the idle speed screw after adjusting one or both air/fuel mix screws?
NO! the linkage between the carburetors has a screw that you adjust that adjust the throttle blades, NOT THE IDLE SCREW! What Litnin was saying is that as you sync the carbs it will sometimes change the idle, then you have to go back and adjust the idle screw.
And no you don't use the air mixture screws to sync the carbs either, the air mixture screws are just that, air mixture.
There is actually a carburetor synd screw. If you have more than one carburetor on this type of bike what happen is the throttle shaft passes through the throat of both carbs, each carb throat has its own throttle blade, there is a link between then that adjust the position of EACH throttle blade. As you turn the screw its pushes each blade it different directions, closing one, opening the other, go the other way to switch the direction of the blades. You will be adjusting them to = balance on the cylinder side.
MarkC
 

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MarkC said:
jeeper78 said:
So synching the carbs consists of just adjusting the idle speed screw after adjusting one or both air/fuel mix screws?
NO! the linkage between the carburetors has a screw that you adjust that adjust the throttle blades, NOT THE IDLE SCREW! What Litnin was saying is that as you sync the carbs it will sometimes change the idle, then you have to go back and adjust the idle screw.
And Nno you don't use the air mixture screws to sync the carbs either, the air mixture screws are just that, air mixture.
MarkC
My bad, I did say adjust "each" carb... You will only adjust one carb with the single screw on the linkage between the carbs.
This screw will move the linkage of one carb and open or close slightly the throttle blade.
If your vacuum on one cylinder is higher than the other, you adjust
the screw so that both read as close to the same vacuum as the other.

As you adjust the screw, if the vaccum decreases, the engine RPM will increase.
So, if the stationary carb is at 4mmHg and the adjustable one is at 6mmHg, as you adjust the carb sync screw, you want to adjust the one
at 6mm down to 4mm. When you do this, the idle will increase,
then you need to decrease idle speed and check it again.
Do this until the vacuum is as close as you can get it between the two AND the idle speed is within spec.
 

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Make sure the engine is warm up so it has a steady idle and if you use the home make manometer, make sure both vacuum lines are tight or else you can't never balance oil level. When i did it the first time, one of my line is leaking and so i couldnt stop the oil trying to goin to my crankcase, took me a while to figure it out. (about 3 hrs later :( )
 

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litnin said:
That's easy. Get a small piece of copper flexible copper wire.
Take one of the plug wires off, wrap the copper wire around the plug tip,
and stick the plug boot back on.
Start the engine. Go over to the side of the bike where the wire is sticking out.
Take a look at your watch, and when the second hand gets to 00, grab
hold of the wire and start counting. Every time you jump and twitch,
that's one revolution.
Litnin!
I swear, for a minute i was excited, i thought i could make a home made tach...technically, it should work though if i can hold about 25,00Volt through my body...hmm, maybe my dog can!! :) i always wanted to buy him a shock colar.
 

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navillustoo said:
Crystal,
I don't know anything about your trike, but if it IS based on a 750 Aero, it'll have only one carb, and no syncing can be or is necessary to be done.

Brian

THAT would definitely present a problem and make the task a little
harder to accomplish! :lol: :lol: :lol:
 

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litnin said:
My bad, I did say adjust "each" carb... You will only adjust one carb with the single screw on the linkage between the carbs.
This screw will move the linkage of one carb and open or close slightly the throttle blade.
If your vacuum on one cylinder is higher than the other, you adjust
the screw so that both read as close to the same vacuum as the other.

As you adjust the screw, if the vaccum decreases, the engine RPM will increase.
So, if the stationary carb is at 4mmHg and the adjustable one is at 6mmHg, as you adjust the carb sync screw, you want to adjust the one
at 6mm down to 4mm. When you do this, the idle will increase,
then you need to decrease idle speed and check it again.
Do this until the vacuum is as close as you can get it between the two AND the idle speed is within spec.
I've never worked on a carburated engine before, but it's becoming more clear to me now. I think the reason I thought of the air/fuel mix screw was that I was reading a service manual section about adjusting them, and I think I remember it suggesting synching the carbs afterward. In what situations would your carbs normally become out of synch?
 

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jeeper78 said:
I've never worked on a carburated engine before, but it's becoming more clear to me now. I think the reason I thought of the air/fuel mix screw was that I was reading a service manual section about adjusting them, and I think I remember it suggesting synching the carbs afterward. In what situations would your carbs normally become out of synch?
Anytime time you change the airflow characteristics of the engine
a re-sync is a good idea.
Even changing an air filter can cause it (it usually doesn't, but it can).
Upgrading to a high flow filter, upgrading to more free flowing exhaust,
rejetting... can all affect carb sync.

One of the biggest things that affect it is time.
Every time the throttle blade opens and closes, there is a little bit of wear.
After a period of time, the wear adds up. Both throttle bodies don't
wear at the exact same rate... so a carb sync every couple of years
helps keep everything "in sync".
 

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navillustoo said:
Crystal,
I don't know anything about your trike, but if it IS based on a 750 Aero, it'll have only one carb, and no syncing can be or is necessary to be done.

Brian
Thanks Brian, I was thinking that but did`nt want to put foot in mouth. :wink:
 

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Discussion Starter · #17 ·
carbs

Thanks all. Tech day is coming up with our Chapter and one of the guys told me to pick up a service manual to find out my carb situation. You all just saved me $75.00 That's what the local dealership wants for it. Now he can concentrate on putting an additional gas tank on my trike so I can go as far on gas as my fellow riders who have goldwings.
 
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