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Discussion Starter · #1 ·
Would a loss of top end power and increasing vibration be symptoms of needing a carb sync? My Spirit 1100 doesn't seem to be running as well as it did earlier in the year. Mostly in the higher RPM ranges. Seems to shudder a bit and doesn't pull through the higher RPM's as well. Before it would pull hard right up to the rev limiter easily in the first 3 gears. There is a more pronounced vibration at idle as well as the higher RPM's. Nothing severe, but stronger than it was. Just wondered if the carbs being out of sync could cause this? I'll most likely sync them anyways but wanted to know if there is anything else I should check?
 

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Yes......

Has it been more than 2 years?
Any rougness?
Any modification or adjustment to ignition, intake, carbs or exhaust, since last sync?
If yes to any of these, check sync.
Could aslo be some crud in the carbs.Check filters, plugs, wires, coils, Battery and charging system. Run some In-tank carb cleaner through.
 

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Discussion Starter · #3 ·
I've only owned the bike a year and a half and I'm not sure the last time it was done or if ever. Currently at 33k and change. Plugs and wires are good. Haven't checked the charging system but haven't had any issues there. I did change the exhaust to the Pro Pipe this spring but had drag pipes before and it was jetted for them by the original owner.

The symptoms I'm noticing are a bit of vibration at idle, however it's not idling roughly. The big thing is at wide open throttle in the upper end of the rev range. It gets a bit rough and feels like it's fighting to gain RPM. That "fighting" sensation is what led me to think carb sync. Also I should mention that it slowly seems to be getting worse. All in all it's not bad. The symptoms are minor enough that a friend who rode it didn't even notice. I only notice from being familiar with the bike.

I'll have to hunt down the supplies for doing the carb sync this weekend and give it a shot. Looks like a fairly simple procedure.
 

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when were the valves last checked or adjusted?-----have you made sure all airbox and carb connections are tight and clamped good to prevent vacuum leaks.

Do these things before you carb sync
----here is some info on a style manometer that i like for carb syncing

As for a carb sync tool, this is the style I like. It works well if you know how to read it. Just remember the fluid levels dont matter--you are just looking for no transfer of fluid between bottles. Also with this style of manometer you have no chance of sucking water into the engine.

First you need to make some port sync adapters. I used a piece of 3/16 brake line from Auto Zone. Cost about 6 bucks for a 30 inch piece. Cut off a couple of 4 inch pieces that will become your adapters. Thread about 1/2 an inch of one end of each adapter with a M5x.80 die. Screw a M5x.80 nut on each one all the way down. Then put a couple of orings below the nuts to help seal against the cylinder head. These are going to screw into the sync port on the head. You should see a small screw and washer on the cylinder near where the carb boots connect to the head (mine are hidden below some fake cooling fins).

Next you need about 15 feet of 3/16 I.D. clear tubing. 5 feet for each tube that goes out to the ports and a couple more feet for the connector tube that goes to the bottom of each bottle.

Last you need a couple of glass bottles that can be sealed up air tight. I like the tall liquor bottles because you can see the levels moving easily and the stoppers can be drilled through. Drill 2 holes in each stopper big enough to push the tubing down through. You can seal or puddy up the stoppers when your done to make it air tight if the tubing is loose in the holes. Fill each bottle about 1/3 of the way up with some colored water so you can see it moving better.

You are done--here is a drawing of how to put it all together. Click on the bar to make it bigger so you can see the notes.



The way this works is get the bike warm and hook this up. If one cylinder or carb is pulling a stronger vacuum its water level will rise because it pulls water out of the other bottle. You turn your sync screw until you get transfer into the other bottle. Then you will find that a very small turn (like 1/16 of a turn) will cause one bottle to bubble or pull vacuum, then a tiny turn the other way will cause the other bottle to bubble. When you find this midpoint you are synced---the idea is to have no transfer of water at all or very very slow transfer, the levels of water may be different but that doesn't matter, you just want no transfer,,,equal vacuum means its synced and thats all this tool does is allow you to see when vacuum levels are equal.

Here is a you tube vid of me trying to explain to some folks on GS forum why water levels dont matter on this style. They are used to 100 dollar mercury sticks or ten foot tall tube type manometers that have to be attached to a step ladder.

YouTube - ‪Carb Sync Manometer‬‏
 

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Discussion Starter · #5 ·
when were the valves last checked or adjusted?-----have you made sure all airbox and carb connections are tight and clamped good to prevent vacuum leaks.

Do these things before you carb sync
----here is some info on a style manometer that i like for carb syncing
Airbox and carb connections are good. The 1100 has hydraulic valve tappets so no adjustment is needed.
 

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Carb sync matters more at low throttle and symptoms of being out of sync gradually disappear as you open the throttle. If you're having WOT issues, sync isn't likely to be your problem.

Sync plays a major role when the carbs are mostly closed, which is at idle. If the carb is only open 3% at idle, and the carbs are 1% out of sync, then one cylinder is running at 3% and the other at 2%. A 33% difference between the two.

When the carbs are open at 75%, a 1% difference is hardly anything. It doesn't really matter if one cylinder is running at 75% and the other is at 74%. That's only 1.3% difference. Not enough to even measure, never mind feel a difference.

--Justin
 
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