Carb Sync - Already? Other solutions Q's - SOLVED (not the carbs afterall)

[junior varsity]

I had the carbs sync'ed when I got to Vegas earlier this summer. Put around 1500 miles since then, and had the valves serviced. Out of the blue the other day, while puttering around Dallas, the bike gave me the same "missing" feeling, where there's a complete absence of power as I roll on the throttle.

This is the exact same feeling I had before I took the bike into Pat Clark Motorsports and Irish Mike sync'ed the carbs and adjusted the idle down some. What gives? Why would my carbs need synced again, already? Is there something I'm doing that's causing them to go astray?

Along the same vein, if I switch to FCR's, the hassle of the carb sync goes away, no? As I understand it, the railed version (not split singles) does not need to be synced. Also, more go-fast juice and all that. But this post is about:

1. Why do carbs work themselves out of sync
2. Why in the bloody hell does it make riding just fine for a few minutes after its warmed up, but later in the day, the bike bogs down upon acceleration?
3. What solutions are there besides a standard sync (and how long should they stay in sync), options like extra red loctite, or FCR's or duct tape?

Educate me friends!

[Bladecutter]

Carbs should always be synch'ed after the valves are adjusted.
This will allow them to stay in synch for the longest possible period of time.

BC.

[junior varsity]

I'm not sure I understand how they work their way out of sync to begin with?

[JimE]

You had the carbs synchronized and THEN had the valves serviced? No wonder. Valve clearance affects opening and closing duration. Opening and closing duration affects vacuum. "Synchronizing" and "balancing" the carbs is the same thing as "making the intake manifold vacuum the same". So basically as the velves wear, clearances change, and balance is lost. Hence why they need to be "synched" again. Also minor wear and tear on linkage and carb slides can contribute. So the lesson is: always synchronize the carburetors after a valve adjust. Make sense?

[junior varsity]

You had the carbs synchronized and THEN had the valves serviced? No wonder. Valve clearance affects opening and closing duration. Opening and closing duration affects vacuum. "Synchronizing" and "balancing" the carbs is the same thing as "making the intake manifold vacuum the same". So basically as the velves wear, clearances change, and balance is lost. Hence why they need to be "synched" again. Also minor wear and tear on linkage and carb slides can contribute. So the lesson is: always synchronize the carburetors after a valve adjust. Make sense?

The carbs were synced in Vegas because the bike had extreme difficulty running. Road it back to Dallas, and got the valves serviced shortly thereafter, so there was a large amount of miles in between the two, over a short few days.

Makes sense about the duration affecting vacuum.

[needtorque]

I dont know.  I would suspect somthing else amiss here.  My 01 M750 never had the carb sync done in 10k miles.  Before and after I did the valves it ran fine. 

[junior varsity]

I had never needed it done until recently either. My only other thought is whether the addition of spaghetti headers may be messing with things. The cans haven't changed in years, but the headers were changed (right before the valve job) - the other thing, is that the bike felt good, nay great, right after the valve job. Ran like a top all the way home from the shop, and its a not a short ride (>45min), so I figured if something was to be 'amiss', it would have been amiss then.

[extra330]

this may be a stupid question but what about the belts being a bit loose? It stands to reason that when the belts loosen up a bit the timing will change too. If one belt is a bit looser than the other one the cylinders would be out of sync, no?


Mike

[junior varsity]

Hmm... I will check the tension. the belts were replaced at the valve service, so although I will check, I tentatively rule that out as unlikely.

My guess about the carbs being out of sync is because of the nearly identical feeling that occurred while riding around albuquerque and las vegas, and when i took it in, they adjusted, and ran like a top.

[junior varsity]

Solution:

Took in to see Stuart the other day (formerly with AMS), and his first thought was fuel filter before carb sync, but would check it out for me anyhow.

He asked me what I had changed recently. Only a quick release fuel cap. We checked the drilled hole for the tank vent (obviously when gas leaves the tank, something has to fill the void, namely air). The hole didn't line up perfectly with the tank's hole and the rubber that goes between the two, so with that sealed off, I was indeed having troubles getting fuel out of the tank and down to the motor.

After some fiddling, I was back on the road with ZERO problems. Took it back to Stuart because I was already there, and y'know, I just really 'need' that Dyno test.