Re-Sync?

[LT Rider]

I pulled the carbs for my Audiovox instal..will I need to re-sync now?
Thanks.

 

[Rossi]

If after everything's back together, the bike runs the same as before, you're good.

But it's probably a good thing to sync the carbs after re-installation anyway.

 

[dwalby]

Re: questions about carb sync tools

My Hg Carb-stix got kicked over in the garage several years ago and lost enough Hg to make it unusable. Finding replacement Hg seems about as difficult as buying Plutonium, so I started looking at the alternatives available today. Seems that MotionPro now makes a carb-stix that uses a non-toxic liquid, and works similar to the old Hg version. Also saw the STE tool in the maint pages here.

How many of you have used the new MotionPro version with the non-toxic liquid, does it work as well as the Hg version? How many of you have used both systems and prefer the STE tool?

thanks,

Doug

 

[Bigmak96]

will I need to re-sync now?

I don't think you will know unless you check them. Unless they are way off.

 

[LT Rider]

Re: questions about carb sync tools

My Hg Carb-stix got kicked over in the garage several years ago and lost enough Hg to make it unusable. Finding replacement Hg seems about as difficult as buying Plutonium, so I started looking at the alternatives available today. Seems that MotionPro now makes a carb-stix that uses a non-toxic liquid, and works similar to the old Hg version. Also saw the STE tool in the maint pages here.

How many of you have used the new MotionPro version with the non-toxic liquid, does it work as well as the Hg version? How many of you have used both systems and prefer the STE tool?

thanks,

Doug

I actually use:
http://www.cbperformance.com/catalog.asp?ProductID=572
as discussed on this forum. Check it out. Reeeeaaaally easy. No vacuum hoses to bother with.

BTW...testride confirmed no issues and the CC worked fine. Better than it did on my 1300. I just like the 11 better in so many ways.

 

[Uncle Phil]

I have the SK Flowmeter for syncing the carbs if you need it. Only cost is postage out and back. Takes longer to remove the bodywork than it does syncing the carbs with it and the results are good.

 

[sennister]

Re: questions about carb sync tools

I actually use:
http://www.cbperformance.com/catalog.asp?ProductID=572
as discussed on this forum. Check it out. Reeeeaaaally easy. No vacuum hoses to bother with.

BTW...testride confirmed no issues and the CC worked fine. Better than it did on my 1300. I just like the 11 better in so many ways.

Since you have a flow meter it is a no brainer. I have one as well. Anytime I pulled plastic I would check it. Since it is so easy to do. Too bad there isn't an easy way to use it on the 1300.

 

[dwalby]

Re: carb sync, myth or reality.

I've been riding and synching carbs for over 30 years now and I was wondering what people really think about carb synchronization in general. I've not only adjusted them, but purposely mis-adjusted them just to see what would happen. I never noticed any difference in the idle with them significantly out of adjustment. I never actually left them in that setting, so I don't know if it would have any symptoms during a ride, but I really doubt it. The concept of synching the carbs would seem to only affect idle anyway, when the butterfly valves are almost completely closed and a little difference in the openings would affect the relative flow through each cylinder. Once the butterflies are open much wider for normal riding, very small differences in their adjustments would seem to be meaningless at that point.

So my own personal experience with this over the years is it was a worthless exercise in fiddling with things with no real benefit. Since I had the gauges I generally did it after each valve adjustment anyway, but since I kicked over my carb stix several years ago I stopped doing it altogether. Haven't noticed any difference in the idle over that time, so I can't see any problem with not doing it ever again. Anybody have any contradictory stories to tell about their experience?

 

[JPrieST]

Re: carb sync, myth or reality.

Anybody have any contradictory stories to tell about their experience?

Your experience is what it is. I won't contradict you. BUT....

In my case I have had 2 times that I was getting a frequent random "hic-up" when running steady at 1800 to 2000 rpm through the neighborhood. Carb sync worked both times. Even IF it only makes a diff at lower rpm it's well worth it to me.

 

[GitSum]

I think it makes a difference

Carb synching is a little more than just making sure that the butterflies are open the same amount - that would be a "bench" synch which can be done with a feeler gauge or even a drill bit.

You are trying to establish a mechanical relationship that should be linear across the rpm range and takes into account how much vacuum each cylinder pulls (which will effect the fuel/air mixture). A good carb synch will compensate for wear items like valve clearances and compression.

It will not fix all your problems, but it is a good start

 

[dwalby]

Carb synching is a little more than just making sure that the butterflies are open the same amount

Please educate me if I'm wrong, but the only adjustment available for carb synching is a screw adjuster that determines how far each of the 4 butterflies is open at idle.

You are trying to establish a mechanical relationship that should be linear across the rpm range

please explain what you mean by this, it makes no sense to me in the context of carb synching. Once you open the throttle, the idle stop screws are no longer in contact with the throttle butterflies, so there's nothing to adjust to produce the 'linear mechanical relationship across the rpm range' you mention. Its just the cables pulling the butterflies through their travel, but nothing there to adjust that I'm aware of, other than the slack adjustment of the cable itself inside the cable housing.

and takes into account how much vacuum each cylinder pulls (which will effect the fuel/air mixture). A good carb synch will compensate for wear items like valve clearances and compression.

yes this is true, the butterflies can be adjusted at idle to match the vacuum between cylinders, to compensate for the things you mention, but only at idle. And the point of my post was that even if you adjust them the wrong way, so that the vacuum between cylinders is totally off, the idle doesn't seem to change. If you keep adjusting even further off then eventually you can effect idle, but my point is I've seen the 4 columns of Hg totally off and couldn't detect any difference in the way the bike idled, either in smoothness or RPM.

 

[GitSum]

When you synch the carbs your are trying to develop a 'relationship' so that all four cylinders draw in the same amount of fuel/air mixture.

In a perfect world, all four intake valves would open the exact same amount to let the fuel/air mixture in, all four cylinders would have the exact same compression to draw the same amount of fuel/air mixture in, and all four exhaust valve would open the exact same amount to expel the burnt charge.

In reality, valve clearances change and piston rings wear - this all effects the ability of each cylinder to draw in the same amount of fuel/air as the other cylinders

Chance are - we don't want the butterflies to open the exact same amount. Each cylinder is different and that is the purpose of the synch to begin with - to try to get all four cylinders to draw in the same amount of fuel/air. (to compensate for these wear factors) The should result in a smoother running engine.

You keep mentioning "idle" - idle has nothing to do with it. The throttle cable connects directly to the the "master carb" (#4). You are adjusting the linkage of the other three carbs to try and match the master carb. It shouldn't matter if you set this relationship at idle, 2,000 rpm or even higher. Once you establish this relationship - it should not change, it is "linear". (Do your valves open more at 6,000 rpm compared to 1,000 rpm??? Does your compression change also at higher rpms ???) NO


As JPrieST posted "your experience is what it is". I on the other hand will continue synching my carbs

 

[dwalby]

When you synch the carbs your are trying to develop a 'relationship' so that all four cylinders draw in the same amount of fuel/air mixture.

In a perfect world, all four intake valves would open the exact same amount to let the fuel/air mixture in, all four cylinders would have the exact same compression to draw the same amount of fuel/air mixture in, and all four exhaust valve would open the exact same amount to expel the burnt charge.

In reality, valve clearances change and piston rings wear - this all effects the ability of each cylinder to draw in the same amount of fuel/air as the other cylinders

Chance are - we don't want the butterflies to open the exact same amount. Each cylinder is different and that is the purpose of the synch to begin with - to try to get all four cylinders to draw in the same amount of fuel/air. (to compensate for these wear factors) The should result in a smoother running engine.

yes, I'm aware of all those things, so we're on the same page so far.

You keep mentioning "idle" - idle has nothing to do with it. The throttle cable connects directly to the the "master carb" (#4). You are adjusting the linkage of the other three carbs to try and match the master carb. It shouldn't matter if you set this relationship at idle, 2,000 rpm or even higher. Once you establish this relationship - it should not change, it is "linear". (Do your valves open more at 6,000 rpm compared to 1,000 rpm??? Does your compression change also at higher rpms ???) NO

But here's where we differ. Idle has everything to do with it. At idle is where the engine is most susceptible to minute adjustments of the butterfly valves. At idle the butterfly valves are almost completely closed, and due to the low rate of airflow the engine vacuum is relatively high. There's a small adjustment screw for each of the other 3 carbs, used to micro-adjust the openings of each butterfly so each cylinders vacuum is equal to the master carb cylinder.

Let's just say for the sake of argument that at idle the butterfly air flow opening is 0.010" or 0.020". If you adjust one butterfly by 0.001", you've increased the opening by 5-10%, that's a fairly significant adjustment, and you'll see a noticable vacuum change because of it. Now open the throttle, and say the butterflies are now open by 0.250", or even 0.500". That same 0.001" adjustment is now virtually nothing, since its 0.2-0.4%, and at running speed you probably won't even be able to measure it, much less notice it.

So when you say the throttle response is linear, I think you're saying the same thing as I am, a 0.001" difference at idle is a 0.001" difference at WOT, no argument there. But that 0.001" difference is practically meaningless to air flow at all other throttle settings other than idle, that's why I keep saying that idle is the point at which carb synch adjustments are typically performed, because that's where the adjustment is most meaningful and measurable. Like I said earlier, I've been doing these adjustments for 30 years, and I remember the instructions with the carb stix always stressed that the adjustments be performed at idle, which makes sense to me based on my comments above. If you wanted to, you could also slowly increase the throttle to check other RPMs, but that wasn't as important or sensitive to adjustments as idle is.

Finally, your suggestion that the engine behaves identically at idle, 1k, 2k, or 6k RPM is a bit oversimplified, and its not linear at all. The volumetric efficiency of any engine varies non-linearly with RPM, that's why torque curves are never flat, or even a straight line. The usable compression changes significantly over the RPM range, because the engine fills the cylinders with air differently at different RPMs (because the butterflies are restricting air flow to the desired amount based on the throttle setting). The mechanical compression ratio doesn't change with RPM, but at small throttle openings you may only be filling the cylinder with 10% of the air it could theoretically draw with no restriction. As you open the throttle, that number could increase to say, 50-60%. As you open the throttle further, and RPM increases, then the throttle restriction isn't what reduces the amount of air the cylinder can breathe in each cycle, its the speed of the intake cycle. As the pistons move faster and faster, the amount of time the valves are open decreases, so the amount of air that can be pulled in tends to diminish, and as a result the peak torque (peak volumetric efficiency) is always achieved at something lower than peak RPM.

Edit: I looked at the latest Carb Stick instructions to see if anything has changed over the years, and here is what they say about the procedure using the latest version of their tool:

10. Start the engine and bring it back up to its normal operating temperature. With the engine at the proper idle, adjust the carburetor adjustment screws so that the SyncPRO™ fluid columns are approximately the same height. Once this is accomplished you have completed your carburetor synchronization.

 

[mtnpat]

Re: carb sync, myth or reality.

Your experience is what it is. I won't contradict you. BUT....

In my case I have had 2 times that I was getting a frequent random "hic-up" when running steady at 1800 to 2000 rpm through the neighborhood. Carb sync worked both times. Even IF it only makes a diff at lower rpm it's well worth it to me.

Sounds like my bike....when carbs are out of sync I would get also what I would call a hiccup at 2000 and 2500 rpm. After syncing carbs it goes away and bike runs great, motor revs faster and smoother. The problem with my bike is that I can't seem to keep the carbs in sync for more than a couple hundred miles.