Carb Synch Question

[alvald83]

When i synched my carbs, i can get it almost perfect then when i hit the throttle its moves further apart then takes about 30 seconds to settle back into my final adjusted spot. What is causing this? I did notice on my way home(i was doing this at a friends house) that i hadnt completely open the choke, it was just a few mm's from being completly open.

Could this effect the tuning in that way or is this unrelated? I will try to re-synch before i leave on my trip.

I did notice a little pop pop pop on decelleration that i didnt have before but that could be related to last of the SeaFoam that is still in my tank. BTW, i also changed the plugs at the same time.

[GolfVenture]

Others more knowledgeable will chime in but I believe that is normal. Now after you get it synced at idel, some will resync at 2000 rpm, somehtiing a bit closer to normal operating rpms. I do that also. But even after you do it at 2000 rpm then blip the throttle the sync will go off again... normal.

[GeorgeS]

This is Normal, No TWO ( or 4 ) carbs, or Cylinders, are exactly the same. !!

 

( Mechanically impossible ) So you are going for the best average.

Basicly, Don't " blip " the throttle, After setting at idle, slowly bring it up to about 2000 to 2500 RPM, Then adjust to try to get a Happy Medium, between the two.

 

Also, before you start, be sure the Basic, Settings of the Throttle cables, is CORRECT. ( ie: full closed throttle plate on the #2 Carb !!! )

 

Then set the Master idle, to " Just makeing contact with Linkage "

Then back out the Sync Screws, to " Just makeing contact with linkage"

Then set the Master Idle for about 900 RPM.

 

NOW , you are ready to hook up the gauges, to actually do the SYNC Proceedure.

And the Adjustments of the SYNC screws, should be + or - Less then 10 degrees of rotation. If you have to turn those screws a turn or more, something is most likly Wrong, Someplace .

 

Good luck --- Also

[Condor]

Besides all the above you might get a can of Deep Creep and after cleaning all the linkage with a carb cleaner, spray it down with the Creep. Even the choke pistons... It will allow the linkage to act faster. The exterior of these carbs can get pretty groady.....

[joboo]

I read this a couple of times and still not sure whether you had the choke on when you were syncing the carbs but you definitely do not want the choke on at all when doing a carb sync. Even though these are constant velocity carbs they are operated on different circuits, the pilot circuit at idle which "hands off" to the mains circuit at above idle is really what you should be checking with the sync operation. The choke is a separate circuit that contributes to the pilot and the mains. One of the reasons that you should sync at idle and at the higher RPM is to make sure that the fuel air mix is constant (which was aptly pointed out is really an average) through the range. Anytime you throttle you are changing the vacuum and it will vary like mentioned in a previous post but should even up pretty quickly with a steady rpm. Just my 2 cents worth.

[mbrood]

A lean problem gets better as the engine heats up. If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the idle mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at 1000 rpm!

A rich problem gets worse as the engine heats up. If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the idle mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.

 

 

 

Remember the mixtures screws can affect not only idle, but low speed up to about 2000 rpm and after any adjustments, you want to resync the carb vacuum at 1k.

[Condor]

Here's something I've run into a couple of times and found the cure by accident. I'm not saying this is the case here, but when I've stolen another bike because it doesn't run, a couple of times I've found the sync screws on #4 or #3 carb screwed in to far. The end result is when doing a sync ,and with the idle at 1000 using the knurled knob on the left side, after the sync is done the thing won't return to idle right away. Sometimes it will take as long as 30 seconds. What's happened is the previous owner... not knowing what he was doing... tried to adjust the idle by using the sync screws to do it, and it will work..sorta. This over rides the #2 carb, and either #3 or #4 is actually controlling the idle. When the long return to idle happens I will back off all the sync screws on the right side of the carbs a couple of turns, set the idle to 1000 using the proper way, and start the sync over. It's actually a little more than that and I do have a write up I can send anyone interested. When it's done the motor will snap back to idle without any hesitation.

[joboo]

Thanks Good info!

[twigg]

Some people "overthink" this.

 

The manual says "sync at idle" ....

 

So sync at idle and forget what happens higher up the rev range.

 

The reason is pretty simple. If you sync anywhere other than at idle you are running a serious risk of never being able to achieve a stable idle speed.

[joboo]

Some people "overthink" this.

 

The manual says "sync at idle" ....

 

So sync at idle and forget what happens higher up the rev range.

 

The reason is pretty simple. If you sync anywhere other than at idle you are running a serious risk of never being able to achieve a stable idle speed.

 

Don't want to start a pi**ing contest Twigg but there is a significant difference between the carbs on an 86 and the carbs on a 96. The internal circuits are different, even the mikuni book refers to the 86 carb thumb screw as a throttle adjust rather than an idle adjust for the thumb screw on the 96. The air mixture is ported differently so the diaphragms are different, because the pilot jet (air) is located behind the diaphragm you would probably not want to sync at a higher RPM for those carbs. The 96 carbs however, are not ported that way and the circuits "overlap" differently with the change in RPM. The porting is evident if you put an inspection mirror down the throat of the two different carbs and count the holes. I think experience for whatever model is going to be slightly different and it is good to hear from those experiences. You did bring up something that is important and that is for folks to be sure to identify their bikes so that they can get the help for the bike they have. Sorry Dude just my

[alvald83]

Another change made before synching was that I also changed to a reusable foam/oil air filter. I got it by mistake, but still used it because I was leaving on a short trip so I oiled it up and installed. Since these allow more air flow is there an adjustment that needs to be done? Because I've never used this type of filter before, I ordered a paper replacement before I leave on my trip. Just curious if changes need to be made when using these types of filters. ( I may re-install it after my trip)

[Prairiehammer]

@joboo: The OP was asking about his 1983 carb synching...what "96" are you speaking of? Your RSTC? As you said, different beasts. Twigg's comment is valid for the OP's '83. IMHO

Edited May 7, 2012 by Prairiehammer

[twigg]

Don't want to start a pi**ing contest Twigg but there is a significant difference between the carbs on an 86 and the carbs on a 96. The internal circuits are different, even the mikuni book refers to the 86 carb thumb screw as a throttle adjust rather than an idle adjust for the thumb screw on the 96. The air mixture is ported differently so the diaphragms are different, because the pilot jet (air) is located behind the diaphragm you would probably not want to sync at a higher RPM for those carbs. The 96 carbs however, are not ported that way and the circuits "overlap" differently with the change in RPM. The porting is evident if you put an inspection mirror down the throat of the two different carbs and count the holes. I think experience for whatever model is going to be slightly different and it is good to hear from those experiences. You did bring up something that is important and that is for folks to be sure to identify their bikes so that they can get the help for the bike they have. Sorry Dude just my

 

It's okay ... I don't actually get worried by alternate views

 

Here is the thing .... '86 or '96 .... If you have to ask here about carb sync, then it is probably safe to presume that the guy is fairly inexperienced at the job.

 

That said, do what the manual says. If it says different for the '96, then do that

 

It's fine to depart from the manual once you are experienced enough to understand what you are doing, and deal with, and understand the results you get.

 

Anyway ... folk can read the thread ... take note of the varying answers and find their own appropriate solution.

 

It usually works for me

[twigg]

A lean problem gets better as the engine heats up. If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the idle mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at 1000 rpm!

A rich problem gets worse as the engine heats up. If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the idle mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.

 

 

 

Remember the mixtures screws can affect not only idle, but low speed up to about 2000 rpm and after any adjustments, you want to resync the carb vacuum at 1k.

 

With CV carbs it's worse than that.

 

In theory the idle mixture only affects 1/4 throttle. After that the needle takes over to about 3/4 throttle and the Main Jet after that.

 

That's the simple way carbs are described so that folk can begin to get an idea of how they work.

 

In practise the Idle Mixture has a significant affect right up to about 1/2 throttle on a diminishing basis.

 

Now imagine you are on the road .... even when cruising at highway speeds you will rarely have the throttle open more than halfway. During acceleration you will, but cruising not so much.

 

The implication here is that the Idle Mixture setting plays a significant role in most of your riding, and the Main Jet you could virtually run without

 

You will notice a significant smoothing out, and better gas mileage if you take the time to set the Idle Mixture correctly and get the needles shimmed correctly ... unless they are already good to go

[joboo]

@ Prairiehammer, you are right Twigg was speaking directly to the OP. I was referring to the posts in general about why different folks talk about sync at higher RPM. I know when we reply we tend to relay our own experiences, In my first post on this topic I was trying to explain why sync was checked at the higher RPM, unfortunately in trying to keep it to a minimum a lot is left out. Twigg took it right in his last post (Thanks Twigg BTW) in his explanation for an 83. SETTING sync at idle on these years is correct and in all actuality is for my 96 as well. I was trying to point out that CHECKING sync at the different RPM does more for you because of the different types of porting. Again Twigg was right because most of the time when these things are asked the folks asking need a starting place and some of us (me included) tend to go into too much detail and confuse the issue....So the right answer for his year should have been SET the sync at idle, ride> If not responding correctly after ride, check sync again at idle and check again at 2k RPM to facilitate further troubleshooting. My bad, Sorry Twigg you were right!

[twigg]

@ Prairiehammer, you are right Twigg was speaking directly to the OP. I was referring to the posts in general about why different folks talk about sync at higher RPM. I know when we reply we tend to relay our own experiences, In my first post on this topic I was trying to explain why sync was checked at the higher RPM, unfortunately in trying to keep it to a minimum a lot is left out. Twigg took it right in his last post (Thanks Twigg BTW) in his explanation for an 83. SETTING sync at idle on these years is correct and in all actuality is for my 96 as well. I was trying to point out that CHECKING sync at the different RPM does more for you because of the different types of porting. Again Twigg was right because most of the time when these things are asked the folks asking need a starting place and some of us (me included) tend to go into too much detail and confuse the issue....So the right answer for his year should have been SET the sync at idle, ride> If not responding correctly after ride, check sync again at idle and check again at 2k RPM to facilitate further troubleshooting. My bad, Sorry Twigg you were right!

 

Thanks ... It's all good