Synching K Bike Throttle Bodies (applies to all K bikes)

[Skeezer]

Power seems better, Feels like it runs and pullls free'er if that makes any sense.

[frankenduck]

Power seems better, Feels like it runs and pullls free'er if that makes any sense.

Yup. That's the whole point of doing it.

[TaosBrick]

Thought I'd throw this in here for grins - already posted on "what did you do to your motobrick today?"

This seems to work. The thing I wonder about is that one can have it perfectly balanced at idle, but when you bring it up to 5k or so, it starts changing. I'm guessing this would be the same if one was using a gauge of some sort.

So - what's important here? That they all read equal at idle, or at higher revs?

[mjydrafter]

So - what's important here? That they all read equal at idle, or at higher revs?

I can answer that, they need to be equal at idle.  I think above idle throttle position negates the need for air from the idle air passages.  That's how it works on the older multi-carbed bikes.

[TaosBrick]

I can answer that, they need to be equal at idle.  I think above idle throttle position negates the need for air from the idle air passages.  That's how it works on the older multi-carbed bikes.

  So if that's the case, does this mean that what you do for synchronization at idle has no bearing at all on what happens when you crack or open the throttle? ie, you can't really synchronize throttle bodies or carbs for anything other than idle?

Illuminate please.

[Bob T]

I can answer that, they need to be equal at idle.  I think above idle throttle position negates the need for air from the idle air passages.  That's how it works on the older multi-carbed bikes.

  So if that's the case, does this mean that what you do for synchronization at idle has no bearing at all on what happens when you crack or open the throttle? ie, you can't really synchronize throttle bodies or carbs for anything other than idle?

Illuminate please.

This is a very good question. 

[mjydrafter]

Well, the k-bikes are injected, and my knowledge of the carb sync'ing process relates to my '82 CB900c.  With those the sync'ing actually moves the throttle butterflies in relationship to each other, and gets the vacuum at idle equalized compared to the #1 carb.  On those carbs you get close by bench sync'ing with a wire guage (guitars E-string), and then fine tune with the manometer.

I think the blue painted screws that are not to be touched are closer to the carb sync screws I'm used too.  I haven't had a chance to read the thread on those screws yet, so I can't speak to what they actually do, but it's my guess that they are set at the factory, and shouldn't need to be moved for normal maintenance.  I would guess that they actually move the throttle butterflies in relationship to each other. 

I assume that when the throttles are opened the more massive amount of air coming in through the butterflies "overpowers" or negates the idle air circuit.

Here is an explanation from someone more knowledgeable than me that may help clear some thing up:

What the carb sync adjusts for is to get an equal amount of vacuum and flow in each intake port at idle, by fine tuning the comparative throttle openings and consequently the flow of each carb's throttle at idle. This fine adjustment changes the amount of vacuum at idle by fine tuning the minimum opening of the butterflies when they are on the idle stop and almost clear shut. It's an issue of vacuum from the motor as an air pump, and thus the flow through the butterflies, and it accounts for other leaks, like the rings and throttle shafts.

I just set mine, they were way off.  #1 was backed out 4-5 turns... reset it to 1.5 turns out and adjusted the others with my gauges to all read at just below 20hg.  This was so easy compared to the CB900c, I'm almost beside myself.  Literally 5 minutes and done. :2thumbup:

[mjydrafter]

I can answer that, they need to be equal at idle.  I think above idle throttle position negates the need for air from the idle air passages.  That's how it works on the older multi-carbed bikes.

  So if that's the case, does this mean that what you do for synchronization at idle has no bearing at all on what happens when you crack or open the throttle? ie, you can't really synchronize throttle bodies or carbs for anything other than idle?

Illuminate please.

To more simply answer your question, I believe the sync is for idle and that magic moment when you crack the throttle, so that each cylinder is starting equally at the same vacuum level.  So it idles nice and smooth and takes off from idle nice and smooth.

[TaosBrick]

Thanks mjydrafter, getting a better picture of it all now. It would seem that open throttle operation is not really adjustable per se, as that mix is dependent on computers, injectors, butterflies, jets, venturis and what have you, which are more or less what they are, if my understanding of these things serves me correctly.

[frodef]

Note that if you find that one or more of the cylinders doesn't respond to turning the brass screws then you probably have an air leak between the throttle body and the cylinder head.  This is easy to confirm by spraying some starting fluid or propane/butane around the boots between the TBs and the head.  If that causes the idle to increase then the 20 year old rubber between the TBs and the cylinder head has most likely cracked and needs to be replaced.

So today I visited a kind soul with a carbtune to have my TBs balanced. Not only did he rather expertly tune the TBs into sync, but he suspected a leak and verified it with some butane. The engine increased speed sometimes and sometimes stuttered or started "knocking" from the butane. Anyhow, I suppose the next step is to look into replacing the rubber pieces you mention here, but I'm not exactly sure which parts it is. Is it the "inlet manifolds" (11611460408) and/or the "bushings" (11611460755)? And/or something else?

Manifold:



Bushing:

[Inge K.]

Depends if the leak was above or or under the TB`s, manifolds under..bushings above.
Anyhow, on a 26 years old bike...I`ll suggest that you change all six...while you have things apart.

Vennlig hilsen Inge K.

[mystic red]

Depends if the leak was above or or under the TB`s, manifolds under..bushings above.
Anyhow, on a 26 years old bike...I`ll suggest that you change all six...while you have things apart.

Vennlig hilsen Inge K.

+1. All the rubber ch!t needs to be replaced. The manifold is optional but why not do it while you're in there? Do the gas lines also.

[Snowy]

I recently balanced my throttle bodies on my K1100RS with a Morgan Carbtune. To start with I balanced them at idle and then used the throttle advance (choke) to put the revs up to 3K to see if they were balanced then but No.1 cylinder was well out. If I balanced them for 3K then No.1 was then out on idle. I found that instead of using the choke to keep the revs static, if I used the throttle I was able to balance the throttle bodies to be in sync at both idle and at 3K. I'm assuming from that that the choke doesn't affect all 4 cylinders in the same way?

[Scott_]

I'm assuming from that that the choke doesn't affect all 4 cylinders in the same way?

The issue of using the choke or the throttle is that the throttle cable connects to direct to Cyl#3 with no butterfly adjustment for it. The "blue" screw adjusters will adjust the butterfly openings of Cyl #2 and Cyl #1 and Cyl #4.

The choke cable on the other hand attaches at the TPS side of Cyl #4, so the linkage connections are not "pulling" the same for #4 and #3.

[frodef]

Depends if the leak was above or or under the TB`s, manifolds under..bushings above.
Anyhow, on a 26 years old bike...I`ll suggest that you change all six...while you have things apart.

Yes... however those manifolds under are somewhat more expensive    I just had a closer look at my bike, and the manifolds have non-OEM clamps on them (as far as I can tell, they have garden-hose-clamp-like screws rather than the one-time clips), so perhaps some PO has changed the manifolds already. The upper bushings had the standard clamps however.

Think I'll get me some starter fluid and see if I can pinpoint a leak (or two) more precisely.

[mystic red]

This method is safer, more precise and a lot less messy.



Look at the pics in this post. One time clamps on one end and multi use on the other. Look like yours?

[tsbt]

This is what happens when you synch all 4 throttle bodies at once without tightening the first screw, my brass nut went flying off into the asphalt abyss on the 4th. I knew the screw was backed out too far in the first place but didn't anticipate loosing it entirely :tongue Could explain the vibrations I experience at 3krpm and 4k and intermittent engine coughs.

[TaosBrick]

Could explain the vibrations I experience at 3krpm and 4k and intermittent engine coughs.

Ya Think?

[tsbt]

Could explain the vibrations I experience at 3krpm and 4k and intermittent engine coughs.

Ya Think?

Originally thought the warp in my rear hub caused the vibes, but that was before I discovered this screw missing. Kind of relieved.

[TaosBrick]

Always good to finally figure something out.  Have some stuf on my /5 that's been having me scratching my head for months now.

[Grim]

I came across this tubing, and thought it'd be fun to try this with three bottles... any thoughts?

Love this home made manometer.

This is my first messing with multiple set up like this but I got to thinking how I balance a carb on a car I wonder if this might be something to add in so I thought I would see what you thought.

I use a Vacuum gauge to set my base idle mixture on my old LeMans. Its connected to a central vacuum port at the base of the carb. The goal is adjust the mixture screws till you get the maximum vacuum. So just back and forth on the idle screws till the vacuum starts to go down. The Premise being the maximum vacuum is going to indicate the most efficient burn and ballanced fuel supply from the carb. 

Of course that wont work for the multiple throttle bodies as there is no central vacuum source. What I think might be of some importance would be to take the first cylinder and adjust it for maximum vacuum with a gauge then sync the rest of the cylinders to it with the Manometer. The goal of course to all equally balance at a stoic fuel mixture.   
Worth the extra step?

[detbmw]

Duck,

I've synced throttle bodies one time, and that was on my R1100RT.

My buddy has a homemade vacuum hose set up that handles two throttle bodies.

So I should be able to use it on my K75S to adjust the first two, cap number two, then pull the fuel pressure regulator hose off (and leave it hanging loose) and sync number one & three.

My point is, I don't HAVE to have a sync tool that does three at once.

Correct?

I received a set of Bosch Type II fuel injectors today and I plan to get them on the bike early next week.

[Lawrence]

And what is a Bosch type II injector?  :dunno2:

[detbmw]

And what is a Bosch type II injector?  :dunno2:

http://www.ebay.com/itm/190820618228?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

[Lawrence]

I look forward to your report on the difference these make in your K-bike's performance!