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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: frankenduck on May 18, 2011, 08:12:51 AM
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Synching the throttle bodies on a K bike is one of the most overlooked, yet most important, parts of keeping your K bike running as smoothly as possible.
WHY? The purpose of synching the throttlebodies is to balance the volume of air entering each cylinder. The usual result is a smoother, better running engine. It's nitpicking but using this procedure you're not actually balancing the volume of air but balancing the vacuum in each throttlebody.
WARNING: On the throttle assembly you will notice some silver screws with blue paint on them. DO NOT adjust those or you will be in a world of hurt unless you really know what you're doing. They are factory set and should not be adjusted.
TOOLS REQUIRED:
Regular screwdriver
Comparative vacuum measuring device (a.k.a. carburetor synchronizer)
There's a few options for a carb synch tool:
I use a TwinMax Carburetor Balancer. www.casporttouring.com (http://www.casporttouring.com) usually has the best price. This instrument compares two vacuum levels. If I recall correctly the TwinMax hoses aren't a perfect fit on K bikes so I went to the auto parts store and bought two feet of vacuum hose. It's cheap.
There are other options out there that will allow you to simultaneously measure 4 vacuum levels like Carb Stix, CarbTune, Carbmate, etc... Theoretically synching the throttlebodies all at once will yield ideal results but a TwinMax does a good enough job in my opinion.
You can also look around on the Internet for methods to build your own if you want to save a few bucks.
PROCEDURE: Synching the TBs is actually quite easy and quick. Usually the major portion of work is removing/reinstalling fairing parts to get to them. If you have an LT or RT model then I did a write-up on IBMWR a while back which will show you how to remove the radio and the fairing pieces. Here's a link to it: K75RT K100RT K100LT K1100LT fairing removal (http://www.motobrick.com/index.php?topic=406.0).
Next, start the engine and get it up to operating temperature. I usually start the bike and then let it idle until the fan comes on.
You will notice that each of the throttlebodies (one per cylinder) has a brass screw at it's base. You will also notice little rubber caps at the base of each throttlebody. On two valve K bikes, there is a vacuum hose on the last cylinder that goes to the fuel pressure regulator.
Turn the TwinMax on. Use the left knob to set it to it's highest sensitivity and then use the right knob to zero the meter.
On the number 1 throttlebody (front of the engine) gently turn the brass screw in until it bottoms out. Then back it out one and a half turns.
Remove the little rubber caps (replace them if they look old/dry/cracked) from the number 1 and number 2 TBs and connect the TwinMax hoses to them. Adjust the brass screw on the number 2 TB until the needle movement on the TwinMax meter is bracketing zero. Number 2 is now balanced with number 1.
Remove the hose from the number 2 TB and replace the rubber cap. Repeat the above procedure for the number 3 TB to balance it with number 1. Then do the same with the number 4 TB.
If you have a 2 valve K bike with a vacuum hose on the last cylinder then in theory it's best to put a "T" vacuum junction on that TB and connect the TwinMax to that but if you're not running dynos and trying to squeeze the last tenth horsepower out of the engine then you should be OK just removing the fuel pressure vacuum hose and connecting the TwinMax hose. That's how I do it.
Remember to turn the TwinMax off when you're finished.
Put everything back together and go for a ride.
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.
Also, if you're replacing one of those boots then it makes sense to replace all of them while you have things apart. You also probably want to replace them with new ones from BMW, not used ones, since I don't see much sense in replacing 20 year old rubber with 20 year rubber.
Here's the part numbers:
K75 or 2V K100: 11611460408 Buy 3 for a K75, 4 for a K100.
K1, K100RS4V or K1100: 11611461621 for the boots themselves and 11611465169 for the O-ring installed at the base of each boot (buy 4 of each)
Here's a link on how to replace them on a 4V K: 4 Valve K Bike Intake Manifold Rehab (http://www.motobrick.com/index.php?topic=624.0)
And, while you're at it, you might want to consider Getting The Fuel Injectors Reconditioned (http://www.motobrick.com/index.php?topic=1064.0).
For K75s and 2V K100s be sure to clean around the bases of the injectors (vacuum or compressed air) before pulling them as crud can build up around their bases and fall into the head if you're not careful.
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The attached PDF (provided by Scott_) file describes the procedure and concept behind fiddling with the silver TB screws with blue paint on them that are factory set and are not supposed to be touched. Fiddle with them at your own risk.
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Here's the Twinmax device, right? http://www.twinmax.co.uk/acatalog/Twinmax.html (http://www.twinmax.co.uk/acatalog/Twinmax.html)
Does anyone know if the 5mm or 6mm adapter would suit the K?
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Hell, I just use the rubber hoses on the TB ports.
NO issues ______________________.
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You can always go to the auto parts store and buy some vacuum hose. That's what I did.
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The attached PDF (provided by Scott_) file describes the procedure and concept behind fiddling with the silver TB screws with blue paint on them that are factory set and are not supposed to be touched. Fiddle with them at your own risk.
404 on the pdf file Scott.
Can you ping me privately with the attachment ? DRxBMW@aol.com
Inquiring minds need to know. :yow
Reason I ask, Ron dicked with the intake screw, hence his bike does have some back snapping. I was under the impression one needed a flow bench for the procedure. Maybe NOT !
What I did, was to realign his screw to match the paint marks. Far better but still has some snap,crackle and pop.
THANX _______________.
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You can always go to the auto parts store and buy some vacuum hose. That's what I did.
Right, I just figured since they sell "adapters" there it'd be easier to just get the correct adapter right away.
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On a sidenote, when they had a slight sale and the exchange rate was decent earlier this year I picked up a Carbtune Pro. When using it I've found that altering the needle valve on one cylinder may cause the pressure level on some of the other cylinders to change very slightly- so your need to kind of tweak all of them at once to get things truly balanced.
A TwinMax won't allow you to do more than two cylinders at once so the results you get might not be as "perfect." That said, I used a TwinMax for several years with good results so I certainly still think it's a great product, just that the Carbtune is a hair better.
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I just have a set of Mercury Manometers (Its what Dos Equis man uses test himself, so I assume its good enough for my bike). It can do 4 cylinders (I bought it for my CB550). Got that sucker to idle at 300rpm once, while it was nice and warmed up.
I think I spent all of 30 dollars on this set. Can't beat that.
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The attached PDF (provided by Scott_) file describes the procedure and concept behind fiddling with the silver TB screws with blue paint on them that are factory set and are not supposed to be touched. Fiddle with them at your own risk.
404 on the pdf file Scott.
OK, I deleted the oringal attachment file and resubmitted it so it should be good now.
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I came across this tubing, and thought it'd be fun to try this with three bottles... any thoughts?
fixed video link (http://www.youtube.com/watch?v=2PiQBr20kM8#ws)
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I came across this tubing, and thought it'd be fun to try this with three bottles... any thoughts?
http://www.youtube.com/watch?v=2PiQBr (http://www.youtube.com/watch?v=2PiQBr)
404 on the video (malformed)
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404 on the video (malformed)
Clumsy me, fixed now.
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I was going to build my own CARB Sync tool. I found a deal on Vacume gauges. How sensitive do they need to be? I was thinking of mounting all 4 to a plate. run all the vacume lines . any thoughts? :hmm:
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I was going to build my own CARB Sync tool. I found a deal on Vacuum gauges. How sensitive do they need to be? I was thinking of mounting all 4 to a plate. run all the vacuum lines . any thoughts? :hmm:
Don't think I'd do it. I work maintenance and work with all kinds of gauges. I have yet to have 2 gauges, let alone 4, that read the exact same.
You want to read the DIFFERENCE between the cylinders, not the individual level.
Your most accurate measurement is to use a liquid level gauge.
Like Drake suggests the Carbtune is the cats meow, the Twin Max would be the next best.
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My 1985 K100RS is the first bike I've owned with FI. I've tuned carbs since forever, but FI is obviously a cat of a different color. The brass screw controls a restrictor in the TB venturi? Is turning the brass screw opening/closing what on a carb would be the butterfly or slide? Does this then change the tick-over? Or, is that a function of the ignition timing? Thanks for you patience....
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With the Brass screw, they adjust "free air" into the mixture, other than what is allowed by the butterfly plates.
Turn the screw in, less air, so then obviously turn the screw out and more free air allowed into the combustion mixture.
I seem to remember that a term used to describe them at one point was "air balance screws".
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Ok. I have the guages and fittings, hose. I thought I would just try one to see what it would read before I opened up the rest.
I tried it on more than one throttle body and the gauge just bounces around ??? If I suck on the tube it shows vacume??I may be in over my head.
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Ok. I have the guages and fittings, hose. I thought I would just try one to see what it would read before I opened up the rest.
I tried it on more than one throttle body and the gauge just bounces around ??? If I suck on the tube it shows vacume??I may be in over my head.
At 1,000 RPM the valves are opening and closing a lot so the vacuum isn't stable. On a TwinMax the needle bounces around but you just adjust the brass screws until the bouncing needle "brackets" the zero. The CarbTune has pinhole-sized flow restrictors in each vacuum hose to minimize the bounce.
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Thanks
So if I could restrick the opening it might work. That helps me alot. Thanks again. :bmwsmile
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Thanks
So if I could restrick the opening it might work. That helps me alot. Thanks again. :bmwsmile
Well, you could do that but I would go with Duck's advice and just get each one to bounce equally on each side of the zero, if you know what I mean.
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Thanks
So if I could restrick the opening it might work. That helps me alot. Thanks again. :bmwsmile
Well, you could do that but I would go with Duck's advice and just get each one to bounce equally on each side of the zero, if you know what I mean.
Scott, that would be good advice if he was using a TwinMax, but he's not.
He's built his own with independant dial gauges.
Yes Skeezer some kind of a flow restricter would help.
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I have restricked the flow and will try tomorrow. As it was the needles were a blur before and you couldn't even see them. I will let you guys know tomorrow.
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Skeezer, you may want to inquire in a pet shop that specializes in aquariums and fish stuff. Look for a bit of hardware associated with the pumps. You should be able to find adjustable valves that can be plumbed into the vacuum lines between the gauges and the injector bodies. Once fitted, you'll have the means to damp them down and stabilize the needles so you can read them.
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Ok. Heres how it went. You guys were correct in the claim that the for Guages would not read the same. Out of the 4 only 2 gave an acurrate reading. so I used them.
Using the procedure erlier in this thread. Throttle responce and Idle seem smoother. But we had an inch of snow last night so a test ride is out for now.
Thanks for the help
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Power seems better, Feels like it runs and pullls free'er if that makes any sense.
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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. :bmwsmile
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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?
CheeP (read: didn't cost a dime) Throttle Body Balancer (http://www.youtube.com/watch?v=wy07uiTDc1E#ws)
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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.
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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.
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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.
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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:
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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.
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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.
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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:
(http://www.motorworks.co.uk/bmw/prodimages/lg/FUA60408.jpg)
Bushing:
(http://www.motorworks.co.uk/bmw/prodimages/lg/FUA60755.jpg)
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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.
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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.
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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?
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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.
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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 :popcorm 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.
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This method is safer, more precise and a lot less messy.
(http://i42.photobucket.com/albums/e336/2006hespelt/Bmw%20Throttle%20Bodies/P1000992.jpg)
Look at the pics in this post (http://www.motobrick.com/index.php/topic,624.0.html). One time clamps on one end and multi use on the other. Look like yours?
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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.
(http://i1165.photobucket.com/albums/q588/thespacebetweenthings/A39C0DEB-F6E0-4C73-9E41-9B69B6F7C382-256-0000006271C55981.jpg)
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Could explain the vibrations I experience at 3krpm and 4k and intermittent engine coughs.
Ya Think?
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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.
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Always good to finally figure something out. Have some stuf on my /5 that's been having me scratching my head for months now.
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I came across this tubing, and thought it'd be fun to try this with three bottles... any thoughts?
fixed video link (http://www.youtube.com/watch?v=2PiQBr20kM8#ws)
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?
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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.
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And what is a Bosch type II injector? :dunno2:
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And what is a Bosch type II injector? :dunno2:
http://www.ebay.com/itm/190820618228?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 (http://www.ebay.com/itm/190820618228?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649)
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I look forward to your report on the difference these make in your K-bike's performance! :popcorm
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I found that before a long trip I'd synched the throttle bodies with the carb-tune and it was running smooth, upon my return 4 days later I had to synch them all over again. Is this something I should do regularly, or am I dealing with another issue causing the bodies to go out of sync? Perhaps it's time for my fuel injectors to be cleaned, not sure. Either way it has me scratching my head.
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Well you can in fact you positively do on the oil head twins. But, their tb's are controlled by a separate cable to each one and you adjust the cable pull to synch again at about 3-4k revs. Setting on the K would be harder and more "mechanical"
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Thanks Duc750, the only other thing I can think of is that the throttle adjustment screw rubber-washers are worn causing them to loosen and twist themselves out as I ride, obviously messing with my perfectly tuned bodies.