Need help balancing TBs

[Westone]

Hi,
Well I decided to check the balance of the vacuum between the TBs on my K75, since it seems pretty straightforward and within my capability. So I made my homemade device with 3 columns of silicone tubing filled with dark 2 stroke oil and hooked it up after warming up the bike. The TBs on cylinders 1 and 2 were pretty much in balance already, however the one on cylinder 3 was way out, dropping rapidly as soon as the engine started, while 1 and 2 climbed at pretty much the same rate. Ultimately I found that there is not enough adjustment to get #3 in synch with 1 and 2. Turning the adjustments for 1 and 2 out 6 turns and closing 3 all the way only somewhat slowed the imbalance, but not much.

It did occur to me that perhaps there was a leak in my homemade device, but I eliminated this possibility by disconnecting the hose for #3, plugging it, and then I was able to synch 1 and 2 with no problem. And there were no air bubbles appearing from any of the connections.

What does this mean? It seems there is not nearly the vacuum at the port on the #3 TB as the other two. Thanks for any help.

[Grim]

I'd check the #3 throttle body/ Grommet/bellow where it attaches to the flange on the head for a vacuum leak. Those rubber grommets/bellows are know to eventually fail with age.

There is a write up I read a couple days ago on how to do it if you find a leak. Pretty straight forward. There is two parts (each cylinder) to replace. The bellow and there is also a O-ring under the flange that bolts to the head.

 Might also consider getting your injectors cleaned and replace the fuel lines while you have it apart.

This is the post I read.
http://www.motobrick.com/index.php/topic,624.msg1572.html#msg1572

[TimTyler]

Try reversing the hoses on your gizmo so that tube #3 goes to TB #1. That will tell you if your device is wack or if TB#3 is wack.

How does the engine sound? If #3 is really that far off your engine should sound really rough.

If there are no air leaks, and the TB butterfly screws haven't been touched, then the brass TB adjustment screws should all be roughly 1.5 turns unscrewed from closed for a balance with a 1k RPM.

[Westone]

Thanks for the replies. The screws with paint on them appear to be untouched. I just installed rebuilt Bosch Type II injectors and it is much smoother.

Grim thanks for the link.

TimTyler that's a good suggestion to reverse the hoses on my gizmo. Hadn't thought of that.

The injectors apparently richen the mixture somewhat, and that could be covering up an air leak on one cylinder which would cause an overly lean condition.

It's raining, getting dark and I'm toasted. Soon as the weather improves I'll take a few minutes to apply these suggestions.

[Grim]

No problem. Making lists of things I need to do on mine and sounds like you were doing the same. Those parts are not expensive $9 each. http://www.2wheelpros.com/oem-parts/1992-1997-bmw-k1100lt-89v2-air-collector-inlet-manifold-assembly.html

[Westone]

Okay I just tested it again, reversing the position of the hoses on my homemade vacuum balance tester, and my tester seems to be working properly. It again indicated the #3 TB to be lacking in vacuum so much as to not be able to bring it into adjustment. So it looks like I'll be reading up on the link Grim provided and ordering some parts.

While looking at this I have also discovered that the radiator fan is not coming on. I let it idle for 10 minutes in the 60* weather we are having this morning and it never came on. I'll be making a separate post on that.

[Westone]

Is there any reason the propane leak test would not work just as well using MAPP gas? That's what I used because that's what I had on hand, and I cannot get a positive result of a leak anywhere around any of the TBs.

Besides brazing copper plumbing joints, I've also used the MAPP gas for my son's potato cannons and it worked fantastically for those.

If there is a leak, which apparently there is from the vacuum test, I'd like to order parts first thing tomorrow morning when the dealership opens in order to have them as soon as possible. But the original problem is the out of whack vacuum on TB #3. Is there anything other than a leak which might cause that?

[lhead]

If a vaccum leak is ruled out, the next thing I'd do is check the valve clearances on #3 cylinder.

[Westone]

Okay, I wondered about the valves but didn't know if being out of adjustment would have the effect I'm seeing. Also, I haven't done the propane leak test before so I don't know if a leak can be ruled out. I put a healthy amount of MAPP gas around the area though, with no noticeable affect on the idle speed. And now that I think about it, if it was sucking that much air so as to reduce the vacuum at the port, it probably would have sucked some in and burned it up.

The clamps on the top and bottom of the throttle bodies are the one-time use type, which I am guessing indicates the rubber pieces are original. So if I did change them all out, and the issue was not resolved, I wouldn't consider it a complete waste of time considering their age.

[Grim]

MAPP will work. You are just looking for a change in idle when it gets sucked in.

If the vales check out and you might look at this as its easy to see. On the throttle shaft that actuates each throttle body is an adjustment for each throttle body. They are set at the factory and then some paint is applied to mark them as adjusted and to seal them. Inspect that paint and make sure somebody hasn't messed with it.

On the cooling:

 I was surprised at how hot they have to show before the fan activates and its more then 10 minutes to activate on my K1100 (103C/217f according to the manual The dash waring comes on at 111c). Its darn near in the red and I will have to have run it pretty hard then get caught at a light for a while to get it to come on. Once it comes on it doesn't shut back off till about midway on the gauge and let me tell you it will dump some heat on you when it comes on. From what I have been told/read that is normal.

Make sure the fan spins free by hand or attempt to power it and verify operation.

[Westone]

I'm no longer worried about the fan. It hasn't been over 75* since I got the bike. It is probably fine, and I've made a mental note to watch for it when it gets hot out. And there's always the idiot light, assuming it works.

TBs #1 & 2 have the silver screw with blue paint. #3 does not have that screw, at least not in the same location as #1 & 2, that I saw anyway. Maybe it's behind some of the extra plumbing on #3 and I didn't see it. The paint on 1 & 2 is 25 yo, but it appears not to have been touched and in the original position.

I plan to try the leak test again just to be sure, since I am inexperienced with it.

[Westone]

The fan came on today after it sat idling for 26 minutes and I juiced the throttle a little. It was easily heard.

A second MAPP gas leak test did not induce any noticeable change in the idle, and it was thorough around the upper and lower portions of the TBs. I guess checking the valve adjustments is next and I plan to get some valve cover gaskets before opening it up.

ETA: While ordering the gaskets at the dealer I spoke with the mechanic who services my K. His opinion is it is very unlikely the valves are out enough to cause this situation, without also causing some other symptoms, mostly running poorly from being so out of spec. Still, I'll check them when the gaskets come in, but am looking at getting into the TB itself to see what's going on.