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A friend brought me his 1993 R100GS with a problem. It starts and runs fine up to about 4500 rpm, but under load in top gear (passing or climbing a hill) and it starts to shake. Feels like one carb is getting starved for fuel. I pulled the bowls off to have a look see and found it had been converted to the independent black alcohol proof floats. These are not covered in any BMW manual, does anyone know the method for checking fuel levels and set up for these? Is it the same level as with stock floats, or do I need to buy a Bing manual? Also found it was low on motor oil, one carb was cocked about 15 degrees off plumb, there was water in the transmission oil and the white o-ring and shim in the oil filter cover was installed backwards. Other than that... I've started with a full tune up and oil change. Sure is pretty, though:

Tim Shepherd wrote:A friend brought me his 1993 R100GS with a problem. It starts and runs fine up to about 4500 rpm, but under load in top gear (passing or climbing a hill) and it starts to shake. Feels like one carb is getting starved for fuel. I pulled the bowls off to have a look see and found it had been converted to the independent black alcohol proof floats. These are not covered in any BMW manual, does anyone know the method for checking fuel levels and set up for these? Is it the same level as with stock floats, or do I need to buy a Bing manual? Also found it was low on motor oil, one carb was cocked about 15 degrees off plumb, there was water in the transmission oil and the white o-ring and shim in the oil filter cover was installed backwards. Other than that... I've started with a full tune up and oil change.

That shuddering sounds a little like a holed diaphragm in one carb. I've had that experience on a couple of bikes. Can you induce a shudder in, say, 4th gear by applying full or heavy throttle at low rpms? If not, then back to your line of inquiry.

Also, have you eliminated impaired fuel flow to the carbs as a possibility? Crossover tube OK and flow past the float needle OK?

I don't have any experience with those alcohol proof floats. I wonder if there is a way to hold the floats up while you carefully remove the float bowl and compare the levels of the residual fuel in each of the bowls.

I also wonder if you can weigh the alcohol proof floats and determine if one side has heavier floats. You might already have a digital postal scale which would do the job.

About the water in the transmission oil, do you know how it got in? You probably already know that the "usual" way the water gets in there is to dribble down the speedometer cable, past the rubber boot, and into the transmission. Happened on my R100/7.

Lastly, if your inquiry points to the floats, what about simply buying a new set of stock floats and installing them? If you don't need them you just don't need them yet. I keep a new set of floats in stock because I know there will come a day when on of my bikes suffers from a heavy float.

Ken

If the tune up and carb balance doesn't fix it I'll be checking the diaphragms next. Shuddering only happens at 4-4500 rpms in 5th, advance is OK, timing is on the mark, plenty gas flow. The independent floats ride up and down on pins attached to the float bowls, they are not physically attached to the float needle lever. Water in transmission got there through the speedo cable boot, it's old and loose. He said he washed the bike before riding the 90+ miles to my house. Hopefully no damage was done. If it's not the diaphragms, I'm tempted to swap to new stock floats, but he is on a budget and it would require changing the float bowls too. Not cheap!

Snowbum has an article on the independent float kits:

http://bmwmotorcycletech.info/bingindependent.htm

Kurt in S.A.

In my experiance problems with diaphragms show themselves around 3000 rpm, problems with float bowls bing set too low results in an inability to rev much past 4000/4500, it just feels like a total lack of power.

That does sound like a match for my recent float level problem. With the independent floats, is there a way to check float level with fuel flow? Pull the bowl, then manipulate the floats to find the point where fuel starts to run down your (gloved) fingers?

The independent floats system does not "check" for level like the old ones, using the float surfaces and the carb body.
You have to measure from the flange surface of the carb to the opposite side of the metal lever to set the needle valve.
The picture in the manual shows the carb body upside down so I'd assume you need to remove the carbs to do this.
The dimension for 53,54,84,64, and 94 types is 10.5mm. For a 55, it's 8.5mm.
You still set this by bending the little finger that operates the float needle.
Tims recommendation to change the diaphragms is probably a good one, too. My bike started to go wimpy at over 4K when I tried to pass...and I usually downshift from 5 to 4 when I'd do it.

Well, I think I may have found the problem(s). First of all there was water in the gas, so I drained the tank, cleaned the petcocks and am currently waiting for everything to dry out before I reassemble. Next, as I was putting the carbs back on, one of the rubber snorkels inside the airbox was dislodged. When I opened the airbox, I found the rubber snorkels had been installed on the wrong sides, with the intake pointed straight up and pressing against the air filter. I won't know until I put it all back together correctly, but we shall see...

Tim Shepherd - Big Island Airhead Guru

Tim Shepherd wrote:Well, I think I may have found the problem(s). First of all there was water in the gas, so I drained the tank, cleaned the petcocks and am currently waiting for everything to dry out before I reassemble. Next, as I was putting the carbs back on, one of the rubber snorkels inside the airbox was dislodged. When I opened the airbox, I found the rubber snorkels had been installed on the wrong sides, with the intake pointed straight up and pressing against the air filter. I won't know until I put it all back together correctly, but we shall see...

Well, we don't know if it will fix it, but you'd think it HAS to improve it.