To preface I had this issue among others before giving up and taking it to a reputable BMW dealer for service. They adjusted the carbs and floats. It ran great. I put 20 miles on it. I had it out today and as I went to turn down a street, it started idling rough and felt like it was on one cylinder. I pulled the right carb bowl and as soon as I did it started filling with gas. I closed it up and tried starting it. Ran fine after that. Any ideas?
Had the same issue before they worked on it. I’ve been putting seafoam in the fuel to help keep everything clean. Maybe this is causing the float needle to stick?
I might try replacing the float needle and needle sleeve. I’ve always got them as part of a rebuild kit from Bob’s bmw. Maybe I’ll order them from Boxer2valve this time to see if theres a difference.
I would first check the operation of the floats. Turn the petcock and drop the float bowl. Manually move the float up/down and check for how it works or if something could be interfering. Then hold the float up with a finger and open the petcock...be ready to catch the gas and again operate the float to ensure that it works correctly. Note that gas should shut off when the horizontal line on the float is even with the top body line of the carb.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.
I checked the float level. Stops fuel when parallel to carb body. I believe I found the culprit. In the bottom of the carb bowl, I found little black specs. It must be coming from either fuel lines or the carb just cleaning itself from the seafoam. I have inline fuel filters so can't be coming from the tank.
Also I noticed the brass vent tube coming up from the bottom of the bowl. If the carb is overfilled, should it drain out there? I've never seen it drain through that. I'm wondering if it's clogged and the carb bowl isn't filling because air has nowhere to go.
Sometimes when things are too clean they hang-up from friction. Try spraying wd-40 on the needle valve and float axel. Also try spraying gumout through the vent tube.
Another thing to consider; several years ago I had a portable generator that I used daily on field jobs. It would run for a while and then appear to run out of gas while the tank was full. I tore down the carburetor and found no problem. Eventually I discovered the problem. It was dirt in the fuel tank. When it was not running enough gas would get through to fill the carb, but when running it would not feed fast enough to keep the carb full.
I would pull the fuel valves out of the tank and make sure they are clean and the bottom of the tank is clean.
All good advice from the others. I had a similar situation. The bike would run fine for awhile then would quit. I found that a piece of tank liner was floating around and would intermittently float down to the petcock and close off the gas. Once the engine died and the pull of the carb stopped, it would start again.
This weekend I'll drain the tank, check the fuel taps and screen, and then report back. On the topic of fuel, does anyone use any additives? My go-to has always been sta-bil and seafoam. I saw Amsoil offered a motorcycle octane boost and was considering giving it a try.
For storage, I use stabil for long term (more than two months).
You don't need an octane booster as long as you use the highest octane fuel you can get with 10% or less Ethanol. I am running 9.5 to 1 compression in my current bike as well as my now gone bike, I have never had problems with pinging using 93 octane 10% ethanol or 90 octane no ethanol.
I am not sure what Sea foam is, is it a cleaning agent or stabilizer? I quite frankly never have had a problem with cleaning agents because I go through so much gas and I am picky about where I buy it at. St.
I use 93 octane with 10% ethanol. Seafoam is a cleaner and stabilizer. I've had good luck with it. My stuff sits a lot so fuel has a tendency to go bad. The seafoam seems to keep things running clean in the carbs. A good example is this John deere gator I have. It was sitting for a bit and I started it up and had it running when the carb started leaking out the overflow line. I quickly turned it off (it has a fuel pump) to stop it. I'm pretty certain the float stuck. I dumped a whole bottle of seafoam in the tank, started it up, and sped up and down a field. After that no more problems.