Forum bmwbike.com

Hi Drew,

Well I guess you are right! I thought Bing would be smarter than that. I guess this is how you can differentiate a Brit bike from a BMW. The Brit bikes leak oil and the BMW leak petrol.

THanks again for your input into this.

Pierre

At last! I am not alone! My problem is similar to yours, Pierre.

I bought brand new Bing carbs for my R50 and have never been able to achieve a correct mixture at tickover and idling speeds. It is always too rich.

All carburettor specifications are correct. The air filter is standard. The ignition timing is accurate.

The float needle levers are set at 22mm and there are washers of approximately 1.5mm thickness on the floats. If I lower the float height, even slightly, by bending the levers, the mixture becomes far too weak! If I raise the height, it naturally becomes far too rich...instead of just too rich.

Another strange thing is that when I fit the correct Bosch 242 plugs (short reach 1955 engine), they only last about 100 km before one, usually the righthand side, fouls up and dies.

So I am running the R50 on NGK B8HS plugs at the moment. It spits when cold but at least they burn the mixture and I can accelerate and cruise fast, at normal R50 speeds. But the mixture is still too rich, especially low down and at tickover.

I was wondering if there was a problem with the remanufactured Bing carbs. Could it be that the carb/float bodies are machined according to the earlier central float needle type specifications and are simply not compatible with the lever action float chamber tops because of this 4mm difference in float height?

Oh, by the way, here's a tip: be careful of using the niton or neoprene-tipped float needles with 98 octane unleaded gasoline. The additives in the 98 octane can cause the tip of the needle to stick to its seat. Not good for pistons when it happens at 5000 rpm-plus while overtaking a truck. Use 95 if you can't get LRP (en France, c'est Super) gasoline.

Anyway, I'd be interested in any comments about new Bing carbs for /2s and hearing if anyone has had problems with them.

Prosper Keating

These carbs with lever tops can be set up so that they do not drip. Mine do not ,even when tickling. Adjust the float until the fuel height is correct following the manual. I have a thick shim on top of my float, I haven't measured it but it looks like about 2mm. Unless radically high or low, the fuel level in the bowl will not affect the idle mixture. The idle jet and idle mixture screw control this. As long as there is fuel in the bowl, it has to move through the jet to get into the venturi, it can't get there from the bowl directly since the overfow in the mixture screw will lead it to the outside first. If you are having mixture problems, I suggest carefully cleaning and setting up the carb according to the manual. Replace the jets and jet needles if you haven't already, PO's often clean jets by reaming them with steel wire and ruin them, and you cannot see the damage with the naked eye. I will mention that even a perfectly set up carb can appear to run rich if the timing is wrong, so have a look at that also. You are right about the fuel needle tips.... I use nitromethane in my fuel and it causes the tips to swell, I have to watch them carefully. I did trim them down so that they won't drag the bore of the needle seats.

Unfortunately...I have already tried all of this! I have experimented with float heights ranging from 20mm to 25mm, which is quite radical. I have the washers you describe on tip of the floats. The idle is either far too rich or too weak. These are new carbs from Bing, or were new a couple of years ago, and they have never been right. I would never clean jets with anything but solvent and compressed air. I believe that this pair of carbs is simply a duff pair and I was thinking of contacting Bing to ask them about it. I bought them through a French dealer...which was probably my first mistake. BTW, the ignition timing is absolutely spot on...or as spot on as one can get it with used parts. The only suspect area is the piston rings. I am not sure they are as good as they should be. Maybe I'm too used to running British machines! Would dodgy piston rings lead to sootiness at low revs in a BMW boxer?

Stumped of Paris...

PK

Prosper Keating

Afterthought:

The only time I have had the bike running satisfactorily - not 100% but not bad - with these new Bing carbs was when I swapped the lever tops for the old-style centre feed tops from a worn out pair from the 1950s. I may go back to this set-up. I wonder if the centre feed float needles are still available.

PK

Hi prosper,
re your bings leaking, especially when propped on the side stand-join the club-my 69S has always done it regardless of float height settings.Also, my plugs are usually sooty-I'm resigned to the fact that these bings are just not particularly good carbs compared to amals and others. If it wasnt such a departure from original looks Id like to fit a replacement carb such as Dellorto or Mikuni if it could be done. No one could have had more trouble with his BMW 69S than I have(oil consumption 200 miles a pint, sooted plugs, loss of compression, engine knocks, etc) so take heart and just soldier on.