R51/3 Carburetor

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R51/3 Carburetor

Postby IsaacM » Thu Nov 12, 2015 9:48 pm

My dad has an R51/3, cleaned and serviced the carbs, replacing all the replaceable parts. Tank has been cleaned and rinsed out. He has managed to get the back to a decent idle, but the moment he opens the throttle it cuts out. I will only get to the bike this weekend maybe to actually hear what happens, but thought I'd post here to get some direction.

My knowledge is around the R75/6 with completely different carbs but from his explanation it sounds like an"air" noise from the carb just before it cuts out. From what I can gather both carbs were assembled identical.

Thanks for any pointers.


Re: R51/3 Carburetor

Postby charlton20 » Mon Nov 23, 2015 10:03 am

Hi Isaac.
I have had a similar problem with my R50 and the fix turned out to be that the air jet mix was wound out to far and when idling it ran fine but if you opened the throttle rapidly it just got to much air with insufficient gas and it would die, you then had to take the throttle back rapidly to not stall the motor but if you took the throttle up slowly it would survive then you could give all that you want of it. So first thing that I would look for is screwing in the idle air mix so as to give it more gas at low speed. Another thing to look for is that the volume of air being drawn in to the carbies is equal in both carbies, there is a wonder tool for this and it is a EMPI Carbie synchronizer, although it is made for VW bugs it is a must have tool for BMW Bing carbies. Bing carbies are notorious for being buggered no matter how many new parts you replace in them, I have learned this the hard way and the alternative is to buy new ones and they are seriously expensive. Another thing to look for is distorted flanges where previous repairers have over tightened the carbies to the head studs, they will leak air in there and give you all sorts of grief.
Happy Fiddling. Frank in AUSTRALIA

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