leaky flat top carb

[TomHoldom]

Hi,
I have leaky carb. (1979 R65)
with the float bowel removed lifting the float to horizontal stops the flow, so does that mean my float may need replacing (I have flat tops). Does anyone know what they should weight - mine is around 18 or 19 g. I tried to test the float action by holding is in petrol but wasn't convinced this was a good technique.
Any help appreciated.
Tom

[donbmw]

Can?t tell you the weight of new floats. Just going by the age of your bike and the looks of the floats I would change them. I have changed mine multiple times on my bikes in the 40 plus years of owning them. The last time I I changed them I went with the alcohol safe floats from Bing. You have to call them for these floats to get the one like the stock floats.

[TomHoldom]

ok, thanks - probably worth changing both sets while I'm at it ?
I was looking at getting from UK's Motobins - they give this part number:  BMW: 13 11 1 254 766 . Is there any way to check this the right part. My carb ref is 64/32/2040

[Bob_Roller]

I found an old float been sitting for years it weighs 13 grams .

[TomHoldom]

Is it possible to re-install my new floats without dismounting the carbs - bit tricky to get the float needle back in I imagine.....

[Barry]

Hi,
I have leaky carb. (1979 R65)
with the float bowel removed lifting the float to horizontal stops the flow, so does that mean my float may need replacing (I have flat tops). Does anyone know what they should weight - mine is around 18 or 19 g. I tried to test the float action by holding is in petrol but wasn't convinced this was a good technique.
Any help appreciated.
Tom

When I installed new floats I weighed them on super accurate lab scales at 12.495 Grams. Call it 12.5 grams. That was lighter than I expected as 13 grams is reckoned to be the standard weight.

You can run floats at 13/14/15 grams or even in a pinch at 16 grams but you are definitely on the slippery slope beyond 15 grams. Floats that weigh 18 or 19 grams are sinkers.

My old floats did the same as it happens also on flat tops but the fact that they are flat tops is not the issue and the floats are no different to the dome top Bings. Those Motobins floats are the correct ones .

You can install new floats with the carbs on the bike but yes it's tricky. Note the pivot pin is supposed to be driven out in only one direction because one end of the pin is serrated and you don't want to be driving the serrated end through both lugs and risk breaking a lug off.  If you look at the installed pin carefully you should just about be able to see which side is serated and then drive the pin out from the other side which might mean removing the carbs.

[TomHoldom]

OK, I got it running again after more than a year sitting. Neither carb :happy leaking after replacing both floats. The issue I have now is the engine is racing once I get going. I can slow it by braking with it in gear, and it will then revert to normal revs. Any ideas?
Could be choke related ? I've not had it warm enough yet to turn the choke off.
(for future posting, would this post be better located under a new subject?

[svejkovat]

Stays revved coming to a stop. Can slow it in gear to return to normal.

That was cured, for me, by discovering and replacing a broken spring in the "bean can".

If you've never inspected the timing advance mechanism you might want to just check this anyway. It's pretty easy to do on your bench top. For starters you might just remove the little oval inspection window on the "can" first while it's still mounted and shoot a little aerosol lube into the works. Then go for a ride.  It may just need that little bit of unsticking. If it fixes the high idle then you're golden. If not you might remove the can and disassemble to inspect anyway. Clean and lube it. Check that everything is in order.

There are half a dozen things that can cause the issue you describe. Unfortunately I monkeyed with them all before I found the broken spring jamming up the works in the timing advance. But we learn, eh:)

[donbmw]

OK, I got it running again after more than a year sitting. Neither carb :happy leaking after replacing both floats. The issue I have now is the engine is racing once I get going. I can slow it by braking with it in gear, and it will then revert to normal revs. Any ideas?
Could be choke related ? I've not had it warm enough yet to turn the choke off.
(for future posting, would this post be better located under a new subject?

Shouldn?t need the choke but just for a few minutes if the carbs are working right. My starting procedure is full choke on start, at least half after start up or just enough to keep running, shortly after ride off choke is off. This is only the first start of the day and regardless of how cold the day is.

[TomHoldom]

Appears to be a choke issue. Once warmed up it seems to run well once the choke is off

[donbmw]

Check your fuel bowls. There is a small jet or orfice in the bowl where the tube for the choke circuit gets its fuel from. When I bought my R90 I didn?t know I had a problem with starting until the cold weather came. It was running on one cylinder until it warmed up. Found this was stopped up.