The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: TomHoldom on July 04, 2025, 09:28:29 AM
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Hello again,
Having got my 1978 R65 out again for the Brittany summer, it started up fine for a small ride.
I then made the mistake of leaving it a week or so in quite high (for Brittany) 34 degrees celuis, to find that the right carb. had dried up and was subsequently blocked.
Initially it didn't appear to the petlock, as it would start up and run on one cylinder, but a few days later there was an obstruction in the petlock which has now cleared.
The problem I have been left with is the right side carb (flat top) is dripping (quite fast).
The float mechanism works (i.e. when I lift the float the petrol stops), so perhaps unsettled something while looking for the initial problem when is was not getting petrol, and now the float is perhaps catching on the side of the bowel, though everything appears to be in the correct place.
Any ideas appreciated
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If the float is not hanging up on anything a common cause is the float absorbing fuel and becoming heavier that it should be .
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Corrosion of the brass stub coming into the carb got me! it looks like little bits of tissue paper, just enough to intermittently lift the needle valve very slightly. It's not obvious. Red tank liner, black bits from deteriorated hoses and rust are conspicuous in their circling the float bowl like little sharks.....
If you pop the fuel pipe off and stick a cotton bud in it, you'll maybe collect this delicate gunk. It looks like a moths wing that got wet. Then blast it with carb cleaner.
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Another thing it could be is the needle seat being a bit pitted. The dealer in Austin, TX, told me years ago to put valve lapping compound on the end of a sharp pencil and give the seat a quick "grind" then rinse out the grit. I've had that work a couple of times but the most likely cause is probably a heavy float.
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Thanks for the ideas - I'll have another look.
I thought it was a bit too much of a coincidence for the float to suddenly loose buoyancy just at the moment I had been tinkering....
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Well, its got me a bit stumped ....? Cleaned, checked the bouyancy of the floats - all good.
the mechanism works with the bowl off - clearly stops the fuel by lifting the floats level, but still drips with the bowl replaced.
I can only think that the floats must be catching on something, but I can't see what - I'll upload a video of the me lifting the float to stop the fuel supply
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Try removing the offending bowl and fill it with fuel to the normal level and then let it sit on the bench to see if the bowl is leaking. If it is look carefully at the brass overflow tube to see if it's cracked or a loose fit in the bowl.
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Here are 2 videos: the first showing me operate the float to cut fuel, the second showing the drip once the overflow is reached. No leak in bowl
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and the drip.....
(videos short due to size limit)
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any more ideas.....? any clues from the short video clips....?
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any clues from these photos...?
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any clues from these photos...?
Yes. Are the carbs level (float bowl datum) when the bike is on its centre stand? That rh one looks twisted towards the engine at the top, and therefore not level. Hard to tell from here though.
Think DIY shelf and spirit level. You know, when your screwdriver rolls off one end 😜