38mm Dellorto Pumper carbs

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Joined: Thu Apr 24, 2014 3:20 am

Re: 38mm Dellorto Pumper carbs

Post by rd400f »

I dont have the answer but I can tell you that my BMW R90S has the metal carb tops and they have an M7x1 thread.

So none of the angled elbows that I see advertised have that thread.

They are all M6

Google tells me that BMW might have changed from angled to straight "elbows" because of possible cable wear worries?

Unfortunately my carbs have one angled and one straight "elbow"

Also the cable's are different lengths for angled versus straight....yet another thing to look out for.

Tis a tangled web

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Joined: Fri Oct 27, 2006 3:00 am

Re: 38mm Dellorto Pumper carbs

Post by herbg »

I have since read in Andy Schweitzer's book, "BMW Boxer from /5", on Page 45, that the curved guide tubes were dropped in 1975 as they wore out the throttle cables. My newly acquired 1975 R90S does not have the curved guide tubes. Interestingly, on my bevel-drive Ducatis, none of the Dell'Ortos had this guide tube.
Herb in Ontario ...
1969 BMW R69S
1975 BMW R90S
1999 BMW R1100S (Sold)
2005 BMW R1200 GS (Sold)
1972 Ducati 350 Desmo
1978 Ducati 900SS
1985 Ducati Mille S2
2013 Ducati Multistrada 1200S

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Posts: 79
Joined: Fri Oct 27, 2006 3:00 am

Re: 38mm Dellorto Pumper carbs

Post by vechorik1373 »

I've seen photos of early, 1974 R90S Dell'Ortos with angled elbows at the top cap of the carbs. However, many later R90S
don't seem to have the elbows attached.

The 1975 R90S was equipped with the angled tube on the slide lid also. I know for sure, I bought a new R90S in 1975.
BMW came out with a service bulletin sometime in late 1975 stating that due to the exposed throttle cable rubbing the inside of the bent steel tube, it caused premature cable failure. Not only did you have to buy the replacement straight cable adjuster with the jam nut (13 11 1 264 281), it required new throttle cables, 32 73 1 236 617.

If you want to be a 100% purist and have it look correct, with the bent steel tube, these are the parts you will need:
13 11 1 260 877 the bent tube
13 11 1 260 878 jam nut for the base of the bent tube
13 11 1 260 875 cable adjuster for the top of the bent tube
13 11 1 260 876 jam nut for cable adjuster
32 73 1 233 356 long throttle cable for the bent tube R90S
ALL of the above parts are available still. I had them all in stock, when I owned Bench Mark Works.

I'm looking at a low mileage 1975 R90S and the carbs don't have any angled elbows on the top caps. Is this correct for the model year or have they been removed for easier adjustment (Ducati-style)?
Technical Adviser, Former owner, Bench Mark Works
662 312 2838 cell 9 am to 4pm CST PLEASE!

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