Dellorto carbs on a R100

[STEVENRANKIN]

Some guys, back in the day, bought into the go-fast aura of the R90S “superbikes” hook, line, and sinker. Del’Ortos on an R100 are mostly that—if they had been a really great improvement, presumably BMW would’ve used them for more than three years.

Yes, some guys did buy into the BMW go fast bikes and look. BMW was on the ropes for sales due to its image of being a gentleman's touring bike. The R90S opened up the market for them.

I want every bit of power I can get on my Airheads as long as it is reliable and plays well. The Delortos worked very well. Just as well as the Bings. However, there was just a bit more acceleration advantage with the Delortos due to their accelerator pumps.

I can imagine BMW chose the Bings over the Delortos not because they didn't work nor because the Bings were so much better but, because the Bings were cheaper to buy and they did the job almost but not quite as good as the Delortos.

I love my Bings up until it is time to pass a line of slow moving cars. Then, I would love to have that little extra shot of power from an accelerator pump Delorto.

If you love touring and crusing bikes, fine, stick to the Bings. St.

[khittner]

My decidedly un-calibrated butt dyno never discerned much useful acceleration difference between either of the two R90Ss that I once owned, and the Bing-equipped R90/6 that I had in between them. But I didn't take any measurements, and both 90S bikes had been modestly decompressed to work adequately without dual-plugging on the available high-test fuel supplies, so I probably didn't have all of their go-fast capability at hand. All three of those bikes had original or added-on "S" fairings, and I did prefer either Silver Smoke or Daytona Orange to the placid Monza Blue of the 90/6, and the extra storage compartments behind the cowled seats were sort of handy.

I remember complaining to my mechanic, the lamentably-late Bill Fleming, proprietor of Freeport, Illinois' former C&D BMW, about the short-lived, apparently heat-vulnerable, cable boots on the Dell'Orto carbs. Those rubber cable boots, which are necessary to keep rain and wash water out of the slides, only seemed to last about a year or two before crumbling away and needing replacement. Bill was evidently similarly chagrined by the feeble cable boots, which he replaced with regularity. His advice to then-bachelor-me: "Konrad---never buy or use German or Italian condoms." Still my favorite bit of airhead mechanic's advice.

[RPGR90s]

Long time stock '74 R90s owner. I've always like the Dellorto's, although IMHO, they require more tinkering, fussing than the stock Bing's Ive had on my R75/5 and '93 R100RT. With the Bing's, once synched they almost never changed, no matter the weather.

With the Dell's, once the weather changes from spring to summer to fall, adjustments are needed, at least for the mixture.

For trouble free operation I would take the Bing's every time.

[toooldtocare]

A friend of mine had Dell's on his Motorsport. It never ran any better than my Motorsport.

Wayne

[lkchris]

A MAJOR advantage of Bings compared to Dellortos is that Bings automatically adjust to altitude changes.

[swall]

How so?

[khittner]

If I have the theory right: On CV Bings, the throttle butterfly opens and closes the main air passage through the carb body. The less-dense air at altitude will suck the diaphragm/jet needle assembly less, allowing somewhat less fuel to flow into the intake passage, and will effectively keep the air-fuel mixture appropriately leaner for high-altitude operation. Available total power will, of course, be down somewhat because of the relative lack of available air and fuel, but that performance loss is likely to be less so than an engine with slide bore carbs where the fuel flow through the throttle-opened jet (unless the jets are changed when operating at altitude) becomes effectively richer with the reduced-density air supply, and combustion becomes less stoichiometrically optimal.

[PGlaves]

If I have the theory right: On CV Bings, the throttle butterfly opens and closes the main air passage through the carb body. The less-dense air at altitude will suck the diaphragm/jet needle assembly less, allowing somewhat less fuel to flow into the intake passage, and will effectively keep the air-fuel mixture appropriately leaner for high-altitude operation. Available total power will, of course, be down somewhat because of the relative lack of available air and fuel, but that performance loss is likely to be less so than an engine with slide bore carbs where the fuel flow through the throttle-opened jet (unless the jets are changed when operating at altitude) becomes effectively richer with the reduced-density air supply, and combustion becomes less stoichiometrically optimal.

Compared to fuel injection, carburetors are at best crude mixers of air and fuel. They can somewhat compensate for pressure changes but do so poorly. Some compensation is better than no compensation but the effect is limited. I had a friend who inherited an R75/6 from his father-in-law from Missouri (800 feet MSL) and the bike was relocated to New Mexico (6,700 feet to 9,500 feet MSL within 20 miles). The bike ran crappy (tech term) until I rejetted it for him.

[lkchris]

How so?

Less dense air means the diaphragm raises the needle less.

Recall that Bing makes carbs for aviation.