Carburettors.

[Le singe]

I've now fitted the carburettors to my 1100. People with a very long memory will remember me talking about this conversion at the end of summer!
The object was to remove all the injection system and replace with a 'standard' ignition system and 2-off 40mm Bings.
The list of items that have been removed has grown considerably, first the injectors and the Motronic unit, then all the related wiring, as I decided to gravity-feed the carbs, the fuel pump was removed from the tank, a reserve feed can be fitted so the fuel-level gauge was also removed.
Without the gauge, I decided to remove the rider information display. A replacement plastic speedometer/revcounter housing was sourced without the cut-away for the display and this was fitted.
Without the RID, it was possible to remove all the wiring for the gear position indicator and temperature guage.
The hazard warning lights switch was removed,again with all it's wiring, then all the 'safety' switches, clutch, sidestand,etc.
The wiring harness has been stripped of all the now surplus wires.
While everything has been apart, I've replaced every fastener possible with stainless steel.
At the moment, the carbs are fitted, the wiring is ready for the ignition unit to be connected, the choke cables are fitted, just the throttle cable to make and the fuel line adapters to fit to the tank.
Another 6 - 8 weeks should see it done!

 

[cookie]

i think that's what bmw should have built in the first place as a go anywhere bike

 

[Tsiklonaut]

Go anywhere - nowadays reliable EFI does it better indeed, no altitude sickness, no hassle retuning them and i've never heard EFI caused brakedown somewhere, rather carbs do that, but you can repair them more easily tho. But why to have more hassle...

Indeed - let us know about performance and fuel consumption if you get it done!

I'd guess you'll have increased fuel consumption (dual spark head would be better for "pissed-in" fuel, just like airheads), but probably better performance indeed, modifying intakes gets even more out of it. Reason why BMW oilhead rally bikes had Bing carbs and better intakes.

Margus

 

[Le singe]

I've posted this before, but it's worth another look.
R1100RS motor, bottom curve of each pair, standard Motronic system.
Top curves of each pair, 40mm Bings and one-off ignition system.

 

[Warthog]

OK so more power out of carbs. But tuning can do that too.... Having missed the first thread you mentioned, can you fill me in as to why you undertook this mammoth task?

At first glance I like the idea. In my mind there is something nice about simplicity. I love my GS, but it does seem very complicated with all its gubbins. So much could go wrong,even though it may not happen often...it only takes once. Another reason why I'm tempted by a Guzzi: nice and simple
But I'm sure you had a better reason before starting this project, not least because I think resale might be a tad difficult....do tell.

 

[jonnie comet]

Please keep us updated on this project....very interesting for us mechanical anoraks...

 

[Le singe]

Re-sale is something I'm not too concerned about, I've only had the bike 3 years!
As a standard package, the bike is great, it does exactly what BMW claim, however, it is grossly in-efficient, probably due to emission and noise laws,etc.
Yes, you can buy a chip and spend an hour or two on the dyno and see a gain, but when you compare the range of gain given by using the carbs, they've got to be considered. BMW must have been aware of this when they fitted the carbs to the Dakar bikes.
Fuel injection is superior to carburation, no question about it, however the BMW system is flawed by it's crudeness and the inability to re-map it accurately enough. Also, unlike injection, the carbs can accommodate minor changes without adjustment, whereas injection can need another trip to the dyno.
For me personally, the summer is for riding, the winter is for modifications, I think at times I find the modifications more interesting!
You're right in saying there are further plans, I've now acquired 4 spare cylinder heads, plus a complete engine unit, so next winter's project will be headwork.
The whole project is planned, but I don't want to complete it too soon!
Mechanically, owning an 1100 is boring, they just don't seem to go wrong,(yet!).
I'm not looking for peak power figures, but a really strong mid-range, these engines become fragile at sustained higher rpm. The other benefit of the tuning work will be increased mpg, so the more I tune the engine, the richer I will become!

 

[Steptoe]

Just curious, seeing as your fitting carbs. Why use crappy bings, and not mikunis. ???

 

[Le singe]

If they were good enough for the Dakar bikes.....
Seriously, they are almost an exact fit, if the bike was a 150 brake per litre jobby, I would have used Mikunis or perhaps Dell'Ortos, but this is 72 brake per litre, I don't think the difference between the Bings and the other makes would be very noticeable at this stage of tune.

 

[Warthog]

Thanks for the explanation. I think an number of others have said with "keep us posted". Like them, this is something I'm eager to follow: one of the more imaginative GS projects IMO and pretty worthwhile. Best of luck!