I put Siebenrock on my engine a few years ago (but I also changed the camshaft and ported the tops).
My experience is that if you drive the Siebenrock-kit as a you would drive a R80 it will give you better mileage then the R80, but not much..

IMHO most mileage problems are caused by the carbs, and if you clean them and change the needle and jet (the jet the needle goes through) every 20-30kkm it should be fine.

All jets should be original:
Main jet 135
Idle jet 45
Jet 2.68

Fuel Consumption problem with R 80 GS
 

:thumbup1:
Hi Ali Baba and others,

I've written to Bing carburetor about the subject and they recomended to change needle jets and main jets. Normally you've should done this every 25 K kms they say (or let's say 30-35 K kms). Mine is already 44 K kms and sure it is needed to change.

I am going to make additional change of float and bowl kit which are alcohol resistant.
Total cost seems like 300 USD.

I've spoken the main and the best BMW service center named Borusan in Istanbul and they said we don't have enough knowledge to solve your high fuel consumption problem (low mileage). So I decided to solve problem myself. Hope FrankWarner and GS Workshop reads this thread as they too tried to help me a lot with you about this problem.

For info:
www. bingcarburetor.com
e-mail: bingcarburetor@bingcarburetor.com

(I was speaking to Fay)

Not quite the same as a GS, but my 78 R80/7 gets 16km/litre, 45mpg. Mileage recorded on an accurate bicycle speedo on a 11Kkm trip.

300USD is a lot!
I normally pay less then 150USD for a complete overhaul kit (incl diaphragms) and the needles and jets.

But then normally I don’t change the floats, I’ve changed them once in close to 200kkm. I seem to remember that there was an issue with the alcohol resistant floats, but I can’t remember…

Too much ?
 

Hi AliBaba,

It's like this:

Alcohol Resistant Float & Bowl Kit that comes as an addition to the #6 Kit. Both Kits together @ $282.73

44-051/145 Main Jets 2 @ $5.40 = $10.80

The Manual is $10.50 (carbs)

Shipment $ 36.00

A question: Sometimes I see it's said 32 or 40 mm carbs? What size is my CV carbs? 32 or 40 mm?

Thanks a lot,

Samy

You should have 32 mm carbs. Close to the cylinder there is a number, mine is a bit dirty so it’s hard to read but it’s something like 64/32/xxx. The second number (32) tells that it is a 32mm. If you have 40mm you will have a hard time reducing the fuel-consumption…

The needle is #9 here: RealOEM.COM * BMW K12 R80GS/96 CARBURETOR CAP/PISTON/STARTER HOUSING

The jet in question is not the main jet, but #9 here: RealOEM.COM * BMW K12 R80GS/96 CARBURETOR-FLOAT ASSY/JET

The needle moves inside the jet and vibration makes it touch and they both wear. The main jet (#13 on last link) should last “forever” it has no mechanical wear.
Prices might vary; I have always bought the parts at BMW.

Fuel Mileage on airhead
 

I believe the most efficient 'airhead' BMW's were the higher compression (9.2 to 1 as opposed to 8.2 to 1) R75 and R80 models of the late 70's and early 80's ~ 4.5-4.75 liters per 100km. So if fuel economy is the top concern, that would be the setup to have.

I still think that if you are going to convert to 1000cc's the best way to do it is with the complete cylinder/ piston/ heads/ carbs/ exhaust from a stock BMW engine. Fortunately, this is easy to do and pretty much a straight swap with only new gaskets needed. Doing it this way gives you a base line for tuning that you can then stray from if you choose.

Intermittent Loss of Power at high speed
 

Following up on your intermittent loss of power at sustained speeds of 80km/h. I'm on a road trip in Turkey right now having the same problem. Just to clarify, you fixed this problem by cleaning the carbs (again) or sorting the inition issue.

Could be either with me. The crankcase breather sometimes pours oil down the air intake like to the carbs, but I've also recently put on a large 43L tank that may have effected the CDI mounted underneath it.

Thanks for any help you can provide. M.

unfortunately the bike was stolen and crashed so i never got to fix the problem. if you have oil leaking intp the carbs i would try that first though.

Info wanted on Ignition Control Module
 

Hello
I have a 1984 BMW R80RT
A few days ago I was riding and the Bike suddenly stopped. No Spark what so ever. From reading several blogs I suspect that my problem may be the Ignition control module. Because parts are very hard to find and also expensive I would like to know if there is a I can test this unit. I have removed it and have on my workbench. I can not find a schematic diagram and the repair manual I have ordered is delayed. If this unit is good I will go the next step and check the impulse module.
Thanks

You might just want to check it by using another coil, any old 12v coil will do just to check out the electronics. Although I will concede, sudden total catastrophic failure is normally electronics. It wouldn't hurt to check no wire has fallen off also :)

You might also want to be sure you have installed the needles in the right slot.. wrong by one can make teh sort of fuel mileage difference from the norm that you are having.

About the ignition problem.. If you dont find anything wrong with the ignition components, check the neutral switch. That little sucker foold me pretty good..
If you have spark with the clutch in, neutral switch is the problem.
Its easy to change, you only have to take the gearbox out of the bike.......
Good luck

yngve
r 80 gs

Have you solved your problem ?

My R100RT ran on 5.7L/100km at 90km/h which was fine since I am used to 6.5L/100km or there about... on my R80/7RT (rebuilt/overhauled/modified).

My Siebenrock kit (barrels, pistons and heads) have been using anything from 9L to 5.9L/100km at 90km/h constant speed... it is settling down now and seems to be stabilizing around 6.2L/100km at 90km/h.

As for jettings:
BING Power Systems GmbH · Nürnberg
BING POWER SYSTEMS GmbH
click on Service, then on Tuning Manuals
BING POWER SYSTEMS GmbH - Tuning manuals
You will need to fine-adjust the jetting depending on if you move the carbs from the original bike/cc-volume.
I really like the Bing 40mm on 800cc; much smoother running though the down-side is a huge loss in accelleration speed. Top-speed same or just a tiny bit better. Mileage is a tiny bit better. So the trade-off was ok for me.

The impulse module.=
Second Hall Effect Sensor for an Airhead

There is a link there to flashes site on testing the impulse module ...

But - the easy way to test ... where the impulse module connects to the control module near the alternator - dissconnect the impulse module, short the centre connector (that goes to the control module) to ground .. if you get a spark then the control module, coil, HT lead, spark plugs are all working. Always best to test insitue - saves dissassembly, and test everything inbetween (wiring etc).


The clutch and netral switches do no effect the ignition circuit - they effect the starter motor circuit .. red herring.


-------------------------
You should start a seperate thread - makes it easier for others to find the information on that subject.