Anyone know anything about mass airflow sensors?

[Vamana Gupta]

18 minutes ago, Buckster said:

If you find the specs of the sensors you can make them easily enough. They are a very simple and readily available semiconductor device.  You can test them with a multimeter, just power up the circuit then look for a fluctuation in voltage when you run a magnet near them.

Let's start with the basic numbskull...before he starts waving around magnets on a magic wand ...

[Nute]

Earth connection was the first thing I looked at, injectors are new, loom is the original and the bike ran (briefly and like a tractor) before I pulled it apart. Continuity, where I can check it is fine. They are crank position sensors, two of them, at 0 and 180 degrees from memory when I pulled the cover off.
 

Depending on how long I spend at the pub tonight I will have a look tomorrow and see what sense I can get from them as Ian suggests with a magnet. I assume I’m looking for a gradual change 0-12v across the signal and ground ( there are 3 wires) ?

[Catteeclan]

That a 2v model Nute?

[Nute]

On 31/12/2025 at 20:12, Catteeclan said:

That a 2v model Nute?

Yes, a 1983/4 RS

Hall effect sensors were OK and got it running today after a soaking in petrol after a connection to the fuel rail leaked. Fortunately the exhaust stubs weren't hot enough to set it all alight

Runs a bit rich but I've not had it up to temp yet, ran out of time. If anything I expected it to be lean due to the difficulties in getting the induction post air flow sensor all airtight. Id love to get rid of that thing.

I now have to decide if  Im going to keep the original loom or bit the bullet and rewire it with motogadget. Also need to deal with the front end - decided to keep the original forks and brakes and rebuild it all, and change all the lights. 

 

[Catteeclan]

I have a repair manual I pulled from somewhere, it's got some good info should you need it.

[Nute]

Cool, thank you !! Is it a physical book ? 

I downloaded a manual and then printed it out, its getting a bit dog eared and oily now  Its been really useful although the photos are all b&w and hard to see any detail  as its from 40 years ago. There are also some brilliant web sites maintained by real enthusiasts with a lot of good info.

Ive been looking at a tank cap& lights - headlights, indicators, brake lights etc. There are some nice looking ones on the "restore/ custom your BMW" type sites but they are very pricey. I ordered some chinky equivalents and some have turned up - appear to be very nice quality at 25% of the cost, although not tested / tried fitting them yet.  

[Catteeclan]

11 hours ago, Nute said:

Cool, thank you !! Is it a physical book ? 

I downloaded a manual and then printed it out, its getting a bit dog eared and oily now  Its been really useful although the photos are all b&w and hard to see any detail  as its from 40 years ago. There are also some brilliant web sites maintained by real enthusiasts with a lot of good info.

Ive been looking at a tank cap& lights - headlights, indicators, brake lights etc. There are some nice looking ones on the "restore/ custom your BMW" type sites but they are very pricey. I ordered some chinky equivalents and some have turned up - appear to be very nice quality at 25% of the cost, although not tested / tried fitting them yet.  

No it's 3.1mb. It's all about trouble shooting with wiring diagrams and testing methods.

[Nute]

I have the troubleshooting the EFI one, but if you are happy to share the more info the better !

There are a few really good forums with lots of useful info on them, motobrick.com & K100-forum are both very good.  Some of those guys have rebuilt any number of them and know them inside out. 

[Nute]

Slightly annoying day, put some new exhaust headers on the bike, then noticed a very slight coolant weep around the base of a stub on top of the block. It's buried in amongst everything else, pretty much the first thing I put back on when putting it all back together.  I put a new o ring on the bloody thing when I was reassembling it.

Whilst trying to work out the best way of getting at it which won't involve taking the whole thing apart again I noticed a tiny drop of fuel drip from the underside of the tank. Not sure if it is a tank leak or a pipe /joint ... sigh...gave up and came inside for a fish finger sandwich dinner (chef is away with her mates)...

 

[Buckster]

22 minutes ago, Nute said:

Slightly annoying day, put some new exhaust headers on the bike, then noticed a very slight coolant weep around the base of a stub on top of the block. It's buried in amongst everything else, pretty much the first thing I put back on when putting it all back together.  I put a new o ring on the bloody thing when I was reassembling it.

Whilst trying to work out the best way of getting at it which won't involve taking the whole thing apart again I noticed a tiny drop of fuel drip from the underside of the tank. Not sure if it is a tank leak or a pipe /joint ... sigh...gave up and came inside for a fish finger sandwich dinner (chef is away with her mates)...

 

German shite.