Rev counter reading half the rpm it should?

[nzspokes]

My BMW needed a new dash unit after the old one shit the bed. Common for this model.

So I got a cheap TM speedo unit. Works well apart from the rev counter is on half rpm. So far I have used the internal adjustment of the speedo unit and it is set to its best setting. Any other settings take it down to quarter or below.

The motor is a single but with twin spark. So on the off chance they fire at different times I run both to the speedo. No change.

Have tried a DRD speedo healer on the signal side and it makes the speedo jump all over the place. My guess is its not able to handle the signal speed.

Ive been living with it like that for 6 months but during all this I thought I may as well ask for ideas for a fix.

So any ideas?

[onearmedbandit]

Can't help but I remember once buying an aftermarket rev counter in the early 90's, read wrong when I installed it. Turned out there was a switch on the back for 4, 6, or 8 cylinder engines. Flipping that switch made the rev counter read like yours is.

[nzspokes]

Can't help but I remember once buying an aftermarket rev counter in the early 90's, read wrong when I installed it. Turned out there was a switch on the back for 4, 6, or 8 cylinder engines. Flipping that switch made the rev counter read like yours is.

Yup I had one like that as well, was the first thing I checked. On this one its programmed through the screen and it is set on single cyl.

[jellywrestler]

Yup I had one like that as well, was the first thing I checked. On this one its programmed through the screen and it is set on single cyl.

no matter how many cylinders the thing has it should only really be taking a signal off one coil, why would it take it from any more? maybe it's taking the signal off a sensor and used to a crankshaft sensor and maybe this ones off a cam sensor which of course runs at half crankshaft speed. how good can you write with twink, you may be able to altar the numbers?

[nzspokes]

no matter how many cylinders the thing has it should only really be taking a signal off one coil, why would it take it from any more? maybe it's taking the signal off a sensor and used to a crankshaft sensor and maybe this ones off a cam sensor which of course runs at half crankshaft speed. how good can you write with twink, you may be able to altar the numbers?

Ive got it coming from the coils, the trigger feed.

[F5 Dave]

Wasted spark is quite common but if the ignition doesn't use it you get 1/2 revs as it only fires once per 4 strokes. You can buy cct adaptors but you will be modifying then to fit which will be a bit tedious.

[nzspokes]

Wasted spark is quite common but if the ignition doesn't use it you get 1/2 revs as it only fires once per 4 strokes. You can buy cct adaptors but you will be modifying then to fit which will be a bit tedious.

Google is not helping me, whats a cct adaptor?

[FJRider]

Google is not helping me, whats a cct adaptor?

https://www.google.com/search?q=CCT+Adapters+for+speedos&rlz=1C1OKWM_enNZ896NZ896&oq=CCT+Adapters+for+speedos&aqs=chrome..69i57.18194j0j8&sourceid=chrome&ie=UTF-8

[jellywrestler]

https://www.google.com/search?q=CCT+Adapters+for+speedos&rlz=1C1OKWM_enNZ896NZ896&oq=CCT+Adapters+for+speedos&aqs=chrome..69i57.18194j0j8&sourceid=chrome&ie=UTF-8

it's the rev counter that's faulty, not the speedo so i'd suggest cct is circuit adapter

[nzspokes]

Well I didnt know such the thing existed but this could be the go.

https://www.ebay.com/itm/UNIVERSAL-TACH-ADAPTER-CONVERTER-COP-1-2-3-4-5-6-8-10-cyl-to-any-4-6-8-Tach/141979625888

[Honest Andy]

Wasted spark is quite common but if the ignition doesn't use it you get 1/2 revs as it only fires once per 4 strokes. You can buy cct adaptors but you will be modifying then to fit which will be a bit tedious.

Sooo... if this does have a wasted spark, then that makes 2 sparks per 4 strokes. So if the gauge is set as a 2 cylinder, that should work?
Or is it going to halve the reading again?
From half to a quarter
Or in other words a quart
which is 750ml
otherwise known as a big bottle
which holds more beer
and there seem to be a few empties around my chair
and my heads getting wooozy
:blink:

(another beer later...)
Is there a "2 stroke" setting?