Or am I missing something ??

Just knowing if it's wasted spark or not. Briggs carb'd motors are from what I gather normally wasted spark. As our motor is an EFI I was unsure if the engine management produced a wasted spark or not.


The weekend did not go to plan so I still have no idea if changing the settings will give a better result.

So the tiny tach has a wire which wraps around the HT lead to a spark plug.
Every time the plug fires this sends a signal to the unit.
So 1 hit every revolution for a 2 stroke or a wasted spark 4 stroke and 1 hit
every 2 revolutions for a standard 4 stroke.
I can't work out what the number of cylinders has got to do with anything.
On a wasted spark 4 stroke you get a signal every revolution regardless of
whether it is 1 , 2 or 12 cylinders,
Or am I missing something ??

They don't use a standard connector, i'll add a picture below.


I'll take a look for that connection when I am out there again this weekend, we've got a collection of manuals and service books Etc. out there too, looks like we've found our teabreak research task 

The OBD on the Briggs & Stratton EFI is this little chap.


[mmg]3530[/mmg]

OBD-M is the standard OBD connector AFAIK.  However, Briggs use a Delphi MT05 ECU and probably don't use the standard connector - its' more likely to be this one

However, the OBD connector doesn't have a tacho signal on it (you can read the rpm using an OBD scanner but that's another story!).  There will be an unconnected connector/wire somewhere in the engine harness that'll have the RPM signal on it (have you got an engine wiring diagram - RPM is on J1-6 on the MT05 ECU?).

Thanks John, it appears I was indeed missing something. As for the ECU signal I have been looking for something with an OBD-M connector but have found nothing yet, however I'm probably not asking the search engines the right questions!

The Briggs EFI is probably a wasted spark engine (the carb versions are) in which case it should be set for a 4 cylinder engine and should read twice the values you are seeing (idle is usually around 1200-1500RPM to ensure adequate splash lubrication to the head - check the spec?).  As it has a throttle body the ECU will increase RPM at idle when the engine is cold so it could well be above 1500rpm for a bit.

As its' EFI there should be an output from the ECU that has the exact RPM on it as a 5v signal - you can get 'proper' tachs that will work with EFI engines directly.

I would share your discomfort. Check with a known RPM ie the vibrating wire type?
Ideally-  you don't want to be revving up to 4000 even if short lived?
Generally they are "fool proof" however.
"Non taken " I hear you cry!

I purchased a tiny tach for use on the 1387 Squadron Surveyor but am having trouble with the readout. It's being used on a Briggs & Stratton Vanguard EFI engine, when set for 4 stroke 2 cylinder operation I get a tickover reading of 850rpm and max revs of 1980rpm. Neither look right to me. Setting it to 1 or 4 cylinder operation either halves or doubles the readout across the range. I was expecting flatout to be in the region of 3600/4000rpm and tickover 500/1000rpm.


Am I being daft and have missed something?