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Does anyone have one of these installed on their scooters, I would be amazed to see the fuel economy of the thing whilst riding!

For those who don't know, a vacuum gauge is pretty much a fuel economy gauge, {it connects to the intake plenum of the engine and measures the stoichiometric fuel to air ratio and outputs this as a reading on a dial of litres per 100 km}. These things are around $30 or so from Malz or Mitre 10 or Super Cheap.

I noticed while driving a relatives camry altise recently, it had a digital one. Driving an average speed of 80 km burnt 14 litres per kilometer, not to mention it jumps to 30 or so when getting up to speed.

On a side note channel 7 recently reported the camry as putting out 223g of carbon per litre or something, while the prius did 110g per litre.
Another thing to think of with increasing fuel prices and environmental awareness.

Jet Jockey:

Driving an average speed of 80 km burnt 14 litres per kilometer,

 

That would probably be a handy gauge to have on a scooter instead of a massive clock like the X8 has.

As for the mileage of the Camri... Did you mean 14km/litre?

 

Well time is kinda important but then again clocks are everywhere, on wrists, mobiles, towers, the sun...

Whoopsy Daisy...yeah I meant 14litres per 100 km.

The only bad thing about them is they're designed for 4,6 and 8 cylinder cars and modifying your scooter in any way means you have to take it to the pits after the modding is done. Well Im not sure about that but its the same for cars, I got done for putting metal pedals on my car...but they looked soooo cool on an 84 corona.

Jet Jockey:

it connects to the intake plenum of the engine and measures the stoichiometric fuel to air ratio

Ahhh ........ No it doesn't,    it just measures Vacuum - how open or closed the throttle is - NOT the stoichiometric fuel to air ratio

For that you need an actual oxygen sensor or lambda sensor

 

 

thanks for making me not look like an idiot. Maybe Im thinking of a different gauge.

Fuel injected cars already have a lambda sensor an air flow meter and fuel measuring so just using the existing engine sensors as the input and a quick algorithum outputing to "on the fly" fuel consumption figure on a added display on the dash is easy --- for a carbied scoot without the sensors is expensive, not impossible.......  hummm a project..... now where's those car wreckers???? 

99% of Oxygen sensors found on regular cars are the narrow band type and have only a very small range right around Stoich (14.7:1), go a little bit either side of that and it will immediately change to ~.2v (lean) or ~.8v (rich).  The only time they are actually used to influence the fuel metering is during whats called closed loop mode, which is only active during light throttle cruising.  Just as an example a Delco ecu from an early commodore requires less than ~50% throttle for 120 seconds, coolant temp >90c and some other stuff I can't remember before it will go into closed loop / lean cruise mode and even then it will only start to decay the AF ratio slowly until the Oxygen sensor drops to .2v then it will richen again to .8v and repeat, if you have a guage on the sensor it will flash from rich to lean several times a second until you use more than 50% throttle.

Wow I'm really digressing here but this is going somewhere.

I do a lot of K's in a 4age Corolla towing a trailer and bikes all over the place, this particular engine runs a MAP (manifold air pressure) sensor rather than a MAF (Mass air flow meter) and calculates when to go into closed loop based on inlet vacuum and throttle position.  At 110km/h you can be in 5th gear at ~30% throttle and 3200rpm or 4th gear around the same throttle and 3800rpm.  Now everybody would assume that 5th gear is the best option for economy because of the lower revs but the vacuum guage shows 7-8Hg in 5th and 11-12Hg in 4th even though they are the same throttle openings.  Atmospheric pressure remains a constant so in spite of the increased revs the engine is obviously consuming less air for the same ammount of power produced, plus it meets the conditions to go into closed loop.

So obviously it's not so easy on a scoot because you can't simply change gear to get the engine into the most effecient range.  Potentially there could be some gains to be made by running the vacuum guage to see what's going on then tuning the variator to have the engine in the sweet spot for your most common speed, you could also then play with the pipe to get the most effective scavenging at your chosen rpm but as an everyday thing it is not going to be much help.

You can get a good wideband with a guage for around $500 (search for LM1 they are very good) which will allow you to jet the carb to the optimum settings, fairly significant investment if your not going to use it for other things as well, any tuning shop that has a dyno will have a wideband attached to it.  Just a note on this for two strokes I don't have much experience with the auto mixers and don't know how reliable/consistant they are but I would be very nervous about tuning near the limit with an auto mixer.  2 stroke will also significantly shorten the life span of any type of Oxygen sensor, running a wideband for a day or to to set it up is fine but long term they will not last.

Sorry for the ramble slow day at work, please don't get me started on the false economy of the Prius.

Cliffnotes:

Vacuum guage will display vacuum in Hg (inches of mercury in a manometer) not fuel air ratio.

Easy to install just run the hose to the nipple on the engine side of the carb body with a T-piece so you can still hook up the petcock vacuum line, and if you want hook the backlight up to your dash backlight.  You will not be defected for this as long as the guage is in a sensible location.

No real advantage to runnning one day to day but they are pretty cheap and handy to have will show up any vacuum leaks that are often mistaken for carb problems.

 

 Ill give them a side note on the false economy of the Prius

On a side note of the prius, but the amount of shipping they do with the prius cars to installl all the parts and moving it around it ends up having the same carbon footprint as most larger cars even when you take its fuel economy into account.