Poor MPG on 78 questions

[JereandJess]

78 Bus, 2.0 Hyd, FI

We bought this bus over 9 years ago and it came to us with dual 40 Webers on it. 2 summers ago we converted back to the stock FI. You can read about our troubleshooting adventures and final solution with Colin's help here if you are so inclined:

http://www.thesamba.com/vw/forum/viewto ... sc&start=0

Well after 2 years the bus is finally registered and insured and ready to go. We took it to Vermont on about a 150 mile cruise 3 weeks ago and then this week I took it about 140 miles to deliver some stuff for work.

After doing the math it only got about 15-16 MPG, much lower than the 20ish we used to get with the webers, doing similar driving.

What can I look at or adjust to help improve the MPG on this bus? Tires have not changed, and are inflated properly, new air filter, plugs are gapped properly.....

Any help/suggestions are appreciated.

[vwlover77]

It may be that the Webers were running too lean, giving you "false" fuel economy, with the potential for overheated heads.

Is your engine completely stock? Mine has a "performance" camshaft that I believe kills my gas mileage.

The first thing to look at would be the business end of the sparkplugs to see if the engine has been running too rich or too lean. Can you post a photo of them?

['55 Ragtop]

On my wife's '77 Westy, we have the same engine you have. The only thing I changed is the Monza style exhaust to get rid of the cat converter, timing checked spot on, recent tune-up and we were getting 26-27 mpg on our Maupin trip!

[Amskeptic]

After doing the math it only got about 15-16 MPG, much lower than the 20ish we used to get with the webers, doing similar driving.

What can I look at or adjust to help improve the MPG on this bus?

Check your odometer calibration. My odometer, don't know why, has been reading 9/10ths for every actual mile I've driven. Had to multiply my mpgs by 10%.

Tire inflation should be 33/37 with passenger tires 33/44 with LT tires.
Brakes should not be adjusted too tight.
Timing should hit 28-32* at 3,200 RPM without vacuum and 40+ with.
AFM should be adjusted using the black cog/wiper adjustment screw so that you have instantaneous rpm drop towards lean when you nudge the wiper barely 1/16" of an inch at 3,000 rpm. At idle, you should have the wiper in the middle of the range, i.e. for any nudge of the wiper towards lean, the rpm should drop equally to any movement towards rich.
Colin