M400/440-3/Performer 800/bad milage less power

[PMUT]

Hi All,
the work on our old lady goes forward.

We have Dodge M400, TH727, 440-3 with an Edelbrock performer 800 carburetor.
The average fuel consumption is by 35l/100km or 6,7MpG on a near flat trip.
In the hills we have about 40l/100km or 5,8Mp.

At a hill with 10% slope, the speed drops from 50mph to 25mph, which is a pain.

For my understanding the engine runs much too rich.

A look into the Performer 800 has shown, that the provirus owner has changed the stock calibration to >16< out of the calibration manual (see attachment).

Is this a normal configuration for an 29' long motorhome with an max weight of 16.000 pound?

Many Greetings
Ulrich

[PMUT]

now with the right attachment.

[Oz]

I can tell you your mileage isn't out of line with that carb. 750 cfm is the appropriate carb for the 440.  I put a 750 performer on mine, coupled with the performer intake.   Power for passing and on hills/mountains was definitely much better.  But MPG... 5 to 6 mpg.

Is it too rich?  One way to check is to look at your spark plugs.  They should be tan on the diode. If they have a dry, black soot, or even wet, you're running rich.

[Elandan2]

On our rig, I found that I had to richen up the primaries in order to eliminate problems due to ethanol fuel. I changed the primary rods two steps and completely eliminated any missing and backfiring when at WOT. After changing them, the engine actually now runs better at cruise with a higher vacuum indication. But of course, as Oz has said, your gas mileage is probably about right.

[PMUT]

I can tell you your mileage isn't out of line with that carb. 750 cfm is the appropriate carb for the 440.  I put a 750 performer on mine, coupled with the performer intake.   Power for passing and on hills/mountains was definitely much better.  But MPG... 5 to 6 mpg.

Is it too rich?  One way to check is to look at your spark plugs.  They should be tan on the diode. If they have a dry, black soot, or even wet, you're running rich.

Thanks, I will check and change the spark plugs, lets see how they look. Found an comparison in the wwnd will also add some pictures.

[PMUT]

On our rig, I found that I had to richen up the primaries in order to eliminate problems due to ethanol fuel. I changed the primary rods two steps and completely eliminated any missing and backfiring when at WOT. After changing them, the engine actually now runs better at cruise with a higher vacuum indication. But of course, as Oz has said, your gas mileage is probably about right.

OK, will check this also.

Vacuum: Good point.
I was not able to get more then 17mHG while adjusting the idle mixture screws. Maybe it's also related to the fact that it runs too rich.
All gaskets  and at the carb has been changed so I dont expect an leak there.

[Elandan2]

For a late model, low compression 440, 17" of vacuum at idle is good. Mine pulls about the same at idle. What I noticed when I changed the metering rods, was while at a steady speed of around 60 MPH on level highway, the engine went from around 7-8" of vacuum to 12-14". As far as fuel economy, I have found that is way more enjoyable to watch the scenery rather than the fuel gauge.