Fuel consumption is WAY up...ideas?

[jrhone]

I was getting about 20-25 mpg and suddenly I am getting more like 10-15 mpg. Nothing has changed about the car. I suppose I need to have it tuned, it has not been tuned for about 18 months since this motor was installed. The car runs GREAT...tons of power, and torque...no smoke. It could be running very rich maybe? I am planning on going DCOE 40s in the near future, so I am not too interested in redialing in the carb..its a Weber 38/38. It was purchased new when I did the motor install. Ideas? Hoping its a common issue with an easy fix. If not I'll wait til I tune the DCOEs.

[ray_]

How's your odometer?

GL,

Ray

[jrhone]

Not basing it on odometer readings...thats broken....I am basing it on how frequently I have to fill up under my normal driving scenarios. Also on a long trip...I can gauge how often I need to fill up by the distance I have traveled. In driving from the Bay Area to my place, I usually need a tank and a half of gas...last week I needed more like 2 and a half tanks. So an extra tank for a 500 mile trip. With a 12 gallon tank it normally puts me at 27 MPG normally. 16 MPG on the last trip. To me thats a significant drop.

[ray_]

Wow. How do the plugs and tailpipe look? Is your new chrome bumper turning black?

Turn the rig around and run some high speed video. ;-)

GL,

Ray

[jrhone]

Actually...YES I do have some black buildup on the rear! Just swapped plugs...and I have not checked the new ones...but I was just noticing today the dark area below the bumper....I made a mental not the wash that area better next time I washed the car...but is that indicative of running rich?

[ray_]

Yeah, carbon/soot is absolutely an indication of rich running. Did u change the plugs before this problem occurred? What plugs are u running?

Cheers,

Ray

[jrhone]

Gotcha...yes it was like this before...but probably not as bad....I am running NGK BP6ES plugs....like I said...just put them in 2 weeks ago.

[stultis]

Throw in some BP5ES and gap to .024". Also when you pull the plug see which if any are fouled. You might have just been running too hot of a spark plug, forcing the engine burn more fuel.

Might just be an easy fix.

[ray_]

Yep, that you said... but you didn't say whether the problem surfaced before or after the plug change.

;-)

Cheers,

Ray

...I am running NGK BP6ES plugs....like I said...just put them in 2 weeks ago.

[c.d.iesel]

something may have changed with the float level?,

or a jet is coming loose down inside the float bowl?

dirt blocking air correction jet?

if you can't sort out 38/38 'tuning' problems then

prepare yerself for sleepless nites and

more high gas consumption with

ill 'tuned' DCOE's

[KFunk]

Throw in some BP5ES and gap to .024". Also when you pull the plug see which if any are fouled. You might have just been running too hot of a spark plug, forcing the engine burn more fuel.

Might just be an easy fix.

The BP5ES would take it even hotter. The BP6ES is the middle of the range, while the BP5ES is hotter, and the BP7ES is colder. I run BP6ES in my 02, and BP7ES in my air-cooled Yamaha.

[Patman]

Hello John,

First.... Love your car and the images you've been posting.

Now, are you basing this after your trip up Hwy 1??? I windy road with down shifts and acceleration will kill your gas mileage.

Also, are you planning on leaving California (land of tree huggers and flower sniffers)???? Your 76 will never pass smog now.... With the DCOE's forget about it.....

Cheers,

Patman

PS: I'll be down on HB and NB this weekend so I'll be looking for your car on the road.

[jrhone]

Hello John,

First.... Love your car and the images you've been posting.

Now, are you basing this after your trip up Hwy 1??? I windy road with down shifts and acceleration will kill your gas mileage.

Also, are you planning on leaving California (land of tree huggers and flower sniffers)???? Your 76 will never pass smog now.... With the DCOE's forget about it.....

Cheers,

Patman

PS: I'll be down on HB and NB this weekend so I'll be looking for your car on the road.

Hey Pat! Well my car wont pass smog now...lol...don't worry it wont need to...no I am basing it on my way BACK down the 5 which was all highway, flat and straight and at 75 mph. I noticed it on the way up but thought maybe it was my spirited driving...but thats not it.

[Patman]

Have you checked your fuel return lines? The return line to the tank can leak. I just replaced one (well, supervised the new owner) on my old 76 last Sunday.

Just a thought. Good luck!

Patman

[Chris_B]

Plug changes are not likely to cause the kind of fuel mileage change you describe and the soot at the tailpipe. Seems like the most likely cause (if this is indeed carb related) would be excessive fuel getting in the system. Think defective or clogged needle valve, or excessive fuel pressure (not sure how that would happen [clogged return valve might do it...]).