I want my, I want my, I want my MPG

[VaGuS510]

I have a problem, I get 12.5 mpg. What is wrong? The car runs fine. If it isn't warmed up I have to rev it out to get going without it backfiring. That tells me that car is running lean. I also have an air/fuel ration gauge that tells me the engine is running lean. The spark plugs also tell me that the engine is running lean, they are all white on the tips. So...how am i getting 12.5 mpg when my Z is running lean.

Setup: 1973 240z w/L28, round top SU carbs, header, 4 speed

All miles were city and I even drove the car easy the whole time.

My only guess: The manual says the white tips on the sparkplugs are a sign of the car running lean or the sparkplugs not seating well. If spark plugs arn't seating well then they arn't providing a good seal. Could the same symptom be from bad piston rings. This engine is old and i am sure it has over 100k miles, it makes valvetrain noise and such. If my assumption is right and my rings are bad, would I get bad gass milage? Also, my compression is 130-140 psi. A leakdown test might tell me more. Let me hear what you think. Thanks.

[VaGuS510]

Also, my oil seams thin, it drips off of the dip-stick. It was replaced less then 500 miles ago, and it is almost as black as 3000 mile old oil.

[VaGuS510]

Also, their is no obvious gas leak, if it did leak it would have to be while the engine is running and reving because it doesn't leak while sitting at idle, or when i leave the car sit for a few days.

[Dtsnlvrs]

Your fuel pump may be leaking....remove the dipstick and smell it...if it smells like fuel, replace the fuel pump.

[montoya_fan01]

Also, my oil seams thin, it drips off of the dip-stick. It was replaced less then 500 miles ago, and it is almost as black as 3000 mile old oil.

That doesn't sound normal. What could be thinning your oil? Water? No, that would turn it into brown mayonaise. anything else? Hmm....... I wonder, could it be...........

Clue: Does the oil smell like regular old, normal oil?

Also, their is no obvious gas leak, if it did leak it would have to be while the engine is running and reving because it doesn't leak while sitting at idle, or when i leave the car sit for a few days.

What is the condition of your carbs? Have they been rebuilt? are they working properly? doesn't sound like it from the symptoms you describe.

If the missing gas isn't powering your engine properly (and being burned in the form of "normal" gas mileage), and isn't leaking externally, there are only a few places left that it could be going.

[VaGuS510]

I will check the fuel pump out, that is something I didn't think of.

I am sure the carbs are fine. This is the second set that i have had on the car and both resulted in bad gas milage. Plus it seems to run well, it doesn't bog down or anything. It doesn't have much power but that is expected.

[Carl Beck]

Hi VaGuS510

How exactly - are you measuring or calculating your mpg figures?

Describe the typical trip to/from work, school or whatever - what time of day, how many miles each way.

How long do you have to keep the choke on before the car warms up?

I drove my 72 Z back and forth to work each day, about four miles one way for several years. On the highway at a pretty constant 70 mph - it would get between 25 and 27 mpg. In town, used for work and a few side trips - 12.5 to 14 mpg.

Choke on to start, then within the first two miles I'd be easing the choke off as the engine came up to full operational temp.s'. Stop and go traffic...

If your driving 20 to 30 miles to work each day, using the freeways in the city... then your mileage would be expected to be much higher...

Gas Mileage isn't just a function of engine tune...

FWIW,

Carl B.

[Dtsnlvrs]

Ditto what carl said. When I was commuting all of 2 miles to work each day ( I live in base housing) I got about 12-13 MPG with stock L-24 and SU carbs, But would get close to 30MPG on road trips. Built a new 2.8L with a slalom grind cam, headers, triple 40's etc....same commute (2 miles) yields closer to 17mpg, however highway mileage dropped to a at best 22mpg. But do check out the fuel pump....seen it happen before on Z-cars, as well as airplanes.

[zeewhiz]

although this won't help, I did find your reference to Dire Straits (or the police if you want to really get into it) in your subject line to be funny!

[VaGuS510]

I got the idea from a Toyota advertisment that i saw a few days ago, and a little bit Dire Straits never hurt nobody.

Anyways, I am planning on replacing my fuel pump. This seems like a good idea because the one on the car currently is old, really old. It sat on the car for 12 years without pumping an ounce of gas, I imagine that the diaphram (sp?) is cracked.

I was thinking about just replacing it with an electric fuel pump. Any suggestions as far as a good pump to use.

I searched the forums for MPG and found most people get about 15-20 in the city. I found I got 12.5 mpg because I went only 150 miles and my car took 12 gallons at the pump. The driving was city with a little freeway (a couple miles every trip). Sometimes I let it warm up for a few minutes, and other times I just take off, either way the choke is only on for a few minutes.

Thanks for the replies.

[hls30.com]

I want my I want my MPG

Now look at this fuel system. That's no way to do it,

She's running way to lean down the Freeway,

That aint runnin', that's no way to do it,

not running for nothing, no performance in this Z,

Now that aint runnin', that's no way to do it,

Let me tell ya these posters aint dumb,

Say tune the carb with your middle finger,

If it's stuck you better add your thumb.

gotta tune these twin carbureators,

Custom Needles for the old Sus,

We gotta get these gears a movin',

We gotta make theses tires scream.

The spindle pins with the threaded wedge and the white crap,

Yea buddy a bur locked it in,

The Son of a bitch wouldn't come out for nothing,

I finally got it and with these carbs I'll win.

I could have taken off 8 bolts and a linkage,

I coulda had great running carbs,

look at that Video, Car's running perfect end to end,

Man I could drive that,

A/F is up there, whats that, burbling noises,

pinging on the pistons like aboosted Z,

Oh that aint bad, but it aint good either,

Gatta get this car running like a well tuned Z.

Now this aint workin it's way to late to do it,

Can't tune a car where there ain't no light,

Now this aint working-this aint the way to do it,

don't run for nothing and gas aint free.

[Dtsnlvrs]

I think it would be better if you tried that with RUSH's Red Barchetta