Gas Mileage 1300 pre-1979

tvmaster

tvmaster

True Classic
First thing: lately, I've been getting just under 20mpg, 65% city, 35% freeway, mildly hilly SoCal terrain. Seems low to me. The engine is running nicely though. Is this likely just a carb tweak?
Second thing: for the first time ever, the 1974 carburetor fan didn't come on after spirited driving. Didn't come on at all that I remember, which it always has for nearly two years. Temperature on the instrument cluster didn't indicate wild over heating or similar. First place to look is the thermostat sensor screwed into the base of the carb?
 
Under 20 mpg is pretty low for a stock 74. I do better than that with dual DCNFs and a cam. Around 30 is a good number for mixed driving. When near stock, I got close to 40 on the highway.
 
Yup, agreed it should be better. Any ideas on where the first problem may be? I don’t smell fuel anywhere, and there doesn’t seem to be any noticeable leaks of liquid which I see anywhere. What’s a likely culprit, besides a heavy foot?
 
dllubin said:
How about checking the plugs to see if the mixture is off or if it is just your heavy foot.
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I know my foot is a little heavy - I've never got what the MSRP stickers claim a car is possible of, my Mazda 3 said 29mpg, I got 22. The Abarth, easily 30-34 according to others, me, 24mpg on average. I assume the plugs were replaced by the Master Mechanics at WD, but you never know. Any idea of a good link on how/where to check 'the mixture'? I did tweak the carb about six months ago, and the engine seems to idle and run well, but it's possible I tweaked something in error?
 
You can get an idea of what the mixture is like from the color of the plugs. There are plenty of articles showing what they should and should not look like. Ideally, they should be a light tan color. If they are black, you are running rich.
 
dllubin said:
You can get an idea of what the mixture is like from the color of the plugs. There are plenty of articles showing what they should and should not look like. Ideally, they should be a light tan color. If they are black, you are running rich.
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Excellent. This applies to ANY car, these articles - same rules for most? Do remember I’m a retired editor, and a very very green auto mechanic. lol. Scratch mechanic - enthusiast.
 
tvmaster said:
Excellent. This applies to ANY car, these articles - same rules for most? Do remember I’m a retired editor, and a very very green auto mechanic. lol. Scratch mechanic - enthusiast.
Click to expand...
What were you editing? I'm guessing it was not related to automotive mechanics.
 
GregS said:
I would be checking all the jets in the carb to see if they are the correct factory sizes.
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I had them all out for a good look and clean a few months back. All were in good shape, but no, whether they were the factory jets I would not know. But I do know someone local who would :) thanks
 
The jets all have numbers stamped on them showing the size. The stock sizes are listed in the manual. It was common to go up a size or two on the main jets as part of a desmog.
 
TV: Before you mess with the carb jets (which you won't since you say you do not work on cars). try this: Do a real world gas mileage test.
Drive on the freeway 405 when there is no traffic 6am Saturday morning and go south. Drive at 60 mph. Chances are you will be in the slow lane and the semis will be passing you. Your gas mileage test is this: Steady state driving at 60/ no fast acceleration and no on the gas/off the gas (be smooth). Here is the way to do it.
Start early in the morning ( no traffic to get in your way). Drive 5 minutes to the gas station and fill up the tank. Set the nozzle to max fill. When it clicks off, set the nozzle to min volume and when it clicks off, you are filled. Write down the miles on your odometer. What is the tire size you are using? Then drive 2 or 3 hours and return home to the same gas station. Record the miles driven since your morning fill. Refill using the exact same fill procedure. Miles divided by gallons = mpg. If you get 30mpg, your X is just fine. 27 needs improvement. Below 25, something is wrong. It could be something as simple as the choke is staying on. Or, it could be the wrong jets. Some "tuners" go to richer jets to reduce cold engine stumbling off idle. Richer jets may cure off idle lean condition, but kill fuel economy. The correct jetting for a stock USA spec 1300 X with the stock carburetor is: (Assuming yours is a 1974 X)
Carburetor: Weber 32 DMTRA 200
Primary Secondary
Idle jet: 47 60
Main jet: 110 110
Air corrector 200 195
Modifications to the engine like higher compression or a non-stock cam will change what jets are right are right for your engine.
Let us know what results you get with this steady state cruise fuel economy test. Mine was 30-32.
 
johnph said:
TV: Before you mess with the carb jets (which you won't since you say you do not work on cars). try this: Do a real world gas mileage test.
Drive on the freeway 405 when there is no traffic 6am Saturday morning and go south. Drive at 60 mph. Chances are you will be in the slow lane and the semis will be passing you. Your gas mileage test is this: Steady state driving at 60/ no fast acceleration and no on the gas/off the gas (be smooth). Here is the way to do it.
Start early in the morning ( no traffic to get in your way). Drive 5 minutes to the gas station and fill up the tank. Set the nozzle to max fill. When it clicks off, set the nozzle to min volume and when it clicks off, you are filled. Write down the miles on your odometer. What is the tire size you are using? Then drive 2 or 3 hours and return home to the same gas station. Record the miles driven since your morning fill. Refill using the exact same fill procedure. Miles divided by gallons = mpg. If you get 30mpg, your X is just fine. 27 needs improvement. Below 25, something is wrong. It could be something as simple as the choke is staying on. Or, it could be the wrong jets. Some "tuners" go to richer jets to reduce cold engine stumbling off idle. Richer jets may cure off idle lean condition, but kill fuel economy. The correct jetting for a stock USA spec 1300 X with the stock carburetor is: (Assuming yours is a 1974 X)
Carburetor: Weber 32 DMTRA 200
Primary Secondary
Idle jet: 47 60
Main jet: 110 110
Air corrector 200 195
Modifications to the engine like higher compression or a non-stock cam will change what jets are right are right for your engine.
Let us know what results you get with this steady state cruise fuel economy test. Mine was 30-32.
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Thanks. Actually, I’ve had all the jets out and checked/cleaned them. But I didn’t take note of the fine print on them. Should be easy enough to do. And yes, that’s how I always measure my usage: from fill-up to fill-up, and zeroing odometers. Last tank was 18 mpg, the choke appeared to be returned to off as I always do after warming up for a minute or two.
Fuel filter was new two years ago. My only worry is fuel is escaping somewhere it shouldn’t be, but there are no external leaks anywhere I can find. The vacuum hoses coming/going to the carb seem secure, but I am unsure if the WD gang changed their size, routing, etc.
 
Be aware that cruising at steady state puts you firmly on the idle jet, not the main jet. I would check that the choke plate is fully open after the motor is warm...say 20 minutes of driving. Check the plugs, if they are black around the nose of the plugs then something is wrong. Are your tires at the right pressure? Are you a lead foot constantly mashing down on the gas, which causes the accelerator pump to shoot a squirt to raw gas straight into the carb venturi?

Even a non mechanic can do the above so just take your time and we will all confuse you but help you hopefully sort this out!
 
Lots of good advice given above. I wanted to chip in some MPG numbers for you that I have seen. Please note this is the same car with different engine/transmission combo's.

Again, this is all in regards to a 1974 X 1/9

1. Stock 1300 - 32 to 38mpg
2. Stock 1300 with Free flow exhaust - 32 to 38mpg. It was just louder! ;)
3. 1300 with 40/80 cam and dual 42 DCNF's - 10 to 14 mpg.
4. 1500 with 40/80 cam and dual 42 DCNF's - still 10 to 14 mpg.
5. 1500 with FI - 32 to 37mpg
6. 1500 with FI and 3.57 final drive - 37 to 40mpg
7. 1301 Uno Turbo with Stock turbo - 38 to 42 mpg
8. 1301 Uno Turbo with Aftermarket turbo - 40 to 43 mpg.

Of course, this is all based on what I saw, what the pump said, etc. So, not exactly scientific, but should give you a better idea. Pretty impressive how good the initial cars were, with really only the addition of FI and a turbo making a significant difference.
 
I believe I’m as stock-as-possible to that first, 1300, minus all the pollution parts which were removed by Wheeler Dealers. Hence my concern they re-routed all the hoses to the right places, and chose the correct replacement sizes.

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tvmaster said:
I believe I’m as stock-as-possible to that first, 1300, minus all the pollution parts which were removed by Wheeler Dealers. Hence my concern they re-routed all the hoses to the right places, and chose the correct replacement sizes.
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Here is the info from the service manual if you are going to check the jets:

X19_Service_Manual_1974_to_1978_USA_Final 25.jpg


One other thought: If WD desmogged the car, depending on what they did could result in some unexpected ignition advance issues. That distributor has a very large centrifugal advance range as well as vacuum retard. The vacuum retard gets tempered by a delay valve in the line but if that was "desmogged" without any other changes you could get some strange effects. I would check the static timing as well as that at full advance (about 5000 rpm for that distributor) and see if they are in range.
 
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