‘74 X19 miles per gallon (mpg) not very good. Likely solution?

[tvmaster]

Not that I usually care about this kind of thing…
SoCal climate, some hills, mostly non-freeway driving, however…
The master mechanics removed all the pollution equipment when they over-hauled the 1974, mostly original equipment car.

Its averaging between 14 and 18 miles per gallon (mpg) at best.

Fuel used is either 87 or 91, it doesn’t seem to make a difference, but being a car that isn’t driven a great deal, a tank can last several months.

The carb appears to be the original carburetor. Air filter looks reasonably clean, although a little gunky where the blower air is positioned.

I cleaned out, sprayed and inspected the carb jets last year and all looked good. Also adjusted the idle on directions from my crusty old Mr. FIAT repair fellow. When warmed up, it idles around 750-850.

Fuel, as seen through the clear fuel-filter, looks clean. Oil and filter changed less than 2k ago.

Any ideas where to look, or what other symptoms may be contributong to such lousy mileage?

My suspicion is that the master mechanics did not reconnect the carb hoses correctly after deleting the pollution kit, but at my level of newness, this is above my pay grade. The electircal system seems to be working fine now, ie I’m not getting any parasitic draws of notice.

Photos available upon request if needed for possible clues…

Any thoughts are appreciated, thanks.

 

[fiatfactory]

possible causes (in no particular order)

1) Piedi piombo?

2) Does the 74 US version have the 4.42 (12/53) final drive ratio? That would drop MPG compared to a 4.077 final drive.

3) Tyres pumped up? 10% down on tyre pressure certainly increases consumption.

4) If the car sits for extended periods does fuel evaporate? does your garage smell of fuel all the time? The light volatile component of the fuel evaporates first, and what's left isn't as potent, a lot of fuel loss by evaporation may infact have something to do with emissions device removal.

and finally,

5) it's a well known fact that chromed bumpers increase MPG, as does bright green paint,

SteveC

 

[Joe F]

As a reference, I have dual DCNF's and get about 22mpg in non-highway driving. My motor was also totally de-smogged.
Without any detailed info, there are two areas that you can look at to improve milage: timing and carb tuning.
Timing is the easiest thing to check, all you need is a timing light (and know how to use it).
Carb tuning is way more complicated and can get you into trouble. Factors like jets and tubes can vary your performance and milage, but not much.

Last bit of advice an old Italian mechanic once told me..."If it ain't broke, don't fix it"

 

[dllubin]

A stock 74 without the emission equipment should be getting around twice that mileage. First thing I would check is to see if all the carb jets are the correct ones. Then, I would pull the spark plugs and check the color. Then, I would check the timing, both at idle and higher rpms. The 74 distributor has vacuum retard and if that got hooked up wrong during the emissions delete, you could get some weirdness.

 

[johnph]

My freshly rebuilt 1976 1300 with new catalyst and all emissions control devices attached and operating got 30+ mpg cruising at 60 mph on level CA freeways. Oh, I did replace the Ducellier points distributor with a Bosch electronic unit from a Yugo. Mine had a 4.08 r & p.
You might want to check that the choke cable is fully opening the choke butterfly. Who needs a choke in LA county?

 

[Ulix]

If you get 17mpg or less, the car should be running extremely badly with no power at all.
If that is not the case, could your mpg calculation be off?

 

[carl]

Make sure your cam is timed correctly, easy enough to check, requires no tools....just eyeballs.

 

[Steve Hoelscher]

Fundamentals are the place to start trouble shooting: Fuel, Air, Spark, Timing, Compression.

Fuel: Check the mixture. If its running rich the spark plugs will be dark. The carburator could just need cleaning and/or adjustment. That's a maintenance item on a these engines.

Spark: If its a 1300, with a points type ignition, check the points gap and dwell. Weak spark or inadequate dwell will cause the car to loose power and use fuel.

Timing: Check both the cam timing and ignition timing. Camshaft timing will cause loss of power and poor fuel economy but so will ignition timing. You will need a proper timing light to check/set ignition timing. That process includes the vacuum and menchanical advance.

Compression: Low compression due to either worn rings or leaking valve seats will cause the car to run rich and loose power.

The car likely needs an 'old school' tuneup. That is, a carb cleaning and adjustment, points cleaned and adjusted and ignition timing reset. Before electronic ignition and fuel injection these systems required regular service to keep the car running efficiently.

 

[tvmaster]

wow - thanks for all the suggestions and knowledge on this folks. It would appear I have a long list of checking and learning ahead of me.
Power with the car seems what you would expect for 67bhp. It doesn’t hesitate or stall, but can take a while to turn over when it hasn’t been driven in a few days. I’ll write all this down, and start at the start. Considering the engine was pulled, cleaned and replaced, I’d like to think anything that was needed was done. I believe they bought a carb kit if I remember the parts-list, but it’s hard to know if all was hooked up properly when they dumped the emissions gear.
Wheels/Tires are 13”, and I keep them inflated properly.
Speedometer/odometer is pretty close to dead-on accurate. It’s six miles to my mother-in-laws house. Trust me, it’s a number I can’t forget.

 

[Steve Hoelscher]

wow - thanks for all the suggestions and knowledge on this folks. It would appear I have a long list of checking and learning ahead of me.
Power with the car seems what you would expect for 67bhp. It doesn’t hesitate or stall, but can take a while to turn over when it hasn’t been driven in a few days. I’ll write all this down, and start at the start. Considering the engine was pulled, cleaned and replaced, I’d like to think anything that was needed was done. I believe they bought a carb kit if I remember the parts-list, but it’s hard to know if all was hooked up properly when they dumped the emissions gear.
Wheels/Tires are 13”, and I keep them inflated properly.
Speedometer/odometer is pretty close to dead-on accurate. It’s six miles to my mother-in-laws house. Trust me, it’s a number I can’t forget.

Oh, one thing I forgot. Its a '74, so it should have a manual choke. Be sure that the choke is fully opened. If its even slightly closed it will cause the car to run rich and use more fuel.

 

[tvmaster]

Oh, one thing I forgot. Its a '74, so it should have a manual choke. Be sure that the choke is fully opened. If its even slightly closed it will cause the car to run rich and use more fuel.

Definitely a good point, as I always use it for the first mile or two after a cold-start. I'll do 1/4 tank with that in mind and measure then...

 

[ng_randolph]

Definitely a good point, as I always use it for the first mile or two after a cold-start. I'll do 1/4 tank with that in mind and measure then...

No need to wait; I don't think Steve was suggesting you're inadvertently leaving the choke on. I think he is suggesting that you should have a look at the carburetor and check that the choke plate is fully open when the choke knob is pushed in.

 

[Dan Sarandrea (Phila)]

Let's start with two old school checks that (1) are well within the ability of most home mechanics and (2) are appropriate for an old school car.

Before you being, pop round to your local major auto parts store that loans tools (actually they don't loan, you buy them and then bring them back for a refund). Assuming you don't own these already, acquire a vacuum gauge and a 3/8"drive torque wrench. Then ask the salesperson for an old-school spark plug gap gauge, the kind that uses different wire thicknesses rather than a flat style or feeler gauges:

https://www.amazon.com/Lisle-67900-Spark-Plug-Gapper/dp/B0009OR9A6/ref=sr_1_7?

For both of these tasks, we'll need someone with good knowledge of the US-spec 1974 1300cc for details denoted by *** to help us out with some details.

First task: pull all four plugs, lay them out on a paper towel, take a pic and post it. While they're out, check the gaps***, adjust if necessary, and re-install to the correct torque spec.***

Plug condition and color can tell us a lot about rich or lean mixture.

Second task: connect the vacuum gauge to manifold vacuum (where?***), start the car, and record the gauge say 15-20 sec with your phone. If you have a helper, it might be interesting to a "cold start" version of this as well.

Vacuum gauge behavior can tell us a lot about valve timing and valve train condition.

 

[tvmaster]

No need to wait; I don't think Steve was suggesting you're inadvertently leaving the choke on. I think he is suggesting that you should have a look at the carburetor and check that the choke plate is fully open when the choke knob is pushed in.

But I DO inadvertently leave the choke on, not on purpose, but I don't make a mental note to push it fully forward after use and then lock it down there. That's easy to do. I'll check the plate after that

 

[tvmaster]

Second task: connect the vacuum gauge to manifold vacuum (where?***), start the car, and record the gauge say 15-20 sec with your phone. If you have a helper, it might be interesting to a "cold start" version of this as well.

Vacuum gauge behavior can tell us a lot about valve timing and valve train condition.

'Where'? Yes, where indeed. lol. Is that easily findable in the 74 service manual? Those two words, 'manifold vacuum' don't seem to come up there together with a search. Remember who you're dealing with here Dan - electrical I'm pretty good with, but engine? Totally green...

 

[beezee]

Odometer not accurate?

 

[tvmaster]

Odometer not accurate?

It's pretty good - within 1/10th mile every 10 miles, maybe better.

 

[EricH]

If you are 100% sure of your distance measurements and fuel use measurements (you can fill the tank until fuel is visible looking down through the filler cap, fill to the same level every time) and you're getting mid-teens mpg across several gallon+ fillups... yes, something is wrong.

Much good advice above and also

Where'? Yes, where indeed. lol. Is that easily findable in the 74 service manual? Those two words, 'manifold vacuum' don't seem to come up there together with a search.

The search term you want is "auto vacuum gauge readings". It won't be in the manual because there's nothing here that is X1/9-specific, it applies to pretty much any four-stroke gasoline engine, the only X-specific thing is that you want to connect the gauge to the big nipple on the intake manifold underneath the throttle linkage.
The vacuum gauge will cost you a few tens of bucks and you'll probably get your money's worth just from the entertainment value of knowing what's actually going on in response to various throttle moves.

My suspicion is that the master mechanics did not reconnect the carb hoses correctly after deleting the pollution kit, but at my level of newness, this is above my pay grade

There's not a lot to reconnect on a '74. The vacuum line to the gulp valve for the air injection system should be plugged (because the entire air injection system has been removed and the ports in the cylinder head plugged), and the vacuum line to the distributor's vacuum retard can be plugged. Keep the tiny short line on the sparkplug side of the carb that connects to a the vacuum pot that unloads the choke, nothing awful will happen if the evap control and blowby systems (which are worth keeping) are misconnected or completely removed.

Check your ignition timing. If you don't want to buy a timing light, see if you can take advantage of one of the FLAPS loaner programs.

Check your cam timing. This is easy, just turn the motor over by hand (transmission in neutral and socket on the crank puller or transmission in 4th gear and right rear wheel jacked off the ground, then turn the wheel with a socket on one of the lug bolts) until the cam timing mark is one the pointer, then verify that the crank timing mark is also at its pointer.

 

[tvmaster]

If you get 17mpg or less, the car should be running extremely badly with no power at all.
If that is not the case, could your mpg calculation be off?

Nope - same calculations work on all the other cars. And the engine runs really quite well. Hence, quite confused. When we figure it out, I’ll be sure to post. Odometer/speedo seems to be accurate as well…

 

[tvmaster]

If you are 100% sure of your distance measurements and fuel use measurements (you can fill the tank until fuel is visible looking down through the filler cap, fill to the same level every time) and you're getting mid-teens mpg across several gallon+ fillups... yes, something is wrong.

Much good advice above and alsoThe search term you want is "auto vacuum gauge readings". It won't be in the manual because there's nothing here that is X1/9-specific, it applies to pretty much any four-stroke gasoline engine, the only X-specific thing is that you want to connect the gauge to the big nipple on the intake manifold underneath the throttle linkage.
The vacuum gauge will cost you a few tens of bucks and you'll probably get your money's worth just from the entertainment value of knowing what's actually going on in response to various throttle moves.There's not a lot to reconnect on a '74. The vacuum line to the gulp valve for the air injection system should be plugged (because the entire air injection system has been removed and the ports in the cylinder head plugged), and the vacuum line to the distributor's vacuum retard can be plugged. Keep the tiny short line on the sparkplug side of the carb that connects to a the vacuum pot that unloads the choke, nothing awful will happen if the evap control and blowby systems (which are worth keeping) are misconnected or completely removed.

Check your ignition timing. If you don't want to buy a timing light, see if you can take advantage of one of the FLAPS loaner programs.

Check your cam timing. This is easy, just turn the motor over by hand (transmission in neutral and socket on the crank puller or transmission in 4th gear and right rear wheel jacked off the ground, then turn the wheel with a socket on one of the lug bolts) until the cam timing mark is one the pointer, then verify that the crank timing mark is also at its pointer.

Thanks sir, this is a lot to unpack - but I’ll begin. I’m mostly confident about the ignition timing just because Mr. Old FIAT guy checked and adjusted that when we first got the car. Does it fall out of timing often?
The hoses - this will take studying time. As always, greatly appreciate the time to explain to the newbie