As the title suggests, I seem to have a problem. I should be getting somewhere between 4.5 and 6 km/l. (10 -15mpg). Sent her in for a carb tuneup. According to the carb shop, her timing was also very far advanced which was brought back into line. The first noticeable thing was that when she came back she sounded louder, not as quite as before.

I am assuming this is all related to my fuel consumption at the moment. So my question is does advancing the timing have such a big impact or did the carb guy just get her running a bit rich.

Also have this funny feeling that too much fuel is being dumped actually causing the motor to stall for example, I have a bit of a steep drive way and noticed the other day is that if I put the pedal to the metal, she actually cut out, gradual to moderate acceleration got me up the hill.

By the way, she is a stock ford with stock air intake filter setup and stock motorcraft carb, although she sports a set of branches now, due to the previous owner being unable to source a replacement for a cracked manifold.

If some of the descriptions seem odd, its because I'm from South Africa and terminology may be a bit different.

Thanks in advance.

PS: Truck is a 1979 model with no EFI.

 

There are so many variables that impact MPG that it is mostly impossible to explain the "why". For the engine itself, the ignition and fuel delivery systems must be operating properly. Gearing, tire pressure, manner of driving, quality of fuel, etc., all impact MPG.

 

Welcome to the forum, JayceLayne!

Tell us more about your driving style and truck [F150/250/350?] as well as transmission.

 

Hello from the other side of the globe! One quick question about terminology, what is a new set of braches? I haven't heard that term before (everything else, yes.)

Other than that, has it always been getting poor mileage? Or just after the mechanic tuned?
Do you have a vacuum gauge you can put on the engine? That can tell you a lot about what's going on.
When was the last time it had a tune up? New spark plugs, distributor cap and rotor, etc.
Some quick ideas.
An ignition component in need of replacement.
The mechanic timed your engine with a light but your harmonic balancer has slipped, so it's now at a wrong setting.
Your ignition module is going out, giving poor performance.
The carb wasn't rebuilt correctly.

Some others may have other ideas too.

 

With the mileage I would say that every little detail adds up, as other members have mentioned. I would write out a list of possible changes that effect mpg, starting with timing. I would write out about 10-15 things that could effect it, like air cleaner, tire psi, etc., and check them all

 

Thanks so much for all the replies, gives me lots to consider.

Some more detail on vehicle:

1979 Ford F250, 4x2.
Transmission 3 speed automatic, which I believe is commonly referred to as a C4.
I drive it like a granny, because hey I want to be able to stop it later.
I dont drive it too far at any given time, somewhere around 20 - 80km twice a week at most.
Have owned it for about 3 months only. So cant really say if the mileage has been bad in the past as I have just started recording it.
It was apparently serviced shortly before I bought it. New fuel pump, new thermostat in engine bay confirmed PO story.
Have been fixing a myriad of things since then to make it meet its roadworthy certificate.

Some other things:
Mechanic did say though that I had a big voltage drop from my battery to starter. i.e. 12v at battery down to 7V at starter. Another funny thing I noticed was that when I put her in Park, after the carb service is that the engine revs suddenly picked up, more than in the past, like she was running way to fast.

When I drove it home the first day at about 90km/h had a big vibration become apparent throughout the vehicle, it would build and then reduce and build again. Thought I had sorted the problem out, as the pinion seal on diff was leaking so got that replaced and balanced the propshaft, but I still get the vibration. Could this be related to the harmonic balancer spoken about already?

Also, with the installment of the branches by PO (also known as banana branches here) . Is what I think you guys refer to as exhaust headers, the pipe for heating the air to the carb, was removed and another pipe at base of carb blanked off. So I need to weld a small heat box on the header to have the pipe re-fitted.

Ok so in compiling a list of things to check (might need some assistance here), I will start with the following:

1. Check Harmonic balancer as this may explain my engine vibration-but I'm guessing on this one.
2. Sort out heat box on header for warm air inlet into Carb
3. Check for Vacuum leaks as someone local has suggested this could be a problem too.
4. Get carb rechecked
5. Get the Auto electrician to check why I have such a voltage drop, and check all other electrics at the same time.
6. Check Air filter.
7. Make sure Tires are pumped to spec, 170KPa in front and 210KPa at the back, which they are as I check everytime I go the fuel station. If anything I overpump.
8. Make sure rear tyre sizes are spec, as I have some what we call Knobblies on.
9. Check Aircleaner.... ummmm
10. Check that speedometer is not under-reading, or figure out by how much.
11. ..... ummmm

 

"I dont drive it too far at any given time, somewhere around 20 - 80km twice a week at most."

That right there is one of the many variables I mentioned...cold starts and short trips are are absolutely fatal to MPG even in the best running vehicles.

"Also, with the installment of the branches by PO (also known as banana branches here) . Is what I think you guys refer to as exhaust headers, the pipe for heating the air to the carb, was removed and another pipe at base of carb blanked off. So I need to weld a small heat box on the header to have the pipe re-fitted."

And without heat to the intake manifold MPG and performance will also suffer.

 

Thanks for that. Looks like point 2, is actually the first port of call. What I will do for other members of the forum, is work through this check list and update my findings. Might be useful for others in the future.

 

Look closely at what Harte3 said regarding lack of heat to the intake manifold.

From what I gleaned from this thread, you realize the need for the preheated air to the carburetor and noted that it is missing due to the use of "branches" [headers].

Do you know that there may be as many as 3 areas requiring heat from the exhaust manifold as designed.?

1. There is a metalic shield covering the exhaust manifold. An approximately 2" diameter flexible hose attaches to the shield and connects on the other end to the underside of the snorkle [air intake]. On the snorkle is a vacuum operated servo which is controlled by a temperature sensor located in the air filter housing. When cool, the warm air is drawn from the manifold area. As the temperature increases, the amount of vacuum is reduced and the valve opens allowing a mixture of warm and cool air to enter the carburetor. This prevents icing within the carburetor.

2. There is an approximately 1/4" metal tube which draws clean [filtered] air from the top of the carburetor neck [attached by originally a red rubber hose]. The metal tube connects to a port on the exhaust manifold near the #5 cylinder. Opposite where the tube connects, another ~1/4" metal tube connects to the choke housing. This part of the tube is covered with a thermal insulation. The purpose of this tube is to introduce heated air to the bimetallic spring which opens the choke in sync with the engine as it warms up. On many carburetors [varies with the year], there is also a small electric element located within the black plastic choke housing cover located on the firewall side of the carburetor. This "heater" also provides heat to the bimetallic spring mentioned previously. The electric current comes from the "s" stator of the alternator and is about 7 volts. The current is provided only when the engine is running.

3. The original exhaust manifold is bolted to the intake manifold and provides direct heat to the bottom of the intake manifold where the carburetor mounts. This heat is controlled by a flap and bimetallic spring located in the exhaust manifold. This heat is what Harte3 was mentioning. If using "branches", one can fabricate a plate to mount to the bottom of the intake manifold. With two appropriate fittings, hot coolant can be routed to flow through this area. Normally, the hoses going to the heater core [5/8"] are spliced to accomplish this.

I hope this helps.

 

RE: #3 F-250 restorer and AbandonedBronco have posted pics of the plates they have made...really quite simple. F-250 restorer has made and sold a number of these but me thinks shipping to South Africa might be rather costly.

 

1986F150six that was a great reply, I followed most of it, struggled imagining the coolant aspect of point 3. I sense I better get some pictures posted of my setup or lack thereof , helps others explain to the inexperienced like me where to look and not too look. Will try and get some up tomorrow night when I get home from a business trip that I a on.

Harte3 getting anything from America is costly. When I look at buying stuff on ebay, I normally double the price just to cover shipping costs.

 

The heat/cooling plate provides a stable temperature range for intake/carb operation...something that carbs seem to like. Tuning them for wide swings in operating temperature is nearly not possible.

 

Thanks Harte3. Was just wondering if I should not just get an original exhaust manifold, in trawling some of the local classifieds I found that I can pick up an inlet and exhaust manifold for $80 or less. It should then address all 3 heating aspects properly which where mentioned by 1986F150six.

Feeling a bit frustrated that local exhaust shops, clearly lack the understandingand offered poor advice and solution to the PO, which I now have to rectify. But anyway. Thats why I bought a running classic I suppose

 

Yes, you can do that. If you do obtain a stock manifold set make sure you check the mating surfaces for "true". Once removed from an engine they tend to warp and then are a source of vacuum and exhaust leaks via blown gaskets. A machine shop can clean up and true the mating surfaces if needed.

 

Sorry for belated post, had been in hospital for a procedure.

Today I think I got to the source of the problem or just uncovered another one.

Now when I got the carb set, I also got the propshaft balanced because I kept getting this vibration and hum at about 80km/h. Also I have battled adjusting the right rear drum brake, which I had almost forgotten about until a friend on another forum suggested a dragging brake as a cause for increased fuel consumption.

So today, I pulled off the right rear hub....


All that grease should be somewhere else.



and that bearing should be round.

Inner bearing looked okay, the seal looked alright so where did all that grease come from?

Also shouldn't my shafts be shiny.



At least the splines looked ok I think.



Also found that the brake cylinder piston was only working on one side.... Still need to pull that. Then I went to the other side and well, it was nice a clean as far as brakes go, all worked, but hey this is odd where the other wheel was just grease, I could not find any grease on this one.

So tomorrow, drums going in for a skim as one is badly scored, then take the brake shoes in to check the brake lining, worried about uneven wear. Find new bearings and get someone to check the inner hub bearings, as my bearing extractor is about 3mm to small. Hopefully have it all back this weekend if I can find the spares this week.