Another poor gas mileage thread

[IslandJ]

About a month ago or so I adjusted my timing for the first time since I had my 60 per the FSM. Woah was it off! It was WAY advanced.
A week later I adjusted my carb per the FSM.
The carb was rebuilt a couple years ago by Mark's Offroad and always had a leak or two. Still haven't attended to that.
After the timing and carb tune the truck went from getting 12.5mpg to about 8.5mpg.
Prior to tuning I had detonation when accelerating hard or heading up hill, so I usually drove around easy on the skinny peddle.
Starting has become noticeably harder in the morning as the sight glass looks to be empty and I have to pump the gas quite a bit and pull the choke all the way out. Once or twice in the am, three times maybe if it was a chilly night.
Lil bit of a rough idle till the ol girl seems to get her fill of gas in her cup.
Fuel pump is OEM, with not that many miles on it, maybe 5000 or so.

Where should I start lookin Mud? Thanks!

 

[NeverGiveUpYota]

Fuel filter for cheap starters.
I did read a very interesting article on valve seating last night, (its on my thread) regarding tractors but still it made a TON of sense. If you’ve got a bunch of built up carbon on your valves, you will have issues starting. But that’s getting way deeper than your asking...

 

[Seth S]

Are you still running egr and aux air systems? Are all of your vacuum lines good and routed correctly? How are your plug, cap, rotor, wires, air filter, etc?

 

[klinetime574]

What kind of carb “leak” are we talking about here? You mentioned something about that.

 

[IslandJ]

@NeverGiveUpYota Brand new fuel filter on it as of a few weeks ago. Valves adjusted by a cruiser mechanic last year, he said everything looked good and barely needed any adjusting.

@Seth S the engine is running stock egr and aux air system. I should test the egr valve. All vacuum lines are routed correctly as far as I know. I replaced them all with silicone hoses a while back. Plugs, cap, rotor, wires and air filter at the same time. Worth a look though.

@klinetime574 there’s a hyper link in my og post but here’s a direct leak.
Leak in question is on the second page.

fj60 carb leakage?

Yeah I get a huge rush of air when I take the original gas cap off after it’s been warmed up. Would you elaborate a bit more on the check valve addition? I appreciate the insight. hey jason , if no loose fasteners then ................. Ok so there's another possible reason u have a...

forum.ih8mud.com

Does the drop in mpg accruing after adjusting the timing back spec make sense at all or does it seem more coincidental?
The hard start was always there after a day of sitting but definitely worse these days.

 

[doug720]

About a month ago or so I adjusted my timing for the first time since I had my 60 per the FSM. Woah was it off! It was WAY advanced.
A week later I adjusted my carb per the FSM.
The carb was rebuilt a couple years ago by Mark's Offroad and always had a leak or two. Still haven't attended to that.
After the timing and carb tune the truck went from getting 12.5mpg to about 8.5mpg.
Prior to tuning I had detonation when accelerating hard or heading up hill, so I usually drove around easy on the skinny peddle.
Starting has become noticeably harder in the morning as the sight glass looks to be empty and I have to pump the gas quite a bit and pull the choke all the way out. Once or twice in the am, three times maybe if it was a chilly night.
Lil bit of a rough idle till the ol girl seems to get her fill of gas in her cup.
Fuel pump is OEM, with not that many miles on it, maybe 5000 or so.

Where should I start lookin Mud? Thanks!

The highlighted lines above likely contribute to the lower mileage - your driving it harder and faster.

Beyond that, carb leaks can't make MPG better. Fair chance you have at least a few issues with the systems and parts mentioned. A lot of parts all have to play well together to get decent mileage. Is the engine sound otherwise?

Being in LA, the smog police have no mercy for an old simple vehicle that was not designed to meet emissions. The 2f had a primitive nightmare added to it 30-40 years ago., and time is an evil bitch to keep at bay

With careful tuning, manuals and time, you will get at least some of the mileage back. But these are old, heavy, 4 wheel drive bricks powered by a tractor engine.

Keep at it.

 

[Seth S]

As a reference point: In stock but old condition and emmissions components working at a questionable level and also with vac lines in questionable shape: I had no pinging or detonation that I was aware of and starting the truck was always hard requiring multiple cycles of 4 gas pedal pumps and cranking....worse in the winter time (sub freezing). When I did the full desmog I figured out that all the vac lines that attached to the distributor had actually broken and the distributor was never getting a vac advance signal.

With the desmog done and all remaining vac lines replaced with new silicon I find that the truck starts almost immediately and hot starts are so much better (even with the carb fan currently disconnected). First test drive with the new vac lines on the distrbutor advance I had a lot of pinging....and when I moved the advance to the smaller advance port I still had some pinging....however I still have to verify the base timing....as someone may have advanced it as a fix for the lack of vac advance.

I am running the factory stock carb and have no known fuel leaks and when I filled up yesterday I was getting around 13.4 mpg with most driving below between 200' to 700' elevation.

 

[OSS]

Retarding the timing will lower MPG (and reduce pinging if it was pinging). Driving with a dainty pussy foot on the gas pedal with overly advanced timing will eek out more miles per gallon than setting the timing correctly. Correct timing on the 2F is when the engine can produce the maximum amount of torque at around 2000 rpm and not ping.

If setting the timing to the FSM recommended 7° BTDC kills detonation at the expense of 8.5 mpg, then the engine is in need of a good tune up and some troubleshooting.

Check the function of the EGR system and vacuum advance system. The emissions FSM has all the info. If that does nothing — suspect the carburetor (after you tune it up)

Also the usual stuff like properly inflated tires and no excessive weight.

 

[IslandJ]

Thanks all. Ill go through all the standard tuneup procedures and check the EGR.
It did pass with flying colors a year ago though. Even the cruiser mechanic was kinda surprised.

 

[Seth S]

Modern efi/ignition systems are very efficient at listening for knock and advancing the timing as much as possible. They listen so closely and cycle so fast that you should never hear knock now except in the most extreme situations....but they basically advance until they hear knock then back off and repeat.

 

[klinetime574]

The slow cut valve leak shouldn’t hurt too badly. The main shaft on the other hand definitely could. How many inches of vacuum does the engine pull at idle? I’ve got a vacuum gauge installed inside the cab so I can watch at all times. Kinda overkill but it looks cool.

 

[IslandJ]

I’m not sure on the vacuum. I added a vacuum gauge to the list of new tools to get.

 

[IslandJ]

Another note i forgot to add is in 1st and 2nd, while moderately accelerating or holding RPM's between 18000-2300, there is a subtle surging or pulsing in momentum. 3rd-4th I dont notice any surging.

 

[DFXR]

Here's a question for you - when it passed smog a year ago, did the smog tech actually check your timing or did he just write it in? Because if he did actually check it, and it was way advanced, he probably would have failed you on the visual. Some guys don't actually bother though, or they do you a favor by writing in the correct/required amount of advance.

What I am getting at, maybe, is that your vac lines to the vacuum advance on the distributor are reversed. It's a common thing to do if you are bypassing a sticky EGR valve - you bypass the valve and then swap the lines at the vac advance to make up for the hotter combustion temps caused by no EGR. Maybe somebody before you did this? Easy to check the correct orientation if you have the emissions manual.

 

[IslandJ]

@DFXR I honestly couldn't tell you. It was a cruiser mechanic that took it to "his guy". Im guessing his guy over looks the visual, I dont know.
I'll pull out the emissions manual and double check the lines.
Thanks