Bad Gas Milage at Freeway Speeds

LT

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So I have a 76 FJ40 with a 79 2f, with a rebuilt aisin carburetor powering 35" bfg's with 4.11's. Initially I didn't have the return fuel line hooked up, so I got that fixed and now that is working. And then proceded to change out the spark plugs to the stock plugs and gapped them .055 because I have a h.e.i. distributor. But i'm still running into the same problem.

My in cab vaccum gauge is reading 6 - 7 psi at speeds 55 mph +. Woody was suggesting possibly bad timing but my rig accelerates with no hesitation. Any of you 2f gurus have any ideas on what could be the reason for such a crappy vacuum reading? At idle is sits perfect at 850 rpm at 21 psi on the vacuum gauge. Thanks.

Travis
 

tucker74

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You mean yours only gets bad milage at freeway speeds?

(I couldn't help it man :flipoff2: )

Tucker
 
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I was thinking about this and looking at the vacuum 101 guide. I wonder about a restricted exhaust system.
 

LT

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It is completly desmogged. Everything is capped off at the carb and whatever else the previous owner did to the engine (had a weber carb when I got it). I also run a hooker header.
 

Poser

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" Bad Gas Milage at Freeway Speeds "


Welcome to the world of modified bricks with wheels and very inefficient internal combustion engines.


What kind of numbers are you talking about here?


What kind of mileage do you really think that you are ‘ entitled ‘ to?


If you are SERIOUSLY concerned about this, pick something up that gets better mileage and park the Land Cruiser.



Good luck!



Should be inches of vaccum and not psi....


-Steve
 

LT

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I know it's supposed to get s***ty gas milage, i've been driving Land Cruisers since I was 15 and i'm 22. Usually i'm running around 10 - 12 inches on the vacuum gauge but now it's worse than usual.
 

Poser

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Find the leak....or get your right foot off the floor. ;)
 

LT

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I don't comply with the later part :flipoff2: I guess I'll just have to start checking leaks at the higher rpms because at idle the vacuum stays perfectly still and so does the rpm gauge.
 

Poser

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Well,


Agree or not, if you have your foot in the carb, your gauge will read closer to zero.....


that is just a fact.


Good luck!


-Steve
 

Poser

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While you are rolling down the road at 55mph, if you remove your foot from the carb, does your reading increase?
 

LT

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Yes, it does. There seems to be this fine balance on the gas pedal where I can get it to raise the vacuum reading to go an inch or two higher. I only go 55 mph on back roads if i'm stuck behind people :flipoff2: I usually keep it at around 2700 rpms on the freeway which is I think around 70 mph or something like that.
 
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Did you smog it? Maybe the power valve is staying open dumping too much fuel into the carb?

That sounds awfully big(.055") for a spark plug gap. I used to gap my plugs at .050 but my jacobs coil says .007" over stock or like .039".

Have you checked the timing at like 2500 rpms. Maybe the advance curve is not right on the HEI.
 
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sorry... i didnt see what you mpg was?
also you are most likely going to start to lose mileage the more you go over 55mph. I know GM did some research and had it on one of their websites.
 
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MPG??? My 2f/sm420/3spd w/38" TSLs gets 8mpg on the road :eek: When I run the Rubicon, I have to take a 5 gallon can with me just to make it to South Lake. Horrible milege :crybaby: I would never drive 500 miles in my cruiser. I wouldn't even drive 100 miles.
 

65swb45

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These are very rough numbers, but I figure you lose 2mpg on 35s vs 33s, and 1mpg for each 5mph over 55.

So at 70, you're losing 5mpg over 33s at 55mph, which brings you back to 13-14mpg.
 
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Poser said:
Welcome to the world of modified bricks with wheels and very inefficient internal combustion engines.



Good luck!

X 12

Try slip streaming tractor trailers; it will improve your mileage, bet you have to pay attention to what you are doing or "SPLAT".
 
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65swb45 said:
These are very rough numbers, but I figure you lose 2mpg on 35s vs 33s, and 1mpg for each 5mph over 55.

So at 70, you're losing 5mpg over 33s at 55mph, which brings you back to 13-14mpg.
It's all relative.

I run a hot 2F. SM420, 4speed t-case and 35" tires.
During Cruise Moab I was getting between 15-19mpg.... 15mph rolling around moab, 19 on the highway comind from SL to Halls Crossing, then from Halls Crossing to Moab..

I also had my foot in it, driving 75-80mph...

Timing, ignition, and carburation are key...
 
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GreenWeeny78 said:
Yes, it does. There seems to be this fine balance on the gas pedal where I can get it to raise the vacuum reading to go an inch or two higher. I only go 55 mph on back roads if i'm stuck behind people :flipoff2: I usually keep it at around 2700 rpms on the freeway which is I think around 70 mph or something like that.
At 70-75 I get like 12mpg. If I cruise on backroads at 50-55 I get 15-18. It's a brick with big tires pushing through the wind at 1300 rpm below redline. Of course it's going to get terrible mileage. My 77 I had that was bone stock with 31's was only slightly better than my 79. I would say if you are anywhere over 10mpg at 70 it's about normal.
 
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