By "hot" he means his 2F is "souped up" or "built". An sm420 is a very old 4 speed chevrolet transmission that is fairly popular because is have a very low(7:1) first gear.
really bad gas mileage
- Thread starter a77fj40
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
By "hot" he means his 2F is "souped up" or "built". An sm420 is a very old 4 speed chevrolet transmission that is fairly popular because is have a very low(7:1) first gear.
Basically it is a matter of tuning it up and fixing anything that is not working properly. Rebuilding a good carb or replacing a good distributor isn't going to help. Start with a complete tune up and a compression check. If the compression is bad, then you have to fix this first or nothing will help.
Tigerstripe40
SILVER Star
A 'hot' 2F means that I have done some performance mod's to my 2F so that it produces more low end torque, and a little more horsepower.
An SM420 is a transmission that GM manufactured from 1947 until about 1967 that has a 7:1 first gear, which is VERY nice for offroading.
Well what i did was,
change all fluids, plugs, plug wires, distributer cap, air filter, oil filter, fuel filter. I think i hit 'em all, might have forgotten some. Just the basics.
85roktoy
SILVER Star
So does a 78 have electronic or points in the dizzy? I just changed all the plugs, wires, cap and rotor and I could tell a good bit of difference (in power that is). The old crap looked old as dirt! What about valves in these things? They have to be adjusted right? How often should it be done??
78 is electronic(stock) and the valves should be adjusted if you don't know when they were last adjusted
May as well ensure they are within spec and eliminate them from the equation
That would be a a full tuneup!
My 78 40 with non USA spec dizzy and non USA carb gets about 18 mpg
I run 31" BFG A/T's
Danny
You didn't feel it necessary to check/change the points, or condensor, or rotor, or check/set the timing, or check/set the valve lash?
- Thread starter
- #28
How much will valves that are out of adjustment effect MPG?
Mine's electronic ignition, and i don't know how to set timing or adjust valves. Otherwise, i obviously would.
Hate to make you guys feel bad, but im averaging 18-20 miles to the gallon(cdn)
I have had six 40 series rigs over the last 25 years.
They ranged from bone stock to sm420/37 inch tires ect.
But I have never, ever seen a 40 get 20 mpg. And my 75-78 rigs had no smog equipment to speak of. All were tuned and some had brand new engines, my present one has a hot 2F.
Sorry, I don't believe it.
I read in the TT way back about some guy running 3.73's with stock tires and lean jetting getting 14 or so at 55 mph depending on the wind......
Well dunno I do 67.5 miles a day and I put around 9.6 gallons in after 3 days so about 202.5 miles to 9.6 gallons(and Im figuring in imperial gallons) which quick math says just over 20 miles to the gallon
;p now mind you I do also (according to the build plate, havent confirmed it thou) have 3.73 gears, and for milage I dont bother figuring it out after I leave the pavement, figure Im out playing milage isnt important.Also my dad has always told me when he had his cruiser back in the 70's he would count on his '72 fj40 (bone stock) going 300 miles on a full tank (15.4 gallons (cdn)? which if it didnt i would be along walk to the nearest gas station) and thats right around 20 miles to the gallon.
So dunno what we're doing right.
Anyways cheers all
9.6 UK gallons is approximately 11.5 US gallons... right?
So that converts to about 17.6 mpg. By my book that is very good milage.
My '78 has always calc'd to between 10 and 13 mpg. hth
So that converts to about 17.6 mpg. By my book that is very good milage.
My '78 has always calc'd to between 10 and 13 mpg. hth
A77fj40;
Are u smelling gas fumes? Is there a wet spot under the cruiser after parked for a while? If so, u could have a leaking fuel pump. Its located right side of engine, front, down near the oil pan. U may have to replace same. 7 mpg is way out of line. Should be 12-18 mpg.
Do u have any service records? The chances are that will need new spark plugs and wires. This is just for starters; next will be a carb rebuild. Check timing to see where it is. All this 2F engine needs (for the moment) is a good tune up. Do a compression test to see where each cylinder is; Check timing, replace spark plug wires and plugs and then see what happens.
Get the FSM(s) for this vehicle (Factory Service Manual(s). An auto parts store will carry the Haynes manual #313, which is good for getting u started on general knowledge. I have a post on here in the FJ40 section listing the manual numbers. Read the FAQ's and do a lot of searching on the site to upgrade your knowledge. There are guys on this forum that know almost every part number on an FJ40 - we have no lives...
And welcome...
And PS: pre 1975 FJ40's will get better mpg than later , post 1975, because of smog crap and engine head design. My 1973 used to get close to 20mpg with a tail wind.
Are u smelling gas fumes? Is there a wet spot under the cruiser after parked for a while? If so, u could have a leaking fuel pump. Its located right side of engine, front, down near the oil pan. U may have to replace same. 7 mpg is way out of line. Should be 12-18 mpg.
Do u have any service records? The chances are that will need new spark plugs and wires. This is just for starters; next will be a carb rebuild. Check timing to see where it is. All this 2F engine needs (for the moment) is a good tune up. Do a compression test to see where each cylinder is; Check timing, replace spark plug wires and plugs and then see what happens.
Get the FSM(s) for this vehicle (Factory Service Manual(s). An auto parts store will carry the Haynes manual #313, which is good for getting u started on general knowledge. I have a post on here in the FJ40 section listing the manual numbers. Read the FAQ's and do a lot of searching on the site to upgrade your knowledge. There are guys on this forum that know almost every part number on an FJ40 - we have no lives...
And welcome...
And PS: pre 1975 FJ40's will get better mpg than later , post 1975, because of smog crap and engine head design. My 1973 used to get close to 20mpg with a tail wind.
- Thread starter
- #35
Thanks for the advice and the welcome.
Now that you mention it there is a smell of gas especially after i fill up . but i don't see anything leaking. is there any other way to tell if there is a gas leak that is too small to drip?
Yes, follow the fuel from the tank all the way to the fuel pump. Put ur hand under the fuel pump and feel for dampness; [Last year I experience gas smell, poor mileage etc.; it finally dawned on me that the fuel pump was leaking] then trace the line over the top front of engine to the carb. the carb usually has a solenoid gas shut off valve. When u turn the key on, the valve opens, allowing gas into the carb & shuts the gas off with key off condition. It is possible that this valve is not working, but this alone would not count for 7 mph. The valve purpose is to prevent carb fires (pre 1975 problems)..
What would count is timing, spark plug wires and spark plugs. Off the top of my head, u probably have a points, 1976 distributor (one of the best). Pull the cap and see if there are obvious burned areas and that the points look half way decent.
...
What would count is timing, spark plug wires and spark plugs. Off the top of my head, u probably have a points, 1976 distributor (one of the best). Pull the cap and see if there are obvious burned areas and that the points look half way decent.
...
Last tank on a 1984 EUR spec (no smog) running 98 octane with lots of highway (110 km/h avg) and a little city -
504 kilometers - 65.4 liters
12.98 liters/100km or 21.8 mpg- i'm amazed!
504 kilometers - 65.4 liters
12.98 liters/100km or 21.8 mpg- i'm amazed!
I got 11 US MPG last tank on my '78. on 35" BGF ATs, but that was a lot of DD type driving when the car was in the shop. I know that was a really good tank though. I have gotten less than 1mpg while offroad, and typically see between 8 and 10 for the mixed driving I do.
IMO, I would use the suggestions above and also check vacuum on the intake for leaks.
Mine gets the best gas mileage running 35-45 mph. Anything faster or slower has yielded more gasoline usage for me. 16-17 is my 40's best, depending on head/cross winds.
Mine gets the best gas mileage running 35-45 mph. Anything faster or slower has yielded more gasoline usage for me. 16-17 is my 40's best, depending on head/cross winds.
