I hope you guys can help me with this issue, I usually use my truck to make my trips around town and I get a pretty decent fuel mileage, but once I take the freeway I think the truck mpg gets worse, actually it consumes about a 1/4 of tank in a 30 miles trip going at 60mph and also I have installed a tachometer and I've notice that the engine revs good in between the 1k-3k rpm's range, but when I try to rev it over 3k rpm's it hardly go up. I already check the timing and the tune up were done about 4 months ago.
kinda a stupid question but have you checked to make sure the muffler is not broken on the inside and all restricted? when i got my 73 the factory muffler was plugged really really bad and the motor barely ran.
I think you're right. I remember that the previous owner told me something about the cat (I don't remember what), and I have notice that the exhaust gets pretty hot when I'm on the freeway, but that's weird because I passed the smog check without any problem. I'll try to change the exhaust system the next month.
you've got like a 12 gallon tank. so .25 is something like 3 gallons. a 60mi trip has a avg of near 20mpg. sounds about right. that trucks more then 30yrs old. you've got a ton of air going under it, carb prolly needs rebuilding and the exhaust is restrictive. if this is a auto or a 4 speed thats good milage, a 5 speed could do better. my 75 avg'd about 22mpg with a 5 speed and 4:37's, dropped it 3in and got 25mpg, then upped to a 4:10 and could almost get 30mpg if i kept my foot out of it (read: never). that was with the best functioning stock carb ive ever seen, and ive seen a ton of em. i bet dropped a bit with a newer 3:XX gear set you could see 30 or better avg.
It's a 5 speed and I really don't want to drop it because I use it to go to the desert once every two months or so, do you know where/or in what kind of truck can I find a lower gear ratio?
Have you checked the distributor vacuum advance unit? the diaphram in the advance may be bad or the distributor itself is dirty or rusted and the advance plate is stuck or not moving freely.
Apparently that's the problem, or one of them I think, I checked the vacuum advance diaphragm and it seems to be leaking. I connected a hose into the unit and I used a vacuum gun to make it work but nothing happened, then I blew the same hose connected into the vacuum advance unit and I heard an air noise coming out from the vacuum advance unit, everything else inside the distributor seems to be ok, and the advance plate seems to be fine too and it moves freely, was this the right way to test that out?
That'll work, just need to apply vacuum to the diaphram and see if it holds, if it leaks off then its bad. The advance plate inside the distributor should move back and forth freely with no binding or sticking.
