I've recently begun storing my F-250 in the garage. I used to leave it outside, but a couple months ago I moved to Kentucky from Colorado. There is real moisture here and old vehicles don't seem too fond of it, this truck included.

So it has a home in a small one-car garage, but after sitting for a couple days I have to open the door and air it out, as a fuel smell accumulates. It's worse when the fuel level in the tanks are low. I don't recall ever smelling fuel vapor coming from the truck (maybe a faint smell under the hood, but I attribute that to a normal carb smell), but it sat outside, so who knows.

Fuel economy has taken a sudden turn for the worse also. I used to get a solid 10 average, even hit 12 on the 1100 mile drive out here (all highway), but lately it's 7-8. Not sure if this and the fuel smell are related-- it could be a side effect of moving to a much lower elevation, I don't know. The truck definitely needed a rejet (I had to run premium gas and retard the timing to keep it from pinging when I first got here),so I'm running a 62 jet instead of 59. Truck runs fantastic now even on regular unleaded, doesn't smell rich, has great power, so I have to assume the tune is at least decent and not killing my mileage.

Can anyone give me an explanation of how these tanks are vented / how the lines are run and what things I should be checking? If there is any way to rework things to make them simpler, I'm all for it. From the factory, this thing had a million emissions gizmos related to the fuel venting/charcoal canister which were put back together to the best of my ability, but may not be 100% right-- I'm not even sure how one would test these components - charcoal canisters, and the little vacuum doo-dads that are interconnected to it all. The simpler and easier I can make it to diagnose and maintain, the better. Thanks in advance for any feedback.

 

A few things on the MPG. You put fatter jets in it that does not help the MPG but I would say the big one is the gas blend we have out here.
If you can find gas with out ethanol give that a try.


For the smell I would make sure all hoses are in good shape and connected. You should have a sticker on the radiator support on how all the hoses should run. Check it and make sure they are right.


It should also list the fuel tank vent system. If it is like my 81 F100 with duel tanks, each take have a roll over valve / vent on the top of the tanks. They both tie in together and run up to the canister. Then a hose from the canister to manifold IIRC as it has been some time I did this on mine.


On mine I think there is another hose from the vent to the canister so the carb fumes go to it also.


I cant tell you how any of the stuff gets tested? I don't have any of it on my truck to worry about. Just the tank vents to canister.
Dave ----

 

Don't know if this is your problem, but I had the similar deal a couple of months ago....

Finally learned that my fuel pump was going bad and leaking. I never saw it leak, because there is a frame cross-member that goes right under the pump and any extra gas just rested in the cross member.

Finally found it one night by running the truck in the dark and using a high-power flashlight. Hard to explain, but in this situation it was easier to see the light the gas was reflecting using the flashlight beam than in bright sunlight.

 

The newer cars monitor the evap system and throw a code if it has a leak. And some places in the country pressurize the evap system as part of the emissions test, if it doesn't hold they fail the car.

Garages now have smoke machines they use to detect leaks in this system. It injects smoke into the system and then you can look for where the smoke comes out.

Your truck has vents on the top of each tank. They go over to the pass side frame rail where they tie together and run up from to the charcoal canister. The charcoal in the canister holds the fumes from the tank till the engine is started, and then when it suits the controls of the engine, they will apply engine vacuum to the charcoal canister and purge the gas fumes out of the charcoal, burning them in the engine.

People seem to get some sort of theraputic value out of taking vacuum lines off their engines. Check yours to see if this has happened, or some of them are cracked and leaking.

 

Recently I had begun smelling fuel around my truck too (after switching off); I opened the carb, & the needle valve wasn't shutting off 100%.
It had a depressed imprint around the neoprene tip, from age.
I adjusted the float to put a bit more pressure on the needle valve, which worked as a temporary fix.

But the carb didn't have the correct venturi size for the engine anyway, so I've since bought a non-EGR, non-emissions, Canadian spec replacement.......which interestingly is designed with manifold (not ported) vacuum at the distributor advance port.

Anyway, your needle valve & float level may need checking.

 

Do some checking, I bet that setup took a different distributor too. You may have to go to that different style dist if you can't get it to run right with the manifold vacuum on the original dist.

P.S. Probably had a different radiator sticker with different timing specs also.

 

If the throttle blade(s) were open too much (hi idle) that port would have vacuum.


On another note some like to run manifold vacuum over ported for dist. advance.
Dave ----

 

LOL!! don't forget buggering the wiring under the dash, and ignition timing. -----------

If you did happen to back off on the ignition timing though, that will always affect fuel economy and not for the better. If it's a standard carb and distributor setup make sure the vacuum advance diaphragm is operating correctly. It's good for about a 15% to 20% hit on mileage if it goes bad, or maybe 2 to 3 mpg on a big motor. Maybe it died on the long drive? Couple that with less advance, throw in some corn gas, it starts to add up... Manifold or ported vacuum won't make too much difference overall though it will run cooler at idle with all that timing pulled in, and it will sometimes confuse folks when setting the initial or base timing.

Put a timing light on it and see what your total timing is, vacuum advance disconnected and plugged. See that it works smoothly and no scatter etc. See how it drives on acceleration. Then re-connect vac advance see that it is pulling in as it should.