Fuel delivery issue?

[effjay55]

Posted this in the 40-55 tech forum on accident, but I'll just repost here.
1974 55 series
F.5 engine
3 speed manual

So Ive got a problem Im trying to pinpoint.
The truck starts great, and idles fine. After letting it idle a bit, I’ll go for a drive and initially runs great and pulls strong through all three gears. But then it seems as if when everything starts to warm up it will start popping loudly and bogging and hesitating, almost stalling.

I pull over and checked the sight glass but it seemed ok? Maybe a bit low.

When i give it wot in neutral she purrs along just fine and strong, I can rev it for days, but when moving along it starts giving issues…again this is after everything is sort of warmed up.

The weirdest thing is Ive been driving this thing around trying to troubleshoot so I know Ive used quite a bit of gas, but I opened the fuel cap and saw that the fuel is almost to the top!

I pulled and blew into the charcoal canister house that goes towards the tank, everything is ok. (Orange)

The other top hose goes to the vsv but that one is completely blocked, not sure if its solenoid activated.(Red)

The bottom hose i havent checked yet…(Green)

Anyone know if those two issues are related? (The bogging/popping and the gas tank which seems to have some sort of back pressure)..
The tank did not release any pressure when I opened the gas cap...
Any advice is appreciated.

 

[trainbufftony]

What makes you think this is an Evap related problem?
Seems like good old fashioned fuel starvation.
An FJ55 gas tank should not be pressurized, so that's working correctly.
Like I said in the other thread, see if a fuel filter fixes it for $20.

 

[effjay55]

@trainbufftony Already have one on order! Thanks for response!

In regards to my theory well… Just thought it was weird the gas tank was a little back up! I thought maybe it wasnt venting properly.

 

[RUSH55]

Yes, start with a filter and move down the line - pump, lines, tank pick-up.
Venting issues won’t cause starvation unless it’s under a vacuum, which would be a non-existent situation with the factory gas cap.

 

[PabloCruise]

I am not so sure that is the fuel level you are seeing in your picture.

Good idea checking the pressure in the tank, you don't want a lot of positive, or negative pressure in your tank.

The charcoal canister ideally should be receiving vapors from your tank when the fuel gets warm. The solenoid is designed to allow engine vacuum to purge the vapors in the can under conditions where the engine won't bog when those vapors hit. The green line is a vent so that engine vacuum can purge the can w/o creating a vacuum on the can. Make sense?

Some things you can do to assess your fuel situation...

1. Measure fuel output from the pump? Is the pump putting out what it is supposed to? You can disconnect the line going to the carb and divert to a clear container and measure output. Obviously be careful. You don't want gasoline spraying in your eyes or all over a hot engine.
2. Are your lines clear? You can disconnect those and run compresses air through.
3. How is the tank fuel supply line? You can run some weed whip line, or an old speedo cable (by definition "old", who uses a speedo cable any more?) into the tank and make sure you don't feel any grit.
4. If fuel supply is good, how is the carb?
5. Any vacuum leaks? How does she idle? You can spray some carb cleaner around the base of the carb when these issues are happening and see if the engine RPM changes. If yes, vacuum leak. Make sure the intake/exhaust manifolds are torqued adequately.
6. Before pulling the carb for rebuild, some of our Aisin carbs (is that what you are running?) have bowl drain plugs. You can pull those, and spray some carb cleaner straight in - the jets should be right across the bowl from the drain plugs.
7. If you keep filling your filter w/ crud, it will be time to think about dropping the tank and getting it cleaned out. I have dropped mine 2x. It is a PITA. It will make you feel a sense of accomplishment. Details in my build thread.

Good luck!

 

[RUSH55]

~4.5-6 psi fuel pressure to the carburetor. Good idea to plumb in a gauge if your fuel pressure is in question.

 

[effjay55]

I am not so sure that is the fuel level you are seeing in your picture.

Good idea checking the pressure in the tank, you don't want a lot of positive, or negative pressure in your tank.

The charcoal canister ideally should be receiving vapors from your tank when the fuel gets warm. The solenoid is designed to allow engine vacuum to purge the vapors in the can under conditions where the engine won't bog when those vapors hit. The green line is a vent so that engine vacuum can purge the can w/o creating a vacuum on the can. Make sense?

Some things you can do to assess your fuel situation...

1. Measure fuel output from the pump? Is the pump putting out what it is supposed to? You can disconnect the line going to the carb and divert to a clear container and measure output. Obviously be careful. You don't want gasoline spraying in your eyes or all over a hot engine.
2. Are your lines clear? You can disconnect those and run compresses air through.
3. How is the tank fuel supply line? You can run some weed whip line, or an old speedo cable (by definition "old", who uses a speedo cable any more?) into the tank and make sure you don't feel any grit.
4. If fuel supply is good, how is the carb?
5. Any vacuum leaks? How does she idle? You can spray some carb cleaner around the base of the carb when these issues are happening and see if the engine RPM changes. If yes, vacuum leak. Make sure the intake/exhaust manifolds are torqued adequately.
6. Before pulling the carb for rebuild, some of our Aisin carbs (is that what you are running?) have bowl drain plugs. You can pull those, and spray some carb cleaner straight in - the jets should be right across the bowl from the drain plugs.
7. If you keep filling your filter w/ crud, it will be time to think about dropping the tank and getting it cleaned out. I have dropped mine 2x. It is a PITA. It will make you feel a sense of accomplishment. Details in my build thread.

Good luck!

Even though a new filter helped a ton, I am basically running through all this over the weekend in prep. for the oem filter. I actually really appreciate all the suggestions and tips. Had never even heard of spraying carb cleaner around the carb to check for a vac leak!

Honestly not sure what the carb is, pretty sure its original two-barrel...whatever that is.

In the picture, the fuel was definitely visible, but actually I believe that I was misjudging the amount of fuel I may have had in the tank. I am still not quite sure though. I intend on doing that fuel system flush, but was also thinking of just going ahead and doing a charcoal canister rebuild just in case. I noticed a bit of gassy fumes last drive and it made me wonder.

I will check out your build thread, thank you!

~4.5-6 psi fuel pressure to the carburetor. Good idea to plumb in a gauge if your fuel pressure is in question.

Appreciate the details on the PSI and suggestion!