A little stumped - fuel flow problem?

[Millercorey]

Background - recently rebuilt engine that had been running really well for the last month or two. Guy that dropped in the motor said to make sure to change the oil after 500 miles or a month, and that I should probably just bring it back to him so he could change it and check everything else out while he was at it. Never got around to finding the time to go see him again so I finally just changed it out myself. After I changed it, couldn't get the engine to run again. So here's what I know and what I think:

-put in standard Motorcraft fl1a oil filter and 20-50 oil with 1/2 quart of zinc additive. Everything was added according to instructions
- I don't believe the oil change has anything to do with my issue

-I plan on parking it for the winter and replacing the floor pans, insulating and adding carpet, so I was fiddling with the auxiliary tank b/c I expect to pull it soon (tank has never been used or even tested)

-like an idiot I fiddled with the fuel selector valve, and while it turns just fine, I suspect it broke internally and is stuck between tanks

-after the oil change, I went to start it up and it idled for 15 seconds then died. Not super uncommon when cold bc I need to adjust the carb a bit

-after this, I couldn't ever get it to fire up. I assumed the valve was stuck between tanks so I bypassed the valve. Once I did, it fired up for 5 seconds and died. Won't start up now

-brand new fuel pump and has been running just fine up to this point. Noob so I won't be using the right terminology here, but I know the tank needs to vent. The line sucks gas up, and if not vented, the ln pressure builds until the pump can't suck anymore gas. I think that's what's happening but I'm not sure how or why. Any ideas how I caused this and what to do?

 

[Broncobowsher]

Air cleaner off, look down the carb and cycle the throttle. Check for a good accelerator pump shot. Lack will confirm you are out of fuel like you suspect.

Probably correct on the fuel valve. I would bypass it and just hook to one tank for now. It will not fire right back up as the fuel line is now empty. The engine has to run (or crank over a LOT) to refill the lines and put fuel in the carb. Dribble a little gas in the carb or shoot it with flammable carb cleaner to get the initial fire up.

Vented gas tanks are not the issue. It isn't running long enough for there to be any pressure/vacuum issues.

The suction side of the fuel line (where the fuel selector valve is at) is very sensitive about air leaks. ever have a pin hole leak in a soda straw? same thing can happen on the fuel system. IF there is a slight leak (and a bad fuel valve can make for that leak) it will suck air a lot more than fuel.

 

[Apache Bronco]

If it was me I would remove the fuel line at the carb and crank it to see if fuel is reaching the carb. It sounds like a piece of detrius is moving thru the fuel line and is clogging it.

 

[Millercorey]

True. After I bypassed the valve, I probably only cranked it for 10-15 seconds assuming the bypass didn't fix it. Telling me I should just sit and crank it for longer or prime the bowl (or both)?

 

[Broncobowsher]

I would prime the fuel bowl. The engine will start and run on the prime. A pump on a running engine works a lot better and faster than one on an engine that is only cranking. 5 seconds of cranking does as much pumping as 1 second of running.

 

[B RON CO]

Hi, X2 on the accelerator pump squirt. You can remove the rubber hose at the fuel pump and see if it is dry. You can gently blow that hose back to the tank and listen for bubbles. You also can feed the fuel pump with a rubber hose from a gas can on the floor, under the engine to make sure it runs, but you can't drive it that way. Good luck

 

[73azbronco]

Fuel pressure?

Fuel flow at carb into a bucket while cranking?

Fuel quality? Old, dirty etc?

All of these things can be dangerous and I tend to do them outside of a garage just in case.

 

[ntsqd]

An old & cleaned shampoo bottle with a squirter rather than a pump is great for fulling the fuel bowl thru the bowl vent.

Once running on fuel in the carb bowl, stop engine, disconnect line from pump to carb at pump & add a long hose to the pump fitting. Get it clear outside the vehicle for safety's sake (yours and the Bronco's). Fire up again with hose pointed into a bucket to verify that that the line isn't clogged by debris.

Can disconnect supply line at pump and use compressed air to blow backwards into the tank. Do this gently and with the fill cap off. If this fixes it temporarily all of the rubber hose is suspect and should be replaced.

 

[67RT]

Are u sure it has gas? My gauge says 1/4 when mine is dry. Inwent thru this recently.