712 almost starts; fuel delivery

[michaelh712]

My 712 just started a new gremlin behavior. I can't get to it for a few days, so thought I'd solicit some collective brainstorming ideas in the meantime. It sputtered for a moment on a hill last time out, then all was fine. Went to start it yesterday, it caught on, sort of, then died. Starts with either, or gas down the throat, but then dies. Electrical seems fine, but perhaps a fuel quantity issue? I do get some fuel spray from the carbs.
When I pull the fuel hose to the carb and crank, I do get a small amount of fuel. How much should I expect? Ideas?
Thanks

[75pinz]

I get approx one 20 ounce pop bottle full in about 15 seconds as I was investigating mine recently.

[Twin Pinzies]

I have been pulling my hair out with a fuel delivery issue myself. I have drained and cleaned the gas tank, replaced all the fuel lines, replaced the fuel filter, and rebuilt the fuel pump. The truck runs PERFECTLY until it decides to suddenly "run out of gas" while climbing. Letting it sit and restarting it works most, but not all of the time! I have also replaced the entire electrical system. Still the damn thing acts up every few trips out! The only clue that I have is it starts to runs rich (I can smell it) just before it "runs out of gas." I'm considering rebuilding my carbs... I don't know what else to do!!!!!!

[michaelh712]

WOW, 20 ounces in 15 seconds? I'll have to check again, but mine seems more like 1 ounce or thereabouts in 10 seconds. I rebuilt the top end of the fuel pump last year and that "fixed" that problem at that time. I also need to eliminate a blocked fuel filter or problems with associated hoses.

[Jim LaGuardia]

Sounds like you should be checking that pump Should deliver 2.5 psi

[75pinz]

20 oz in 15 seconds is too much? I just pulled the line off the other and with the engine running at 1150 rpm both pinzgauers here in my garage will fill a 16.9 oz water bottle in less than 15 seconds. I don't have any idea what the pressure is. Just for kicks, I pulled the line off my fairlady datsun and it filled the same water bottle in the same amount of time. YMMV I guess. That is running at high idle which I would guess on the datsun may exceed 1500 rpm.

[milesdzyn]

heres the math for what its worth

one gallon = 128 oz
at 15 mpg @ 60 mph = 1 mile per min consuming 1/15 gallon
128 oz / 15 = 8.5333333333333 oz per min
8.5333333333333 oz per min x (15/60 or .25) = 2.133333 oz per 15 seconds
Of course this is at 4000 plus rpm not at idle so???

Its been a while but I think thats right

Miles

[75pinz]

I think the math is right but the truck won't use all the gas the pump gives it.

[milesdzyn]

Oh yeah also when the fuel lines are attached it is a complete enclosed system so there should be some back pressure that is not present when the fuel line is pulled for testing via the soda bottle.

So what piece of equipment is used for testing the psi of the fuel pump and how is it attached into the fuel system for testing?

Miles

[Jim LaGuardia]

It's called a (low pressure)fuel pressure guage, and goes between the pump and carb inlet

[michaelh712]

Jim,
pressure guage inline with like a TEE connection, or could you just take a reading from the outlet from the pump?

[Jim LaGuardia]

works both ways, with a tee or just on the end of the line. The fuel pump has a bypass valve to prevent overpressurizing.

[michaelh712]

I'm getting 2.1 on my guage, is that too low?

[michaelh712]

Answered part of my onw question. Replaced the fuel filter with a new one and now get 2.6 lbs pressure. Starts with starting fluid then dies, but Still won't start, howevever on its own or maintain. Next suspect carbs?

[Jim LaGuardia]

First pull the tops off the carbs , see how much fuel is in the bowls and remove and inspect the needle valves for debris, use compressed air to clean them . Also check the fuel shut off solonoids, back them out a little and see if it starts and runs.
I'll check for your results when I get back to the house this afternoon.
I'm on my way to check out someone else's clutch disaster