Intermittent Fuel Issues?

[Dat Lurka]

My datto is now a driving project. I've had a issue starting yesterday afternoon. When I get up to speed I start to lose power and sometimes the engine just dies. I get out and check the float bowl and it is empty. After turning it a few times and letting it sit it fires right up and continues to pump the fuel. I get a mile down the road and run out of gas again. Repeat... The fuel filter was trashed but not clogged, I cleaned it and I'm currently using a smaller clear filter so I can see the flow. I pulled the tank plug last night and saw it was nice clean fuel. Then I put a vacuum pump in front of the filter to make sure the line wasn't clogged. Pulled fresh fuel through no problem.

Today I filled up the floatbowl and cranked it up. Fuel was flowing through the filter. I'm a block from my house doing 40 in 3rd and it starts to sputter. Died at the foot of my driveway. No fuel in the bowl, fuel pump not working. I pushed it up to the carport and pulled the send line from the pump and put it in a jar. Turned it over and got nothing. I pulled a vacuum on the line and it pulled fuel through the filter and pump. Put the line back in the jar and turned it over and it was pumping fuel with a bit of air in it. Put the line back on the rail and started it up and it stopped pumping.

Any idea whats going on?

Could the check valve in fuel pump be sticking?

I've never broken down a datto pump but I've had stuck check valves on other pumps and it was pumping the fuel back and forth through the lines.

[Dat Lurka]

Oh yeah, while I was under the truck last night I noticed there was what looked to be a factory electric pump.

It's under the bed near the filler neck. It has what looks to be datsun wiring. The fuel send line is bypassed across the front of it.

Did they have factory electric pumps.

[banzai510(hainz)]

is this a 620 truck? with stock eleltric fuel pump? Can I assume yes But Im doing alot of assumeing here!!!!

 

I will assume the pressure is OK. I dont know if they change pressure if going pump goes bad.

 

But if its electric and the bowl empies try tapping on the carb where the gas goes in the carb while key is still on. There should be a needle valve that lets gas in it could be getting stuck.

I will assume also if you pulled the gas line going to the carb and pointed it in a safe direction it would be shooting gas.

 

 

I had this proplem on my 521 with stock carb.

A Black guy should me how to do this. I would crank the engine and he would tap on the banjo fitting and gas starting going in. I swapped out to a weber

[ggzilla]

Every Datsun 720 I've looked at had an electric pump.

[Dat Lurka]

Sorry should have added basic info.

It is a 620 with L20b. It has a mechanical fuel pump. I noticed what looks to be an electric pump near the tank that is bypassed.

[datzenmike]

'79s had electric pumps when there was factory air. Earlier air was installed by dealers and the pumps were below the dizzy. The '79s compressor was mounted on the mechanical fuel pump studs so an electric was mounted back towards the tank.

 

Be sure no air can be sucked in past a gear clamp or loose fitting.

 

When cranking it over with a hose from the pump it should shoot out like a garden hose. It should fill a US quart jar in a min or less at idle.

[banzai510(hainz)]

OK get soembody to crank the motor and if stock carb( I assume since you have a sight glass as thats how you know its empty)) see if gas is going in or start tapping on the inlet to the carb. maybe you can shake something loose

[Dat Lurka]

It looks like it might be pulling air through the pump. And maybe at a certain speed it pulls more air than fuel. I'm going to replace the rubber lines behind the pump and see if it helps.

 

It's a 77' that had air at some point.

[banzai510(hainz)]

a cracked hose right before the inlet to the fuel paump can suck AIR, than gas.

This happen last year to me on my 521.

[Dat Lurka]

I need to get out there and work on it but we're getting the outer bands of the hurricane and every time the wind blows the acorns hit like an airsoft shotgun.

[datzenmike]

You only need a small amount of air to foul up the pump action. Air expands or compresses just like air makes brake peddles go to the floor. Air will expand like a balloon and take up a lot of space in a fuel line.

[Dat Lurka]

Yeah I'm pretty sure it's a leak behind the pump. Thought about it sober.

Air is easier to pull than fuel. When I get up to speed is sucks more air than fuel and I get cavitation in the pump. I get out and prime the line and it runs till I go fast again.

Gotta get some line from the shop. Maybe tonight.

 

Another Problem: If I have my distributor at 0 I get fire through the carb. I have to run it a bit advanced? ( turned clockwise) to keep it running. When it is cold it still fires through the carb accelerating from idle. Once it warms up it doesn't do it any more.

The distributor seems sloppy. It has new points, cap, rotor, wires. If you grab the distributor you can kinda move it around.

[datzenmike]

Another Problem: If I have my distributor at 0 I get fire through the carb. I have to run it a bit advanced? ( turned clockwise) to keep it running. When it is cold it still fires through the carb accelerating from idle. Once it warms up it doesn't do it any more.

The distributor seems sloppy. It has new points, cap, rotor, wires. If you grab the distributor you can kinda move it around.

 

Distributor at 0?? Timing should be 12 degrees before top dead center.

 

Firing up through the carb when cold is likely that you don't have the choke on or not set rich enough. In the cold the gas doesn't vaporize fully so it doesn't burn properly and acts like it's lean. What you have is a lean backfire.

 

If it does it when warm when you stab the gas from an idle, your accelerator pump may not be working properly. Engine off, look down the carb and pump the throttle. You should see a strong squirt of fuel into the primary barrel.

[Dat Lurka]

By 0 I mean the dash on the plate.

Accelerator pump quit working correctly, it drips instead of sprays. It's new, worked fine after rebuild.

Choke is sloppy.

Secondary does not open.

 

I think most of my problems are associated with carb.

[ggzilla]

Where the distributor bolts down (the plate) the marks are for fine-tuning. Usually it is set to 0.

 

Timing should be set at the crank pully marks (12 before zero). Then later if you want to fine tune it "by ear", you can use the plate to advance 1 or 2 degrees without having to recheck the timing again.

 

Agree with Mike. Even if incorrectly set to 0 timing, it shouldn't backfire (just will be a little down in power).

[datzenmike]

....Accelerator pump quit working correctly, it drips instead of sprays. It's new, worked fine after rebuild.

Choke is sloppy.

Secondary does not open.

 

I think most of my problems are associated with carb.

 

 

After rebuild????? :lol: :lol: :lol:

[Dat Lurka]

Haha it was all working great when I rebuilt it!

It sat while I was doing timing and headgasket. And nothing works correctly now.

[Dat Lurka]

I don't want to fool with it. Ready for a clean and simple weber.

[banzai510(hainz)]

"It sat while I was doing timing and headgasket. And nothing works correctly now. "?????????

 

maybe the oil spindal is in wrong?????

 

you even use a timming light? This will catch it most likely

 

ck the dizy shaft for wiggle. to much wiggle then the points might opn prematurely.

 

 

I dont get what your saying you say it works after rebuild then say the accle pump dont work? Then it wasnt rebuilt correctly or you did it wrong.

 

if you put a BIG ass wrong ohm coil in there it could back fire as your burning up the points. Esp if you took the ballast resisitor out.

 

take seom photos of all this stuff

[Dat Lurka]

Regular coil and resistor.

I haven't timed it with a light yet. I can borrow one once I can return some other stuff lol.

The dizzy wiggles on its mount for sure. I got the drive spindle correct \ at TDC.

I'll find some AAs and take some pics.

 

 

The truck was running when I rebuilt the carb and it ran much better afterwards but never checked the secondary.

The accelerator had a nice solid spray before sitting and now it just drips.

[banzai510(hainz)]

ON stock carbs I think the accelpump throw can be adjusted if is hasnt broke. But a broke diaphrame I assume it might leak gas

[ggzilla]

If the fuel bowl is empty, fix that. Don't mess with the accelerator pump. Hitachi pumps are non-adjustable.

[Dat Lurka]

Ok can it be adjusted? Way to confuse me guys...

 

I have the old working accelerator pump if I need to replace it.

[I'm BLUE]

Weber bro :console:

[Dat Lurka]

No shit :rofl:

Wanna send me one? I'll pay you in time :thumbup: