Datsun Roadster Forum-311s.org

My stroker 1600 has been running well in Central Texas with the temperatures as high as 108. Altitude is about 500’. I’m now on the 3rd day of my long drive to Seattle and a nearing Las Vegas NM, elevation 6400’, temperature about 88 . I had to have the car towed to a shop today. They will look @ it tomorrow but mentioned that they’ve seen a lot of older cars vapor lock.

Fuel tank, fuel lines, hoses & non-OEM fuel pump from Dean are new. Glass fuel filter & carbs gone through. Filter checked for leaks & even bypassed to check. I bypassed the fuel pump with an electric pump, no difference.

When the engine is cool, it starts & runs fine, 100 miles plus. If I then stop for fuel it will run up to a mile or so, then it dies. Carbs & filter are empty. If I blow into the tank I can force fuel into the filter & the car may run another 300’ or til I turn it off hours down the road.

I disconnected the fuel line from the carbs while the electric pump was connected & just got spits of fuel. With the engine off & the electric pump running for several minutes, hardly any fuel made it into the carbs. I tried running with the gas cap off- no difference.

The shop guys said that they sometimes replace the steel fuel line with rubber hose to fix it. They will be looking at it tomorrow morning.

The tow truck driver said that he’s heard of using premium fuel and/or adding some stuff that raises fuel boiling point.

Any suggestions or insights?

If they can’t get it running tomorrow they won’t be able to get to it until Tuesday.

Peace, Pat

If you put a HF vacuum pump on it a few quick pumps it should pull gas to fill the cup my 70 the S bend is small to start with ( just out of the tank ,3/16 line ) calciumed up and wouldn't pull gas removed and it pulled fine ( note that S bend likely is to stop fuel flow siphoning in a wreck with frt. end lower ,like in a ditch )
Be careful getting to far away from stock on a temp line
the gas bowls could be boiling the gas might leave the hood cracked to test

I have had severe vapour lock issues in my SP310 in our Oz climate.
I have solved it by insulating the fuel line from fuel pump to carb. float bowls.
The pump to head line is rigid and I wrapped it with self adhesive insulation.
From there the rubber lines are covered in tubular insulation since they sit right above the exhaust manifold.
So far so good

Descriptions sound more like fuel starvation than vapor locking, but I’m not there to observe..

Thanks for the replies. I should have added that I have fiberglass-lined black tubing on the lines from the fuel pump to the carbs as well as fiberglass wrap on the header. I also put aluminum muffler insulation on the back of the carb heat shield.

I’m not comfortable continuing this trip, as I have higher & equally warm parts of the trip ahead. I’ll head home & take care of dropping the main fuel line temperature.

It’s funny, I’ve driven this car much higher & @ higher temperatures without any problems, just not @ the same time. The higher was about 20 years ago so I suspect gas has been reformulated since then.

Peace, Pat

I concur that it’s fuel starvation and not vapor lock!

Habitat.pat wrote: Thu Aug 31, 2023 8:43 pm
Any suggestions or insights?

Vented gas cap plugged-up?

Nope, not plugged gas cap, it does the same thing with the cap off.

If I blow into the gas filler I get a full stream of fuel out @ the fuel filter.

Right now I removed the filter & installed the electric pump directly between the fuel line @ the carbs. It hardly has any flow. I’m beginning to think I have both defective mechanical & electric pump. If the shop can’t get to it today I’ll hit it again & swap out the electric pump.

A stupid question, I'm sure,....but did you check that you have your "inlet" and "outlet" lines on either of your pumps, going in the right direction ?

Yes. The mechanical pump has arrows stamped & it worked for several thousand miles. The electric pump has “out” stamped on one end.

Thanks for the suggestion, I suspect it’s something that I’m overlooking. I’m hoping the shop will have time today to check it out, otherwise it will be Tuesday before they can look. They already looked @ it this morning & found a marginal connection in the ignition & pronounced it cured. 3 miles down the road it started sputtering & I limped back to them.

Habitat.pat wrote: Fri Sep 01, 2023 11:43 am Nope, not plugged gas cap, it does the same thing with the cap off.

If I blow into the gas filler I get a full stream of fuel out @ the fuel filter.

Right now I removed the filter & installed the electric pump directly between the fuel line @ the carbs. It hardly has any flow. I’m beginning to think I have both defective mechanical & electric pump. If the shop can’t get to it today I’ll hit it again & swap out the electric pump.

Huh I suppose it’s possible you have two duds. Are you going to test the electric for flow issues first?

If that’s not the problem, I would drain the tank to make the sure the pick up is not partially plugged. You can just use compressed air (fuel line —> tank), see what comes out and go from there.

Thanks. I will let the shop look @ it today, they just pulled it in.

As for a plugged line/tank, they are both new but there always could be something that got in.

Pat call Tom Hoagland 719 649 7719, he's in Colorado Springs about 300 miles north of you, way better than turning back. I don't have your number. He's happy to have you bring the car to his home/shop if you can make it. He's happy to trouble shoot where you are now. He'll have the answer.

Correction he's 250 miles north of Las Vegas, NM

Thanks for the contact. The shop said that in this area gas starts to boil at about 100°. Engine compartment is hotter than that. It turns out the electric pump is bad, so I bought a new one & installed it. I haven’t put bot a few miles on it but as long as I’m not stopped, it’s fine but it sputters after sitting @ a light. The pump is in the engine compartment now but I may move it to the tank so it’s not sucking fuel. That way any vapors will be pushed out through the carbs. While I’m at it I will replace the steel line to the front with hose per Tom Walter’s recommendation.

I just found a tree with a good size kerb around it so I can get under to work. I’ll check the lines for blockage while I’m there.

Luckily it’s only 86°.

I’ll post after my trial.