Does this sound like Vapour lock to you?

[nickolai]

Hi guys, long time listener, newish poster.


My 1978 2F (non emissions, NZ new) has been running like a top recently, but over the weekend I had some dramas. I'm pretty handy (technical profession) and I brought the truck to learn about vechiles and have done lots to it myself - gearbox change, front and rear discs, clutch, RMS, cooling system rebuild, suspension lift etc.

sooo...I fired up the truck - started easily as per usual, and drove for maybe 30mins, mainly street driving, around 50km/hr to a shop. Autometer temp gauge showed steady at 190F. I popped into the shop for maybe 10-15mins, came back, jumped in and she fired up fine. Drove maybe 200m down the road and she died. I coasted to the side of the road, and she fired up on the 2nd try.

I let the truck idle for a couple of minutes, then went on my way, and drove on the motorway (freeway) for maybe 20 minutes @ c.80km/hr. Went to another shop for 15mins, fired up again no drama. Then went to another shop, via the motorway. As I arrived, she died again. Coasted to the side of the road.

Popped the bonnet (hood;p) and nothing was obivously wrong, had spark, battery voltage fine, 190F on autometer temp.

Now things get interesting. Fuel in both filters - but the carb sight glass shows nothing. Zero. Zilch. Nada. Turned her over- no change. Still have spark. Waited maybe 20-30minutes, trying to start it during this period. Just as i was about to give up, she fired up...

I was maybe 1km form my house, so I made a break for it and got maybe 300m. Same scenario. Waited a bit - fired up, and made it home.

I ran the truck in the driveway the next day - no dramas.

Here's my diagnosis based on some searching -
-Somehow fuel is vapourising between my most downstream fuel filter and my carb?
-Allowing it to cool sorts this out temporariliy, but the times I limped home may have just been what was in the bowl before it locked again?
-Possible cause is fule line a bit close to heater line and lower rad hose, and deterioration of the fuel line?
-Maybe mr carb Float is unhappy?

What say you wise people of 'Mud?

Here's the specs etc:
-Stock 2F
-No emissions gear
-Recenly rebuilt Carb (2000km ago)
-2 fuel filters (1 before, 1 after fuel pump, near where the hardines start)
-Electronic dissy
- I have F.A.S (Fuel, Air, Spark)

Any help appreicated!!!

 

[JohnnyC]

I would pull the fuel line on the carb and see if the fuel pump is pumping 1st

Did you pull the gas cap just after stalls out? Any vacuum sound?

 

[Pin_Head]

The chances of it being real vapor lock are somewhere between slim and none. More likely is rust or junk in your fuel tank blocking the outlet so the pump cannot keep up. Blow in the fuel outlet to displace the junk and see if your problem goes away temporarily. You might also see junk in your fuel filter, but not always if the pieces are too big.

 

[nickolai]

I would pull the fuel line on the carb and see if the fuel pump is pumping 1st

Was thinking this too. I ran the engine at fast idle for maybe 20minutes the other day in the driveway, so pretty sure i'm getting fuel.

Will give it a crack though, process of elimination!

 

[nickolai]

The chances of it being real vapor lock are somewhere between slim and none. More likely is rust or junk in your fuel tank blocking the outlet so the pump cannot keep up. Blow in the fuel outlet to displace the junk and see if your problem goes away temporarily. You might also see junk in your fuel filter, but not always if the pieces are too big.

Cool, will give that a crack too, and check the filters.

Carb was rebuilt using your videos - they're awesome!

 

[PenguinScotty]

I generally run into the usual harder starts when i have driven relatively hard/fast and then stop for about 15 minutes or so. The fuel evaporates in the bowl and takes a few cranks to make it back up there.

The one thing that's nice about mine is that there is another see-through fuel filter installed before the carb, so i can see if the fuel gets to the carb from the fuel pump. Not sure if that is the case for you, but it's a relatively easy modification that can make troubleshooting easier as well.

However, i've never had this happen while actually DRIVING the vehicle. Like i said, it's usually a 15-30 minute window where it happens, while being put away hot.
Like JohnnyC said, check the fuel pump (which you can do easily with that filter installation).

 

[nickolai]

The one thing that's nice about mine is that there is another see-through fuel filter installed before the carb, so i can see if the fuel gets to the carb from the fuel pump. Not sure if that is the case for you, but it's a relatively easy modification that can make troubleshooting easier as well.

Yip, i've got a see through filter after the fuel pump, just before where the hardlines start.

 

[PenguinScotty]

Yip, i've got a see through filter after the fuel pump, just before where the hardlines start.

Perfect!

Well, then all i have left is to tell you about my fuel tank situation. When i picked up my truck, after it had been sitting for about 3 years, it ran fine, but as soon as you drove it longer, it would sputter and stall. Let it sit for a few minutes, and it would start and drive again for a while.

In the end, the fuel tank was so rusty and sludged up, that only very little fuel actually made it to the carb (It filled the filter). It kind of sounds like the problem that you are having. How old is the tank, has it been inspected? Sitting for a while?

 

[JohnnyC]

All I run is see thru filters... Can't stand not being able to see if there is crud in there

 

[coleman2347]

This sounds almost exactly like a problem I had with an old truck I had, would do the same thing, when it would stop I found that I could pull the gas line at the tank and blow on it (toward the tank) and the truck would start up again. Eventually I pulled the bed for some repair and while I had it off pulled the sending unit of the tank to look inside...I found the foil top from a gas additive in the bottom of the tank. It would sometimes block the line and when I blew on it (the line) it would just fall away to wait to drive me crazy again...never did I get anything in the filters to see....

 

[sadam_husain]

its all a process of elimination of the above stuff mate, typically if its a crook fuel pump that's not pumping enough gas or a fuel line restriction or fuel tank pressurising your problem would be occurring under higher load driving when more fuel is required rather than after you've stopped, you need to check the fuel pump, fuel lines and filters for obstruction, pickup inside tank and tanks venting properly, the other thing I'd be going back to check is the float was reinstalled correctly and functioning properly if the carb has had a recent rebuild 2000km ago