1977 FJ40 will not start when warm (1 Viewer)

[Aussie Alaskan]

Greetings all,

My FJ40 has been a project for the past few months and after getting the engine rebuilt and installed, and the rig on the road again I'm having an issue with it starting once it's warmed up.

Here are the components:

Brand new battery showing 12.7V and 14V+ with alternator charging.
Brand new coil that meets all manufacturers specs for resistance.
Brand new distributor. Electronic pickup type.
Brand new spark plug wires. (HT wire measures 5k ohms)
Brand New NGK plugs all spaced at 32-33 thousands.
Brand New GR starter.
Brand New Taiwan knockoff Aisan carburetor.
Timing is right on the BB.
Freshly adjusted valves. (To spec)
Vacuum is 19 psi at idle from brake booster hose.
No ignitor with the coil.
Brand New OEM fuel pump.
Brand New fuel filter.

Here is the problem:

6 pumps of the pedal, full choke and it fires right up and runs like a champ.
If I shut it off soon, I can start it back up relatively easily.
After being driven for 20 or 30 minutes and shutting down, it is impossible to get it to start again. I've tried the hot start routine with no luck.

Here are the symptoms:

Immediately upon shutdown the fuel bowl window shows half full.
After about 45 minutes, the fuel bowl window is empty, but you can still look down and see fuel flushing around inside, it just doesn't show in the window technically.
After about 45 minutes, the clear plastic fuel filter is also 25% filled with air. Normally it is 100% full fuel during operation. There is no heavy smell of fuel on shutdown like it's flooded.
If I leave the truck alone for about 45 minutes I can start it again. But not before then.
Right after shutdown the starter seems to have ample power to turn the engine, I will get a very occasional rump rump, but it will not fire.
I'll post a few pics of my setup and welcome any and all help.

 

[Aussie Alaskan]

The wiring diagram photo shows how my FJ40 ignition system is currently wired with aftermarket coil, starter and distributor and no ignitor.

Everything works great on a cool engine but it won't start when hot.

I've tested for spark on both a cold and hot engine and I get spark both ways by having someone crank while I hold a spark plug on the ground terminal of the battery. I get an orange spark.

I've gone thru and cleaned up the grounds from the battery to the frame, and from the frame to the block. Both should be well grounded.

 

[bkfj40]

Is the carb cooler fan hooked up?

 

[Aussie Alaskan]

Is the carb cooler fan hooked up?

No carb cooler fan for 1977. So no.
That being said I'm in a fairly cool part of the world (Alaska) and after 20 or 30 minute drive my carburetor is not very hot. Can easily put my hands all over it. No bubbling in the window either.

 

[swixtt]

Do you still have your old carb around?

 

[Aussie Alaskan]

Do you still have your old carb around?

No. I got the vehicle with an engine in need of a rebuild and nothing else.

Here is the build thread for those who are interested.

Builds - New Alaskan FJ40 intro thread

Got my guage cluster all put back together and took it for a 40 mile drive. My oil guage is still low and I'll need to try to adjust the range of the indicator arm, and my speedometer still doesn't work, but I figured out why and have ordered a larger driven gear for it. The 6x17 I previously...

forum.ih8mud.com

I do not have an original carb to test, but like I said it starts and runs just fine when cold.

 

[jbarnhill]

Just to rule out vapor lock have you tried pouring water on the fuel pump to cool down the fuel system and see if it would crank back up. I had a 77 and 78 that had a vapor lock issue but I do live in North Carolina.

 

[Aussie Alaskan]

Just to rule out vapor lock have you tried pouring water on the fuel pump to cool down the fuel system and see if it would crank back up. I had a 77 and 78 that had a vapor lock issue but I do live in North Carolina.

I have not done that. My fuel lines are rubber and are padded/insulated where they run above the manifolds and they typically stay coolish to the touch. Not ruling out vapor lock, but my fuel system doesn't seem to be too hot.

Update to symptoms:

Was able to get it started hot tonight after cranking for ages and pumping the gas pedal several times. 7-8 times. It was stubborn, but it finally fired off.
Seems to indicate a lack of fuel to me.

 

[cbmontgo]

Sounds a lot like vapor lock to me.

 

[Aussie Alaskan]

Sounds a lot like vapor lock to me.

I was originally leaning towards an electrical problem, but after last night's test and after installing a new coil, I'm thinking you guys are right and that it's a fuel related issue and vapor lock seems to a common issue. My rig has the OEM mech fuel pump with a fuel line return. Any suggestions on how to prevent or test for vapor lock?

Elec fuel pump?
More fuel line shielding?

 

[cbmontgo]

I was originally leaning towards an electrical problem, but after last night's test and after installing a new coil, I'm thinking you guys are right and that it's a fuel related issue and vapor lock seems to a common issue. My rig has the OEM mech fuel pump with a fuel line return. Any suggestions on how to prevent or test for vapor lock?

Elec fuel pump?
More fuel line shielding?

An electric "pusher" fuel pump towards the gas tank is one fix.

Non-ethanol gasoline also helps.

 

[jmylie]

My vote is for vapor lock. Loosen the fuel line and listen, you should be able to hear air being sucked in.

Could also be a blocked vent line, open the gas cap, same as above, is air sucked in?

 

[Aussie Alaskan]

My vote is for vapor lock. Loosen the fuel line and listen, you should be able to hear air being sucked in.

Could also be a blocked vent line, open the gas cap, same as above, is air sucked in?

As soon as possible I'll do some tests on the fuel system. I do recall sitting in the driver's seat after a short drive and hearing a very small suction sound from the gas tank supply/return line area. This was after shutting it off. So it may very well be that I've got negative pressure in my fuel system from a blocked vent line.

 

[Pighead]

Is there a fuel return line ?

 

[Aussie Alaskan]

Is there a fuel return line?

There is a return line at the mechanical fuel pump.

 

[45Dougal]

Do you have the correct carburetor insulator installed?

 

[Aussie Alaskan]

Update:

Readjusted the float in the carb, and went for a 30 minute drive last night and shut it off in the driveway and the fuel level was right in the middle of the window. Over the next half hour the fuel level dropped down to where it was no longer visible and I saw vapor rising from the carb while the fuel in the window seemed to boil slowly.

I opened the throttle plate and shined a flashlight down to where I could see the bottom of the intake manifold. The intake manifold showed no sign of flooding and was dry.

While manipulating the throttle linkage the power piston? Struggled to squirt fuel. Almost like there was air instead of fuel.

I squirted a bit of fuel down into the manifold and cranked it. No start.

My next step is to check compression while hot.

 

[Aussie Alaskan]

Do you have the correct carburetor insulator installed?

Yes I do. It's older and 2nd hand, but it's installed.

 

[45Dougal]

Yes I do. It's older and 2nd hand, but it's installed.

Tried running it with the fuel cap off?

 

[Pighead]

Over the next half hour the fuel level dropped down to where it was no longer visible and I saw vapor rising from the carb while the fuel in the window seemed to boil slowly.

So, the fuel in the floatbowl disappears after a hot shut down? That is unacceptable. What if, just for fun, you re-filled your floatbowl before a hot restart?
I vaguely recall a thread mentioning a siphon type carb phenomenon, but paid little attention as i didn't have that problem