1968 Datsun roadster dies after 15 minutes of run time...running out of ideas to troubleshoot...

Hi all - my brother has a 1968 Datsun 2000 roadster that is driving him bat-E36 M3 crazy.  Last year, he de-smogged the car (removed air injection pump and plugged all holes) and installed an electronic ignition distributor.  It starts and runs well, but stalls out after 15ish minutes and can't be restarted for 45+ minutes.  This isn't random; it's repeatable every time he fires up the car...and now that the nice weather is finally showing up, he's anxious to get it sorted.  Here's a troubleshooting list he sent of everything that's been tried to date.  The only thing I didn't see on here is to check for spark after it dies...he's going to do that next.  Any other thoughts or things we could be missing?  The Datsun forums have mentioned vapor lock as to the cause of fuel pressure declining, but it didn't do this for the two years prior to the EI install/smog removal.  I feel like it it is some kind of vacuum/venting related issue, potentially related to the desmog, but this is a pretty straightforward and well-documented process...it's not like he's forging a new path here.

Symptoms:

• Car starts and runs for approximately 15 minutes, then stalls
• Starts again after 45-60 minutes, but stall again after 15 minutes
• Issue is repeatable
• Symptoms began last July after converting to EI ignition (new cap, wires, coil and rebuilt EI distributor) and removing emissions system

Troubleshooting (no help):

• Replaced fuel filter
• Installed/gapped new spark plugs
• Confirmed engine timing
• Checked gas lines for blockage; blew low psi air through feed line and return line (heard bubbling in tank)
• Bypassed gas tank; ran car off gas can first w/mechanical pump, then with external electric pump
• Hooked up in-line fuel psi gauge; starts at 3-3.5 psi (~4 w/electric pump) then falls <1.5 before stalling out
• Replaced oil and filter (smelled gas in oil - possibly from electric pump running when engine stalls?)
• Tested alternator:  13.60-13.70v @ start; 13v warmed up (5 minutes @ 1k rpm and no load); 12.5-12.6 w/full load; jumped back to 13v w/ no load (this was using old battery)
• Removed gas cap to see if it was a venting issue
• Replaced all rubber fuel lines under hood
• Installed new battery (old battery was tested and bad)
• Full carb rebuild by Datsun specialist - new gaskets, floats, float valves, needles, jets, gas inlet hoses, return springs, carb bodies rebushed and shafts repaired 
• Noticed fuel filter has very little gas in it and fuel barely trickles in
• Checked float bowls for fuel (after stalling); approximately half full

Any thoughts/advice/crazy ideas would be greatly appreciated.

Thanks!

Jason

Symptoms began after converting ignition...

I know where I'd start

Is the distributor overheating? Do you still have the old distributor or points parts to reinstall? Since the problems started after the conversion this is where I would start. Go back to square one and see if the problems persist. 

How about the fuel pump or possibly trash in the tank? Will it fire back up if you splash fuel down the carb after it dies? You might also siphon some fuel out of the tank to see if there is debris stopping up the sock.

In reply to Peabody :

Thanks Peabody.  Agreed, odds are good it's something to do with the last work done.  The decreasing fuel pressure (with mechanical or 12V pump) was throwing me when thinking it was the EI.  Apparently it doesn't sound like it's misfiring or running poorly up to the 15 min mark, it just....stops.

In reply to Toyman! :

Unfortunately, the original distributor had to be used as a core for the EI conversion.  He's trying to hunt down a known good original spare, but apparently they aren't super easy to find. 

For fueling, he's tried:

• Stock mechanical pump running off the stock tank
• Stock mechanical pump running off an external 5-gallon gas can
• 12V external pump running off the stock tank
• 12V external pump running off an external 5-gallon gas can

The thought was if there was trash in the tank or the pump was failing, we'd remove those variables....unfortunately, no change.  I don't think he's tried squirting fuel into the carbs, although he did mention the float bowls were about half-full after it stalled yesterday.  Aside from blowing low psi air through the feed and return lines to the stock tank to make sure they were clear, I don't think he's tried siphoning gas to see if it's full of crud.  Definitely worth checking, as I'd assume 50+ years of sediment could be an issue.

Put a noid light on the plugs; I'd try it with the car running cold first so you can see how it fires (i.e., how bright the light is when it's running).  

Old style points ignitions often use a resistor wire or ballast resistor on the power wire to the coil. If you reused this wire on the new ignition, it could be the source of the problem. Try running a clean wire from your battery right to the new ignition and run the engine.

I have a 1970, 1600 that had an issue with the distributor after the conversion to electronic ignition.  I pulled and returned it to the vendor, he diagnosed and fixed the issue over night.  Great customer service. Did you purchase the coil and plug wires from him?

Rotaryracer said:
 

• Hooked up in-line fuel psi gauge; starts at 3-3.5 psi (~4 w/electric pump) then falls <1.5 before stalling out

This is worth looking into, could something in the carb be dumping fuel into the engine causing it to stall when it warms up perhaps? And this happens both with mechanical and electric pumps?

Did he plug the fuel tank vent line when he removed the charcoal cannister?

Sort of sounds like a vapor lock.  Any fuel lines getting over-heated?

Did the original emissions system have external vents for the fuel tank, or did it use a return line to the tank to equalize pressure?

Since the problem started after disconnecting/removing the emissions system and converting to an electronic ignition at the same time, it's easy to be misled by symptoms that could be caused by either.

If there is little to no gas in the fuel filter, and gas barely trickles in, then you've got a fuel delivery problem. Either there's a vacuum building up in the tank as the fuel level drops (because there's no external vent, or the vent is clogged), or the fuel outlet fitting/hose/line is getting clogged by debris in the tank gradually accumulating in one point and blocking fuel flow. Check and/or replace the entire fuel line from the tank to the carbs, just because you blow low pressure air through it doesn't mean it will allow enough fuel to flow.

You tried to eliminate the gas tank and pump by running out of a 5 gallon fuel jug, but did you still use the original fuel LINE?      

I had a 65 Mustang that was doing the same thing. It turns out that I had a pinhole in one of the metal fuel lines. Almost too small to leak, but big enough to suck air and disrupt fuel flow under load. The fuel pump could fill the bowl at idle, but then the bowl would empty when I was driving and the car would die. New fuel lines fixed it. 

98% of fuel issues are spark issues. 

loosecannon said:

Old style points ignitions often use a resistor wire or ballast resistor on the power wire to the coil. If you reused this wire on the new ignition, it could be the source of the problem. Try running a clean wire from your battery right to the new ignition and run the engine.

This would be my pick. Also note there are different coils for EI and points.

I'm liking the ballast resistor and missing tank vent ideas.

As a bonus to the different coils thing, I'd always thought coils worked or didn't til I had one that got weaker and weaker as it heated up.

Jesse Ransom said:

I'm liking the ballast resistor and missing tank vent ideas.

As a bonus to the different coils thing, I'd always thought coils worked or didn't til I had one that got weaker and weaker as it heated up.

I had a Honda SL125 that did exactly this; ran for 10 minutes then died. I've also seen the exact same thing on a Datsun 520 PU.

Purple Frog (Forum Supporter) said:

Sort of sounds like a vapor lock.  Any fuel lines getting over-heated?

^The loss of fuel pressure leading up to the stall is consistent with what's seen with vapor lock.

Previously posted that trying this with the gas cap off made no change.  So I don't think it's the tank going into a vacuum state as fuel is pumped out.  Convert the original distributor back to points or find a good points distributor and make the system exactly like the factory had it.  It sounds like a component is getting hot, like an IC or sensor, and it requires cool down time to work again.  

1.5 pounds fuel pressure is plenty for those carbs, and 1/2 way up is what you see when you open them. Running float level is slightly higher. This is an ignition issue. Either coil or amplifier module is overheating. 

I will throw in a almost clogged fuel filter that restricts flow and after  after running a while cuts it off more , 

it happened to my van coming back from Texas on time.....

outasite said:

Did he plug the fuel tank vent line when he removed the charcoal cannister?

 

100% my guess. My Alfa was this.

With that EI distributor he can't use the stock coil. He needs a MSD blaster 2 or equivalent. Coil is heating/cooling. Rinse repeat. 

Purple Frog (Forum Supporter) said:

Sort of sounds like a vapor lock.  Any fuel lines getting over-heated?

On hot days I had vapor lock on my '66 Datsun 1600.

OP said: "Noticed fuel filter had very little gas in it, and fuel barely trickles in."

That's a Big Red Flag, guys.

Fuel delivery problem, right there. Yes, it's possible there's an issue with the ignition system as well, but it ain't gonna run without fuel.

Remove tank, clean out. Replace ALL fuel lines, and filters. Once you KNOW it has plenty of fuel volume, and pressure, at the engine, ALL THE TIME,  then chase down possible ignition issues....but you probably won't need to.