1 minute ago, ollie said:

1 to 3 psi cold?  That's low to me, I think you're onto something.  Of all the pumps I messed with, even new ones, it wasn't until I found the right seals for the reed valves did it finally resolve.  Then I had to go back and fix all the bandaid tweaks I did the the SUs before hand, to get it semi stable.  Runs like a champ now. 

Yes, cold.  What pressure is normal?

Do you have a link to a kit with the correct seals?

Thanks.

The seals I found did not come in a kit. The rebuild kit I bought had incorrect seals so after a lot more digging, I found the correct profile thickness as the ones in the kits were too thin.  I'll have a look tonight for you.  

 

3 to 5 psi is correct fuel pressure for mechanical fuel pump in our cars. Add heat and it sounds like your pump is really struggling. 

This guy made his own: https://woodworkerb.com/home/datsun-240z-rebuild/datsun-240z-mechanical-fuel-pump-rebuild/

I'm not that patient or talented so I ordered mine I think from McMaster Carr.  I'll confirm later today. 

If you go straight to a temporary tank it will tell you which half of the system is the problem. That will speed up your diagnosis and reduce wasted effort

On 8/28/2024 at 7:24 PM, Patcon said:

If you go straight to a temporary tank it will tell you which half of the system is the problem. That will speed up your diagnosis and reduce wasted effort

Good suggestion, so I rigged that up:

Results:

Fuel looked much more "solid" through the clear fuel line than before, and fuel pressure much steadier at 3 psi on cold start.

Got it warmed up, and it didn't threaten to die at any point, but it didn't run great either.  Idle was miss-y, unsteady even after I gave the carbs some attention with the Uni-Syn.  Worse, at anything over a light load, the car would backfire & refuse to pull, almost like it was hitting a fuel cut.

Takeaway:  3 psi still seems low, especially with zero restrictions in the system.  So I'm still not sure if I have a marginal fuel pump, or a blockage in the fuel lines/filters, or both.

I'm so tired of this.  Been dealing with this issue off and on for ages now and I would really like to solve it.  It didn't used to run like this.  Here's how it ran with the old fuel pump, resealed fuel tank, and a basic tune:

It's not even close to that now.  Something happened between then and now.  Either something went bad, or I screwed something up, and I've got to figure what it is.

Edited September 2, 2024Sep 2 by BoldUlysses

1 hour ago, BoldUlysses said:

Fuel looked much more "solid" through the clear fuel line than before, and fuel pressure much steadier at 3 psi on cold start.

Got it warmed up, and it didn't threatened to die at any point, but it didn't run great either.  Idle was miss-y, unsteady even after I gave the carbs some attention with the Uni-Syn.  Worse, at anything over a light load, the car would backfire & refuse to pull, almost like it was hitting a fuel cut.

Takeaway:  3 psi still seems low, especially with zero restrictions in the system.  So I'm still not sure if I have a marginal fuel pump, or a blockage in the fuel lines/filters, or both.

Some questions...

At the end of your previous thread, you verified the float bowl levesls with the clear tube wet-set method. 21 and 19mm, right? If so, that should be fine.

Was there fuel in the return line back to the red jug? If so, then the pump is providing more than the carbs will take (at idle at least). But here's the rub... These engines really don't need a lot of fuel to idle. In fact, if you fill your bowl up to spec level and start the car with the fuel line completely disconnected, your car should idle for over 30 seconds before you suck the bowls dry. I'm thinking that you have enough fuel to the carbs at idle, but maybe not while driving.

So... Couple things to look at. First, take it out for a drive and get it to die. When it dies, turn off the key and go out to the engine and pull the tube off the bottom of your float bowl. See how much fuel comes out. If you sucked the bowl down, you won't get much out. If you DID suck the bowl down, then it's a fuel delivery issue.

Have you checked the little screen filters inside the banjo bolts at the carbs? If they're clogged, the return line back to the jug will look full, but the carbs won't be getting fuel.

All good suggestions.

Also check the eccentric on the camshaft that drives the pump. Make sure it's torqued properly.

If the cheap ugly fuel pumps aren't too expensive,  I would swap one in to help pinpoint the problem

Several options on rockauto under $30, one under $20

Edited September 2, 2024Sep 2 by Patcon

48 minutes ago, Captain Obvious said:

Some questions...

At the end of your previous thread, you verified the float bowl levesls with the clear tube wet-set method. 21 and 19mm, right? If so, that should be fine.

Was there fuel in the return line back to the red jug? If so, then the pump is providing more than the carbs will take (at idle at least). But here's the rub... These engines really don't need a lot of fuel to idle. In fact, if you fill your bowl up to spec level and start the car with the fuel line completely disconnected, your car should idle for over 30 seconds before you suck the bowls dry. I'm thinking that you have enough fuel to the carbs at idle, but maybe not while driving.

So... Couple things to look at. First, take it out for a drive and get it to die. When it dies, turn off the key and go out to the engine and pull the tube off the bottom of your float bowl. See how much fuel comes out. If you sucked the bowl down, you won't get much out. If you DID suck the bowl down, then it's a fuel delivery issue.

Have you checked the little screen filters inside the banjo bolts at the carbs? If they're clogged, the return line back to the jug will look full, but the carbs won't be getting fuel.

Yep, fuel was feeding to the return line.  And the auxiliary fuel tank setup seems (?) to have kept it from dying.  It was driving/idling around 15-20 minutes in the neighborhood without sucking the filter dry like before.

Checked & cleaned the last-chance screens here.

7 minutes ago, Patcon said:

All good suggestions.

Also check the eccentric on the camshaft that drives the pump. Make sure it's torqued properly.

If the cheap ugly fuel pumps aren't too expensive,  I would swap one in to help pinpoint the problem

Several options on rockauto under $30, one under $20

I'll check the eccentric tomorrow, thanks.

Work today:  Pulled off the cam cover and checked the eccentric; bolt is tight.

So for the backfiring under load, I suspect my timing, so I'm trying to baseline it.

Found TDC by pulling the #1 spark plug and inserting a small screwdriver to feel when the piston was at the top.

Cam lobes in correct position:

Distributor tang at 11:25, small side to the left:

Here's the crank pulley, though:

What's going on here?  I've heard of the rubber separating, but I can't move the two parts independently by hand.

Does someone have a spare harmonic damper lying around and can check if this is normal?

Thanks as always.  You guys are the best.

Not clear what happened or what you're asking about.  Where is the bolt and washer that holds the damper?  Did you just grab the damper and slide it off by hand?  Where is the woodruff key?

 

I believe it is possible to get different year pointers and dampers mixed up. I would make a mark on the damper at TDC and add the other 4 five degree marks by approximation. Or you could use a dial back timing light with the TDC mark to get timing close.

The dampers can shift even if you can't move it by hand

9 minutes ago, Zed Head said:

Not clear what happened or what you're asking about.  Where is the bolt and washer that holds the damper?  Did you just grab the damper and slide it off by hand?  Where is the woodruff key?

 

I removed the damper to try to determine if the parts have shifted relative to each other.  I removed it first (using an air wrench & puller set), then set the engine to TDC using the screwdriver-thru-the-#1-spark-plug-hole method, checked the distributor tang was at 11:25, then slid the damper back on (loosely) to see if the timing marks lined up.  They don't.

 

9 minutes ago, Patcon said:

I believe it is possible to get different year pointers and dampers mixed up. I would make a mark on the damper at TDC and add the other 4 five degree marks by approximation. Or you could use a dial back timing light with the TDC mark to get timing close.

The dampers can shift even if you can't move it by hand

I'm definitely going to index the inner and outer parts of the damper so I can track the shift...

Is there a way to be absolutely sure the engine is exactly at TDC without pulling the head and looking at the top of the piston relative to the deck?

Edited September 2, 2024Sep 2 by BoldUlysses