One-Family 1972 240Z Restoration (HLS30-93069)

[BoldUlysses]

Gradually.  It feels like the float bowls are just running dry, like it runs on 1 carb, then 0 carbs.  It always seems to happen on an incline as well.

Weird thing is that it didn't do it at all over the weekend, and I drove around the neighborhood a good bit.  And several days prior to that, I managed to drive it a couple miles to CVS and back, and then did a short loop around a couple of back roads.  I thought I had the problem sorted with my fuel system overhaul...  Guess not.

[SteveJ]

 It doesn't hurt to check your fuel pressure.  Also, are you sure your float levels are set properly?

[Mark Maras]

The clue that it happens on an incline confirms fuel starvation. Along with a fuel pressure test a fuel volume test could isolate the problem to the carbs. Have you checked the last chance fuel filter screens in the banjo bolts on top of the float covers? Post #13 you mention the front carb piston being a little sticky and a minor problem with the rear carb choke. Are those working OK now?

[Captain Obvious]

3 hours ago, BoldUlysses said:

It feels like the float bowls are just running dry, like it runs on 1 carb, then 0 carbs. 

I'm thinking that if you had more carbs, your engine might run longer? I mean, if you started out with ten or something.....

 

[BoldUlysses]

2 hours ago, SteveJ said:

 It doesn't hurt to check your fuel pressure.  Also, are you sure your float levels are set properly?

I bought an inline fuel pressure gauge, but I haven't used it yet.  Will get it hooked up.  The carbs were rebuilt by ZTherapy about 10 years ago and the car's probably only been driven 20 miles total since then, so I don't have any reason to believe the floats have moved.  I'll check though.

2 hours ago, Mark Maras said:

The clue that it happens on an incline confirms fuel starvation. Along with a fuel pressure test a fuel volume test could isolate the problem to the carbs. Have you checked the last chance fuel filter screens in the banjo bolts on top of the float covers? Post #13 you mention the front carb piston being a little sticky and a minor problem with the rear carb choke. Are those working OK now?

Yes, the carb pistons both move freely, and the carb chokes are both working fine.

I'll check the fuel filter screens in the banjo bolts.

Another potential clue is that the problem seems to worsen the less fuel I have in the tank.  The gauge shows about 1/3 full at the moment.  Got that sinking feeling like I may need to drop the tank and have it reconditioned after all.

1 minute ago, Captain Obvious said:

I'm thinking that if you had more carbs, your engine might run longer? I mean, if you started out with ten or something.....

Maybe it just needs more protein instead...?  😉

[Captain Obvious]

A local buddy of mine had a similar situation and his theory is crud in the gas tank. The crud gets sucked all to one spot as the car runs and eventually plugs the tube feeding the fuel pump. Shut the car off, vacuum stops, and crud settles back out. Car starts and runs again for a while.

Another (simpler) suggestion is the valve on the gas cap isn't working correctly and you're drawing a vacuum on the tank. Maybe pop the cap next time the problem happens and see if there is a big woosh of air into the tank?

That feeling of not being able to trust the car really sucks. All you want to do is enjoy it, and you can't stop worrying. Hope you get to the bottom of it!

[BoldUlysses]

Had to take a step back for a couple of weeks 1) to get some other projects done and 2) for my own sanity and motivation.  Dug back into it today.

It's been raining all day here, so I didn't get a chance to test drive it.  Can you guys check my work?

Found some gunk in the last-chance filters.  Front:

And rear:

Got it all cleaned out.

Grose jets have 1 washer on the bottom:

And I set the float heights to 9/16" (.5625).  Front:

and rear:

Fresh float bowl gaskets also.

Hooked up a fuel pressure gauge thusly:

Reset the mixture screws to 2.5 turns down.  Assuming everything looks good, hopefully I'll get some insight when I'm able to drive the thing again.

[SteveJ]

13 minutes ago, BoldUlysses said:

Had to take a step back for a couple of weeks 1) to get some other projects done and 2) for my own sanity and motivation.  Dug back into it today.

It's been raining all day here, so I didn't get a chance to test drive it.  Can you guys check my work?

Found some gunk in the last-chance filters.  Front:

And rear:

Got it all cleaned out.

Grose jets have 1 washer on the bottom:

And I set the float heights to 9/16" (.5625).  Front:

and rear:

Fresh float bowl gaskets also.

Hooked up a fuel pressure gauge thusly:

Reset the mixture screws to 2.5 turns down.  Assuming everything looks good, hopefully I'll get some insight when I'm able to drive the thing again.

For future reference, you can put the fuel pressure gauge on the line between the fuel rail and the carburetor. I found it easier than trying to connect it to the fuel pump.

[Captain Obvious]

40 minutes ago, BoldUlysses said:

Can you guys check my work?

Well I'm not claiming to be qualified to check anyone's work, but I have a couple comments...

First, the metal portions of those floats looks like they have bent away from the floaty portion of the float. And one of them worse than the other. From what I've seen, the metal hinge part of the float should be pretty much parallel to the top of the float foam portion. Yours look like they have been pulled away from the foam.

Second, you are working on a pair of three screw round tops and they were designed to operate with different float levels in front and rear. So if you mechanically set both floats the same distance from the underside of the lid, I'm not positive that's going to translate to the same level once they are wet in the car. The other changes may come out in the wash, might not.

And last, don't forget that the mechanical set you did there is just to get them in the ballpark. A wet set with a clear tube is the way to confirm that the levels are correct. Any mechanical means is just a preliminary ballpark setting that must be confirmed wet.

[BoldUlysses]

1 hour ago, SteveJ said:

For future reference, you can put the fuel pressure gauge on the line between the fuel rail and the carburetor. I found it easier than trying to connect it to the fuel pump.

Ah good tip.  I'll change it; it would be a cleaner install and allow me to monitor the gauge while I'm on that side of the car.

1 hour ago, Captain Obvious said:

Well I'm not claiming to be qualified to check anyone's work, but I have a couple comments...

First, the metal portions of those floats looks like they have bent away from the floaty portion of the float. And one of them worse than the other. From what I've seen, the metal hinge part of the float should be pretty much parallel to the top of the float foam portion. Yours look like they have been pulled away from the foam.

Second, you are working on a pair of three screw round tops and they were designed to operate with different float levels in front and rear. So if you mechanically set both floats the same distance from the underside of the lid, I'm not positive that's going to translate to the same level once they are wet in the car. The other changes may come out in the wash, might not.

And last, don't forget that the mechanical set you did there is just to get them in the ballpark. A wet set with a clear tube is the way to confirm that the levels are correct. Any mechanical means is just a preliminary ballpark setting that must be confirmed wet.

Thanks for the tips.  I'm working with what ZTherapy provided when they rebuilt the carbs (for the 2nd time) 10-odd years ago.  It looks like the pivot point for the floats is located differently b/t the front and the back carbs.  I guess the danger is the float hits the back of the bowl and can't pivot enough to open up the jet...  We'll see tomorrow.

And thanks for the insight about doing a wet set.  Depressing to realize there's more involved in getting this thing set up correctly given my motivation is where it is, but I'll just have to knuckle through it.

[Captain Obvious]

Yes, the pivot points are different between the two lids. And the mounting surface depth for the float valves into the lids is different too. I took a bunch of measurements of the lids a while ago an think I posted some details.

And about the bent float hinges, I'm wondering of the severe bending of your hinges was done by ZT in order to get them to work right. They shouldn't be like that, but that might be the only way they could get it to work? Ideally, here's what you want your float to look like when the level is correct:

And absolutely check the float levels wet. If the levels are OK, then you're done. if not, use the wet set method to get them right. You can't just measure them dry and assume that's good to go.