Hey, I have a '73 240Z which was switched to round top carbs, and getting close to wrapping up the tank rebuild and starting to look at the engine. I've only managed to drive the car a handful of times since I acquired it due to ongoing work on it, but In the past I would need to crank for like 30-60 seconds before it would start, and until it warmed up if I didn't give it a little gas to keep the revs up a bit it would just cut out. Once the car was warmed up though it ran fine so I'm slowly starting to give the engine a once over.

I noticed that on both sides of the intakes there are open inlets which look like they should have a hose attached.

It seems like they might have been connected to the coolant system. There is a hole near the thermostat that's plugged near the inlet towards the front of the engine

The one towards the front of the engine appears to be just open, and the one in the back seems like there might be some kind of spring mechanism closing a plate or something.

I was curious if anyone could provide a bit more info on these? Should these be capped off?

I did double check the crankcase vent hose in the middle and that is in decent condition.

Those run through the manifolds to warm up a cold set of carbs. They circulate coolant through the bypass lines on the passenger's side and then the thermostat housing. I think they are a potential leak waiting to happen so I have mine disconnected. It's plenty warm in Alabama so they add unnecessary heat through my manifolds. The bigger one near the windshield is actually a thermostat that closes the flow off when it gets to a certain temp and you're right about the front nipple, it goes to the thermostat housing.

Here's a bunch of threads about it.

https://www.google.com/search?q=240z+intake+manifold+coolant+line+classiczcars.com&rlz=1C1VDKB_enUS1121US1121&oq=240z+intake+manifold+coolant+line+classiczcars.com&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIHCAEQIRigATIHCAIQIRigATIHCAMQIRigAdIBCTMwNTQ5ajBqN6gCALACAA&sourceid=chrome&ie=UTF-8

Edited July 28Jul 28 by siteunseen

Awesome, thank you!

Just make sure that the block-off strategy (whatever it might be) used at the Y-connection on the other side of the engine is sound and secure. For example...

Your hard starting issue sounds like a problem with the fuel mix not being rich enough. Are you using the choke when you start it? Make sure both jet tubes under the carb get pulled down all the way when you pull the choke handle back all the way.

Check that the fuel mixture nuts under the carbs are turned down 2.5 turns at least, and that the float levels are correct.

Thanks for the tips, I was using the choke.

I need to give the carbs a once over in general, as it hasn't started right since I got it, I just had to deal with the gas tank first (which has taken forever) so haven't had a chance to get back to it, but slowly getting there

Edited 2 hours ago2 hr by hotsho111

S30.World.com, order one and consider it done.

9 hours ago, hotsho111 said:

hanks for the tips, I was using the choke.

I need to give the carbs a once over in general, as it hasn't started right since I got it, I just had to deal with the gas tank first (which has taken forever) so haven't had a chance to get back to it, but slowly getting there

This was a huge help for me since I had no clue about the carbs. I'll also add mine was a hard start too until I adjusted the valves. That helped a lot.

On 8/2/2025 at 9:12 PM, Yarb said:

S30.World.com, order one and consider it done.

Haha ya, I considered it, but at nearly 800 bucks, and for the first time in more than 15 years decided to pay a local shop to do the work to save the time of doing it myself. They dipped, prepped the inside, and painted the outside and for 500 bucks I'd expect some quality work. I wasn't happy with the job they did and basically ended up redoing most of it myself anyway.

In the end, would have save more money going with the S30.world tank

Thanks @siteunseen ! Will take a read through that once I wrap up the tank