Zsomething

I think the 240-260-280 engines are basically "the same". The 240 came first. The 260 was the stroked version (to compensate for emissions and added weight). The 280 was the stroked and bored version (also to compensate). That's a bit oversimplified, I know. But, that basically explains why there is more info on the 280 mods. You could start with whatever you want/have (and a lot of people probably have). But, the economic route is probably to start with the 280. Since most of the 69-83 components are more or less interchangeable, why not use the work that the Nissan engineers did and start from a bigger displacement in the 280?

If the gunk worked once. It should work again, probably. If the flush causes the leak again. I'd say just put some more sealant in. Alternatively, I think a new after-market radiator would be around $100-200. Or you could roll the dice with a junkyard pull (which might have similar issues). But based on what I've read, most people have luck with improving flow through the engine bay. So, some combination of: front air-dam, hood vents, and electric radiator fan could help too. (Not exactly the cheapest route, though.) I found these links (Your mileage may vary): http://www.datsuns.com/Tech/aerodynamics_and_cooling.htm http://zhome.com/Care/z_cooling.htm

Sorry, I didn't realize this thread was old. ...live and learn...

The plugs are black with carbon. I think one of them was bridged by a carbon piece, because just pulling them and putting them back in made things smoother. I'm pretty sure the plugs are shot. I've got new plugs and wires ready to be put it. I'll check the compression when I get home. To check compression, is the procedure: pull the plugs, attach gauge, attach jumper to starter motor for 5 seconds, check gauge.

I would say that going through the normal stuff would help. In my case, just setting the timing helped a lot. But, if you do a normal tune-up and replace the filters/fluids, it might run good enough for you. If you dig a little more, it might run well without too much more work. I would be a little worried about the ticking. But since you are going to pull the engine anyway, it's probably not that big of a deal if the engine fails.

I was just logging in to say that, after looking at the carbs more closely, the air cleaner mounts into the long hex nuts on the side of the carbs. The setup came apart. So, I never put 2 and 2 together. Thanks!

Some people seem to think that they could eek out just a little bit more with the flat-tops. (can't find it now. But, I think I googled 'round top vs. flat top' and found some flame-war on the topic that was pretty informative). The conclusion was basically that if you really know how to do it, you can get flat tops to really run. But, most people don't have the skill, time, patience, equipment, or luck to make it happen. I guess to each his own. For me the choice is pretty simple: better after-market availability and wider use of round tops = fewer headaches and more information

I've also heard the newer intake is better. It looks like coolant runs to the manifold and to the carbs. Should I just JB Weld over these ports? I have a flapper air cleaner that I can put on with the round tops. But, the 2 screws look like they are too short to hold the top on. Are there brackets missing?

I just bought a '73 240z and it runs rough. The previous owner says it need a (flat top) carburetor tune-up. It idles ok after it is warmed up. But, somewhere around 2,000-3,500 rpms it starts to sputter and pop. The previous owner mentioned that he put a new distributer on the car. So, I figured that I should check the timing. I monkeyed with it a bit and settled on 10 degrees advance then a cranked the tightening screw down (and realized that it was loose before, which seems to me like it could have caused some problems at higher than idle rpms). In the process of checking the timing, I pulled the plugs and checked the air filter. The air filter is very dirty and smells like gas, which seems odd to me. But, I have heard the flat-tops can spit gas into the air cleaner. The plugs are very black with carbon and they smelled like gas (not sure if gas smell is normal for plugs). The vacuum seems ok. From idle to about 3,000 rpm the vacuum reads about 10 psi solid. I haven't checked the compression. But, the steady vacuum needle makes me think compression is pretty close for all the cylinders. So, I it seems to me that the flat-top carbs are the problem. My plan is to replace them with a set of round-top SUs that came with the car. So, I am going to get the rebuild kit from Ztherapy.com, rebuild the SUs, and swap out the flat-tops. How much replacing of hoses, lines, etc. that don't come with the kit will I need to do? Will there be a lot of plugging of coolant tubes that currently go to the carbs? Is using SUs with the flat-top manifold really just a bolt-on replacement? Should I just use the manifold that the SUs are already attached to instead of the flat-top manifold? Are there any parts on the round-top carbs (which are of unknown origin) that I should check before I attempt to do the refit? And finally, am I blaming the carburetors too soon? I know the flat-top carbs are notoriously bad for maintenance (although I have heard some people claim flat-tops are better for performance applications). But if there is some tuning that I can try for the flat-tops, I would love to try it before I go and replace the whole setup. Should I replace the air filter and plugs before or after the carb swap? Mainly, I would prefer to know that everything but the carburetors work before I replace them. That makes troubleshooting (when I bolt them on upside-down or something) a lot easier. Thanks in advance.