I have a 1972 240z with round tops. I rebuilt the carbs with the Ztherapy kit.

I got the car warmed up and tuned them as best I could but when I went to drive the car, it struggled to move along. The car revs up fine while in neutral. I tried messing with the timing and it did nothing to help.

I checked the vacuum advance in the distributor and it appeared to be functioning properly. The spark plugs are new. I pulled the fuel lines that go from the fuel rail to each carburetor and cranked it for 20 seconds or so and they both flowed well and the gas was clean. The float levels have been set properly. I took the return fuel line of and blew air through it and i could hear it bubble towards the back of the car, I'm not sure how easy it should be to blow air through the line but it seemed ok.

Any help would be much appreciated. This car is driving me crazy :ogre:

It is probably timing if the carbs and fuel flow is ok. What do the plugs look like?

Next time, warm it up and try giving it some choke as you put the engine under a load. That will tell you if the mixture is too lean. Some additional info is needed; Was the engine warmed up? How many turns down are your nozzle screws? Color of the plugs? What was your reason for the carb kits? Did it run poorly before? Did you work on anything else when the carbs were off? Given the info at hand, my first choice is it's too lean. Check; fuel filters, fuel pressure & volume, float level. Mark in Portland

It is probably timing if the carbs and fuel flow is ok. What do the plugs look like?

The plugs are clean. I was thinking the timing is the likely culprit because I don't have a timing light.

try rotating the distributor clock wise a little at a time and test drive.

You will hear pinging underload when you go too far.

I know you said you checked fuel, but those symptoms will show up if you have restricted fuel flow too.

I know I spent a week on a wild goose chase before finally looking at my rearmost fuel filter by the tank and finding it disgustingly clogged.

please clarify ' struggles to move along'.

Load and no load is big difference on how it runs.

Get a timing light-they are cheap and this eliminates things

Before you did a rebuild on the carbs, did it drive then ?

please clarify ' struggles to move along'.

Load and no load is big difference on how it runs.

Get a timing light-they are cheap and this eliminates things

Well I tuned the carburetors to the best of my ability, rolled it down the driveway (slight incline) and attempted to drive back up the driveway and had to rev it up and dump the clutch constantly to get it back up.

Before you did a rebuild on the carbs, did it drive then ?

The car sat for a number of years before the carburetor rebuild. I had the gas tank boiled out and sealed professionally and double checked to make sure that none of the lines were clogged (return line and vent lines). I blew out all the gas lines. New filters, coil, distributor cap, points, coil, spark plugs, wires, etc.

Insufficent fuel-probably have to go back and recheck everything. Fuel rail been checked for a good return?

Recheck carb screen filters.-Fuel sending unit pick-up checked?

Did some tinkering today and found that no matter what I did I couldn't get the front carburetor to suck nearly as much air as the back carburetor. Just some more bit of info for you guys.

I uplugged the coil and the fuel line to each car and cranked it for 20 seconds or so again and found that the front carb did not have a steady flow of fuel whereas the back carb did.