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1973 240Z Not Running Right

2331 Views 9 Replies 7 Participants Last post by  allsttr
I just bought a '73 Datsun 240Z from the second owner. This car is all original with original drivetrain. It is an automatic (ugh!). It has been garaged for 10 years. I drained the old fuel in the gas tank, put in fresh gas, put a little gas in each carb and fired it up. It sputtered and struggled to stay running but eventually smoothed out. Now that it is running I notice that when I press down on the accelerator, the car stumbles. The same thing happens when I drive it down the street. I don't know where to start to diagnose the problem. It seems to me that the dual carbs probably need to be rebuilt. But then, maybe the electronic fuel pump is not putting out enough fuel. Can you 240Z guys tell me how you would begin to diagnose the issues. The car has 160K miles on it but I have no history on it. Don't know if carbs have ever been rebuilt. Electronic fuel pump looks old and could be original. Appreciate any help you can give me. Thanks.
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The car should have a mechanical pump on the cylinder head in addition to an electric pump in the rear if stock. If there is no mechanical pump on the cylinder head then someone has added an electric pump that must run all the time. The stock electrical pump only functioned at idle to prevent vapor lock. The stock mechanical pumps diaphram can dry rot and leak making the pump not work very effectively and will also fill the crankcase with fuel. You should pull the dipstick and smell it to see if it smells like fuel. It's a good idea to replace all rubber fuel lines and blow compressed air through the hard fuel lines and of course replace the fuel filter. Check the points in the distributor if still equipped and check the condition of the plugs. Check the car for vacuum leaks and then either rebuild or at least thoroughly clean the carbs, make sure the floats are set correctly, and you should be running pretty good. If the car has had the mechanical pump removed then make sure that the electric pump is wired to be on at all times and check the fuel pressure at the lines going to the float bowls. Pressure should be around in the 3.5-5 psi range. Read the sticky thread for newbies at the top of the forum and you will find links to download all of the factory service manuals and find other great advice.
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Cannonball89 pretty much cover it. However, I would recommend you start with the easy stuff. First thing I would do is check to make sure the dashpot pistons on your carbs move up and down freely.
Don't forget to check the oil in your carbs if you have the sidedraft round tops or flatops. Use 20W oil.
The car has the flat top carbs. Do these contain oil and where do I put it in them?
Ah, flat tops. Well most people will tell you to ditch them for round tops but there is nothing wrong with flat tops. They are technically a superior design and are just a little more complex. The toughest thing about the flats is that there are no rebuild kits available (to my knowledge) and only a very few people know much about them.
Its not a bad idea to install a glass fuel filter before the mech fuel pump. That way you can visually monitor the flow. Drain the float bowls into a cup and check for fragments of decayed rubber lines, which are perfect for clogging up stuff.
If there are no rebuild kits for the flat top carbs, how do you clean them??
Black Dragon shows a rebuild kit for the 240-260Z 73-75, $20 per carb. Part #56-801.

Bonzi Lon
sounds like the carburetors aren't balanced. Do you own a synchronizer tool? If so, can you balance them?
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