'73 240Z wont make it past 60mph

[Zedyone_kenobi]

I had a 5000 rpm issue for a while, but not a 60 mph problem. Just out of curiosity, what is your timing static and at max advance?

[mayitin]

is it a mechanical fuel pump or electric? If you have rust issues then you need to take care of it. You can grab an air compresor and blow air from the filter to the tank and see what it does if it gets fix it will be only for a little bit then you must pull the gas tank out and coat it. Some times in some cars I do not know why but have pre filters they are small and get clog. If it is a mechanical pump do not forget the little spacer.

[Coopfan]

Ok so I have the ZTherapy tape and have taken out the floats and set them per the tape. My idle timing is set at 10 degees with a max of 34. I will get some carb cleaner and try spraying it on the shafts and see what happens.

I've just been out this morning doing some errands and once warmed up fully it started playing up just at normal street speed around 25 to 30mph. It would clear for a bit say half mile and then start bogging down again.

Im thinking its got to be the tank, so will be calling the mechanics this week to have that done and my lines cleaned.

[Zforce]

What exacty happens at 60 mph ? are you accellerating or cruising ? If you back off slightly can you inch it up past 60 ? What type of fuel filter are you using ? I don't care what anybody says the stock filter is a restriction. Also are your rubber fuel lines in good condition ? A leak doesnt necessarily have to leak fuel onto the ground, it can suck air and cause a high speed lean condition. what type of air cleaner do you have ? the stock filter housing is good at low speed but also can be a restiction, I punched a series of 1 inch holes around the filter cover and it cured the high speed power loss like what you are expierencing. One last thing, have you checked to be sure there is no crud clogging up your fuel lines or if there is a kink in the rubber or dent in the hard lines ? And another thing, there could be a hole in the fuel pickup tube inside the fuel tank.

[Travel'n Man]

Ok so I have the ZTherapy tape and have taken out the floats and set them per the tape. My idle timing is set at 10 degees with a max of 34. I will get some carb cleaner and try spraying it on the shafts and see what happens.

I've just been out this morning doing some errands and once warmed up fully it started playing up just at normal street speed around 25 to 30mph. It would clear for a bit say half mile and then start bogging down again.

Im thinking its got to be the tank, so will be calling the mechanics this week to have that done and my lines cleaned.

Do you have original flattop carbs or are they the earlier carbs - what carb was used on the CD? Do they have the same setting? I know where the setting should be on my '72 ........what is the setting for a '73 flat top carb?

Sorry - I missed the 3screw part - just last month I got my carb float level dead on - mine is set at 15 mm front and back - where did you set yours?

Edited December 5, 2010 by Travel'n Man

[5thhorsemann]

Oh and its got 3 screw round tops not flat tops

If you still have the electric pump at the tank end, which was a recall addition to stop the vaporlock problem. Check the filter in the pump, or do what I did and remove it altogether, its not necessary with the round tops. I had a similar problem at 3000 rpm, junked the electric pump and it took care of the issue. As far as tank rust, pull the drain plug and catch the fuel in a large clean tub, you will see if rust is an issue.

[Coopfan]

Rust is def an issue I can get handfuls of the stuff out of the rear filter after a month or so. I know the tank needs boiling

Just did the carb cleaner test on the throttle linkage, and if I spray it on the outside ends of the throttle bodies I got a dramatic drop in rpms. If I did it at idle then it kills the engine. I always had to run the idle above 1000rpm but I thought it was because of the heavy cam a PO fitted. I guess it may have been the shafts leaking all along.

So I guess I have to do both the tank and the carbs, lets hope father Xmas is good to me:ermm:

[Coopfan]

Thanks to the Sunrise Z in Glendale. After they boiled and lined my gas tank, replaced a semi functioning needle valve and slightly bent jet needle, I today briefly hit 95mph on the freeway before taffic made me slow up. Happily cruising at 80mph and no more stuttering once warmed up. All is well!

[a7dz]

I fought a problem like this for over a year and found the return fuel line was plugged. The small line on the right side.