# 1982 datsun 720 help



## wlf89 (Jun 11, 2007)

need help my truck will not idle or take gas right.it was running like a new one untill i quite driving it about a month ago so i could paint it. and now it will not idle or take the gas when i push the pedal just sputters instead of revving up. i took the carb apart and blew carb cleaner and air thru all the jets and holes in the carb but didnt help it. i also noticed my tach is acting screwy goin a constant speed down the road the tach will go from 2000-3000 back and forth which sounds like it could be electrical related but when i choke the carb about half way it will smooth out and run good. i have changed all the filters at the tank and at the carb and blew thru my gas lines they are not stopped up. i can take my gas line off coming out of the pump to check the pump and put my finger over the line and it doesnt seem like it has enough pressure doesnt even blow my finger off the line is this right? any help at all is greatly appreciated this is my ride to work and really need it fixed. thanks alot.


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## smj999smj (Jan 1, 2006)

Carburators typically only run with about 4-7 psi of fuel pressure, so to test it correctly, it would be best to use a fuel pressure gauge. If you have a mechanical fuel pump, the inlet side of the pump should pull a steady 13" of vacuum. You may want to spray some carb cleaner around the intake manifold gasket while idling to check for a change in RPM; this would indicated an intake manifold leak, which is not unheard of on these engines.


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## wlf89 (Jun 11, 2007)

also i seen that the accelerator pumper plunger wasnt coming all the way back up causing a dead spot so i put in a used one i had and it ran good untill i started to leave for a test drive then started doing the same thing again coincedence or the problem you think?


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## rogoman (Dec 16, 2004)

wlf89 said:


> when i choke the carb about half way it will smooth out and run good.


This sounds like a classic case of a major vacuum leak in the intake system. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the motor fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg.


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## wlf89 (Jun 11, 2007)

ok i will give the vacuum lines a check i think autozone has a tester in there loan a tool for that. which line should i use for the test?


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## twinpilot001 (Jul 18, 2011)

Hrres one to try - from experience= disconnect the tack lead!! if the tack is bad ?? it will create problems like ur having. If that doesnt do it -verify the fuel pump is working & carb has gas?? Try putting gas into the float bown & see if starts & runs(bad fuel pump or filter clogged ) also remove the fuel takn cap -vented ok??


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## wilburk (Dec 29, 2012)

Vacuum leaks can come from lines, but also intake parts. EGR is a quick check--reach back there with your hand and push the diaphragm to see if it stutters/stalls out (it should). Check AIV to make sure it's not rusted out!


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## twinpilot001 (Jul 18, 2011)

replace the accl pump with a new one!! never a used one as can cause same problems.I have same pu & also found a good used carb online for 15 bucks -maybe try ebay or online used parts sources?/


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