no power w/pops 2.4

1980-1986 Datsun 720 forums. All 720-specific topics and discussion can be found here.
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Posts: 9
Joined: Thu Mar 26, 2009 6:47 pm
Car: 84 720 2.4

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My fathers truck has no power..runs rough..cuts out when you get on it. He has replaced the carb (weber), coils, plugs and wires. Had the cat conv. removed..Replaced fuel pump and filter. The timing is correct and can't find any vac leaks. I didn't think to ask about rotor button or cap but other than that...any other ideas?


jwrattlesnake
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Joined: Tue Mar 17, 2009 5:34 pm
Car: 1982 datsun 4x4 truck

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Mine has just started doing about the same thing....cant figure it out....acts lkike its running on 3 cyl.....no power at all...so if you find out what it is post it so we can learn from it....there are a few others with the same problem....thanks

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PEZi
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i know it seems like the last possible thing... but to me it looks like fuel delivery.

if it cuts out when you get on it that usually means fuel delivery... if he replaced the pump and filter then its most likely in the carb somewhere

otherwise rotor cap is a great place to look as well

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Joined: Thu Mar 26, 2009 6:47 pm
Car: 84 720 2.4

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I was thinking fuel delivery also so I drained the tank..not a spec of trash. I check the plugs and they where carbon fouled as where the old ones removed and that being the reason new coils purchased. I didn't have my fuel pressure gauge but I would hope the new bosch pump would be sufficient for a 34/34 web. Is it possible that the new weber would be jetted incorrectly? I personally have never had any problems with new webers in the past. thanks............

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PEZi
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well its always best to check the jetting... especially if your at anything but sea level

i'm not sure what your altitude is but it would be good to check

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Car: 84 720 2.4

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I live at sea level....but here is my days work ...I removed the new weber and found trash in the screen so obviously I took apart the carb and cleaned it..clean the lines. Once I got it back together and started it..the idle was smooth but still stumbled or bogged when throttle was pressed significantly. So..though there is a new fuel pump and it checked out in PSI range..It still sounded as if starving for fuel. I added a second inline pump (the old one) and for the first time I had power in 1st gear and most of second w/o stumbling but it remains the same in higher gear. Any thoughts? Maybe I need more fuel pressure(a high performance pump)or is there any issues with the 720 tanks that may cause instability in maintaining fuel pressure?

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Joined: Thu Mar 26, 2009 6:47 pm
Car: 84 720 2.4

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[email protected] wrote:I live at sea level....but here is my days work ...I removed the new weber and found trash in the screen so obviously I took apart the carb and cleaned it..clean the lines. Once I got it back together and started it..the idle was smooth but still stumbled or bogged when throttle was pressed significantly. So..though there is a new fuel pump and it checked out in PSI range..It still sounded as if starving for fuel. I added a second inline pump (the old one) and for the first time I had power in 1st gear and most of second w/o stumbling but it remains the same in higher gear. Any thoughts? Maybe I need more fuel pressure(a high performance pump)or is there any issues with the 720 tanks that may cause instability in maintaining fuel pressure?
I also check the compression and adjusted the valves.......

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Joined: Thu Mar 26, 2009 6:47 pm
Car: 84 720 2.4

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I know that fuel pressure may not be the issue since webers need only 3.5-4.0 so might this be just a volume issue? I read that a Carter 4070 pump is low pressure-high volume and recommended for webers. Anyone out there fimiliar with this?

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PEZi
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i'm not very familiar with what pump is good or bad... but you definitely want pretty high volume

too much pressure will just screw everything tho

doc future
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Joined: Sun Apr 12, 2009 8:16 am
Car: 85 nissan 720

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jwrattlesnake wrote:Mine has just started doing about the same thing....cant figure it out....acts lkike its running on 3 cyl.....no power at all...so if you find out what it is post it so we can learn from it....there are a few others with the same problem....thanks
this is exactly what mine does, i just got it last week like this. seems like others have the same problem. where should i start, i dont want to just throw parts at this thing

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Joined: Thu Mar 26, 2009 6:47 pm
Car: 84 720 2.4

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well I solved the problem...as I stated a new weber was installed early in the process but turns out the jetting was way off from factory. I gradually stepped up the jetting (primary began w/130 and performs as it should on a 147. I hope this helps some of you guys and thanks for all the help!!!!!!!!!!!!!!!!

2kredz3
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[email protected] wrote:well I solved the problem...as I stated a new weber was installed early in the process but turns out the jetting was way off from factory. I gradually stepped up the jetting (primary began w/130 and performs as it should on a 147. I hope this helps some of you guys and thanks for all the help!!!!!!!!!!!!!!!!
just a side note, you may want to put a pressure regulator on the return hose since there is nothing to keep the pressure up its just a loop. My truck was doing the same thing when i got it and the first thing i did was put a reg. on the return line problem solved.


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