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1981 Datsun 720 4x4 wont rev past 4000 rpms


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#1 Chopstk720

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Posted 26 May 2018 - 11:26 PM

So I’m knew to the Datsun family and am still learning exactly how it’s supposed to drive but I love this little truck so far. How ever the motor seems to wind out and be done at about 4000 rpm. It will not even come close to redline. It’s the k24 with the stock carb. The truck does have bigger wheels and tires and I’m almost sure that they have affected the speedo. Would they do the same to the rpm? It feels like it has more in the motor but just will not rev past 4K. Any advice would be great

#2 datzenmike

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Posted 27 May 2018 - 06:04 AM

The Z series are not really high revving engines but it should be able to rev over 4K...thought not very quickly. More info needed. Tire size won't affect it this much

 

 

Is this in every gear or just out on the highway?

 

Does the truck surge ahead and slow surge and slow when you get to 4K????

 

 

Start with checking/replacing tune up parts. This will likely uncover something not right.

 

 

Pull an intake side plug wire off and check for spark, now check the exhaust side. Are both working?

 

Check set the valve lash 0.012" on intakes and exhaust.

 

Check the timing. 3 degrees before top dead center

 

Are the plugs clean and in good shape? They give a good indication of what going on inside the combustion chamber... Are they black? dark brown? brown? light tan? are they very light or white?


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#3 captain720

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Posted 27 May 2018 - 06:57 AM

My 4*4 will just jump up to 5K even with a load of brick in the back (like 1600lbs) although it only does it fast in 1/2/3 on hills. But yeah something is definitely wrong cause mine rev hard and fast, they just make no power past 4500 so there is no point in going higher.

1986 and 0 Nissan 720 kc with a 1984 Z24 (third engines the charm?) http://community.rat...y-first-pickup/
1986 and 0 Nissan 720 kc 2wd http://community.ratsun.net/topic/71766-one-wasnt-enough/

My channel https://www.youtube....KfpiwEzpECyevzw

 

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#4 Chopstk720

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Posted 28 May 2018 - 08:48 PM

I knew the truck had little power to start with but I’ve never driven another one for comparison. I know it takes me sometimes over a mile to get up to 75mph. I’ll pull it all apart tomorrow and do some investigating. The motor purrs and it will do every bit of 85mph it just takes forever to get there because she won’t push past 4K. I also live at elevation (7000 ft) so I do notice a power difference as I come down the mountain. I’m new to Ratsun so I will try and post a video of it tomorrow

#5 Chopstk720

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Posted 28 May 2018 - 08:52 PM

I really feel any small load i put back there just my dirt bike in the bike makes the truck sluggish. Again idk if this just the small motor at work or if something is wrong

#6 datzenmike

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Posted 29 May 2018 - 04:47 AM

 

 

 

Start with checking/replacing tune up parts. This will likely uncover something not right.

 

 

Pull an intake side plug wire off and check for spark, now check the exhaust side. Are both working?

 

Check set the valve lash 0.012" on intakes and exhaust.

 

Check the timing. 3 degrees before top dead center

 

Are the plugs clean and in good shape? They give a good indication of what going on inside the combustion chamber... Are they black? dark brown? brown? light tan? are they very light or white?

 

Start with a check on these things, basically a tune up to be sure something obvious isn't over looked. Add to this checking that the secondary on the carb is free to open. Engine off, hold throttle full open and lift up on the vacuum secondary actuator. This could be something simple like it's stuck.


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