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Got tach working idle is 2000 - 2100 rpms


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my 81 dual cab with the stock 105hp l18 and stock carb/exaust and stock fuel system. idles at just over 1200 when warm and wont stall cold/will idle in second and first. no idea what is going on. maybe the stock carby is playing up?   

 

also getting 100km to a fuel filter with leaves/dirt/sticks/rocks in fuel. fuel system is stock from 81 with a replacement tqank from 12000 ago. 

 

bU92cAJ.jpg

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ON my Datsun 521 My fuel tank hose where you fill up gas is in the wheel well

What happens is water and dirt get passed the clamp thus getting in the fuel tank to rot it out rust dirt ect drain down in there.

Im not a 720 expert but Thats what I think it is.

 

If you bought this maybe the last owner increased the speed screw on the carb to run on the main jet instead of the idle jet as its most likely plugged up.

 

find idle jet clean if clean then find mixture screw and adjust that.

 

I use 2 fuel filter on my truck cause of the water tank in wheelwell to make sure no crud in there. Change more oftn and ck the hose and clamp

 

 

PS Lots of wild hogs there?

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not really .more cows then anything 170 acres plus 500ish acres we rent for beef cattle. 

 

i know the old tank was crushed, the old owner is in fact someone i rent land off. he bottomed it out on a rock in a dip 2 inch hole through the tank. i run 2 filters as well. at one point i know there were 3 filters. 

 

the mix is bad. no timing mark and its set by ear. ton of lose wires off the carb and the factory electronic choke is bypassed with a wire. a few other things are bipassed too. runs perfectly apart from the rpms. timing light does nothing idle screw is as always stuffed. goes from wont start to 1100 - 3000rpm in the gate. it runs okay. after an hour or so however the idle pushes 1600rpm and temp goes into the red. rad is way over pressure. they ended up putting a vented cap on the rad after it broke a number of the overflows. i do have a locking fuel cap (vented) as a few people here steal fuel (157.5c per L for 98)

 

its a 1981 UP720 5 speed L18. 99% stock but d21 break booster and master/slave. plus weird alt (just two wires same as stock just no plug)

 

no one has much info on the dual cabs 81 most of all. im really confused on it. 418,000km by tomorrow afternoon its never had more then a tank a break booster and master/slave plugs and 1 set of new leads in 99. other then all fluids and air filters every 10,000 (inc diff raid brake fluid oils filters (2 every 100km checked every 25km)

 

before i forget it has almost no air intake at the air filter. blocking it drives up rpms but the motor still runs normally. vac lines are cracked or falling apart/missing (factory lines)

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ON my Datsun 521 My fuel tank hose where you fill up gas is in the wheel well

What happens is water and dirt get passed the clamp thus getting in the fuel tank to rot it out rust dirt ect drain down in there.

Im not a 720 expert but Thats what I think it is.

 

If you bought this maybe the last owner increased the speed screw on the carb to run on the main jet instead of the idle jet as its most likely plugged up.

 

find idle jet clean if clean then find mixture screw and adjust that.

 

I use 2 fuel filter on my truck cause of the water tank in wheelwell to make sure no crud in there. Change more oftn and ck the hose and clamp

 

 

PS Lots of wild hogs there?

the workshop guy said my l18 was the same as his 620 l18. i didn't know 620's ran the l18 till then and that l18 5 speed 720's were not all that common. hence why the books don't even list the up720 or the l18 models i have to use a single cab for body a kc for under body and a 620 for motor stuff.

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This is a question?

 

On a 720 the stock tach (you don't say) is connected to the negative side of the coil but is also in line with a 2.2K ohm resistor buried in the engine harness. On trucks without the tach the resistor is missing but the plug for is there and taped up. Follow the harness near the coil and the left side behind the headlights, looking for a bulge in the tape.

 

The plastic plug (white) looks like this. The dark part plugged in is the resistor. 2.2K ohm resistance wired in line will work or pull one from any Nissan car/truck from the 80s that had a factory tach.

 

22Kresistor2.jpg

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This is a question?

 

On a 720 the stock tach (you don't say) is connected to the negative side of the coil but is also in line with a 2.2K ohm resistor buried in the engine harness. On trucks without the tach the resistor is missing but the plug for is there and taped up. Follow the harness near the coil and the left side behind the headlights, looking for a bulge in the tape.

 

The plastic plug (white) looks like this. The dark part plugged in is the resistor. 2.2K ohm resistance wired in line will work or pull one from any Nissan car/truck from the 80s that had a factory tach.

 

22Kresistor2.jpg

 

 

LPwYHHo.jpg

 

 

plus the second one 

 

SPcogIm.jpg

 

 

about 15cm after the headlight connections. in the wiring loom. also runs to the coil and distributor

 

 

npbpLu0.jpg

 

 

this is what you ment i would guess? theres nothing else in the harness that would be even remotely alike 

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Most likely that it... but intended for the stock 720 tach. I don't know about after market ones or if they need or will work with that resistor in place.

yeah aftermarket isnt working atm think it could be im hooking it up wrong or it needs the resistor on the coil

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Well if you are using the dash wire without something in that socket the wire for the tach in the dash isn't connected to anything.

 

For an after market tach the signal is usually a wire connected to the coil - negative side.

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Well if you are using the dash wire without something in that socket the wire for the tach in the dash isn't connected to anything.

 

For an after market tach the signal is usually a wire connected to the coil - negative side.

i was hooking it to the negtive side of the coil it wont get anything. thinking the 2.2k resistor is 100% needed 

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You have a post on this problem.... http://community.ratsun.net/topic/67201-1205-rpm-idle-and-rockssticksleaves-in-fuel-filters/?do=findComment&comment=1286494  Why not use it and add to it instead of yet another post about a fast idle?

 

Fast idle causes....

 

Choke on causing fast idle cam to operate. Choke heater not working or choke heater relay not working. Linkage stuck, jammed or dirty.

 

Throttle cable too tight or needs adjusting.

 

Idle speed screw needs adjusting

 

Foreign object caught in primary or secondary throttle plate or secondary throttle plate stuck part open.

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Well if you are using the dash wire without something in that socket the wire for the tach in the dash isn't connected to anything.

 

For an after market tach the signal is usually a wire connected to the coil - negative side.

 

Fyi an aftermarket L18 distrubtor is wired backwards. Just figured id let you know. (Check the pos term if you dont get signal from the negtive. And sand back the terms.

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don't know. had a friend with a 620 king cab with an l18 look over mine. ended up having to swap the coil leads and try different setups. his distributor was the same funnily enough. it had a positive and a negative but positive was wired to negative and negative to positive. seems common. few things on other datsun forums. youtube has a vid or two on it. 

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my 720 is not intaking any air now from the filter. No idea whats up. Dont even know where to start being used to a holly and all. Replaced the air filter as well. Its not blocked. And the motor the last day or two is reving dangerously high and Temps are pushing redline. Last hour or so its struggling and pushing 7000. Somethings wrong. No idea what. Changing idle seems to last a few hours then it juat goes back to this. Carb is not blocked and throttle return is normal. No smoke for now. Also had suprise rain today. Cab is full of water in the floor pans. Motor is seemingly uneffected. Also starting to have issues with the pedal (gas) not working/responding. Even idling or in some cases losing power on the freeway at 110km/h.

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