hi i am new and having trouble with carb on 82 720

[i need help & guidance]

hi, i  dont know where to look , next

 i have been trying to figure out where else to try and clean or adjust

.......... to start ,,, to resolve issues with  a 1982 720 2wd king cab / with automatic trans .

 1. to get it to idle & run normal ...and not stall letting off gas pedal when coming to a stop. 

2. not idle too high after adjusting the idle and after restart. the previous idle setting is not same after restart .

and

3. trying to fix engine from stalling/hesitating  when accelerating.. because engine tries to die unless you hold foot on gas and keep idle up enough for truck to take off from a stop

 

the fuel tank is new ,

the fuel pump is new ,

the fuel hoses and filters around tank are new. 

fuel is about at center of sight glass when looking at carb with engine off .. i dont know how to raise fuel level in sight Glass if i need to

 

  i replaced fuel and fuel tank / fuel pump parts

sprayed carb clean ,

sprayed wd 40 on linkages and any parts around carb body and worked them back and forth

replaced air filter , and cracked vacuum hose /leaks & other stuff ,

 

and ordered a haynes manual for 720 trucks hoping it explained the carb adjustment s in detail  . .  but it has not arrived yet... maybe today

 

i did read an article by an axle addict about a magic hidden relay in the dash, but my truck is just before this relay was used .

because it is not in the dash up above the blue and black relay only a air vent tube is there i took that off and nothing ese is up there

 

 i took truck to smog place 2 days ago and it only failed high hc at idle,  everything else passed ..

 

the lee way for idle at smog place and still pass is 350 to 1350 rpm .. so smog idle is pretty lenient

[datzenmike]

The best manual is the Nissan factory service manual (FSM) for your year of truck. Far superior to the Haynes which is 1/5 the size and covers all years but poorly. 

 

 

To get a good strong idle you need a good strong intake vacuum.

 

Loose or cracked hoses connected to the intake will leak vacuum.

Make sure EGR valve is clean and  not prevented from closing by exhaust deposits. EGR is supposed to be closed tight at idle.

Make sure the carburetor is bolted down to the intake and gasket not leaking.

Adjust the idle mixture and speed screws when engine is warmed up.

Make sure choke is fully off when warmed up.

Warmed up is half way up the temperature gauge, about 15 min of running.

 

Make sure the valve lash is correct. I think it's 0.013" for both on a hot engine. A tight intake valve won't close properly and will leak vacuum.

Make sure both intake AND exhaust side plugs are firing.

Make sure your ignition timing is correct.

 

 

[i need help & guidance]

i will take pix

and post updates

i just now got the idle cut off thing out

and cleaned it

[i need help & guidance]

i want to upload pix from my digital camera

but i dont see the attach image  key ..  . . . . . . . . up there  ^^^  . . .

 

 i dont know how to post pix from my computer file to this thread 

 

.... help

 

do i have to be a member for day before i post any pix ?

 

 thank you

[i need help & guidance]

does the the slow closing throttle diaphragm

have to be in contact with the linkage tab ? 

 

or can linkage tab be bent up slightly to make contact with pushing rod thing ? 

 

there is  tiny  gap between rod / plunger thing and linkage tab ..

 

it looks like slow closing vacuum diaphragm- has an adjustment screw on top,

but i cant find any info online to see what adjusting screw does.

so dont want to turn it yet

[datzenmike]

To post pictures you will need to get a free account at a picture hosting site such as image shack, imgur or whatever.... but I do NOT advise Photobucket. You picture aare taken and stored there. When you want to post one here you go there and copy the image information and bring here. Down in the lower right corner just above the Submit Reply is the 'insert other media' click it and past the info.

 

I assume you 720 is an automatic?

[weldingrod]

Not a reply to this topic, but as long as we are discussing 720's............................................

 

Is there an aftermarket fuel return line check valve available anywhere? Nissan dealer says 7-8 weeks and $75-90.

 

1984 Nissan 4x4 720.

[datzenmike]

It's actually a check valve for the vapor line to the charcoal canister to prevent fuel being expelled if the truck turns over.

 

17330-P7900 20 years ago they were $20 at the dealer. Try NAPA?

 

Where's yours? Not totally necessary you can run without it, Just keep the wheels on the road..

[i need help & guidance]

hi, thank you.

 

it looks like i have alot accomplished.

 

my questions right now are .

 when connecting vacuum gauge to set air fuel mixture

what is the level of vacuum i am trying to achieve ?

my highest vacuum  i am getting is  just under 20 with air/fuel screw backed way out .. compared to before.

any further tinkering result in less vacuum reading . so i just try needle set to highest vacuum with least fluctuation

also....  i had turn the idle way down at carb.

 

  idling now --- while in drive --- with foot on brake .. i am getting 675 to just under 700 rpm at idle .

i cant back screw out anymore and get any lower rpm ..

 

........... the engine idle is really smooth . .. compared to before

 

  * what carb adjustment is made to squirt fuel or whatever is done = in to carb--  when revving ----.  because it hesitates briefly like it wants to stall ?

 

but   if i feather the gas pedal  normal....  it throttles up fine, ..... but if i try and step on throttle. it stalls hesitates for a split second then catches right up

[datzenmike]

You want maximum vacuum.

 

As for the idle mixture turn in till idle drops then out till it drops off... select a point in the middle of the good running range. If the idle goes up, turn it back down. Repeat till you cannot improve the idle quality and the idle is about 650-700.

 

The accelerator pump is what squirts raw fuel into the primary to prevent a lean mixture when throttling up just off idle. The diaphragms wear out.

[i need help & guidance]

accelerator pump  . . . where is this located on my carb ?

 

once i get this replaced . .  i will  be rolling !!!!

[datzenmike]

On the right side farthest from the engine. Has a linkage to it an a rubber dust boot. Probably can't buy separate, have to get a re-build kit.

 

[i need help & guidance]

can you explain how the adjustment screw on accelerator pump   functions ?

 mine has a philips head screw going through  a spring  with  angled tab linkage on top to push bellow looking thing

 

 

[i need help & guidance]

hope this works  

[datzenmike]

The Z24 are set and sealed at the factory. The Z22 probably are a Philips head but all do the same thing. They look like this...

 

 

Like a valve, tightening in reduces the gas to the idle circuit, opening makes it richer. When the fuel and air are just right the engine usually increases in speed so it needs to be turned down which will mean re-adjusting the mixture. You may have to go back and forth 7 or 8 times to get it right.

[i need help & guidance]

this is my carb from top .. see accelerator pump adjust screw going down through a spring on front of carb linkage  .. right near accelerator pump ...

 

i was removing the idle cut off thing , to clean it... when i took this pic

 

. 

[datzenmike]

That isn't the mixture screw. Looks like something to limit the amount the accelerator pump can pump.

 

This is the idle mix screw on the Z24 carb.The plug has been removed.

 

[i need help & guidance]

yes. i already set the air fuel mixture screw with the vacuum.- 20

 

  on my carb- i have some kind of linkage on the accelerator pump with a philips screw passing down through a spring

it has a tab angled on it to respond to the throttle .

 

i dont know if i should turn accelerator pump screw  clockwise or counter clockwise to solve the hesitation issue.

 

once you have the air cleaner back on and vacuum lines hooked for truck to run correctly....,. you cant reach this screw to adjust it

[i need help & guidance]

see air box covers up any access to adjust

[i need help & guidance]

here is the screw ... i want to learn how to adjust 

[datzenmike]

 Work the throttle and see if the pump is moving. Try to adjust to get more travel.

 

The accelerator pumps do wear out. It may need replacing.

[i need help & guidance]

i cannot believe how good my truck is running already.

what brand of carb is on my truck from the factory ?

 

i am wondering if a kit can be ordered

where i can just take the accelerator pump out of the carb rebuild kit.

 

https://www.aliexpress.com/item/Brand-New-Car-carburetor-Repair-Kits-K11-4671HAD-for-NISSAN-Engine-parts-Car-Carbutetor-Repair-Bag/32837992826.html?spm=2114.search0104.3.78.119f79bd7wAoRL&ws_ab_test=searchweb0_0,searchweb201602_2_10065_10130_10068_10890_10547_319_10546_317_10548_10545_10696_453_10084_454_10083_10618_10307_537_536_10059_10884_10887_100031_321_322_10103,searchweb201603_51,ppcSwitch_0&algo_expid=ab1545a0-4cb0-48f7-93ab-0ffe28d445b1-12&algo_pvid=ab1545a0-4cb0-48f7-93ab-0ffe28d445b1

 

  

[datzenmike]

The 720 gas engines were all Hitachi.

The L20B was 340 or 30/34

The Z22 was a 342... or 32/34mm

The Z24 was a 384 or 34/38mm bore. Unfortunately one of the stud holes on this carb does not match all the others so it won't swap. 

 

 

I just measured and confirmed this. The accelerator pumps are likely all the same but just to be safe order for a Z22 truck..

[i need help & guidance]

i found this

rebuild kit with accelerator pump

 

it has the part i need .. total is $ 39

[i need help & guidance]

i also found this carb .

but it is for the z24 engine it says

 

carb