I got my dream pickup, a 1981 720.

[Thomas Perkins]

You need to remove that broken bolt and put a new one in it.You see where the worn part is.After getting a new bolt in,  turn distributor and align it up to the worn mark.Might get lucky and hit the timing mark on the head.My bolt is pretty much centered.Never in 31 years of owning my truck has my timing jumped.Get a set of easy out and new NGK spark plugs and wires.Wires have cylinder numbers on them and get a new distributor cap and rotor from Auto Zone ,comes with a lifetime warranty.What I use.They are good.Harbor Freight has good timing lights for 35 bucks.Easy way to align up time marks is,put in 2nd  gear and pull truck and marks will align up.Works for me, even can push back wards.Never had to time it, my vacuum line came off,I thought timing was off.I never ever lossened the 2 screws.Here is my distributor with cap off.Set bolt is in middle.

Edited October 22, 2025 by Thomas Perkins

[datzenmike]

If the 'button' is falling out it's done. Get a new distributor cap. 

 

There is no time for replacing the wires, it's done by looks. If they look bad they most certainly are. Good insulation in the wires and cap/rotor ensure that the spark has only one possible path to ground and that's the spark plug. 

 

There is no vacuum on the vacuum advance to the distributor at idle so putting finger over hose end will do nothing. 

[TinKanTosser]

I'm a consistent screw-up with drilling and easy-outs. Drilled the hole slightly off center and then broke off the extractor in it, now I can't drill through the extractor and it's too dark out. Surprised the Nissan bolt was soft to drill through while the extractor is as tough as a Toyota bolt. If I hadn't tried to use the extractor I could have just drilled the hole until empty and gotten a bolt with a nut tonight, now it's too late.

I didn't think anything of the button falling out because it was only held in by the spring being wrapped around it. The cap seems like new but I can go ahead and get another one and new plugs. Can anyone answer why they have separate NGK parts numbers for intake and exhaust spark plugs? Some other makers listed on RockAuto do but a lot don't, and I suspect it doesn't matter very much.

Ordered new plug wires already with my parts order arriving tomorrow, the ones coming from the coils don't look great so maybe that's a clue. Tomorrow I'll work on drilling out the bolt + extractor and replacing it.

 

59 minutes ago, datzenmike said:

There is no vacuum on the vacuum advance to the distributor at idle so putting finger over hose end will do nothing.

I meant the open port on the manifold on the VSV or whatever it's called here. In the last few frames you can see me cover it but what happened afterward is the idle stayed the same and kept going up and down at the same rate. I have a cap set to cap it off (until I follow a diagram and get the vacuum routed) but didn't notice the open port until yesterday.

[Rustbin]

The intake and exhaust have different heat range ratings. Lots of penetrating oil helps loosen busted bolts, I try to drill them out till I'm near the threads then use a punch or something similar to knock the remaining bits towards the center of the hole to bust them out, then finish up by chasing the threads with the correct size tap.

[NC85ST]

To drill out that bolt, remove the distributor and then remove the distributor mount. It only has 2 bolts, then put it in vise to drill out the bolt. Also, without that bolt, your distributor won’t stay in time and the engine will die or run very, very badly. 
P.S. Don’t snap the distributor mount bolts. If they don’t want to come out easily, leave them alone.

[TinKanTosser]

Sorry for the lack of updates, had persistent rain and then caught a cold. Got pissed off about wasting so much time on the botched bolt so I just swapped my distributor mount with the one on my dad's truck, and his was missing a bolt outright. It was never necessary. The 720 has two bolts on the distributor, and unless it's for some kind of ground, I can't see a second one serving any purpose.

I got my new cap, wires, and plugs on it, and when I went to crank it the battery was dead. I have it charged now and just have to find the time when I'm not working and it's not near freezing after dark to try running it, fingers crossed. Looking forward to the fun stuff like changing all the fluids and the seized fan clutch/water pump, then I'll be on the road. Also found rust through the door and the floor pan around the drain plug, luckily my neighbor has a welder so if I prep all the needed spots he'll probably help me with all of them.

Sidenote -- I'm amazed by how big everything is on a Datsun compared to any Toyota -- it's like Chevrolet sized. The oil filter is big, all the bolts are bigger; especially the crank bolt which I don't even have a socket for, it's bigger than a 25mm and smaller than a 30mm. Speaks to higher quality and thoughtful design? Lot of Toyota parts and fixtures are quite literally toy-sized.

[toshts]

29 minutes ago, TinKanTosser said:

Sorry for the lack of updates, had persistent rain and then caught a cold. Got pissed off about wasting so much time on the botched bolt so I just swapped my distributor mount with the one on my dad's truck, and his was missing a bolt outright. It was never necessary. The 720 has two bolts on the distributor, and unless it's for some kind of ground, I can't see a second one serving any purpose.

I got my new cap, wires, and plugs on it, and when I went to crank it the battery was dead. I have it charged now and just have to find the time when I'm not working and it's not near freezing after dark to try running it, fingers crossed. Looking forward to the fun stuff like changing all the fluids and the seized fan clutch/water pump, then I'll be on the road. Also found rust through the door and the floor pan around the drain plug, luckily my neighbor has a welder so if I prep all the needed spots he'll probably help me with all of them.

Sidenote -- I'm amazed by how big everything is on a Datsun compared to any Toyota -- it's like Chevrolet sized. The oil filter is big, all the bolts are bigger; especially the crank bolt which I don't even have a socket for, it's bigger than a 25mm and smaller than a 30mm. Speaks to higher quality and thoughtful design? Lot of Toyota parts and fixtures are quite literally toy-sized.

Crank bolts a 27 - thing that always throws me is that the oil drain plug is a 22 or atleast the 4 oil pans in my garage all are. I think I still have a spare distributor, pedestal, timing cover, oil pump/dizzy drive shaft if you end up needing any of it but it sounds like you got it sorted. I wish the petcock for the radiator had more of a nipple to get a hose onto but it isn't too bad

[ggzilla]

Toyota had a "full size" model called Toyopet in days gone bye

 

The crankshaft bolt is 27mm

[TinKanTosser]

3 minutes ago, toshts said:

Crank bolts a 27 - thing that always throws me is that the oil drain plug is a 22 or atleast the 4 oil pans in my garage all are. I think I still have a spare distributor, pedestal, timing cover, oil pump/dizzy drive shaft if you end up needing any of it but it sounds like you got it sorted. I wish the petcock for the radiator had more of a nipple to get a hose onto but it isn't too bad

The oil drain plug threw me so bad. Every Toyota I've ever worked on, and it's been a lot, has had a 14mm plug. I went feeling around under here with a 14mm socket, then kept going higher in disbelief until landing on 22mm. Helps prevent rounding stuff off I guess? IIRC my Corolla has a 17mm crank bolt -- it looks half-round as it stands, lol

I remember seeing the 22RE guys asking for part numbers on bigger oil filters because the Toyota ones are so small and stubby, but the ones the 720 takes are full-size already. I thought about making a thread asking for those with knowledge to compare and contrast classic Toyota and Datsun design, any interest? The post-83 22RE had me wracking my brain with its timing chain.

[datzenmike]

7 hours ago, ggzilla said:

Toyota had a "full size" model called Toyopet in days gone bye

 

The crankshaft bolt is 27mm

 

Pretty much the same as the L and Z series crank shaft bolts... has to be for 87 - 116 ft. lbs. tightening torque

[TinKanTosser]

Alright, requesting expertise for real now.

New plugs, wires, cap. I connected what I think is the idle cut (small metal cylinder?) to the wire that gives it power when the switch is on. It runs, like this:

https://imgur.com/l5h2kdqhttps://i.imgur.com/l5h2kdq.mp4

Is it running on all cylinders?

No one is working the throttle, it's going up and down like that completely on its own. Should I suspect the mechanical fuel pump?

From the truck I have a blue wire and a blue wire with a stripe. The striped one supplies power when the switch is on (makes the idle cut thing click) and the solid blue does not. Thus wouldn't it be a ground? Ground shouldn't go to the choke, right? What does go to the choke?

 

I don't mean to sound impatient but if this carb is causing me any issue that's not easily fixed I need to go ahead with my Weber plans. Hauling is one thing but I really just need to get on the road with this and start working out its problems, lest it sit for the winter and finally rust through in more places.

What jets do you recommend for a 32/36 on a Z22? I have seen a couple different answers, seems like it's subjective? Even with my Weber jetted for a 1.6l 4A-LC should I just bolt it on as it is for testing?

This noob thanks you all.

[ggzilla]

The idle-cut solenoid usually has a single wire, and is grounded through the case

The choke heater always has a single wire

Does your 720 have the three-wire connector or the two-wire connector?

11 minutes ago, TinKanTosser said:

From the truck I have a blue wire and a blue wire with a stripe. The striped one supplies power when the switch is on (makes the idle cut thing click) and the solid blue does not. Thus wouldn't it be a ground? Ground shouldn't go to the choke, right? What does go to the choke?

[ggzilla]

In the video, you can tell the engine is not firing on all cylinders by looking at it -- it is rocking back and forth

[TinKanTosser]

1 minute ago, ggzilla said:

The idle-cut solenoid usually has a single wire, and is grounded through the case

The choke heater always has a single wire

Does your 720 have the three-wire connector or the two-wire connector?

It has two wires, previous guy cut the connector. This is all unless there's supposed to be another coming from a different place. Maybe the stock 81 carburetor didn't have an idle cut, only electric choke? Reminding everyone this is a Chinese repro that likely was made to cover all years of 720. This truck was likely sold in Alabama originally considering it's earliest use might have been by the Huntsville body shop that painted it.

[ggzilla]

Weber jetted for 1.6 liter will generally run OK on a 2.2 liter engine. What have you got to lose, put it on and see how it goes. On the other hand, if it is incorrectly jetted for 1.6 liter will likely be incorrectly jetted for 2.2 liter

 

But none of that will solve the idle-cut and choke heater wiring problems, which modern Weber 32/36 has both the solenoid and electric choke

[TinKanTosser]

2 minutes ago, ggzilla said:

Weber jetted for 1.6 liter will generally run OK on a 2.2 liter engine. What have you got to lose, put it on and see how it goes. On the other hand, if it is incorrectly jetted for 1.6 liter will likely be incorrectly jetted for 2.2 liter

 

But none of that will solve the idle-cut and choke heater wiring problems, which modern Weber 32/36 has both the solenoid and electric choke

My Weber has no electrics. I stupidly bought a manual choke one for "simplicity", but on the Corolla I just never hooked it up and drove it all summer without a choke. Every start was easy, heat soak on hot starts is what made it start like crap, lol

[ggzilla]

Heat soak on the 720 will not be a problem if you use the Weber insulating gasket and the factory 720 heat shield underneath that

 

But ... if the Weber is jetted correctly, it will be difficult to start in winter without the choke working. It the weber is jetted extra rich you can get away with it. Extra rich jetting will run OK, but may foul the plugs and eventually contribute to ring wear. For that reason, I recommend after you get it running, fit a choke cable and jet it down to best power. With a weber 32/36 it involves main jets, air jets  and emulsion tubes. The difference between running OK -- and running with maximum power along with max fuel economy

[TinKanTosser]

14 minutes ago, ggzilla said:

Heat soak on the 720 will not be a problem if you use the Weber insulating gasket and the factory 720 heat shield underneath that

 

But ... if the Weber is jetted correctly, it will be difficult to start in winter without the choke working. It the weber is jetted extra rich you can get away with it. Extra rich jetting will run OK, but may foul the plugs and eventually contribute to ring wear. For that reason, I recommend after you get it running, fit a choke cable and jet it down to best power. With a weber 32/36 it involves main jets, air jets  and emulsion tubes. The difference between running OK -- and running with maximum power along with max fuel economy

Yes thank you. I'll definitely run the choke cable, was going to on the Corolla as soon as the cold necessitated it; now it's about time. Will have to wait on adaptor plates to come in but I'll go ahead and order them whether I get this carb working or not

[datzenmike]

Once set, carburetors mix fuel and air in the correct ratio. Carburetors don't know or care about the displacement of the engine they are on.  An A14 at 2,000 RPMs moves the same volume of air as a Z24 at 1,166 RPMs in a 720. You can put an A14 carburetor on a one liter larger Z24 and it will run just fine but it is smaller and more restrictive. 

[TinKanTosser]

Good news!! Blown head gasket.

But I put my Weber on it and it started up right away with a perfect idle, no misfire. The cheap carb the previous guy put on it was a piece of junk; its throttles appear to be sized for a 521 and no matter how we tried to tune it it would barely run. I certainly haven't lost anything by bolting on my Weber, it's free reliability and performance.

 

So it blows a healthy amount of steam when blipping the throttle after idling a while etc. and it slowly reached operating temp, then slowly kept creeping up until it was about a cm away from the "warning" mark on the gauge, then I blipped it once more to blow the water out and shut it off.

Considering that the compression's good I want to try a bottle of Blue Devil head gasket sealer just to get me through the winter, we've been in a hard freeze here when it should be fall and I'm sure it'll get bad again.

 

Question I have, especially for @datzenmike, should I try re-torquing the head bolts now that I know it's blown, or does that have no hope of helping? Good to do before I use the Blue Devil? Am I an idiot for even considering using a sealer?? I will watch my oil religiously.

[datzenmike]

It's getting cooler and damper and all exhausts will steam on start up. If it is a head gasket and coolant is going out the exhaust smell it. It will smell like sweet antifreeze. Also another clue is coolant loss and constant topping up of the radiator. Driven long enough the coolant steam will get past the rings and color the oil so it looks like coffee and cream. So make sure it is the head gasket.

 

Only the Z24 needs the head bolts re-torqued and it's not a fix but a preventative measure. If the gasket is blown replace it now. It's under your control when and where you do this rather than it blowing in the dark 20 miles from home Xmass eve and doing it in the cold. The gasket is only $30.

[TinKanTosser]

12 minutes ago, datzenmike said:

It's getting cooler and damper and all exhausts will steam on start up. If it is a head gasket and coolant is going out the exhaust smell it. It will smell like sweet antifreeze. Also another clue is coolant loss and constant topping up of the radiator. Driven long enough the coolant steam will get past the rings and color the oil so it looks like coffee and cream. So make sure it is the head gasket.

 

Only the Z24 needs the head bolts re-torqued and it's not a fix but a preventative measure. If the gasket is blown replace it now. It's under your control when and where you do this rather than it blowing in the dark 20 miles from home Xmass eve and doing it in the cold. The gasket is only $30.

Today was a mild temp and the exhaust blew white way past the point that it should if it were condensation, and it blew from the exhaust tube under the hood, not just from the muffler. Basically it will clear up 100% then rev it up and it will blow a white cloud every time. I ran it as long as I could before dangerously overheating. It still has the old coolant in it so it's probably lost the sweet smell even if I'm smelling for it.

 

The fan clutch is stuck solid and not loose. I've bought a thermostat to put on and test it with before proceeding. If the Blue Devil won't cause harm I'd like to take the chance on it, I have a backup vehicle and if it blows suddenly away from home I can stop and let it cool down. I have several bad experiences tearing something down for a simple job and then getting stuck in a dead freeze with a broken off bolt and no time to get to it.

 

I do realize it could also be an intake leak, so I'll make sure none of those bolts have backed out. If old coolant causes overheating this quickly I'll change it before proceeding.

[datzenmike]

Hard to say if it's steam or just normal condensation in the exhaust. 

 

1/  The coolant recovery bottle overflows or needs to be topped up, does it?

2/  In time the oil will begin to turn milky, does it?

 

 

These two above are pretty definitive that the head gasket is faulty. Overheating could be a number of things though a blown head gasket usually presents with over heating.  If over heating AND 1/ and 2/ it's practically positive the head gasket is blown. You can't keep driving it if it over heats. 

 

Additives to the cooling system to fix leaks rarely work. They are used by the desperate. 

[TinKanTosser]

So the overheating was just the thermostat. Changed it and it holds temperature perfectly for as long as I want to run it. I bled the air out of the radiator and it really doesn't seem that abnormal, except... you know how when the thermostat opens, the level usually goes down and kind of leisurely flows from one side to the other? It never did that, it kind of stayed high the whole time I ran it. It probably should have had a good deal of air in the system but not much came out, and the radiator level didn't drop considerably when  the coolant from the block circulated through. But maybe it's totally fine.

The thick white steam is still just as bad, had more of it at idle than before also, and today has been over 70 degrees and very sunny, out in the open so it feels like 80. The engine/exhaust makes kind of a burbling noise like when one runs rich, but I tried going lean as it would tolerate and it kept on. Could be an unrelated thing.

 

It's a good thing I had to buy a water pump with my fan clutch because my water pump is bad too, making noise when returning from a high rev. I'm thinking the course of action is to go ahead and change that, put in all fresh antifreeze, and drive it a while and see what happens.

Mike, I respect what you say about going ahead and changing the head gasket if I do find it to be blown. I know it's been talked about to no end here, but the wedge for the tensioner is what concerns me most, because that's ideally not something I can afford to screw up with so little good weather left. The one currently sold on Amazon is reported by many to be too short, I see what people have said about cutting a wooden clothes hanger or folding a garden hose(??) and it all seems a bit unreliable given my tendency to get anxious and screw things up.

 

About the possibility of an intake leak, I put a wrench on the upper bolts and they wouldn't budge, so none of those have backed out (major problem on Toyotas). Couldn't see to access the lower bolts. Wise to replace the intake gasket as a precaution before head gasket or no? What's the probability of an intake gasket leak if no bolts have backed out?

[datzenmike]

Last L4 head gasket I did I took the head off with the manifolds attached. Did this by myself but with help it would be a snap. This eliminates breaking or stripping an bolt and failing to get everything to seal back up again. 

 

I would run just water till you sort out the head gasket. Once sure the HG is ok then drain and fill with distilled water and a quality antifreeze.

 

The thermostat is the highest point on the engine and any air will migrate there. Once the thermostat opens any bubbles will pass into the top radiator tank and it will seem like the level drops.... just top it up and you're good.