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My 1971 521


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The end of the fuel pick up has no filter, or anything on it.  Just the end of the pipe, close to the bottom of the tank.  There is a drain plug on the gas tank of a 521.  Get the tank real close to empty, have something that can catch the gas, pull the plug, and see what comes out.   If you get a lot of crud out of the tank, let the gas you pulled out settle, and put the plug back in, put that gas back in the tank, and repeat the process.


Compression should be higher on a L-16.  Should be at least 159. at 350 RPM, and less than 10% difference. 


Ill drain it tomorrow and see what comes out.  I never had to "get the truck running" as it was running when I bought it and ran fine for the most part since then.  As far as compression goes thats what I was told it was by the PO.  I plan on having the engine looked over soon by a local Datsun mechanic will make sure they do a compression test. 

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It doesn't sound like a fuel issue, rust in the tank usually has a certain symptom, it starts missing and then dies, when the fuel pump quits pumping the fuel back flows in the pickup tube in the tank and clears it, then when you turn it over the bowl fills up and it starts again and runs till the pickup tube clogs again, when there is a lot of rust in the tank it eventually just will not run anymore till you blow the fuel line out with compressed air from the front, this is a cycle that repeats itself over and over till you get sick of it and finally drop the tank and fix it.

The same thing can also happen with a fuel filter, it can get clogged and kill the engine, but when the engine dies, the fuel can reverse flow and knock the dirt off the filter element and it will then run for a little while before starving the engine again, I have been known to tap on the filter when it is not running to knock off a bunch of dirt to get it home in the past, now I just carry extra filters in all my vehicles, especially the diesels, the pre-filters get plugged up easy with diesel fuel, and sometimes the pre-filter element gets sucked flat because of the fuel pump on the injector pump is so strong on the 720 diesel injection pump, I have even heard of it getting sucked into the fuel line itself from other diesel owners, but that has never happened to me.

Sometimes they just need a tune-up, sometimes the ignition switch start screwing up, sometimes the starter don't like to work when they get hot, and sometimes you have to wiggle the wires down on the starter because they get loose or greasy, normally if it will not turn over for me I turn the ign. on, put it in neutral, take a big screwdriver I always have with me and I jump the two big posts on the starter till it starts, if that don't work I push start it and start looking for a replacement starter, but I have seem to have had a lot of issues with starters on my work truck until recently, I found a good aftermarket one and have not had an issue since.

The 521 has two wires that supply power to the coil, a black wire with a white line is the keyed power for the coil thru the ballast resistor when the engine is running, and the second wire is black with a red line, this wire connects directly to the positive side of the coil or the positive side of the coil side of the ballast resistor that supplies the coil with a full 12 volts while the engine is being turned over when you are starting it, you need both wires.

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Wayno, if it is the starter than that would be 2 problems because the starter wouldn't cause the truck to backfire/lose power on the freeway.  


Fuel filter looks ok?? 




I got the Haynes and Clymer repair handbooks and have been reading them to learn as much as I can.  There are also two 'reputable' shops, banzai and datsunspirit, one of whcih I am going to have my truck looked over by.  Would love to meet some local enthusiasts in MD but they seem to be a rare breed here on the east coast.  






Anyone know any Datsun enthusiasts in Maryland?  

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I have had mine backfire and didn't give it much thought unless it kept backfiring, and if it did I would have looked at the carb first to see if the fuel level was correct, next I would have looked at the timing, then I would look at the cap/rotor, wires, plugs, points, but you said it only did it once.

I have also had mine start backfiring/missing in the past, once I set the valve lash I didn't have an issue anymore, these trucks were made when there was lead in the gas, since they took the lead out all we have had is unleaded gas, this has side affects, one of them is the valves sinking into the head because these engines have brass seats, now if your able to keep your foot out of the pedal it will likely be a long time before you start having issues, but if your foot is always pressing on that pedal hard like when your on the freeway and trying to keep up with everyone, the valves will start sinking into the head, check your valve lash.

I suspect you have an L16, am I correct?

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Wayno yes to L16, and it backfired/lost power twice on me on that drive across the bridge...died a handful of other times as well.   Never checked the lash, is that hard to do?  I have the service manuals which walk me through it but never done it before.  


For shits and giggles I replaced the fuel filter with a clear NAPA one and the fuel is clear as day.   Haven't had time to check the gas in the tank but I will soon.  There  was some debris in the old one but no idea how long it had been on there.    


If anyone cares its NAPA part: FIL 3053



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There sure are a lot of 521s on the east coast having issues right now.

I have never had my engine die because of valve lash issues, they just run bad and backfire out the carb or miss like crazy, but it still runs.

Watch that filter, the next time it dies before turning it over, pop the hood and look at the filter, if it has as much fuel as it does in your photo, it's not likely a fuel issue, it still could be one if rust flakes are blocking the fuel pick up tube, but not likely, as the fuel filter would be empty or at least below the filter element inside the filter.

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  1.  Fuel filter has debris in it so safe to say my tank needs to be cleaned.
  2.  Missing the bottom bolt on the alternator, anyone know what size that is? No idea if it was ever there or worked itself loose but my alt belt is loose and no way to tighten  the alt without the bottom bolt.  Stuck a ziptie through it for now.  
  3.  Radiator fluid started coming out the overflow hose, temp gauge stays right below center when driving.  Not sure if the cap or the radiator needs to be replaced?  Radiator hoses have been replaced but the radiator itself seems to be OEM.  
  4.  Missing gasket under the oil cap  (not sure what its called?) Gasket goes on the valve cover itself.  






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140 is fine on the compression ration. 99% its fine I bet. for a L16 I never got higher


oil cap is fine also I don't think mine has one either( O gaskets) is it leaky??????? if not don't worry.


why would the Radiator need to be replaced??????????  Its not over heating. Is is leaky???  I usually drill a 1/8 in hole in the thermostat if it not a by pass on the stat housing to the water heater line. U shape hose.


change the rad cap or get a flip lever type if you don't run a resivoir.


Your truck has minor issues that Datsun guys deal with everyday. This might not be a Rig for you.


Run the stock fuel filter and put another in line one right before the fuel pump. that should take care most of the dirt ,rust and change it out every 2 years at least. The 521 tank Fuel hose gets wet and water may run down the line inside and rust out the tank or dirt debris.  ( I have never cleaned my tank)


as for the back fireing?  Yuo got a old stock carb on there and maybe its on its last legs of life. So I would get ready to get a weber DGV 5A manual choke carb on order.


Now if you think the carb is clean, I would run some canned carb cleaner throw and and rev the shit out of it and put a rag on top of the carb to suck thru all the junk in there.  Now if you think carb good I would look at the distributor for slop and wiggle in the shaft and points wear.   Also make sure the coil is stock. Don't be a Moron and put the wrong shit in there and make it worse cause the new coil looks COOL. Condensor grounded good  and the wires inside.



mike Klots has a vedio on how to do the valve las. Bit if your truck is ildeing good I hardly think the valve lash is bad.

Bluehand vedios on youtube. look it up

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Haha thanks Hainz.  It is the truck for me and all of this is new to me so I am doing my best to try and learn.  


The reason I am bringing all this up is because I took it to this old 'Datsun mechanic' and he had me all worried about this shit.  Oil cap was leaking but I think that was because it was loose.  Radiator isn't leaking as far as I can tell, just started coming out the overflow hose today.    Like I said only backfired twice and its been running well since then.  Just dog slow but I guess that is expected.  


Inline fuel filter in between the stock one and the fuel pump? Something like this?



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L-16 alternator bolts are M8-1.25.  Same diameter bolts holds bottom alternator bracket to the block, and the alternator pivot to the bracket.  The front bottom bolt screws into a nut welded to the bracket, the rear alternator bracket bolt uses a nut on the bolts.  Try to get metric grade 10.9 bolts.

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It's supposed to dump fluid out the overflow hose. It's doesn't appear that you have an actual overflow container, so it won't refill itself. It just means you need to periodically add coolant.

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When you fill the radiator to the top when it is cold, then start it, the coolant expands and has to go somewhere, so it goes out the over flow tube, that is normal, and then when you park your truck for the night the coolant cools and lowers in the top of the radiator making it look like it has a leak or something, but if you leave it alone and don't ad any coolant, it should stay at that level all the time, if you were to remove the cap when it is totally warmed up the coolant will be at the top of the hole.

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Yeah no overflow container.  Popped the radiator cap just a little while ago and it was at the top, it then burped and the level dropped immediately.  Went ahead and bought a new rad cap and going to attend to the alternator as well.   


Got a wicked vibration in the steering wheel between 45-55 so I think the wheels need to be balanced, doubt they would be bent with the tall sidewalls on them.  Probably will get them rebalanced tomorrow.  

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Got the wheels balanced today, guess the fronts were out of round so they balanced all 4 and moved the fronts to back, truck seems to be better, only slight vibration at speed now.  Blew the turn/reverse lights/combo fuse as well, tried putting a 20AMP in there instead of the 10A and then truck struggled to turn over.  Put a new 10A in and it started just fine.  Not sure why that one would blow but its been problematic before.  


Got the alternator tight, was able to get the back botled down but the bottom front I couldn't get the 8x1.25 bolt to thread through so I just left it empty for now.  


Also noticed a ton of fluid on the slave, the rubber on the flex fluid hose has split right at the bed and I can see the hose inside it.  Almost like its twisted too much, hard to get a picture of it but I will try later today.  Clutch/flywheel was replaced/resurfaced back in 2010 but no mention of replacing the slave.  


Finally went to pickup my door card but the shop forgot to put the clips on it, hopefully have it back today or tomorrow. 

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best to get the bolt in the alternator asap as L16s use the smaller bolts and they tend to break!!!!!!!!!!!!! also in the block and its a mofo to get them out also




remember order only 521 stuff as 521 seem to use SAE threads on certain stuff asamble I think the salve hose is a SAE thread. The motor is all metric.


Unless you got a noticable leak(slave) I wouldnt worry to much about it

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I was able to get that bolt started in but its too long, as it wont thread all the way in.  I will get a shorter one for that front bottom mount but then I should be OK, threw a ziptie on it for now.   Alternator is tight with just those two bolts..which is one more than its had since I bought it.  :(


Pictures of the slave..cant tell if its brake fluid or just oil leaking down from the engine.   But that flex hose rubber sheath is broken and exposing the hose inside it (bottom right corner of bottom pic).  





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Spray it off with some carb cleaner and wipe it with a rag.  check in a couple days.  It is probably oil leak at the valve cover.


I sprayed it yesterday and its wet again today.  Have a leak somewhere but unable to find it, the old "datsun mechanic" I talked to seemed to think it was the head gasket.  


Anyone know the size/length of the clutch hose? Will a clutch hose from a 510 fit?  

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OK I think your clutch hose is fine enough unless you have OCD.


what one needs to do is put the slave hose on 99% threaded if before one puts it on the trans to do the final tightning.


also make sure that slave is adjusted correctly where you have abut 1/16 play at the fork arm. YOu see that jam nut and hal ball threaded on there? you need to adjust that soemtimes so you dont wear out your T/O bearing

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