1970 521 With L20B running horrible

[kcobb454]

Ok after nearly 45 years of playing with Datsun L series, I am stumped! I have a 70 521 with an L20 with 5speed that was running absolutely amazing until the other day when it started all of the sudden running horrible as if it had water in the gas or a stuck float..ended up having to trailer it home. I did all of the normal troubleshooting including, draining the fuel tank (no water at all and no rust) impressed with that. I changed the fuel filter pulled the carb and drained the fuel (Weber 38 DGASW) less than 300 miles on carb. Float is not stuck. Change points, condenser, rotor, dist cap, plug wires, plugs and Coil and nothing has changed, still running terrible if I can even get it to start. I even did a compression test and have 170 in 1,2 and 3 and 167 in #4. I have blue spark in the points and coil wire. This is the first time in all of my years that I have been stumped!
one time during the long process of trying to figure it out, I was able to get it to start and it was sitting there chugging like it was running on two cylinders and all the sudden it changed and went back to smooth and I was able to wick the throttle two times and then it went right back to running horrible then died. Now back to the same crap 😩

what am I missing???

 

[datzenmike]

Does it have an EGR valve? Remove and clean it with a wire brush.

[kcobb454]

No smog stuff aftermarket intake

[datzenmike]

Good. Check for a vacuum leak under the Weber. Adapters are known to crack or leak.

 

 

Can you see the distributor part number stamped into the side of the body? 22100-?????

[kcobb454]

There is no adapter for the carb. It’s an Offenhauser intake manifold. 
The distributor is the original as far as I know. I will see if I can find the number on it later today when I get a chance to work on it. 

[banzai510(hainz)]

This simple fix

Sure the condensor is working or grounded.

Dist shaft isnt loose wobbles.

 

choke flap not stuck closed

 

when you ordered a coil hopefull it was for a 521 and use the ballast ressistor

you ck for spark?

 

Edited July 17, 2024 by banzai510(hainz)

[Stoffregen Motorsports]

There's going to be something obvious. A loose wire or a jet that fell out, torn accel pump, etc.

[banzai510(hainz)]

55 minutes ago, Stoffregen Motorsports said:

accel pump, etc.

Usually lots of gas coming out from there when that happens

[kcobb454]

Yes I ordered the coil that came stock on the 521

the points and condenser are new. I have gone over all the wire connections they are all fresh terminals with dialectic grease and shrink tube. I like things done right😉

I was looking at a wiring diagram and it appears that one of the coil wires goes to a relay. Any insight on that, could it be failing and cause a problem?

[datzenmike]

Relay???

 Is it white porcelain? with wires at each end? that would be the ballast resistor. If not that post a picture of it.

 

 Go over all the connections you made and check they are tight. This includes the wires into the points. A loose wire may run but the shaking of the engine makes an intermittent connection. While running, wiggle every wire at connectors and look for a change in idle. Wiggle the key in the ignition switch. Is the distributor firmly bolted to the timing cover?

[kcobb454]

Yes I ordered the coil that came stock on the 521

the points and condenser are new. I have gone over all the wire connections they are all fresh terminals with dialectic grease and shrink tube. I like things done right😉

I was looking at a wiring diagram and it appears that one of the coil wires goes to a relay. Any insight on that, could it be failing and cause a problem?

[datzenmike]

You already said this. Is the 'relay' white porcelain with wire at each end? Maybe a picture?

[kcobb454]

 

I can’t seem to figure out how to post a picture or video on here lol

 

I do know what a ballast resistor is☺️

 

as far as a coil wire going to a relay, I said that a wiring diagram that I was looking at shows that one of the wires goes to a relay it shows it is a 4 wire relay.

Like I said earlier it ran flawlessly and then all the sudden it started running terrible! It’s not missing any parts or any thing weird like that.

I have done every troubleshooting thing I can think of with no avail. I was just hopeful someone might know of some uncommon thing that may be different than all of the common sense trouble shooting exercises.

even though it has blue spark, it seems very weak.. does anyone know how many volts should be coming from the ballast to the coil? I feel like something is interfering with the spark at the end of the coil wire. 

[kcobb454]

I have to almost ground the coil wire to get it to ark..seems to me it should be snapping and jumping to the ground I’m holding it up to, I almost have to touch it to the ground to get the spark. The points spark very well. 

[kcobb454]

The ignition voltage to the ballast is 11.34v   The voltage coming out the other end of the ballast to the coil is 6.87v

[kcobb454]

12.14v to the distributor/points

[datzenmike]

During start battery voltage is sent to the coil around the ballast si it should be close to 12.6 or what ever the battery reads.

Key in the on or run position battery is run through the ballast resistor which drops it to 8v???

 

The points should not have 12.4 volts to them only what ever is fed through the coil.

 

34 minutes ago, kcobb454 said:

The ignition voltage to the ballast is 11.34v   The voltage coming out the other end of the ballast to the coil is 6.87v

 

Should be battery voltage from the ignition switch, maybe just slightly less for wire losses.

Output from the ballast resistor about half the input.

 

34 minutes ago, kcobb454 said:

12.14v to the distributor/points

 

Can't be. As only 11.34 was into the ballast and 6.87 to the coil. The other end of the coil goes to the points. Can't be more than that.

 

41 minutes ago, kcobb454 said:

I have to almost ground the coil wire to get it to ark..seems to me it should be snapping and jumping to the ground I’m holding it up to, I almost have to touch it to the ground to get the spark. The points spark very well. 

 

You should get at least a 1/2" - 3/4" spark from the coil.

 

What's the voltage on the coil positive terminal?

What's the voltage on the negative coil terminal?

[kcobb454]

I will follow up tomorrow, have to quit for the day. 
thank you for all the input so far, I appreciate it. 😉

[banzai510(hainz)]

Above appears to be correct what you said.

That relay thing is for a the dual points if you still have this.

Photos would help what you have.

 

what basic stuff I do is . just pour gas down the carb and try to start it. Or use the accell pump on the truck to fill it with gas vapor. If ignition is soemwhat right and timed it will fire off.  I pull the coil wire and place near ground and see if sparks

anothing basic thing I do is see if the rocker arm lash pads are under the rocker/valve in case on falls off or a tight valve but you said you got good compression numbers so kinda rule that out but ez to check out.

 

PersonallyI wish you didnt change to much on the truck most coils dont go out, and maybe introduced a proplem. But I still think this a ez fix.

 

One time I put new points in and truck didnt run. but the old back in and it ran. then put the new it it ran. Fuck if I knew what happen.

 

going to a pretronix(use you point coil and ballast set up or a matchbox ignition would be good also.

 

 

key here is besides changing the coil and wires out you dindnt remove the oil pump or pull the dist out so everthing is still timed per what you had.

Edited July 18, 2024 by banzai510(hainz)

[Stoffregen Motorsports]

2 hours ago, banzai510(hainz) said:

 

PersonallyI wish you didnt change to much on the truck most coils dont go out, and maybe introduced a proplem. But I still think this a ez fix.

 

One time I put new points in and truck didnt run. but the old back in and it ran. then put the new it it ran. Fuck if I knew what happen.

 

 

Right, it becomes harder to diagnose a problem the more parts you change.

[kcobb454]

I hear ya! I have the coil I took off. And believe me, this is normally an easy fix for me. I am not an inexperienced mechanic, I am just dealing with some weird ass gremlin! I have it narrowed down to very weak spake at the coil wire, fuel is not the issue at this point. Someone prior to me put the l20 in it and has done some butchery on the wiring and I am starting to think there may be an issue with some wiring. I have some time available today so going to get back at it and see what I can figure out. 

[kcobb454]

I did bye the way clean up the wiring a long time ago as you can see in the pics but not sure what all has been done further into the harness, it has had someone in it. 

[banzai510(hainz)]

Looks coorect to me.

the right side of the ballast is the feed 12volt wire goes left to the plus side coil. the other wire is the HOT START that bypasses the resisitor.   I think my wire is Wht /black that feeds the ballast if I remeber right, its a little fatter comes from fuse box

 

you said this was running for years so the wiring had to be good(assuming)

Edited July 22, 2024 by banzai510(hainz)

[kcobb454]

Agreed. It was running excellent and it just went from that to running rough to worse and had to trailer it home. My brain is starting to hurt from it lol

[kcobb454]

I admit I’m not great at wiring but this should be pretty simple and so far no proving to be simple.