720 powerless and lope on start

[datsun7204x4]

Bogging at highway speed question:  So the 720 resurrection is going fantastic IMHO.  Emergency brake is adjusted, chassis fluids have been changed, plugs, wires, cab, rotor, oil for the engine. Weber carb upgrade, 235/75/15 tires on centerline wheels, wheels came with the truck.  Delay wipers, wipers, signal and all other lighting is fully functional including the dashboard indicator for four-wheel-drive. I am super happy with a truck at the moment. That being said, here is my question: I set the timing to 3 degrees btdc, and I couldn’t hit 40, I set it to 5° btdc and I was able to comfortably hit 50. At this point, tuning by ear, I have set it to around 10° btdc, and it does fine up until about 50 in 4th…..and then if I try and go close to WOT, it sputters and backfires. and really just feels like it’s working way too hard. I’ve read threads about the spark issues, and I wonder if maybe the valve lash needs adjusting. It’s got low end for days.  Also I’m running straight pipe.   

[datzenmike]

The Z series engines run on dual plugs. Dual plugs require less ignition advance so if one side stops working it will act retarded and any advance will make it seem to run better.

 

Check that both the intake and exhaust side plugs are firing. Pull a plug wire off each side, stick an old plug in the end, lay on a grounded surface and turn engine over with the starter. Got spark on both sides???? Likely the exhaust side isn't working

 

 

 

Definitely check valve lash so we can ignore that. 0.012" hot setting.

 

Confirm ignition timing at 5 degrees BTDC.

 

Lack of top speed (if confirmed both side plugs are now working) is likely a fuel delivery problem, possibly dirt or sediment in the secondary jet. Best to pull carburetor off and clean both and the float chamber.  Change the fuel filter first as it may not be allowing enough fuel through. They are a cheap and easy fix 

 

[datsun7204x4]

Awesome information! Thank you!

[datsun7204x4]

Update to the bog problem. The previous owner mounted a new aftermarket fuel pump and I see that the filter bulb Is more than half full of air.Is more than half full of air.

[datzenmike]

Air in the filter really doesn't indicate much.

 

If you disconnect the outlet hose from the pump to the carburetor and add a longer one that can safely reach a suitable container you can run the pump and check the volume delivered. The stock pump should deliver 1.4 liters in a minute or less. I'm not sure how long the timer on the relay will allow the pump to run without starting. If only 30 seconds then half that amount.

 

Check for spark in intake and exhaust sides.

[datsun7204x4]

Thank you again for your reply!  The previous owner put a universal fuel pump on this that will not fit behind the brush guard on the frame. I am wanting to find the OEM equivalent to this pump. Does anybody have a line on or a link to a really good OEM equivalent to this pump? I am convinced that my high speed bogging has something to do with this. Regardless of whether or not it actually has anything to do with it, I really would like a pump that would fit behind the brush guard 

[720_Jeff]

As you say, you want an OEM or OEM equivalent pump and mount it in the proper place.  

I'd caution you and others will also.  Many have purchased inexpensive pumps and had them fail in a short time, say a year or so.  So, don't be tempted by the ebay $30 pumps that look really close to OEM, but likely inferior quality.

These are some options:

 

Charlie69 has sworn by these pumps for years.  Suspect he has one in each of his trucks, he has/had multiple.

https://www.pegasusautoracing.com/productdetails.asp?RecId=2698&utm_source=google&utm_medium=cpc&utm_campaign=FAC-477060&gclid=EAIaIQobChMIwv3f0rGW6wIVIRh9Ch1j4AIEEAQYASABEgKAfPD_BwE

 

The Nissan part number, which I believe applies to the 82, although could be wrong is:

17020-10W00 

Believe they are still available, as several vehicles used them.  They are around $125.  At that price, I'd probably go with OEM, rather than the Facet.  Charlie69 was a big fan of those, but I believe they were available a few years ago at a much better price, with a large price difference between the OEM and the Facet

 

 

[datzenmike]

17020-10W00 is confirmed for Z20 and Z24 carburetor 720s. 

[datzenmike]

 

On 5/12/2022 at 10:12 PM, datzenmike said:

The Z series engines run on dual plugs. Dual plugs require less ignition advance so if one side stops working it will act retarded and any advance will make it seem to run better.

 

Check that both the intake and exhaust side plugs are firing. Pull a plug wire off each side, stick an old plug in the end, lay on a grounded surface and turn engine over with the starter. Got spark on both sides???? Likely the exhaust side isn't working

 

 

 

Definitely check valve lash so we can ignore that. 0.012" hot setting.

 

Confirm ignition timing at 5 degrees BTDC.

 

Lack of top speed (if confirmed both side plugs are now working) is likely a fuel delivery problem, possibly dirt or sediment in the secondary jet. Best to pull carburetor off and clean both and the float chamber.  Change the fuel filter first as it may not be allowing enough fuel through. They are a cheap and easy fix 

 

 

10 hours ago, datsun7204x4 said:

Thank you again for your reply!  The previous owner put a universal fuel pump on this that will not fit behind the brush guard on the frame. I am wanting to find the OEM equivalent to this pump. Does anybody have a line on or a link to a really good OEM equivalent to this pump? I am convinced that my high speed bogging has something to do with this. Regardless of whether or not it actually has anything to do with it, I really would like a pump that would fit behind the brush guard 

 

 

You're getting sidetracked on the fuel pump. To lay to rest take for a drive up a steep hill. If it acts up in a lower gear then possibly the pump, clogged filter or float set to low and the engine is running out of gas because it can't deliver it fast enough. I don't think so because you earlier said that advancing the timing added 10 MPH to the top speed. Adding timing wouldn't affect fuel delivery. The truck runs so obviously getting some fuel so assume it's working fine for now and eliminate the other causes. Replace the pump, but it's not a priority right now.

[datsun7204x4]

Thank you for your reply! Yes I am currently at 12° btdc I drove it about 100 miles total and I am getting about 13 miles to the gallon.  At this point I am leaning toward potentially a bad distributor? This one for me is really a ghost. The truck is incredible. Floats down the road at 70, every thing works on the interior, dash lights, wipers, dome light, indicators for the four-wheel-drive, and so on…. No death wobbles. I really want to make this truck a daily. Thank you for all your help!

[datzenmike]

The timing for a Z22 is not 12 degrees. It's probably around 5. Maybe you are simply reading it wrong and everything is fine.

 

Check that you have spark on both intake and exhaust plugs. If one side is not working the engine will seem retarded and advancing will seem to help. The problem is it's supposed to have both plugs working and less advance. 

[datsun7204x4]

Both coils have spark at least both sides of the number one cylinder have spark. 

[datsun7204x4]

When I shine the timing light on the marks, and give it a bit of gas, it advances as if the vacuum advance on the distributor is working.  It feels like a fuel starvation issue. Seemingly idles fantastic, Does fantastic first through third years, fourth year bugs, fifth year is really bogging, and of course then there’s the 13 mile per gallon fuel consumption.

[datzenmike]

Now we are getting somewhere. Find out what the proper timing is and set it. 12 is way too much and it may run but it isn't good for it. 

 

Do you have this timing scale on the Z22? Zero is the top point. Each point is 5 degrees of advance. I think the Z22 should be around 5 degrees or the second point down.

 

 

To check timing the idle must be near 700 RPM. There is no vacuum advance at 700 but if you don't know the idle RPM pull the vacuum advance hose off the distributor before setting the timing.

 

Revving above idle will incur some vacuum and mechanical advance, this is normal.

 

 

 

With engine warm, check that the choke plate is vertical or fully open like this...

 

... and not partly close or closed like this...

 

If the choke is on you will get terrible mileage.

[Stinky]

Set your timing.

[Zac]

Hello folks, I have been searching the forums for an answer to a similar problem I have been having with my 86 720. It has all the symptoms described above and it turns out my exhaust side coil is not getting any voltage. So only my intake side plugs are firing. I have tested both coils and they are good. But I am not getting any incoming voltage to the coil for the exhaust side when running. I chased the wire (the red one) and can't find any breaks or damage. Does anyone know if it is possible that the ignition control unit can have one output line go bad and the other still be working? Or maybe I overlooked something else?

[datzenmike]

Change the first fuse on the left side of the fuse box. The side closest the driver's door. 10amp.

 

This is actually for the exhaust side coil but after so many years the leads to the distributor cap could easily have been switched by accident. The other coil (actually the intake) uses no fuse and is powered directly from the ignition switch.

[Zac]

I did check that and the fuse is good. I had hoped it was going to be that simple but no such luck.

[Zac]

22 minutes ago, datzenmike said:

Change the first fuse on the left side of the fuse box. The side closest the driver's door. 10amp.

 

This is actually for the exhaust side coil but after so many years the leads to the distributor cap could easily have been switched by accident. The other coil (actually the intake) uses no fuse and is powered directly from the ignition switch.

Oh, and a little more info, after checking the fuse, I tried just running a jumper from the - side of the coil to ground. But then I realized there was no power getting to the coil in the first place.

[datzenmike]

If it was wired properly then power to the intake coil and the module in the distributor comes directly from the ignition switch. If you have any spark then this is connected and working. The exhaust coil is as mentioned, from a fuse.

 

 

Did you replace the fuse or just look at it. If just looked at, swap it with another 10 amp fuse to be sure. If this gets it going then the fuse was bad even if it looked alright.

 

 

If all else fails jumper a wire from the connecting both coil + positive terminals together. This way the exhaust coil will be powered by the intake source.

 

 

[Zac]

22 minutes ago, datzenmike said:

If it was wired properly then power to the intake coil and the module in the distributor comes directly from the ignition switch. If you have any spark then this is connected and working. The exhaust coil is as mentioned, from a fuse.

 

 

Did you replace the fuse or just look at it. If just looked at, swap it with another 10 amp fuse to be sure. If this gets it going then the fuse was bad even if it looked alright.

 

 

If all else fails jumper a wire from the connecting both coil + positive terminals together. This way the exhaust coil will be powered by the intake source.

 

 

Thanks Mike, I appreciate the help. I did finally figure out the problem just a few mins ago. The module in the distributor had corrosion on the terminal for the exhaust coil. I pulled the connector off (it was kind of loose too), cleaned and tightened it, now the coil is firing. I will have to wait till tomorrow for a test drive but everything seems to be running smooth now. Not bad for an engine with 397k miles on it lol.