Carburetor problems, possibly electrical. Help.

[mas84_720]

OK so heres the deal. I bought an 84 720 with rebuild motor and many new parts. Was told it wouldnt idle because it needed a carb rebuild. After much work I found out that it was a newer electric feedback carb put on a non feedback truck and wouldnt work. So I bought a Weber.

 

Thats where im at now. I put in the new Weber (from webercarbsdirect.com) and followed everything correctly, and it started right up. Still idled a little fast and seemed a bit rich still but not as bad as before. With some troubleshooting I got the idle dialed down with the throttle cable and timing adjustment but.... I found that the wire from the original fuel cutoff solenoid wire to the carb's electric choke/fuel cutoff had no power.

 

This confused me... shouldnt it die and not run with no power. It even states to test the fuel cutoff solenoid to remove the wire with the engine running and it should die.

 

So I traced the wiring back and got a portion of the wire that had power and spliced it there so now it has power and no change at all. I can put on and remove the wire repeatedly and its like it doesnt even care. No change in operation. No clicking. Nothing.

 

This morning it stumbled really bad with a cold start... kinda like the choke isnt working right... but once its warm it runs smooth. Still seems to lack power on the higher rpm range though.

 

I am going to pick up a timing light and get that dialed in exactly but any ideas on what to look for or what to try would be appreciated.

 

Oh and the truck does have a tach but is not operating so hopefully i can get that fixed this weekend also to make sure the idle is 100% correct.

[Telkwa]

I found that the wire from the original fuel cutoff solenoid wire to the carb's electric choke/fuel cutoff had no power.

 

Do you mean the wire that originally supplied power to the idle cut is now going to the choke?  That's just not right. 

[datzenmike]

Thats where im at now. I put in the new Weber (from webercarbsdirect.com) and followed everything correctly, and it started right up. Still idled a little fast and seemed a bit rich still but not as bad as before. With some troubleshooting I got the idle dialed down with the throttle cable and timing adjustment but.... I found that the wire from the original fuel cutoff solenoid wire to the carb's electric choke/fuel cutoff had no power.

Making a timing adjustment to adjust the idle speed is wrong. Set the timing on a warm motor to 3 degrees BTDC. Before making any carb adjustments check the valve lash. A tight valve will ruin manifold vacuum and make dialing in a carb a waste of time. Do this on a hot motor and set all valves to 0.012"

 

This confused me... shouldnt it die and not run with no power. It even states to test the fuel cutoff solenoid to remove the wire with the engine running and it should die.

The idle should cut but you've adjusted the carb without it to get it running.

 

So I traced the wiring back and got a portion of the wire that had power and spliced it there so now it has power and no change at all. I can put on and remove the wire repeatedly and its like it doesnt even care. No change in operation. No clicking. Nothing.

12 volts on the idle cut and you should hear a click when the key is turned on. You won't hear it with the motor running. Try a jumper wire from the battery direct to the idle cut.

 

This morning it stumbled really bad with a cold start... kinda like the choke isnt working right... but once its warm it runs smooth. Still seems to lack power on the higher rpm range though.

Is the choke heater connected? If you have power to the idle cut solenoid you can us it to power the choke too.

[mas84_720]

Do you mean the wire that originally supplied power to the idle cut is now going to the choke?  That's just not right. 

 

 

Yes, the directions that came with the carb say "Connect the male push on connector to the wire connected to the original idle cut off solenoid."

 

If this is wrong what should it be connected to?

 

Making a timing adjustment to adjust the idle speed is wrong. Set the timing on a warm motor to 3 degrees BTDC. Before making any carb adjustments check the valve lash. A tight valve will ruin manifold vacuum and make dialing in a carb a waste of time. Do this on a hot motor and set all valves to 0.012"

 

I didnt just make a timing adjustment to change idle... everything was screwed up from previous owner trying to make other carb work. He messed with every screw and adjustment on the carb trying to make it idle with the old carb that wasnt even plugged in.

 

 

 

The idle should cut but you've adjusted the carb without it to get it running.

 

I actually adjusted nothing on the carb as far as mixture screw or primary idle screw. The only thing I adjusted was the throttle linkage, backed out the idle speed screw a bit(the one that the throttle linkage rests on),  and then moved the timing a bit to where it sounded right.

 

 

12 volts on the idle cut and you should hear a click when the key is turned on. You won't hear it with the motor running. Try a jumper wire from the battery direct to the idle cut.

 

There is no click or anything with power applied, tested with voltmeter.

 

EDIT: I think i have a Weber without an idle cut-off solenoid. I found another picture of another Weber that had it labeled and i definitely dont have anything where it is labeled on that one.

 

 

Is the choke heater connected? If you have power to the idle cut solenoid you can us it to power the choke too.

 

There is only one connection on the carb for a wire. The instructions provided by Weber say that the connection is for both the idle cut-off unit and the electric choke element.

 

EDIT: Because of the previous edit im suspecting the choke possibly needs to be adjusted. Found some instructions on how to do that (says they come factory set but in some cases may need to be readjusted). Im going to be checking the valves like you suggested( hopefully not the case, completely rebuilt motor with brand new head, hopefully it was done right) and getting timing dialed in this weekend. Will also work on the tach so i can be accurate on the idle rpm.

[datzenmike]

Got ya. Set the choke on a cold motor. Should click closed when gas pedal stepped on. But just enough to close. You can loosen and adjust it. Once you get it working right you can add more if needed.

[mas84_720]

Thought i would share some pictures of the truck. 84 Datsun/Nissan 720 King Cab 4X4. Body lift with 31x10.5x15 tires.

 

This is when i bought it.

 

These 2 are after getting in some mud yesterday. (4 wheel drive works great)

[mas84_720]

Found the problem. The fuel pressure was only 1.5psi with the return line, removed return line and its a steady 3.5psi. Wasnt something I would have guessed cause the other carb ran so rich.

 

Now its running strong and I got good power, gonna run a little seafoam through it tomorrow to clean out all the crap from it running rich/lean so much, fresh set of spark plugs, and fine tune timing and carb settings again.

[Telkwa]

Do you think the fuel pump is tired out?  Or maybe the internal filter (I believe there's one near or inside the pump) is plugged up? 

 

Are you planning on running without the return line indefinitely, or just until you figure out the reason for low psi? 

[datzenmike]

The return line should have a restriction in it so pressure will build.

 

This is the L20B return and has a small hole restriction.

 

Have you moved or modified the return? There carb isn't stock when you got it so maybe the PO changed something?

[mas84_720]

I didnt see any kind of restriction on the return line. The fuel filter is brand new and the pump looked fairly new when i got it. I was just going to run without the return line, I ran an entirely new feed line to the carb with no return. Will it hurt it without a return line?

[mas84_720]

Got the timing set to 3 deg btdc, took it for a drive, and BOOM my muffler exploded wide open. Rebuilding the exhaust now, and changing out the spark plugs to new ones. Found the fuel tank vent wasnt venting either (could these be related?) so im also reworking that. Gonna get a new check valve and run a whole new line, does this need the canister or can i just vent it open, the canister looks very bad.

 

Also cant get the tach to work, checked for power to the wires and checked the resister with a meter, all good so must be bad gauge?

 

This truck is gonna be half new by the time i get it running good again.

[Telkwa]

Fuel pumps are positive displacement pumps, aren't they?  I'm pretty sure that any positive displacement type of pump should have a relief built into it.  Deadheading a positive displacement pump is generally not a good idea.

 

 

[datzenmike]

The pump has a built in regulator. The return line orifice isn't for setting this. The hole is the same size for different pump speeds so the pressure would change too.

[mas84_720]

Just found today that the 2 coils were mislabeled by previous owned so i have intake coil plugged into exhaust slot and exhaust coil plugged into intake slot. I think i remember reading somewhere that the two coils are not exactly at the same time, intake fires first. If this is true then that could have caused the off timing, and the loss of power, right?

 

 

Also i think i remember seeing that the intake 1 wire should be at about 9:00 position... mine is labeled on the cap and its at like 7:00. does this seem wrong?

[datzenmike]

That's a myth. Coils are fired together at the same time.  So it will run the same if the coils are swapped. (just swap the wires on top of the distributor cap)

 

Normally power from the battery goes to the ignition, from there it splits with power going directly to the intake coil and at the same time to the fuse box where it goes through the first fuse on the left hand side and from there to the exhaust side coil. 

 

What can happens is the fuse blows and the truck runs very badly on one intake side plugs. .

[mas84_720]

could it be the dizzy is swapped 180? or would it not run at all then?

 

i am just exhausted lol. i have checked and/or replaced everything i can think of so far.

[datzenmike]

Won't run 180 out.

 

 

Things to check:::

 

Valve lash is 0.012" for all.

Timing 3 degrees BTDC

Check that there is spark on intake and exhaust side plugs when running.

 

Confirm wiring is correct.

 

 

If you check the above then we can forget about this being an ignition problem.

 

 

 

.

[Telkwa]

That's a myth. Coils are fired together at the same time.  So it will run the same if the coils are swapped. (just swap the wires on top of the distributor cap)

 

Normally power from the battery goes to the ignition, from there it splits with power going directly to the intake coil and at the same time to the fuse box where it goes through the first fuse on the left hand side and from there to the exhaust side coil. 

 

Thanks for clearing that up.  I was a little worried that I might get the coils backwards before I bolt my truck back together, and wondering about the repercussions.  I still have one question re: NAPZ coils.  There are two wires (+ and -) attached to each coil.  The pair of wires to one coil is noticeably heavier gauge than the other.  Any idea why that is? 

[datzenmike]

I've seen that. Maybe to tell the intake from the exhaust? Brown is intake and Black/White stripe is exhaust.

[mas84_720]

Ok just checked all the valve lash, a couple of them were a little tight, got them all at .012-.013. Now there is a loud ticking when running.

 

Gonna open it back up and recheck the valve lash tomorrow. Also is the filter inside the fuel pump changable without getting a new pump? I already changed the external filter between the tank and pump. And im looking at getting a fuel pressure regulator and running a new return line from that.

[datzenmike]

Sorry should have said set them hot. But better a little loose that too tight. You can set them whenever. First thing is get running well.

 

The filter is replaceable. Try Nissan $5 for 16404-28530 maybe cross reference it. There is also a magnet in the bottom lid don't loose it.

[mas84_720]

Ok Im making some progress. I have new plugs, new wires, double checked timing, and set valve lash. I have double, triple, and quadruple checked for vacuum leaks everywhere, and none. I have a guage on the fuel line and getting a steady 3.5 psi. I took it for a test drive and its running stronger than ever, still seems a bit rich and getting small backfires if I mash the gas pedal too fast. I did successfully hit 70mph on the speedo (its about 10% off cause of bigger tires) so about 77mph on a very slight downhill. Is this a reasonable top speed to expect on a 4x4 with 5 speed and 31" tires?