L18 backfiring under load

[Chyvv]

G'day all,

I've just spent 2 straight weeks setting up my car in preparation to drive it to my new place. I meticulously made sure EVERYTHING is set up as best I can, I have replaced points ignition with EI, checked valve lash, made sure the carby is set up correctly (my carby guy managed to swap the primary and secondary venturis somehow 🙄) and set the ignition at the factory 7deg BTDC (Aus market stock timing) with vacuum advance removed and plugged whilst setting it.

Despite this, the drive here was extremely sketchy and unpleasant, I spent ages setting up the carby so that it wouldn't backfire whilst free-revving (it was backfiring at full throttle), and yet at low rpm under load, it bucks and spits and backfires out the intake. The only way to avoid this somewhat is to wind the motor all the way up to accelerate, and even then it seems to be making no power.

Brand new EI distributor, freshly rebuilt Nikki carby, fresh fuel, painstakingly have eliminated every potential vacuum leak, just set valve lash, as they were done up slightly too tight (they now seem to be slightly loose, but this may just be because I did the adjustment while the engine was cold) everything set exactly as it should be and I'm still having issues! 
The only possibilities I can think of:

-The distributor has a point on it for a ground wire, however it is bolted to the engine and has both positive and negative wires connected to the module. Could it need a ground off the distributor still? Would the lack of a ground even cause issues like this? I'm running a brand new, but still points-style coil, with ballast resistor still installed in the circuit, however what I've read on this forum would suggest that installing a proper EI coil is simply preferred, and that not doing so shouldn't cause issues like this.

-The anti-dieseling solenoid is receiving a weak signal and cutting fuel as a result? Or could it be a combination of this and the former, as the signal for the solenoid comes from the coil? I can hear the solenoid click when the key is turned to 'on', and the car will run and idle.

 

I'm really baffled, I have put so much work into setting this up right and have gotten nowhere.

(worse still, one of the brakes makes continual noise whilst moving and the speedometer has stopped working too!)

[datzenmike]

Point coil and ballast will work just fine. Getting the proper EI matching coil and removing the ballast will provide a much hotter spark.

Ground through the mounting bolts is fine but who knows? Easy enough to make a ground wire and try it.

Idle cut solenoid only affects the idle circuit and won't affect driving under load.

 

 

 

I would inspect the ignition wires, cap and rotor. There is no replacement time or mileage on them...  if they look sketchy then time to replace them. Voltage can jump from one wire to another. Rotor and cap can develop a carbon track which is where the spark has found a path to ground or another wire. Once burned it's easier to use the next time. Under load it takes more voltage to jump the spark plug gap and high voltage ALWAYS look for a short cut. Make the spark plug the easiest path by having good wires and cap. Don't forget the coil! Inspect the insulator around the center lead. 

 

 

That small crack was the cause of high voltage arcing to the ground post in front of it. It was hidden under the rubber nipple and only did it turning corners in town and then stepping on the gas. Random.

 

Plugs should only be NGK BPR6ES maybe BR6ES?, Better check. NGK only, and inspect the white porcelain insulator for cracks and carbon tracking.

 

 

Two other things...

Lean backfire. Wrong secondary jet (too small) or blockage producing a weak mixture will often backfire through the carburetor. Also severe lack of power.

 

Bad intake valve sealing. Valve may not be making good seal at the seat. One or both may be damaged. Valve cannot contain the pressure generated when the cylinder fires. A leak down test on all cylinders may show a hissing sound at the carburetor when the cylinder is pressure tested.

[banzai510(hainz)]

if car runs and idles its fine on the selionoid switch on the carb.  most later Datsun after 1972 in the states had a 123volt wire for this (USA)  dont know in aussie. if it was on the car  but I would use that one instead oof using the + side coil.

 

it should run with the point coil and the ballast but I believe you want the + side of the ballast to power the module. Meaning not go thru the ballast reisitor.  Only the coil needs tha ballast otherwise will get hot and cook it.

Also is the distributor close to the center of its movment.?  if you had to crank the distributor all to one side to get the 7 deg then maybe the dist spindal is off.

 

Carbs usually work fine as they just work on vacuum and only really need to watch the accel pump when you push the gas does gas squirt in the carb. If not then that will be a issue of bogging out back firing also.  also if out of time.

Put motor to TDC. and look where the rotor points too and hope its pretty much on the #1 plug wire. and you have adjustment on the distributor.  One should go ez between 0 and +25 Btdc  with a timing light

 

[Chyvv]

44 minutes ago, datzenmike said:

Point coil and ballast will work just fine. Getting the proper EI matching coil and removing the ballast will provide a much hotter spark.

Ground through the mounting bolts is fine but who knows? Easy enough to make a ground wire and try it.

Idle cut solenoid only affects the idle circuit and won't affect driving under load.

 

 

 

I would inspect the ignition wires, cap and rotor. There is no replacement time or mileage on them...  if they look sketchy then time to replace them. Voltage can jump from one wire to another. Rotor and cap can develop a carbon track which is where the spark has found a path to ground or another wire. Once burned it's easier to use the next time. Under load it takes more voltage to jump the spark plug gap and high voltage ALWAYS look for a short cut. Make the spark plug the easiest path by having good wires and cap. Don't forget the coil! Inspect the insulator around the center lead. 

 

 

That small crack was the cause of high voltage arcing to the ground post in front of it. It was hidden under the rubber nipple and only did it turning corners in town and then stepping on the gas. Random.

 

Plugs should only be NGK BPR6ES maybe BR6ES?, Better check. NGK only, and inspect the white porcelain insulator for cracks and carbon tracking.

 

 

Two other things...

Lean backfire. Wrong secondary jet (too small) or blockage producing a weak mixture will often backfire through the carburetor. Also severe lack of power.

 

Bad intake valve sealing. Valve may not be making good seal at the seat. One or both may be damaged. Valve cannot contain the pressure generated when the cylinder fires. A leak down test on all cylinders may show a hissing sound at the carburetor when the cylinder is pressure tested.

Plugs are new NGK, and either of the ones you mentioned, can't recall. I bought them new, put them on the motor over a year ago and haven't touched them much since. NGK plugs are gapped from factory so that is not my first thought as a source for the fault. The leads are about 2 years, old NGK leads (replaced within months of me buying the car in mid-2019). The cap is brand new with the distributor. Again, the coil is new and undamaged.

The secondary jet was placed where the primary should be by the guy who rebuilt the carb, the two have been swapped now to be in the correct positions.

The head on the motor is fairly recently reconditioned, within 3 years and only run for about 30km worth excluding what I've done with it, which until now has all been idle. I doubt the seats are burned out at all.

 

[Chyvv]

5 minutes ago, banzai510(hainz) said:

if car runs and idles its fine on the selionoid switch on the carb.  most later Datsun after 1972 in the states had a 123volt wire for this (USA)  dont know in aussie. if it was on the car  but I would use that one instead oof using the + side coil.

 

it should run with the point coil and the ballast but I believe you want the + side of the ballast to power the module. Meaning not go thru the ballast reisitor.  Only the coil needs tha ballast otherwise will get hot and cook it.

Also is the distributor close to the center of its movment.?  if you had to crank the distributor all to one side to get the 7 deg then maybe the dist spindal is off.

 

Carbs usually work fine as they just work on vacuum and only really need to watch the accel pump when you push the gas does gas squirt in the carb. If not then that will be a issue of bogging out back firing also.  also if out of time.

Put motor to TDC. and look where the rotor points too and hope its pretty much on the #1 plug wire. and you have adjustment on the distributor.  One should go ez between 0 and +25 Btdc  with a timing light

 

I can switch the + side of the dizzy to run off the + side of the resistor just fine, but would that produce symptoms like this?

The base plate of the distributor took some modification to set in the correct position, so the spindle *may* be off, but that shouldn't affect anything as long as I have the timing still set up correctly, right? I have some amount of adjustability either way, and it is set at factory setting, so this surely wouldn't be the issue. 

The accelerator pump works fine. sprays fuel when it's pumped, and not in any odd pattern or anything. Looks to be working well.

I spent over a week painstakingly doing what you described in that last sentence, the only irregularity I want to point out in setting the timing is that I have to hold the pickup for the timing light in very specific positions against the #1 plug wire to make it work, though I had put that down to me potentially having damaged the timing light

 

[banzai510(hainz)]

52 minutes ago, Chyvv said:

I have some amount of adjustability either way, and it is set at factory setting, so this surely wouldn't be the issue. 

it should be able to go from Zero to +25 on the Timing light. using  the distributor timing slot. 

My experinece is when people put dist in and its clocked to one side to keep it running it will not adv enough when it speeds up and goes out of time. this is all what I can think of right now. Meaning the mount is wrong(doesnt match the dist) or the spindal is off a tooth

 

I think in aussie you guys used local made Bosch

 

 

only other thing I can think off is tha cam timing is off , but highly unlikely

Edited August 31, 2021 by banzai510(hainz)

[Chyvv]

21 hours ago, banzai510(hainz) said:

it should be able to go from Zero to +25 on the Timing light. using  the distributor timing slot. 

My experinece is when people put dist in and its clocked to one side to keep it running it will not adv enough when it speeds up and goes out of time. this is all what I can think of right now. Meaning the mount is wrong(doesnt match the dist) or the spindal is off a tooth

 

I think in aussie you guys used local made Bosch

 

 

only other thing I can think off is tha cam timing is off , but highly unlikely

 

Again, the timing slot has been modified but it has adjustment in both directions. As long as I can get it in the correct position to set the timing, it shouldn't affect anything whether the spindle is out a tooth or not. I have been setting the timing with a timing light, and not simply by sound or using the marks on the plate. The important thing is: the rotor button is passing under the contacts for the right plugs at the right times and distributing spark. The strength of that spark is the only thing left that I could question, though with a new coil, I don't see how it could produce symptoms this severe? The standard dual-points dizzy is Bosch yes but I'm using a repro aftermarket EI dizzy because the standard one is burned out and would require a bit of work to fit EI stuff to. Many people run these distributors around here without issue.

 

I doubt the cam timing is off. This engine was reconditioned to some extent, fitted to a rally car for 1 event, then removed and given to me. I don't see it being a mechanical issue with the engine, though obviously the valve timing needs some minor adjustment as I haven't adjusted the valves hot yet. But again, this is more than a little stumbling or hesitation, this is severe kickback and backfiring through the carburettor under load, no matter what I do to the carby.

It's got me stumped and really frustrated, over a year's work just to get this thing running and it still wants to kick me in the balls.

 

[datzenmike]

I know you say you put new plugs wires etc. on, but this is only a partial guarantee that they are good. Sometimes things slip by or there's unknown damage to them. Take some time and carefully inspect ALL the ignition components looking for a possible place for the spark to escape. Run a ground to the ground lug on the distributor body.

 

 

 

 

As long as you can set the proper timing that's all that matters as far as distributor position.

 

Did you connect the EI module to the +12 supply and not through the ballast yet? The ballast voltage would be dropped to 8-10v and that wouldn't be good.

 

On your L18 is there a timing scale bolted to the timing cover or is it a pointer? If a pointer then the pulley will have 4 or 5 little notches in it. As the pulley turns clockwise the last notch to pass by the pointer would be TDC not the first.

 

Cam timing is easily checked. With valve cover off set to TDC compression on #1 by turning clockwise, up to and stopping on the notch. (no backing up, has to be clockwise to gather all the slack on the tensioner side)The back side of the cam sprocket has a V groove in it. Just above it on the cam thrust plate is a small horizontal etch mark. The V should be directly below or just slightly to the right of it. The original sprocket should have a hole in it where you can see this from the front. L16/18s are set on the #1 sprocket position from the factory. Normal wear or milling the head will move the V to the left. If it is to the left this can be corrected by moving the sprocket to the #2 position. If by chance you are on the #2 then you would move to the #3 position. The cam below is perfectly timed. Here's what you should see.

 

 

If it runs it can't be out too much.

 

 

.

[banzai510(hainz)]

does the timing go between 0 ant to +25 BTDC when you adjust the dist retard and advance???????  If not then thats the proplem.

 

 

I put the orginal dist back in and see what happens.

 

 

ck the cam timing at TDC.

 

 

UNless your not charging correcotly I think its a dist proplem, Unless the motor was pulled out for another reason