Hi everyone!
1971, 4.2, twin 175CD2's, with 37,000 miles, was running great, then it "smoothly" quite running while driving down the road with no indication of any issues. No roughness, just died. I was able to get it started after a dozen tries, but had to keep the rpm's up, and brake-torque it to get home. The next day, it started and idled fine. Couple of days later, idled fine, smoothly shut off, and will not start.

Here is what has been replaced
new battery, plugs, plug wires, pertronix electronic ignition conversion, swapped out carbs years ago, new fuel pumps, one new tank, K&N air filter, fuel filters, etc...

One thing that happened prior to this was the smell of gas, one of the float bowl plugs was halfway out and leaking, which I replaced with new, and went ahead and replaced the other just because.

There is gas in both tanks, there is gas to the carbs, starter spins fine and fast, there is 12v at the coil, switching either pump makes no difference.

If you spray brake cleaner in the carbs it momentarily catches. Otherwise, nothing happens, it just spins.

I put the originally carbs back on. The only difference is the ones on it had the receptacles for the large emission "Y" pipe that goes between them, but I never had that and had both plugged, and it ran fine like that for 8 years.

It was running, and the beauty of this is it is either "gas" or "spark" lol!

I am at a loss, and need your assistance.
Thank you!

 

I don't see any check on the ignition coil. You may have a bad connection to that, or it's internally failing. I had something similar on an Ariel Square Four motorcycle in the late 60s. The coil was earthing itself. I wrapped the coil in insulating tape and then managed to get home OK. New coil fitted and then we were back in normal business !

 

Thanks Fraser!
I will check that out tonight, and I have a spare coil as well.

 

Put in a new coil, 12 volts at the coil, and nothing......

 

Sorry this didn't work. I think now you've just got to go back to basics, and check for spark at the spark plugs, correct timing, fuel getting to the plugs, cylinder compression values, etc.

 

You say that the engine responds to brake cleaner sprayed into the carbies. That indicates that the ignition system is working properly.
The problem appears to be in the fuel system BUT you appear to have overhauled that as well.
I am wondering about the possibility of water contamination in the fuel system. That will definitely stop the engine from starting
All of the XJ series are prone to water getting into the fuel system if the drain holes adjacent to the fuel filler caps are blocked.
I would have a serious look for water starting by pulling a couple of spark plugs to see if they are dry or wet,
Also drain the carbies into a glass bottle. Water will sit below the gas in a well-defined separation line

 

Again, thank you all for your assistance.
Okay, checked fuel, which has the fuel fresh stuff in it, and is 93 octance, and the plugs looked great and dry.
Went back to basics, pulled a plug wire, attached a spark plug to it, and grounded the electrode on the head of the engine.... no spark at the electrode.
So.... even though the rotor, cap, and pertronix ignition components are only a couple of years old with about 1,000 (yes that is correct lol), miles on them, I guess one of them could be bad.

 

If you remove a plug immediately after trying to start the engine, the plugs should look a bit damp if the fuelling is working and the engine is not firing.

 

Still not running…. Swapped out the electronic ignition for the original points/condenser and then brand new ones. Nothing.
Then, pulled the plugs…..Houston……


These were NGK platinums, putting Champion coppers in tomorrow.

 

Put in the new plugs, nothing….
But, tonight, I pulled a plug, put a spark plug in the end and set it on the engine, we have spark!!!!!!
So, the ignition passes!

Back to fuel. I have gas to the carbs.

 

It has to be some sort of fuel contamination, possibly diesel.?
Years ago, a neighbour's wife accidentally put some diesel into a gasoline car. It wouldn't start.
We ended up having to drain the whole system and put in fresh gasoline.

 

Tried all new fuel in both tanks, and added sta-bil pre and post fuel change. Still nothing.

I am going to try new carbs.

 

Does your engine have the fuel cutoff switch installed by any chance ?

70s engines have up to 4 oil sensors:
1 (Green) mounted on the oil filter housing for the oil pressure gauge
2 (Purple) mounted forward of the oil filter housing that illuminates the low oil pressure instrument panel light
3 (Blue) mounted to the rear of the oil filter housing drives the EGR vacuum equalization solenoid (but this should only be present for 73 on engines)
4 (Red) mounted to the rear of the oil filter and switch 3, cuts power to the fuel pumps until there is oil pressure

I did encounter this problem many years ago on a series 2 coupe and discovered the problem by accident, the red pressure switch was failing and the engine refused to start even though it appeared it had everything fundamental going for it. If I remember correctly I just pulled the connector of the pressure switch and it started right up.

EDIT, thinking about this a little more and casting my mind back 30 years (sketchy) - I believe the fuel cutoff pressure sensor wire needs to be disconnected and grounded to work.

This might be worth checking before replacing more parts.

 

Thanks for the great info and photo!
On ours, there is only the oil pressure sender, the temperature sender, and the oil pressure light. I could/did not find a pressure cutoff switch.

And, double checked last night... when cranking, there is spark for sure.
When the ignition is in the "on" position, fuel came out at the carbs with the fuel line disconnected.
*BUT....... before, starter fluid/brake cleaner would cause a momentary "start", now it does nothing.....

 

Okay, good.....that eliminates that possible problem.

Is your car equipped with an AED (Auxiliary Enrichment Device) ? If so then a faulty AED can create problems with cylinder flooding to the degree that the car won't start or run.

I suspect this because you say you have spark but engine starter fluid fired into the intake has no effect, a bad AED could have fouled the plugs again and they look like they have been running very rich. Another possibility is that a faulty AED has washed down the cylinders and you have low compression.

So....

Pull the plugs and recheck that they aren't fouled - verify that you still have spark.
A quick compression check would confirm that all is well there - if it's low a few drops of engine oil into the cylinder will help restore compression.
Clamp the AED fuel feed hose, effectively shutting off the choke.
Try starting with starter fluid injected into the intake.
If you have a start condition then 'theoretically' she should start up and you'll need to fix the AED or convert it to a manual choke (a much better option).
If you don't have a start condition then it's back to fuel feed and carburation.

 

Hi, and thanks!
No AED, plugs are clean and new, I will do a compression check.
I know it is going to be something silly……

 

You have fuel and spark but still cannot start.....
Have you double-checked your spark plug leads are in the correct order? You mentioned that they were replaced as part of the trouble-shooting, so there is a possibility that they could have ended up in the wrong positions. An easy thing to check and worth doing as it would give you these symptoms if incorrect. I'm sure you will know #1 cylinder is the one at the back of the engine nearest to the firewall. Firing order is: 1,5,3,6,2,4 and the distibutor rotates anti-clockwise.

 

Excellent advice, triple checked just to make sure.

New note, the plugs are bone dry after repeated cranking……

I am going to pull the float bowl plugs to see if there is gas “in” the carbs. This is a double check, but….

 

Okay, something to throw into the mix.... and I hope this not only helps us, but may be of benefit to the rest of the "leapers."

Originally, we were only running one tank, with a Facet fuel pump (Napa), zero issues. We had the other tank replaced, added the second new pump, Facet as well, all of the factory plumbing, etc... It was running fine on either tank. Both pumps still power and flow. It has worked this way for almost two years without issue.

But..... these fuel pumps do NOT have a check valve. If these symptoms occurred shortly after the additional fuel pump, I would definitely suspect it, but.....

 

I’m thinking that this isn’t the problem since from an earlier post you state that fuel is being delivered to the carbs – so fuel delivery seems to be okay.

I would suspect fuel preparation, but you also say that you have a no start condition using engine starting fluid sprayed into the intake – this would indicate no or weak spark. Is this still the case?

While on the spark subject, are you getting a bright blue or orange spark? If you’re getting an orange spark then you may hit the threshold of spark failure under compression from a marginal power source (e.g. bad primary coil to distributor high tension wire, bad rotor arm or cap).

Going back to fuel preparation, the only thing I can think of that may cause both carbs to fail simultaneously would be if both float chambers are full of junk and the floats are jammed closed. But until I could get a start condition with starter fluid (which I hate), I wouldn’t be ripping the carbs apart just yet.

How's your compression ?