Backfiring

[UAB807F]

Hi Randy,

Well, look at it this way; you might not have fixed your car but you've got a heck of an interesting thread running on the forum !

Reading your comment about the coil having a crack & leaking oil, that does make me wonder if it's been overheating. It could be mechanical damage but we know the rating was lower than specified and the consequences mentioned are overheating in both the coil & ignition module, so if the lower spec has caused the coil damage I would be concerned about the integrity of the ignition module itself. You mentioned the makers had a website - do they have a user forum or email support where you could ask them what likely damage the lower rated coil would produce ?

But I have no idea how to check if a little magic box is working properly so I could only replace it with either a new unit or OEM contact breaker points & condenser. The only things that come to mind about the distributor now are the rotor arm itself and if some plastic from the cap has managed to jam open the bob weights underneath the mounting plate to give full advance. A very long shot but easy enough to check.

Going back to the webers it seems the last thing to check is if the pump jets are actually squirting and the only way I know of doing that is to pull off the carbs & manually open the throttle & watch for the fuel at all 4 inlets. I'm not convinced this is the problem because it it starts from cold without choke but by turning over & pumping the throttle, that tells me that they are squirting in extra petrol to enrich the mixture & start up. And with fuel problems the plugs are a good indicator, generally speaking if they are white/glazed then there's not enough fuel, black/wet and there's too much. Grey or light brown and it's about right.

It's always more rewarding to solve a problem by diagnosis & logic, but everyone has chipped in with sensible options and it's beaten us all so far. So in my book that means swopping out parts until it works and it's some consolation that at least 2 of the replaced components (cap/coil) have shown significant faults which would have let you down at some point.

Brian

(and don't worry about not having a "spares bin" - the way this is going pretty soon you'll have a better stock than any of us !)

[ardee_selby]

Randy,

I really hoped it would have started to behave by now! (Some might think it's because you call her "Christine" )

WRT to my earlier post about debris and "fit & forget" electronics...even if the bits of the electrode aren't doing anything nasty, distributors do need some occasional maintenance to keep the throw-out weight mechanism healthy.

Something tangible to check for...a simple mechanical device you can see/feel with no electrickery involved!

Good luck...

[Sea Ranch]

Just running out the door, but . . .

Would mechanical advance weights being jammed open mean the car would start and idle not too badly, but then have rough running right off idle? Seems that when I apply throttle is when the rough running happens.

But worth looking under that plate inside the dizzy to see what's there . . .

Thanks for your kind words and helpful thoughts!

[ardee_selby]

Just running out the door, but . . .

Would mechanical advance weights being jammed open mean the car would start and idle not too badly, but then have rough running right off idle? Seems that when I apply throttle is when the rough running happens.

I see it as the opposite...starting & idling is one thing but the advance mechanism "jammed shut"* would really make it's presence felt when trying to increase speed. (* jammed open/shut isn't quite how I would describe it...you'll see what I mean when you get into it...)

But worth looking under that plate inside the dizzy to see what's there . . .

Yes, worthwhile, to eliminate etc etc

Thanks for your kind words and helpful thoughts!

We're with you Randy....take heart, you'll get there, and having got there...there'll be no need to go back!

[Sea Ranch]

Okay, Richard. That's a good tip, then. Because it's as I try to take it off idle that I get the problems. It would also account for all that material that came off the inside of the cap: where did that center electrode and phenolic go? Could have been burned up in arcing, but all of it??

Limped the 5 or so miles to work today and remembered a couple more things:
-the tach is not registering real engine speed. Seems that when it runs rough, it stops increasing engine speed on the gauge, even though clearly the engine is running faster.
-the rough running seems to be one or more cylinders cutting out. Last I checked (yesterday), #2 cylinder especially was the one: very black with soot (unburned fuel, right?), which seems to me means that it's not firing properly, but I suppose it could also mean an over-rich mixture there.

Still leaning to ignition, and if/when I get the car to Chicken Hole's garage this aft, I'll be opening up that distributor

Thanks, folks,

Randy

[bill308]

Hi Randy.

There are still a lot of things to check and check again.

1. Connect a timing light to Number 1 cylinder and confirm ignition advance is smooth while accelerating and deaccelerating the engine. Compare the advance to the WSM for your distributor.

2. Put the timing light on each of the spark plug wires and confirm each plug is firing with no misses.

3. Confirm carb balance at idle and just off idle. Shorten the throttle linkage with the cable adjustment screw and back off the throttle stops. Create the condition where the only support is the throttle cable at say 1000 rpm. Measure and equalize the air flow either with a SK Unisynch or drill and tap the intake manifold to measure manifold vaccum with a manometer system as used for motorcycles (best). Nip up the throttle stops for an idle speed of 600-800 rpm idle. Check and balance again using the throttle stops. The first part of this balance process will ensure balance as you come off idle, up to about 2000 rpm. This is where balance is most important. The second part (throttle stops) will ensure balance at idle.

4. Adjust the idle mixture as required. Check the plug color and replace plugs as required with new ones and repeat as required to obtain uniform, clean looking plugs. Have a couple of sets of plugs on hand as it is folly to try to tune with fouled plugs.

5. Further mixture adjustments for driveablilty will require jetting changes and really need a wide band O2 instrument for best results.

I hope this helps.

Bill

[StressCraxx]

+1 on replacing the Crane XR700 ignition unit with points and condenser. Its not an expensive test.

I had one for a long time, many years ago. They came with a 10 year warranty at the time and I went through 3 of them under warranty. They lasted longer than points but hated the Southern Calif heat. I put it in my Elan soon after I bought it and worked for exactly one month. Symptoms were similar to what you have experienced. Sometimes would start right up, then start to fail when the engine bay got warm. I had the Lucas coil and ballast resistor.


Regards,
Dan Wise

[RogerFrench]

I've tried to resist posting in this thread since there are opinions a-plenty, but here's acouple of observations.

1. Plugs can often spark outside the cylinder and look wonderful, but that doesn't mean they'll fire under compression. Not a plug problem but a high-voltage issue.

2. Ballast resistors are always by-passed when starting a car, so that the full 12 volts goes to the coil instead of 6 or 8.

3. High voltage comes not just from the coil getting 12v, but from the kck in the rear it gets from the condenser when the points open or the equivalent from the electronic gizmo.

4. Every symptom so far would indicate to me a faulty condenser or electronic box. You don't have a condenser. Ergo, I suspect the Crane.

[Sea Ranch]

Ladies and Gentlemen,

Allow me to begin the final round of updates . . .

Here is a pic of my old defective coil (you can't quite see the leaking oil and crack on the top) . . .


And here is a pic of my brand new defective coil . . .


Yup. Far as I can tell, my new Pertronix Flame Thrower is defective. Don't know how or why. But this afternoon I made it over to Jason's "little shop of horrors" (Saabs and Datsuns in various stages of restoration; very cool, actually ) and put a strobe light on my new ignition wires. First we looked to see if the distributor was advancing and it clearly was. Then we checked for spark misses and all four cylinders showed misses. Swapped in the wire and cap set from Jason's '69 Plus 2 and car was still missing. Put the strobe on each wire, and then on the coil-to-distributor wire and it was missing, too. I said, "It's a new coil." Jason and mechanic Paddy said, "Could still be defective." So they whipped out an old Bosch they knew was good and I swapped it in.

Presto. My old car back. So I swapped my wire and cap set back in. Car still ran well. So . . . I will be looking for an exchange at the store where I bought the coil (and double-checking things, too).

Thanks for your recent posts.
-Roger, I agree that the spark-plug-on-a-cam-cover-bolt doesn't show the true picture of what's happening inside the combustion chamber; seeing the plugs soot up showed there was a lot of unburned fuel and I have to say I agreed with Ross that the carbs probably didn't slip into super-rich state in a minute's time last Monday when the car turned foul.
-Dan, that's an interesting story and good perspective on the Crane unit. I will be phoning them to talk about failure modes so I'm ready for that eventuality and able to diagnose it.
-And Bill, I am definitely going to get a proper strobe timing/diagnostic light because that's exactly what we did (and why I wanted Paddy's help). The light confirmed where to look for the problem. Was so obvious - with that tool - that my spark leads were missing. And I will also be studying your carb balancing process to try out this fall. THANKS!

A parting question: could a failing coil, sending erratic pulses to the dizzy cap, have caused my burned out center electrode, or could it have happened the other way around: bad center contact, too much resistance, stresses the coil etc.??

And a mighty THANK YOU to all for your encouragement and technical advice; I needed both!!!. And of course to Jason (Chicken Hole) and Paddy for your time, expertise and generosity!!!!

Randy

[ardee_selby]

Randy,

Finally...what a relief!!

Have just read through the complete thread again...some checklist, eh? (and a host of red herrings)

Let us know how you get on with the loose ends e.g. success or other of carb repair, exhaust blowing etc

[UAB807F]

aw shucks, just as this thread was getting interesting as well..... and what do you do ? go and fix it !!!

Well done mate. I really felt for you at times back there when it seemed to be going in circles. Great news to hear it's sorted.

Brian

[Sea Ranch]

Thanks, Richard and Brian.

Have just read through the complete thread again...some checklist, eh? (and a host of red herrings)

Yes, a great checklist, really. I don't consider any of it to be red herrings, as the operational symptoms really were inconclusive. I have to say, though, that the strobe timing light appears to be the obvious and direct tool for confirming spark problems. Gonna get me one soon.

Well done mate. I really felt for you at times back there when it seemed to be going in circles.

Yes. My fault. I was truly going in circles because I was relying on my senses and driving impressions instead of on an objective diagnostic tool (like the strobe light). Apologies to all, but I've learned a lesson (or two!).

Let us know how you get on with the loose ends e.g. success or other of carb repair, exhaust blowing etc

Right. After I swap in a new replacement coil, I will be revisiting the Weber float pivot repair (the JB Weld melted so I will try out a simple repair with small gauge stainless wire, and include some pix). Then on to carb set-up (see if I can get them a little more fine-tuned, clear up some light surging at certain speeds, and get them running clean enough to pass our government "air-care" program next spring). Repairing the exhaust manifold leak scares me. That will wait till the car is off the road for the winter.

Randy

[UAB807F]

Hi Randy,

Going off topic now, but when you mentioned buying a timing light as a diagnostic tool I thought it might be worthwhile showing these things. They are no use for setting up timing, etc, but for diagnostic use to see if a plug is firing they are excellent. Mount between the plug & cap, turn the engine over and if the plug is firing you see a spark. I bought this set fairly recently as a pack of 4, very cheap from a local motor factor.



This is how they are in use



Obviously not as good as a timing light but they are small and one will easily go in your toolkit for the odd occasion when you decide to do some roadside maintenance......

Brian
(yes, I know the engine is scruffy, my excuse is that I only replaced the rear seal last night and it's work in progress)

[Ross Robbins]

Congrats Randy What a relief. And I would NEVER say I told you so. That just isn't like me to rub it in. I mean I just wouldn't remind you of the lesson I learned that 92% of all carb problems are electrical, as that would be rude wouldn't it?

Seriously, I had a hard time learning that lesson but now I remember it well and bet you will as well. Happy Trails.