Backfiring

[robertverhey]

Checking those jets and accelerator pump is quick and easy, might be worth ruling it our first. I chugged-chugged for a few days once, then found that the accelerator pump plunger on rear carb had broken, so was only getting a squirt into two out of four.

Robert

[Sea Ranch]

Yup. Thanks, Robert.

I went through the pumps and pump jets earlier. When I step on the pedal from idle and it falls flat, I do think that maybe it's not getting fuel to go along with the air. But when I hear the unburned fuel popping in the exhaust, then I think it's ignition (not to the mention what sounds/feels like running on 3 cylinders briefly, off idle).

But I will go through some more fuel/carb ideas tomorrow, I guess.

[UAB807F]

Hi Randy,

Shucks, I really thought you'd caught it with that distributor cap. I must admit I haven't got a clue where your problem lies and I think by this time I would be abandoning the engineer's diagnostic approach and heading for the "replace one thing at a time until it's working" method. (which explains why I have a lot of spare parts in my workshop) A few random thoughts that might spark (bad pun ) an idea;

The fact you're now finding that you get fuel burning in the exhaust would make me think that you're passing un-ignited fuel so it's either too much fuel to ignite or a random lack of ignition spark which lets the unburnt fuel through.

So, excess fuel to start with. Blocked jets would cause lack of fuel and they seem to be clear anyway. If the float height is correct (already checked) and the inlet valve is closing securely when the float chambers are full to prevent flooding, then I'm not sure what else you can do. (and flooding would be present when cold & affect two cylinders) Incidentally I do wonder about the JB weld repair and longevity, but in your position I'd do exactly the same thing for now.

On to random ignition faults. I once had an HT lead connector (push in type) which was corroded & loose which gave random misfires. Now the Elan cap has screwed connectors but I think I'd check the coil & plug cap connections next. Easy to do & tick off the list although I'm not convinced that's your problem because it would be present when cold as well.

Rotor arms (previously mentioned) have been known over here to have poor quality supplies with them failing early in life. You can only do a visual check or replace with a new one but I think it's something I'd consider. With the central electrode missing it will have been getting quite a spark across the gap so must be worth checking out for cracks or tracking.

Plugs - easy & cheap to replace the full set but again from the photos you posted they looked ok. I'd close up the gaps to .025" until the problem was solved as a shorter gap is more likely to spark than a large one under load. Go back to a larger gap when it's working ok.

Coil - we've already had the "failure when hot" mentioned several times and it must be on the list for a replacement. I think this would be my next move after the visual checks.

I also have electronic ignition on my Elan and although I have a vague idea of what it's doing to me it's a magic box and I have no idea how to fault-find other than "it works or it don't work". If the car started easily though I think I'd put it last on the list. Only after the visual checks & replacing the coil, rotor arm, distributor cap would I revert to points and condenser to see how it ran then. Sorry, that's not scientific but I'm struggling for what else to do.

Brian

[ardee_selby]

Hi Randy, I just now came to this post and must say I admire both your dogged persistence and the excellent advice you have gotten.

+1 on that...

Though looking at my own tuppenceworth, I seem to have asked more questions than providing answers

But if you don't mind...here's another one. When you removed the distributor cap, was there any sign of the missing electrode, either as a lump, or as dust? Wondering about the debris contaminating the rest of the distributor and side effects of this.

[Robbie693]

But if you don't mind...here's another one. When you removed the distributor cap, was there any sign of the missing electrode, either as a lump, or as dust? Wondering about the debris contaminating the rest of the distributor and side effects of this.

I was wondering the same thing; did you check the distributor was advancing Randy? Maybe the missing electrode is stuck in the advance mechanism..? Long shot maybe but, you never know.

Cheers

Robbie

[Sea Ranch]

Hi, folks. Getting back at things.

I, too, thought of where the center electrode from the old cap went; I looked and couldn't find it (and was disappointed). I found some amount of grit inside, on the lower edge where things might drift to. Cleaned it out with finger and very light air pressure.

If timing advance is the problem, that would show up cold or hot, correct?

As for coil, I'm pondering the ballast resistor issue before I buy: I have a "Flame Thrower" coil installed (from Petronix, I believe). The resistance across the positive and negative terminals is about 1.5 ohms, which I believe means that it does NOT have internal ballast resistance. I see no sign of an external ballast resistor.

So I am assuming the car does not have a ballast resistor installed (I will check and compare voltage at battery and at positive terminal of coil when I start it - if they are the same, I can assume there is no external ballast resistor installed).

If this the case - no ballast resistor - this might indicate a failure mode for the coil, as the ignition system's website says that my Crane Cams Fireball XR700 module NEEDS a ballast resistor or both the module and coil will overheat and fail. (http://www.cranecams.com/404-405.pdf page two)

In any case, I will be going out shortly to buy a coil (with internal ballast, or including an external ballast resistor), along with a new set of spark plugs.

Any thoughts?

Randy

[Sea Ranch]

Back again, adding the "database" (so far, data about how NOT to make a light bulb; eventually I'll figure out the right combination )

Through messing around with the car, I've missed my window of opportunity to buy some parts today, so that will wait 'till Sunday. But I've "discovered" a couple more insights:
-car is hard to start, seems to like having a lot of "pokes" on the throttle and no choke to get started (thereafter it's happy with some choke while cold). Normally, it leaps to life.
-glitchy throttle response from cold, through to full operating temperature; so the condition is NOT temperature related, as I thought yesterday.
-further, the bad throttle response is contained mostly in the lower throttle positions. I refer to throttle positions rather than rpm because it's not so much engine speed related as it is throttle position.

With these observations in mind, I am moving back to carburetion, not ignition. Which makes me CRAZY because I can't seem to nail down what I'm looking for, nor where to look. But it is what it is. If the poor throttle response is when cold or hot, and if it's in the lower range rather than with the speed and throttle position up, and if I have to use many "squirts" from the throttle to get the car started (even when it's warmed up), then it seems more likely that I've got a lean or rich condition, and not an ignition problem. If the the coil is bad, you'd think it would show up at least as much (and probably more) at high speeds. If the advance is stuck due to junk in the dizzy, then poor timing would show up as revs build, not at low speeds.

And the original symptom, last Monday, was like I was running out of fuel. So . . . I'll be looking inside my carbs next, I guess, for some crud that's not supposed to be there, breakage, etc.

On a related note, found this info on testing for the presence of ignition ballast resistance . . . someone might find it useful . . . helped me determine that my Flame Thrower coil has no internal ballast resistor and that there's no external ballast resistor in the circuit either . . .

Quick Test for Ballast Resistance
You can determine if your vehicle has external ballast resistance with this simple test. Disconnect any wires going to COIL-. Reconnect battery. Turn the ignition key on but do not start the engine. Use a volt meter as shown in Figure 23 and read voltage between COIL+ terminal and ground. It should be about 12 volts. Then momentarily jumper the COIL- terminal to ground. If voltage at COIL+ terminal drops below 8 volts, there is ballast resistance between the ignition key and COIL+ terminal. To determine if your coil has internal ballast resistance, use an ohm meter as shown in Figure 24. Coils with internal resistance will read 3 to 4 ohms from COIL- to COIL+ terminals.

[robertverhey]

Well call me stubborn but i still think those accelerator squirting arrangement may be suspect. With mine, everything looked fine, jets were clear, float chambers clean, galleries open....but it wasn't until I actually took the carbies off and looked for the healthy squirt from each tube that I realised something was amiss. In my case the plunger lever (upside down "U" shaped metal thing in carburettor body that goes up and down when you accelerate) was broken at the bottom where it hooks into the piston....so it was going up and down okay but wasn't taking the piston with it.

Part number 61 on this site http://search.aol.com.au/aol/imageDetai ... 3DimageTab

To rule this out you actually need to see the fuel squirting.

On another matter, I've had cars popping and banging on over-run and it wasn't unburnt fuel that was the casue but timing being way out

You'll get there!

[Sea Ranch]

Hey, Robert . . . thanks for hangin' in there with me. And a great tip. I pulled the pump jet covers (screw caps on the top cover and fuel came up there when I operated the throttle linkage, but I haven't gone where you're talking yet!

Thanks. I do believe I'll take off the mounting nuts and tip the carbs back and see what I see coming out when the throttles are opened . . . see if the pumps are pumping, etc.

Thanks, pal

[UAB807F]

-car is hard to start, seems to like having a lot of "pokes" on the throttle and no choke to get started (thereafter it's happy with some choke while cold). Normally, it leaps to life.

As an aside Randy, I've never (yes "never") used the choke to start my Elan from either hot or cold. With Webers the traditional way was to give a couple of pumps on the accelerator, squirting fuel into the inlet tracts then turn over and generally they start first turn. It's usually a bit rough for the first mile or so with a low tick-over but does keep going.

Back to your car. Question - if you think it's a fuel starvation then why not run it until it packs in then before restarting take out a plug ? If there's no fuel the plug electrodes will be white. If it's sandy or dark grey then it's ok and you're back to looking at the ignition. In the photo at the start of the thread, apart from 2 plugs showing a rich mixture the others looked about right to me.

But if your car always started easily on choke and doesn't now, then logically it can only be that now using the choke you have an over-rich mixture or an increasingly worse ignition fault. If for some reason it's running rich (JB weld failed ?) then you should find the plugs from that carb showing sooty deposits or even wet as at the start of the thread. Otherwise you're back on ignition.

As for coil, I'm pondering the ballast resistor issue before I buy: I have a "Flame Thrower" coil installed (from Petronix, I believe). The resistance across the positive and negative terminals is about 1.5 ohms, which I believe means that it does NOT have internal ballast resistance. I see no sign of an external ballast resistor.

This sounds interesting. I have the Pertronix ignition, as you say the supplier of "Flame Thrower" coils. Here's a quote (in red ink as well) from the instructions;

"Six and eight cylinder engine coils require a minimum of 1.5ohms resistance. Four cylinder engines require a minimum of 3ohms resistance"

Sounds to me like you have the wrong coil ? (or a very unique, 8cyl Elan )

Brian
(edit because I pasted the wrong quote... doh.... it is early over here)

[Sea Ranch]

Wish I knew how to "multi-quote"!!

In regards the Webers and choke, I have heard (and read) that, yes. Though I'm not fond of blipping the throttle to keep a cold engine running; I prefer a little choke to settle it into an elevated idle till it's a little warmer and the oil is flowing well. But agreed: Webers are the bomb. I really like them.

"If there's no fuel the plug electrodes will be white." See, now why can't I have some sort of see-through plug so I can view what's going on inside?? I suppose if I had the money, I'd have diagnostic tools to tell me about the condition of each spark plug and lead, etc. So if the cylinder is starving of fuel, the plug electrode should be white-ish?

As for the coil . . . yeah, interesting. The Crane Cams material says my XR700 module requires ballast resistance and I don't have any: either external or internal to the coil (my coil measures 1.5 ohms). But it appears that this combination will run (as mine apparently has for probably many years). The problem is heat build-up in both module and coil, from 14 volts to them, and eventual failure. That sets off bells in my head, and apparently yours, too. Perhaps the coil is deteriorating fast and went from only bad when hot to bad cold as well, and will soon stop putting out at all.

I suspect what will happen tomorrow is I will approach from both ends: fuel and ignition. And if I get the problem cleaned up, I promise: I will give honest and accurate details on which camp had it right Fuel or ignition?

[UAB807F]

Good morning Randy, or I suppose it's evening where you are ?

See, now why can't I have some sort of see-through plug so I can view what's going on inside?? I suppose if I had the money, I'd have diagnostic tools to tell me about the condition of each spark plug and lead, etc. So if the cylinder is starving of fuel, the plug electrode should be white-ish?

You can, it's called a "Gunsons Colortune" ( http://www.gunson.co.uk/item.aspx?item=1822 ) but unfortunately they are only for setting up and not driving around with....

Yes, generally white or glazed, basically running too hot. There are loads of pictures on t'internet and most UK car manuals would have a page with half a dozen colour photos showing plugs in various conditions. Yours looked ok to me though - or more correctly, they looked like the ones in my car (which may or may not be a good thing !)

[Robbie693]

I was told recently by Paul Matty that an indication that a coil is on the way out is that the rev counter wavers slightly...

May be a help..?

Regards

Robbie

[Ross Robbins]

RANDY,

I am reminded again of the aphorism that 92% of all carburetor problems are electrical

I drove that sucker hundreds of miles from sea level to 12,500 feet above it with those carbs and they were fine. SO either something has gotten into the jets to obstruct them (which you have checked and found OK), the float level is off (which you have checked and repaired even if temporarily), and that leaves the coil which IS something that can produce the symptoms you have. Isn't the cost and simplicity of swapping out the coil worth a try???

[Sea Ranch]

Gentlemen,

It's my sad duty to report to you that I have installed a new Pertronix Flame Thrower coil (3 ohm) (removed the old Flame Thrower and found that the top/cap had a crack and it was leaking oil) and got no change in performance. I've also replaced the spark plug wires with a new set and got no change in performance.

So electrically speaking, that means cap, coil, wires and plugs changed. And it runs as rough as ever. Could be something faulty with the parts I put in, but that's a long shot. Unfortunately, I don't have a "spares" bin to use for swapping things in/out.

I was scheduled to pay a visit to Chicken Hole (Jason) and his mechanic today but put it off till Tuesday. IF I can limp the car along the 15 or so miles to him, we can swap some parts between our two cars and see if that helps narrow things down.

I'm going to have a bath and meditate on whether and what I can dig into next. I agree, it sounds like ignition to me, too, Ross, but . . .??

Randy

RANDY,

I am reminded again of the aphorism that 92% of all carburetor problems are electrical

I drove that sucker hundreds of miles from sea level to 12,500 feet above it with those carbs and they were fine. SO either something has gotten into the jets to obstruct them (which you have checked and found OK), the float level is off (which you have checked and repaired even if temporarily), and that leaves the coil which IS something that can produce the symptoms you have. Isn't the cost and simplicity of swapping out the coil worth a try???