Backfiring

[Sea Ranch]

I see. But right now the plugs spark when out and there is no combustion when in and turning over the motor (cold).

So I'm still inclined to hunt down fuel problems. I'm just about to go out and pull the plugs, put a little fuel into each hole, button up and crank it over.

[Sea Ranch]

Alright; a little update here (this little problem is persistent, if nothing else) . . .

Here's what I've done:
-pulled plugs, tested each for spark (good)
-cranked engine lots, no combustion
-pulled plugs; they were dry
-pulled cap/screws off the four pump jets, depressed throttle linkage and got instant squirts of fuel in the pump jet ports
-figured this must mean there is now fuel in the intact tracts (or close to it) so cranked some more; no combustion, but when I pulled the plugs again, the electrodes were wet. Fuel was now getting in , but still not combusting. Tested the wet spark plugs for spark and they sparked readily.
-pulled the four pump jets, blew compressed air through their ports (assuming these passages lead directly to the intact tracts?)
-re-assembled, and got a "kick"; cycled the throttle linkage some more and . . .
-motor started; had not started or kicked all yesterday.
-used some choke to keep it warming up at 2000rpm, then drove around a bit, brought up to full water temp (84 degrees on my dash gauge)
-brought it home, choke off, reduced the idle speed to about 1100 and it kept running (previously it would idle only for a minute before it seemed to just run out of fuel and die)

Here are what I think are some important observations:
*It still doesn't like much throttle off idle; it falls flat and has to be gently coaxed up, but once over ~2000 rpm it revs more freely and actually feels like it's old self. But it still pops and surges here and there.
*Also, when I was idling it after the drive, I pushed hard on the throttle linkage 2 or 3 times to see if it would stall. It didn't stall, but bogged down each time, and then abruptly had a LARGE backfire out the muffler. Presumably there was a lot of fuel fed into the cylinders that didn't get burned; just passed through and then ignited in the muffler.

SO . . . perhaps now it's not the carbs but rather this mysterious ignition: flaky coil that is sparking the plugs but not enough to cause reliable ignition? Is this possible?? Or tracking inside the distributor cap?

It just may be that I have two problems similtaneously (though I'm always skeptical of this): fuel and ignition. The motor is definitely running better than Monday, but nowhere near right yet.

I await your astute observations

[Sea Ranch]

Uhmm . . . Gentlemen:

Take a look at following pix . . .

I know that virtually each of you, to a man, suggested various electrical issues, but I kept coming back to "there's spark at the plugs". I don't know: was there a carburetor AND an ignition problem? Too soon to tell, but clearly there is a distributor cap problem, no?? There's no center "rotor" electrode left: just burned out phenolic that used to support a carbon rod, and badly burned spring material buried in there.

Off to the Vintage Lotus Electrical/Ignition Parts Store ( ) tomorrow to get me a new one!!!

[UAB807F]

I think you've taken the weight saving thing too far.......

For the first time this looks like you've got a good lead, but I'd never have guessed it. When Billwill mentioned the rotor arm I thought he might be on to something because over here there have been a few complaints about the quality of replacement rotor arms for older cars, but I'd never have thought it would run at all with the central electrode missing from the distributor cap.

Brian

[Sea Ranch]

Cool, eh??

I have to assume it was arcing the whole time and creating tremendous heat, etc.

And yeah, I'll have to look elsewhere for weight savings, now

Tracked down my distributor number (with a mirror and flashlight) (23D4) and hoping I'll find a cap before the weekend.

Speaking of which, yours comes 8 hours before mine; you're up very early this morning, Brian!

Have a great day . . .

Randy

[Galwaylotus]

Alright; a little update here (this little problem is persistent, if nothing else) . . .
Here are what I think are some important observations:
*It still doesn't like much throttle off idle; it falls flat and has to be gently coaxed up, but once over ~2000 rpm it revs more freely and actually feels like it's old self. But it still pops and surges here and there.
*Also, when I was idling it after the drive, I pushed hard on the throttle linkage 2 or 3 times to see if it would stall. It didn't stall, but bogged down each time, and then abruptly had a LARGE backfire out the muffler. Presumably there was a lot of fuel fed into the cylinders that didn't get burned; just passed through and then ignited in the muffler.

SO . . . perhaps now it's not the carbs but rather this mysterious ignition: flaky coil that is sparking the plugs but not enough to cause reliable ignition? Is this possible?? Or tracking inside the distributor cap?

I've just come into this thread but is the ignition timing correct? If not, you'd get spark but not at the ideal time. Also confirm advance and whether you have vacuum advance on your distributor.

[hatman]

Have you bypassed the anti-theft switch yet?

[ardee_selby]

Uhmm . . . Gentlemen: Take a look at following pix . . .

Randy,

Those pics, combined with your broken carb pics, makes me wonder how it ran at all !

When you said "So I'm driving home from school/work and get within a block of my house when I've run out of power..."

Were there no symptoms, or hint, of what was to come before that happened?

Still, whoever first said "90% of carb probs are ignition faults" may have another notch in his/her belt.

Don't forget to get some new exhaust gaskets on as soon as you can.

(An observation...the guys with "ye olde worlde" points ignition probably get inside at regular intervals...whereas electronic jobbies sold as being "fit & forget" could mean the rest of it is also forgotten about...I did a bit after fitting Lumenition)

Good Luck and keep us posted..

[UAB807F]

Speaking of which, yours comes 8 hours before mine; you're up very early this morning, Brian!

yes, my wife goes swimming 3 days a week, four of them go at the crack of dawn before the pool gets crowded. By the time I was typing that she'd already left for the pool, waking up our chickens and no doubt everything else on the way !

So - did a new cap fix it ?

Brian

[Sea Ranch]

I've just come into this thread but is the ignition timing correct? If not, you'd get spark but not at the ideal time. Also confirm advance and whether you have vacuum advance on your distributor.

Right. I have not yet checked timing. I was working on the assumption that the car had run well and then not. And I'm assuming the timing has not slipped enough in such short order to cause the symptoms. But now that I've got the cap off, I will be inspecing inside the dizzy. It has no vacuum advance, by the way.

Thanks

[Sea Ranch]

Have you bypassed the anti-theft switch yet?

Yes, thanks. I noted your thought and have read of how this feature can be a problem.

I discovered a while back that the anti-theft wiring has dropped the ignition cut-out feature (presumably when the solid state ignition was installed), though the horn-on feature is retained.

Personally, I really like this anti-theft feature and may re-fit it later in the winter, when I have time

[Sea Ranch]

Speaking of which, yours comes 8 hours before mine; you're up very early this morning, Brian!

yes, my wife goes swimming 3 days a week, four of them go at the crack of dawn before the pool gets crowded. By the time I was typing that she'd already left for the pool, waking up our chickens and no doubt everything else on the way !

So - did a new cap fix it ?

Brian

Great, Brian; nothing like an early morning swim to get the blood circulating. Or chickens to wake you

I'm waiting for work to end today; I've found a cap in town, which I'll pick up and install this evening. And of course report back.

Randy

[bill308]

Kudo's to you Randy. That distributor cap certainly is a problem.

The other thing I would recommed is to replace the carb top cap at the first opportunity. Sadly, I've had poor results with JB Weld. The couple of times I've used it, it eventually failed. I used it in applications where the thickness was greater then you used, but it was not subject to a fuel soak. It appeared to deteriorate over time, leaving the surface riddled with cracks, as if it continued to cure over time. It maybe that even if it fails, the one end will privide enough support ensure proper float operation, but I would't bet on it. If the JB Weld fails, vibration and floatation loads will likely loosen the fixing at the good end, resulting in a cantelever structure with a loose fixing. The result will likely be a higher than desired fuel level and ultimately a too rich a mixture on the affected cylinders.

Bill

Bill

[Ross Robbins]

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.

I had a similar experience with my Elan racecar. Similar symptoms but not as pronounced. Ragged running at high RPM hard starting power loss and in a racecar this is more than annoying it is infuriating as one loses positions to those who had been vanquished. Ruined the weekend it did. And when I had tried everything and paid hundreds of dollars to others, it turned out to be a duff spring in the center button of the distributor. This of course was not visible on inspection and what it did was bounce off the top of the rotor when hot and under load. Bouncing off the FIA curb probably didn't help either. New cap = problem solved. I hope it does as well for you.

[Sea Ranch]

Well . . .

I don't know how to break this to you all, but . . .

The new distributor cap was needed (as we could see) and definitely helped . . . a lot . . . but there's still more to track down!

I am always surprized to find more than one problem popping up at the same time. Too suspicious. But . . .

The new cap gave me a real nice idle & good revving in the driveway, so I took it out around the neighborhood and as it warmed up I thought all the symptoms were gone. But then I heard a little "fart". Just a faint one: uncombusted fuel burning in the exhaust header, perhaps. And as I drove it more (and the engine came up to full temp, etc.) the revving became more and more glitchy. At first just a bump or two at 3500 rpm. Then below 2000 rpm. Then it became a little tricky to get a clean start from stop. Which was when I realized that it was actually running on 3 cylinders briefly when getting under way, until the revs built a bit. Finally, from idle I could give a strong poke to the throttle pedal and have the motor bog instead of rev. I had the distinct sense that if I did that more than three times in a row, I would get another huge muffler backfire (and I don't know how many more that poor muffler can take before it ruptures a seam!).

All these features (especially the 3 cylinder running) make me think ignition still, but some of these symptoms could point to carburetion, I guess. My understanding/insight is not sophisticated enought to decipher.

So, I will drive it again tonight after it's good and cooled down, to see if heat is actually what leads to the deterioration of performance.

And I will now consider what ignition component to target next. I guess I could end up replacing virtually everything, as when you're looking for a ghost in the machine, you pretty much have to suspect everything: could it be a bad spark plug lead, a bad spark plug, a tempermental coil (as some of you have suggested), or perhaps a faulty solid state ignition component (which thought I really don't like, as I'm not at all familiar with that system - I'm a points and condensor guy)???

But at least it starts and drives, which means I can use it when I need to, and take it to a pro if I have to

Thanks for hanging in with me, folks!! Thoughts on which ignition component to look at next?

I had a similar experience with my Elan racecar . . . it turned out to be a duff spring in the center button of the distributor.

Funny you should mention that, Ross. I have to say that the Chinese-made cap I bought is a nice casting and has brass contacts inside, not aluminum, but the center contact is wobbly and the spring is REALLY light! I hope it's not bouncing, as you say!

The other thing I would recommed is to replace the carb top cap at the first opportunity.

Thanks for the note and insight, Bill. I agree that JB Weld keeps on curing for quite a while and I wish I could have left it longer before installing. But I've had really good luck with the patch on my Suzuki (car) oil pan, so I'm hoping for now.

Randy