Crossing plug wires to make it backfire through the carburetor

[MaximRecoil]

Is this a good idea? Can you damage anything by doing this?

A couple days ago my engine started running like crap at idle speeds; i.e., rough idle, too low of an idle to the point that it stalled once, and varying idle speeds like something would start to bog the engine down and then it would come out of it. There was also a popping/sputtering sound coming from the tailpipe (not very loud; you had to stand near the tailpipe to hear it).

It started doing this the morning after we got a pile of rain, and I thought maybe some water got into somewhere that it shouldn't have. It only had about ¼ tank of gas, so I filled it up and added some K100, but that didn't help. My mechanic friend said his old Dodge pickup sometimes does that, and he switches around two plug wires to make it backfire through the carburetor to clean out whatever crap is in there.

So we did that with my car (318, stock carburetor), and when I switched the two plugs back to the right firing order, it instantly started running beautifully, better than it has ever run since I first got it running in 2011. I was amazed.

So it obviously works, but can it cause any harm to anything? It seems to me that an explosion traveling along a path that wasn't designed for it (i.e., the carburetor) could potentially damage something, especially if you make a habit of doing it.

[Cooter]

Think that's bad, you should see how we clear out busted, old Subaru/VW carbs....

[68 CHARGER R/T]

that's kinda funny I did that on my 440 three weeks ago kept on fouling plugs after a few weeks of running .  crap built up on one of the valves , did that trick and swapped back over again ran mint 

[john108]

Which cylinders did you switch??

[MaximRecoil]

Which cylinders did you switch??

Are you asking me or "68 CHARGER R/T"? If you're asking me, I switched #1 and #2, because they were right up front on the distributor cap. My mechanic friend worked the throttle from under the hood (with the air cleaner removed of course) until he got a good backfire and puff of smoke that he was satisfied with. It only took about 30 seconds.

I wonder if any further benefit could be gained by doing it 3 more times, i.e., with #3 and #4, then #5 and #6, and finally #7 and #8?

[chargerbr549]

I remember my dad doing that alot in the day switching plug wires and making it backfire, he was a chrysler mechanic for over 35 years.

[Cooter]

Tell your 'Mechanic' friend, that's awful hard on rod bearings...ALOT easier to rebuild the carb, and replace those old plug wires/points/ cap rotor/etc. when it is damp outside.

[MaximRecoil]

Tell your 'Mechanic' friend, 

There are no quotes about it, he is a mechanic, and has been since the late 1960s. He was first my mechanic and then many years later my friend, and he never would have been my mechanic in the first place if he wasn't an actual mechanic, and a good one at that; meaning that since I started taking my vehicles to him in 1993 I've never had a problem with his work, and he's also the busiest mechanic around, and has been for as long as I've known him; anyone wanting him to work on their vehicle needs to plan a week or two ahead.

that's awful hard on rod bearings...

Please explain the mechanism by which backfiring through the carburetor causes damage to rod bearings.

Since he has done this many times with his Dodge pickup truck that he built 22 years ago, which weighs 6000 pounds and has always been used as a plow truck, junkyard truck, and general purpose truck (often hauling large loads of scrap iron to a place a few towns over), I'll ask him if he's had any problems with rod bearings in that old 318.

ALOT easier to rebuild the carb, and replace those old plug wires/points/ cap rotor/etc. when it is damp outside.

It isn't easier, considering it only takes a minute to make it backfire through the carburetor. Also, my plug wires are new, the carburetor is a reman from Autoline, and has less than 2,000 miles on it since I installed it in 2011, the car has no points anymore, the cap and rotor button were new at the same time the carburetor was installed, and they are fine (no cracks, contacts are clean with no noticeable wear).

I don't think the rain had anything to do with it in hindsight; rain never bothered it before. I think carbon deposits probably built up somewhere because most of my driving consists of going back and forth to the garage, a mile away, at in-town speed (25 MPH). 

[JB400]

Deleted.  Just send me a pm if you want to know why.

[Cooter]

Obviously, you and your super mechanic friend have it all figured out. I am confused as to why you would post this thread if your mechanic buddy is all that and never had a problem...Sorry I was simply trying to keep you from f*ckin up your sh*t...my bad, good luck.

[MaximRecoil]

Obviously, you and your super mechanic friend have it all figured out. I am confused as to why you would post this thread if your mechanic buddy is all that and never had a problem...Sorry I was simply trying to keep you from f*ckin up your sh*t...my bad, good luck.

I don't have a "super mechanic" friend, nor did I claim/suggest/hint that I do, nor did I claim/suggest/hint that he or I "have it all figured out". In other words, your first sentence is a non sequitur. For that matter, your second sentence is a non sequitur too, given that I never claimed/suggested/hinted that he "never had a problem"; I said I would "ask him if he's had any problems with rod bearings in that old 318".

And I posted this thread looking for solid information, as opposed to mere assertions. Your assertion about the rod bearings may be true, but you provided nothing to support it; i.e., no explanation of the mechanism which would cause the rod bearing damage; not even an anecdote in lieu of an explanation. Also note that you didn't just tell me this, you wanted me to tell someone else this. Right ... and what do I say if he asks why it would cause rod bearing damage? "Because some guy on the internet said so"?

[JB400]

Deleted.  Send me a pm if you want to know why.

[ws23rt]

My friends and I had a lot of fun playing with cars when we were kids. This sounds like the kind of thing we would do just to find out what would happen.

Example was with my 57 desoto---I would be manning the gas pedal and another would start removing spark plug wires. As the engine struggled to run I would give it more gas to keep the revs up.  We got that thing to stay running with only two cylinders left running

In all the years of working on cars and hearing stories this is a first for me to hear.---That intentionally causing an explosion when it could cause damage in the hope that it would some how traumatize an unknown problem to heal itself is like kicking the pop machine cause it ripped me off.

The possible damage to rod bearings is obvious ---Although IMHO is kinda low.  But it seems as thought the intent here is to cause an explosion in the intake/crankcase in the hope that it will shake something loose in the carb?   Hmmm One could hit the carb with a hammer If that was the suspect

A crankcase/intake explosion would do little to dry out a distributor for example or otherwise correct a possible ignition problem.

I wonder if the mechanic involved here got to the point of scratching his head and remembered something from the old wives tales book took a shot in the dark hoping something positive would happen?

It seems that may be the case.   He is now much more likely to do it again    I see an unhappy camper in his future.

[MaximRecoil]

That is exactly what you say.  Then you see what he has to say about it.  It's called cross referencing.

No; I try to avoid making (or repeating) baseless assertions. If I did bring up the subject, it would be as a question, not as an authoritative statement with nothing to back it up. And the question would need some basis too, in order to answer the potential question of "Why would you think that?"

Anecdotes, such as from "chargerbr549" and "68 CHARGER R/T" = good stuff. Solid technical explanations = even better stuff. Mere assertions = not good stuff.

In all the years of working on cars and hearing stories this is a first for me to hear.---That intentionally causing an explosion when it could cause damage in the hope that it would some how traumatize an unknown problem to heal itself is like kicking the pop machine cause it ripped me off.

It isn't the random shot in the dark that you think it is; the mechanism behind why it works makes perfect sense. There is no question that it works (the big puff of carbon-laced black smoke in the air is all the evidence you need; because the carbon/crap that is in the air is obviously no longer where it used to be); the only question is with regard to the risk of damage.

The possible damage to rod bearings is obvious ---Although IMHO is kinda low.  But it seems as thought the intent here is to cause an explosion in the crankcase in the hope that it will shake something loose in the carb?   Hmmm One could hit the carb with a hammer If that was the suspect

The explosion is in the combustion chamber, which then propagates up through the open intake valve, into the intake manifold, and through the carburetor. Some of the explosion will also be directed against the piston in the cylinder. The piston will be in the wrong position, but the force of the explosion against the piston is also less than usual because some of it is escaping up through the intake valve.

As for hitting the carburetor with a hammer, there is a big difference between the mechanics of an explosion (forceful release of gases) and the mechanics of being knocked about with a hammer. For example, next time you reach for the air nozzle to blow some crap out of some tight spot, try a hammer instead. Think it will work well?

A crankcase explosion would do little to dry out a distributor for example or otherwise correct a possible ignition problem.

The distributor didn't need to be dried out, and I already knew the ignition system was working fine.

I wonder if the mechanic involved here got to the point of scratching his head and remembered something from the old wives tales book took a shot in the dark hoping something positive would happen?

No, and I'm pretty sure "chargerbr549's" 35-plus-year Chrysler mechanic father was never "scratching his head and remembering something from the old wives tales book and took a shot in the dark hoping something positive would happen" either. You don't seem to understand why it works (given that you think it is a random shot in the dark with no sound rationale behind it), but that doesn't imply that no one else does.

It seems that may be the case.   He is now much more likely to do it again Cry    I see an unhappy camper in his future.

He's been doing it when called for for at least 40 years.

[ws23rt]

Well this seems all too familiar.

I am responding to a post with my opinion based on my passed experience.

And as it turns out my opinion and past experience has no value on this topic as explained above.

I fully intend to explore all of my previous experiences and get to the bottom of what led me to this point in my life.  If I could have been so oblivious in my understanding of how engines work in the last 45+ years than perhaps there are other  life experiences I should revisit.

I apologize for interrupting the flow of information regarding this thread.

[flyinlow]

Your miss started after a heavy rain. Could be coincidence. Might be something in the ignition system. Take a spray bottle with water and mist the cap,wires and coil looking for errant sparks. If you can safely put a load on the engine this will help find weak components. Don't load the engine in drive for extended periods.

I would not intentionally miss time a cylinder by 90* or 180*.  You might clean out dirt or varnish in the intake system with the back fire. You might "clean out" something else if you do it enough times. I worked at a Chrysler dealership in the '70's when these cars where still daily drivers. I never saw this procedure in the FSM or heard of someone doing It.  

[MaximRecoil]

Well this seems all too familiar.

I am responding to a post with my opinion based on my passed experience.

And as it turns out my opinion and past experience has no value on this topic as explained above.

I fully intend to explore all of my previous experiences and get to the bottom of what led me to this point in my life.  If I could have been so oblivious in my understanding of how engines work in the last 45+ years than perhaps there are other  life experiences I should revisit.

I apologize for interrupting the flow of information regarding this thread.

Familiar? Indeed. You have just posted an editorial rather than replying specifically and relevantly to what I posted, which is something you've done often in other threads.

In my previous post I corrected your errors, such as your invalid comparison between an explosion and hitting with a hammer, and your invalid assertion that forcing a backfire through the carburetor is a random shot in the dark with no sound reasoning behind it. If you believe that my corrections of your errors were actually errors themselves, then present an argument to that effect. If you don't believe that my corrections of your errors were actually errors themselves, then own up to your errors. Either of those two options are relevant and make sense. Simply ducking to the west and making a beeline to deep left field, as you are prone to do, is irrelevant and makes no sense as a reply to my post.

Your miss started after a heavy rain. Could be coincidence. Might be something in the ignition system. Take a spray bottle with water and mist the cap,wires and coil looking for errant sparks. If you can safely put a load on the engine this will help find weak components. Don't load the engine in drive for extended periods.

I believe it was a coincidence, because as it turned out, backfiring through the carburetor not only solved the problem instantly, but it also made it run better than I've even seen it run before (and it is still running great). Also, I'd already tested the ignition system and it was working properly. All the plugs were getting voltage (I didn't test to see if the plugs were actually firing or not, but the ignition system was sending them all the juice to do so).

I would not intentionally miss time a cylinder by 90* or 180*.  You might clean out dirt or varnish in the intake system with the back fire. You might "clean out" something else if you do it enough times. I worked at a Chrysler dealership in the '70's when these cars where still daily drivers. I never saw this procedure in the FSM or heard of someone doing It.  

I wouldn't expect something like that to be in any FSM ever printed, for the same reason that I wouldn't expect "whack it with a big hammer" to be in an FSM for removing a stubborn brake drum.

[ws23rt]

I have a device that will do what your mechanic did to your engine without any possibility of engine damage.

It's a  "Depolaray"   I am not willing to rent it out but when you find out how it works you can make your own and let your mechanic go. 

[MaximRecoil]

I have a device that will do what your mechanic did to your engine without any possibility of engine damage.

It's a  "Depolaray"   I am not willing to rent it out but when you find out how it works you can make your own and let your mechanic go. 

Simply ducking to the west and making a beeline to deep left field, as you are prone to do, is irrelevant and makes no sense as a reply to my post.

[Dmichels]

It is much harder to light off a spark plug under compresion. When you foul a plug the juice decides it is easier to run down the insulator instead of jump the gap. My therory on this trick is the spark plug now has a chance to light off with out compresion. THis heats it up and burns the shit off the insulator. I really do not see it really "blowing the carbon out" or somhow fixing a carb that is out of tune.  If I had an engine that I thoght had a lot of carbon in the cylinders I would burn it out with sea foam or Ford made a product as well. Hear is an article on the subject http://www.hemmings.com/mus/stories/2008/01/01/hmn_feature19.html. If I had a bad plug I would just change it. It is a trick that may fix an isssue and get you going, but it did not solve the cause of the problem. I would also be worried that I would damge the carb
Dave

[MaximRecoil]

It is much harder to light off a spark plug under compresion. When you foul a plug the juice decides it is easier to run down the insulator instead of jump the gap. My therory on this trick is the spark plug now has a chance to light off with out compresion. THis heats it up and burns the shit off the insulator.

The spark plugs were brand new NGKs, installed about a week or two prior to the car acting up. Your theory is unlikely in any event, given that it would require a coincidence to be true; i.e., it would require that the two cylinders you crossed just happened to be the ones with the fouled plugs (and if they were all fouled, cleaning only one or two of them wouldn't make the engine run great, better than it's ever run before no less). And not just a coincidence in my case, but a coincidence in all of the cases where people make their engine backfire through the carburetor and instantly solve their problem.

As far as I know, the dielectric strength of air doesn't increase under compression, so it is not "much harder to light off a spark plug under compression", but if you have a citation that says otherwise, I'd be interested in reading it.

I really do not see it really "blowing the carbon out" or somhow fixing a carb that is out of tune.

Interesting wording there, because you actually can "see it really 'blowing the carbon out'", literally, in the form of a carbon-laced cloud of black smoke. My mechanic friend didn't stop working the throttle and getting backfires until he got the puff of black smoke he was looking for, and then he said, "There, it's done." He didn't have a doubt in his mind that the car was going to run better as soon as I put the wires back to the correct firing order; it was a foregone conclusion as far as he was concerned, because as he often jokingly says, he's "been doing it for a hundred years".

If I had an engine that I thoght had a lot of carbon in the cylinders I would burn it out with sea foam or Ford made a product as well.

If you're going to go the Seafoam directly into the carburetor as the engine is running route, you might as well just use water, as it is much cheaper and works on the exact same principle (steam cleaning), and you run the exact same risk of hydrolocking the engine with either liquid if you don't do it right.

Time will tell if there is an underlying problem that will cause the engine to run like crap again in a few days or weeks, or if it was just the cumulative effect of a couple of years of mostly in-town, short-distance, low-speed, stop-and-go driving.

[Dmichels]

Read up on Paschen's law
This is why high compresion and or super charger motors require hotter coils.
You can foul at a plug almost instantly so being fresh plugs makes no diference
I agree with you about the coinicdence of picking the right wires to cross.
Ok so it blows out some loose carbon. Probally not all that much. What is really happening that makes it run better? THe only thing I could come up with was allowing a fouled plug to light. Maybe a stretch But what else could posibly be happening??
I have only used the seafoam once on an old junk yard moter and it really helped it. Yes you could hydrolock a motoer if your not carfull. but you would really have to dump it in there
Dave

[MaximRecoil]

Read up on Paschen's law
This is why high compresion and or super charger motors require hotter coils.

Interesting, though the dielectric strength of a gas only decreases to a point as pressures decrease, and then it starts to increase again, thus "Paschen Curves", though I don't know the values where these things happen. In any event, with HEI ignition, a ~40,000 volt E-core coil, and an .035" plug gap, a plug would have to be extremely fouled to not fire, considering the coil has 2 to 3 times the potential voltage that a typical plug requires to arc-over.  

You can foul at a plug almost instantly so being fresh plugs makes no diference

If there was some underlying problem that was instantly fouling plugs, then I would expect my engine to be running like crap again already, but it isn't; it is still running great.

I agree with you about the coinicdence of picking the right wires to cross.

Yes, and not just in my case, but in the case of everyone who's had success doing this, which makes the theory very unlikely.  

Ok so it blows out some loose carbon. Probally not all that much. What is really happening that makes it run better? THe only thing I could come up with was allowing a fouled plug to light. Maybe a stretch But what else could posibly be happening??

My mechanic friend's theory is that it blows out the idle jets. It seems to make sense, since my engine was only running like crap at low RPMs. Driving down the street it was fine; it just ran rough and felt like it was going to stall when you came to stop signs.

I have only used the seafoam once on an old junk yard moter and it really helped it. Yes you could hydrolock a motoer if your not carfull. but you would really have to dump it in there

What I'm saying is that you can use water (free or cheap) to accomplish the same thing (steam cleaning), and the risk of hydrolocking is the same whether you use Seafoam or water. My mechanic friend was drizzling water into carburetors of running engines decades ago to accomplish the same thing that many people use Seafoam for. The best/safest way to do it is with a spray bottle set to mist.