Backfiring issue

-
davidcribbs

davidcribbs

Well-Known Member
Joined
May 12, 2015
Messages
73
Reaction score
16
Location
Texas
I have been having some issues with backfiring, and flaming through the carb.

It started a while back with a different issue, but I believe pertinent to the current issue. I have a 1967 Dodge Dart that I have owned for 8 years, and prior to this issue the engine has been pretty reliable, other than having to rewire the car from front to back. It has a 360 in it currently, although I don't know what it came out of, or how many miles the engine currently has on it.

An issue started a while back (about 8 months ago) where it was mis-firing when I accelerated hard, and would surge when holding speed on the highway. After replacing the fuel delivery system (new Edelbrock mechanical fuel pump, new fuel filter & I rebuilt the Summit 600 CFM carb that had been on the car for 8 years), that did not help. Finally took it to a shop for diagnostics, and they told me the carb was the issue. Switched to a Holley 570 Brawler carb, still didn't help. Started looking at the ignition system, and once I pulled the distributor cap, realized all the cap contacts were destroyed. Purchased the Summit electronic ignition that comes with their coil, box and resistor. At this point the car fired right up, and drove great at highway speed. It developed a new issue with a stumble off-idle as soon as I started to accelerate from a stopped position. Started looking at timing adjustments, adjusting floats and air mixture in carb, and even replaced accelerator pump. Not only has none of this helped, but has gotten worse to the point where I couldn't get it to start due to it shooting flames out of the carb. I realized the plugs were pretty soaked, so switched those last week, and amazing enough, I got it started. It would only start and run in idle. as soon as I applied any gas, it would backfire and stall. I have not run a compression check, although I do not think that the compression went to **** all of a sudden, (that may not be the right thought). I am getting ready to pull the timing chain cover to see if the chain or gears are worn and it slipped a tooth. Before I went to that level, I wanted to send it out to you guys to see if I should be looking elsewhere. Although I know I just switched the ignition system, I just have this feeling that maybe that is my culprit. I have nothing to base this thought on other than it is just a feeling.
 
Maybe the sock filter in your gas tank is part of the problem.
 
Put a vacuum gauge on it. Dig into it deeper and you can Troubleshoot the valves

||Tuning Tips||
The most important thing to do when using a vacuum gauge is to connect it to a constant vacuum source on the engine.

Distributor vacuum is at the metering block on the carb(holley).

Timing affects carb settings. Not the other way around.

Adjust each screw watching the gauge until it doesn't increase anymore, then back it off 1Hg. Air filter on. 15 with shake

Also, make sure that both side idle screws are adjusted the same (ie same # of turns out. - you dont want one at 1.5 turns and another at 3.0).
 
Just my &.02. Do some basic diagnostic checks, for example don't pull timing cover to check chain slack, pull distributor cap and put a wrench on the crank bolt, then assess how much you have to move the crank before the distributor rotor moves. This will lead to whether you need to go after the timing chain . IMO, its alot of work pulling that timing cover if you don't have to. Check timing, get a vacuum gauge etc, pull a valve cover and start it, see if all the rockers are moving smoothly and evenly etc. Don't get too invasive as far as tearing the engine apart not until you know you have to. Check and double check firing order, make sure wires are good. I've seen 1 year old Belden wires that look good but are shot. I use an inductive lead timing light to check and isolate the misfire, you just switch the timing light lead from wire to wire looking for the erratic strobe light flashes.
As you go through these checks, take notes at some point something will jump out and you will be able to isolate is it fuel or is it ignition, is it timing or is it broken or worn mechanical parts. OP you mentioned ignition, make sure you have a good ground> I run MP electronic ignition,and I actually made and ran a ground wire from my orange box bolt hole to the rear head bolt hole just to make sure there was a good ground to the ignition box. One other thought you mentioned back fire out the carb, is that constant like its all 8 cylinders or is it once in a cycle like it is just one cylinder?
 
Last edited:
69FBCuda said:
Put a vacuum gauge on it. Dig into it deeper and you can Troubleshoot the valves

||Tuning Tips||
The most important thing to do when using a vacuum gauge is to connect it to a constant vacuum source on the engine.

Distributor vacuum is at the metering block on the carb(holley).

Timing affects carb settings. Not the other way around.

Adjust each screw watching the gauge until it doesn't increase anymore, then back it off 1Hg. Air filter on. 15 with shake

Also, make sure that both side idle screws are adjusted the same (ie same # of turns out. - you dont want one at 1.5 turns and another at 3.0).
Click to expand...
Unfortunately I cannot get it to run without the backfiring and flames shortly after it fires up. I am not really able to diagnose the engine while running. The vacuum problem i thought of as well, but again the engine was running previously, then this problem started. Even after all the fuel and ignition changes.
 
davidcribbs said:
I have put the old carb back on as well, since I agree, this may have been the issue. That did not help either.
Click to expand...
I'm of the school of kiss... On these cars it's always something simple....
Only way it could really be something catastrophic is if it has to do with the cam or the valves... Like not putting oil with zinc in it and starting to wear things out over the last 8 years?...
 
j par said:
I'm of the school of kiss... On these cars it's always something simple....
Only way it could really be something catastrophic is if it has to do with the cam or the valves... Like not putting oil with zinc in it and starting to wear things out over the last 8 years?...
Click to expand...
agree for the KISS theory. I am sure once i get it figured out i will kick myself. as far as the oil goes, i have been running mobile 1 in it since i bought it.
 
Well I would start with the simple diagnostics... If you don't have one a compression gauge is probably less than 30 bucks... Pull all the plugs and run a compression check. If you have good compression go from there. If you don't time to pull the engine...
Then new plugs new wires new rotor new cap and I assume it has an electronic ignition?.. timing timing timing everything comes from timing.... Make sure you don't have any leaky spark plug wires, ones that are hitting the exhaust or worn out and letting spark get out... A lot of times it can be done at night just running the car and you'll see the spark arcing...
While you're doing your compression check I would take the valve covers off while it's turning over and see if I can see anything "NOT" moving or not moving enough like a dead cam. Check for broken valve springs and such but a compression check should tell you A lot of that... Again keep it simple and look for the obvious stuff... Not time to start spending too much money yet...
 
I agree with previous suggestions. In addition, it wouldn't hurt to remove valve covers and have a look-see. You can see a lot on an LA engine. Not too invasive, just 10 bolts.
 
Will it start & idle without backfiring/flames?
If yes: check the Summit instructions as to the reqd voltage for the ign. It will probably be 12v. With engine idling, check with a VOM that the ign has 12v.
 
IF you actually and truly agree with the KISS theory, then STOP just throwing parts at it and do some actual diagnostic work! Or do you just like throwing money away? The compression test would have been my FIRST MOVE!
 
He doesn't know the engines history. Sounds like a timing chain, nylon toothed aluminum cam gear.
 
CRUZE 418 said:
He doesn't know the engines history. Sounds like a timing chain, nylon toothed aluminum cam gear.
Click to expand...
You could be correct. And if i recall it was mentioned how to check for a loose chain.
 
I would say check the cam-timing FIRST, because if it has already jumped a tooth or three, the compression test will be LOW across the board; but without a history, you might not know if your numbers are low by design, or the chain has jumped.
In your case, you are not looking for a precise cam-timing measurement yet. You are just looking to verify a jumped chain. Nothing has to come apart yet, but your balancer TDC needs to be verified.

EDIT
Here is a clue;
Because the distributor is driven off the cam,
If the cam timing changes by itself, then
so will the ignition timing.
So if you come out one day and because the engine won't idle and runs like crap, you crank on the speed screw and then check the timing only to find that it is very retarded, THIS DID NOT HAPPEN BY ITSELF! Well it did, but the timing changed because the cam timing changed. So then, IMMEDIATELY a redflag should pop up in your brain. But instead, most guys will just put the timing back and wonder.
Of course, putting the timing back don't make it run much better, cause the valves are all out of time, and the cylinder pressure went on vacation..

I have personally had this experience, back when I was a young man, in the early/mid 70s .
I was called in to help with a 318 that would only barely idle with the 2bbl WFO, and the ignition very advanced. But in fact, changing the timing while the engine was ticking over, had very little effect, except the back-firing stopped. It didn't take long to figure it out, and when the front cover came off, there were just stumps remaining on the cam-gear, as the nylon was mostly gone. As I recall, the timing chain had jumped several teeth.
The point is this; it only takes a jump of one or two teeth to create chaos. If I could remember how many teeth are on that gear, then I could tell you how many degrees each tooth is, but, I cannot.
 
Last edited:
Verify plug wire routing. That’s FIRST. Then a compression check.
 
Daves69 said:
How old are the wires? While you verify routing, check resistances and for arching between and from your plug wires.
Click to expand...
Sometimes you ca
Daves69 said:
How old are the wires? While you verify routing, check resistances and for arching between and from your plug wires.
Click to expand...
If there is arcing going on, it would be readily apparent if you watch the engine running in the dark.
 
David,
You said that you got it started & that it did idle. Is the idle quality & idle rpm the same as before?
If so, that eliminates a lot of possible causes: slipped timing chain, plug routing etc.
Refer to post #13.
 
AJ/FormS said:
I have personally had this experience, back when I was a young man, in the early/mid 70s .
I was called in to help with a 318 that would only barely idle with the 2bbl WFO, and the ignition very advanced. But in fact, changing the timing while the engine was ticking over, had very little effect, except the back-firing stopped. It didn't take long to figure it out, and when the front cover came off, there were just stumps remaining on the cam-gear, as the nylon was mostly gone. As I recall, the timing chain had jumped several teeth.
The point is this; it only takes a jump of one or two teeth to create chaos. If I could remember how many teeth are on that gear, then I could tell you how many degrees each tooth is, but, I cannot.
Click to expand...
I had a '67 Mercury Cougar with a 289 and was racing someone one night. As the engine really started to pull, I heard a ka-pow and the engine died. Would crank but no start. Pulled the timing cover off and the nylon cam gear teeth were sheared off. The pieces were all in the pan and oil pump pickup screen. Early lesson for a young man with little knowledge.
 
Them nylon teeth gears weres tock junk. An engine with that now would be an indicator of a stock non rebuilt engine Im thinking. I was replacing them on 318s in the late 80s.
 
If I read your description right, you've had the car for awhile and the engine had been running well?

It sounds like it wasn't kept up though, ie: the dirty cap, rotor and dirty carb? Does it run on points? they might be bad too.
Like somebody mentioned above, don't overthink this but now that you've messed with the timing and carb adjustments you're gonna have to go back to the beginning.

First I'd find TDC, then set the timing to around 12 degrees. If it won't start then adjust the timing in tiny tiny amounts until it starts.
Also it sounds like you have your carb throttle (curb idle) open too far, back that off and set the mixture screws to 1 1/2 turns out evenly. If it won't idle do not be tempted to open the throttle more, you need to adjust the timing again so it idles where you want off the timing. If you have the throttle open too far it's sucking gas in and you will experience the off idle "hesitation" you've already described.

Good luck!
 
You must log in or register to reply here.
-

Back
Top