72 Duster, Ethanol gas, intake backfire

-
Kern Dog

Kern Dog

Build your car to handle.
FABO Gold Member
Joined
May 23, 2010
Messages
9,805
Reaction score
28,225
Location
Granite Bay CA
Hey there,
I have a 72 Duster that sits for long periods of time. It is my Brother in law's car and he lives out of state. 360 with a Holley 600 4 barrel.
Here in CA, the blend is supposed to be "up to 10%" but testing has been reported to be around 6%. Regardless, the color of the fuel in the filter and the bowls is a pale yellow green. The last time I put more than 3 gallons of gas in it was several months ago, maybe last fall? Not sure.I did put about a gallon in it recently since I didn't know how much was in it.
My point....
The car idles fine. I did have to replace the needle & seat in both the primary and secondary bowls. Under a load, it sometimes backfires through the carburetor, It is not consistent like it would be with a bad exhaust valve or worn exhaust lobe, just occasionally. The ignition system is old. The engine bay wiring is old. The alternator is not charging even though I have tried three alternators and a different voltage regulator.
Yeah....The car needs work as many do,,,,But my question is: Can old ethanol laced fuel cause a backfire like this OR should I be looking at the ignition system?

IMG_0995.JPG
 
I have seen ethanol fuel go piss bad in about a month just sitting. It doesn't last any time at all. I highly recommend running "some kind" of ethanol fuel treatment. Lucas makes a good one. Until you eliminate that, I don't think I would try diagnosis. That might just fix it.
 
I did a factory type later electronic ignition swap into the car many years ago. It is at 12 degrees initial. I don't know what the total timing is. I guess if the advance springs are sticky and finicky, that could result in some sketchy operation.
I suspect the fuel but I do appreciate the other suggestions.
 
Agree with RRR. If it's any motor other than my DD, I put fuel stabilizer in everything. It makes a huge difference in the crap gas not turning to varnish or clogging the fuel system.
 
I agree that the gas could be a problem but my '70 Charger sits for months sometimes. I use 91 octane with the ethanol in it and the car seems to run fine.
Not trying to cause an argument, just stating an observation. I'll readily admit that the gas in the Duster has an odd color to it that the Charger does not have.
 
I have real nice ‘83 D-150 that is my summer time driver, from April to November and a beater 240K mile 96 GMC Sonoma that is my winter daily driver, typically from December to March. Each one gets filled with Indiana ethanol gas then sets during the down months.
I do add Stabul fuel stabilizer and have never had a fuel issue on either vehicle. Ran these trucks this way since 2011. I too have heard the story that ethanol gas can go bad in a month. So maybe the Stabul makes a difference. But it could be another urban legend. Mainly because it would be easy to do,,,,
I would fix the battery charge issue and drive the Duster daily till I used the fuel in the tank up. Put in fresh and see if the mis fire goes away. The old ignition wiring could also be the issue. So if running fresh gas does not fix it, give it a good tune up, spark plugs, wires, cap, rotor,,,
 
Last edited:
Sta-bil or sea foam are the only 2 products i prefer to use.
Gas goes bad pretty quick nowadays,and not the greatest thing for the engine.
I would say, add premium gas, sea foam and run it.

Check timing and make sure mechanical advance isnt hanging up.
 
Here's hpow I look at it.
It takes three things to get combustion.
Vaporized Fuel, O2, and something to ignite it.
So really the only way for backfire through the carb is when there's spark before a intake valve shuts.
So yea -I'd first check the ignition system for something that will cause early spark. And then sad to say - the valve train.

All our current pump gas has poor storage and looses its light end easily. The light end of fuel is the stuff that vaporizes easiest. Think of it like the tinder and smallest kindling when building a camp fire. Take that away and its much harder to get a good fire started. My experience with old fuel is that the engine misses, and with winter fuel in the tank when the engine is hot sometimes it will just die -especially under load. Doesn't sound like you've got either of these. The other issue with current fuel you've already looked at - sometimes its components attack rubber check valves, diaphrams etc.
 
Kern Dog said:
Hey there,
I have a 72 Duster that sits for long periods of time. It is my Brother in law's car and he lives out of state. 360 with a Holley 600 4 barrel.
Here in CA, the blend is supposed to be "up to 10%" but testing has been reported to be around 6%. Regardless, the color of the fuel in the filter and the bowls is a pale yellow green. The last time I put more than 3 gallons of gas in it was several months ago, maybe last fall? Not sure.I did put about a gallon in it recently since I didn't know how much was in it.
My point....
The car idles fine. I did have to replace the needle & seat in both the primary and secondary bowls. Under a load, it sometimes backfires through the carburetor, It is not consistent like it would be with a bad exhaust valve or worn exhaust lobe, just occasionally. The ignition system is old. The engine bay wiring is old. The alternator is not charging even though I have tried three alternators and a different voltage regulator.
Yeah....The car needs work as many do,,,,But my question is: Can old ethanol laced fuel cause a backfire like this OR should I be looking at the ignition system?

View attachment 1715366848
Click to expand...
There is no snake oil on the planet that you can dump into the tank that will make bad fuel good again.
You will need to remove of the old crappy fuel and refill with fresh fuel.
I have seen carburetors permanently damaged from ethanol that they are adding to current day fuels.
If your rig ran fine in it's current configuration and no runs differently after non use. You most likely have carb issues.
 
Mattax said:
All our current pump gas has poor storage and loses its light end easily. The light end of fuel is the stuff that vaporizes easiest. Think of it like the tinder and smallest kindling when building a camp fire. Take that away and its much harder to get a good fire started.
Click to expand...

Here is another symptom that I forgot to mention.
It may be unrelated or possibly a different problem but even though there is a healthy accelerator pump shot, the car is very hard to start. I had to spray carb cleaner down the throat to get it to fire. I did this several times.
 
Kern Dog said:
I had to spray carb cleaner down the throat to get it to fire
Click to expand...
Carb cleaner is not starter fluid. My dart sat in so cal for 4 years with a half tank of standard off the shelf gas. After a shot of starter fluid it fired right up. I filled the tank with new gas and put 200 miles on it. Filled it again. A few months later I changed the sender and except for a handful of rust spots in the tank it was clean as a whistle.

I couldn't agree with mattax more. if no spark at the wrong time or an open intake valve , no backfire.

I had a dist that had do much up and down slop it would throw spark to any number of cyls. I suspect the rotor would make and loose connection to the center of the dist cap. I put the oem dist back on and the backfire / miss went away.
 
Kern Dog said:
Here is another symptom that I forgot to mention.
It may be unrelated or possibly a different problem but even though there is a healthy accelerator pump shot, the car is very hard to start. I had to spray carb cleaner down the throat to get it to fire. I did this several times.
Click to expand...
Igniting the spark early can make it difficult to start & igniting spark early can cause backfire.
 
we run e85 in our race cars....I have let the 85% ethanol set for over 6 months and never had a problem with it running in the cars......
6% ethanol is not going to make it backfire...check your accelerator pump is adjusted correctly....check your floats.....and your ignition...
 
Dana67Dart said:
Filled it again. A few months later I changed the sender and except for a handful of rust spots in the tank it was clean as a whistle.
Click to expand...
When I was kid, we always kept the cars tanked up if we could. The idea was to limit the air and so reduce the chance of condensation.
But nowadays I don't know what's best when storing stuff outside or in a damp garage.
For the small engines that sit for months (snow thow, leaf shredder) I try to run them low and/or put some real gasoline in them before done running it for the day/week/month. Several companies sell small engine fuel, or some of the lower octane race fuels work (like C9). Saves a bunch of time and not too expensive if not burning it all the time. The car is a little more complicated, but a similar approach has been possible since I've had a somewhat dry and heated garage. Technically most of the storage fuels mentioned before are not for street use, so either drain or take the car to your local drag strip, autocross or such. :)
 
Last edited:
my68barracuda said:
I have real nice ‘83 D-150 that is my summer time driver, from April to November and a beater 240K mile 96 GMC Sonoma that is my winter daily driver, typically from December to March. Each one gets filled with Indiana ethanol gas then sets during the down months.
I do add Stabul fuel stabilizer and have never had a fuel issue on either vehicle. Ran these trucks this way since 2011. I too have heard the story that ethanol gas can go bad in a month. So maybe the Stabul makes a difference. But it could be another urban legend. Mainly because it would be easy to do,,,,
I would fix the battery charge issue and drive the Duster daily till I used the fuel in the tank up. Put in fresh and see if the mis fire goes away. The old ignition wiring could also be the issue. So if running fresh gas does not fix it, give it a good tune up, spark plugs, wires, cap, rotor,,,
Click to expand...

Right! Check the "free stuff" first.
 
Nice car!

At idle, your effective compression ratio could be 5/1 or even less.
At WOT, it will be whatever the design might be, say somewhere between 7.5 and 8.5.
When you tip in the throttle, the effective compression ratio will vary between those two extremes, depeding on the throttle-opening.
>If for some reason, an intake valve to not quite closed; it might idle just fine. But as the effective C/R rises, the burning mixture, and rising pressure, in the chamber could back up into the intake.
But with log manifolds;
>Then again,an overly rich mixture, still burning in a log manifold can force combustion in an adjacent cylinder,that is on it's overlap cycle, and idling very slowly which allows plenty of time for this to occur.
>And of course the simplest reason of all; the 1-2 whammy of a lean missfire and a leak at the flange of a log-manifold. This goes back to the preceding paragraph, but does not require the slow idle speed. With a missfire, a great deal or all of the just inducted mixture never catches fire or escapes burning in the chamber, for whatever reason. Now it's hot, and entering into a hotter still environment.... that may have fresh air in it. If a still burning mixture, or when,lol, from another cylinder comes along and lights it up, that adjacent cylinder is about to go into overlap, which will directly connect that burning expanding , higher than atmospheric pressure, ball of fire, to the lower than atmospheric pressure intake manifold......... which itself is full of a combustible mixture. Thankfully the overlap period is very small, but the fire in the intake has to go somewhere.............
 
I didn’t read all the comments, but about the worst thing you can do with ethanol blended fuel is keep it exposed to the air. It soaks up moisture, and **** will grow in it. When it’s going to be parked, always top the tank off. Fuel stabilizer is good, but it will still absorb water if there is air present in the tank
 
my lawnmower wont last 3 weeks without gumming up the carb jet. Here in the summertime, not alot grows so I dont mow all that often, but I can guarantee the first time I try and start it from a months rest, it wont start and Ill be cleaning jelly out of the tiny carb bowl. I guess the fuel system is not sealed from moisture as well as a car (although they are not sealed well either unless they are EFI, with the Holley and Carter bowl vents wide open) and I live 7 miles from the beach so its not dry weather here with every morning cloudy that burns off by 10. I have a clear bottle I store gas in. If I fill it and cap it, its clear. If I leave the cap off for an hour, it turns yellow. Hygroscopic.....the ability to absorb moisture. Dot 4 or lower brake fluid and blended gas.
 
I’ve actually had green cloudy gas come out of the mower.

Just life nowadays
 
Mattax said:
Igniting the spark early can make it difficult to start & igniting spark early can cause backfire.
Click to expand...

No, early spark almost never causes backfire. Early spark can cause the starter to stall and "kick back." Kick back can certainly cause hard starting.

Sounds to me like this could be a LOT of things and a combination of more than one

1..Stale fuel, as mentioned, replace, use treatment
2...Check plugs plug wires, cap rotor, and replace if necessary
3...Check timing, and check advance mechanism. Sitting long periods can most certainly cause advance weights to gum up / rust etc
4...Carb....Too lean from gum and varnish, and accelerator pump working poorly
 
You must log in or register to reply here.
-

Back
Top