Hello! New to mopar and new to forum.

I bought a 77' new yorker few months ago and its awesome boat.
But now few days back it just suddenly started backfiring in carb and jerking alot when pressig gas.

It has the lean burn box in it, but i think someone has converted it or at least tried.
Theres the Orange ignition box, and ive heard it fails alot and causes jerking and backfiring,
So i changed it and ballast resistor to test, but did nothing.

Any ideas how i start checking and what?
Cheers

 

Does it run good at part throttle and easy inputs? But get exponentially worse when more throttle is applied?

Your are correct to start with basics. Fuel, Spark and Air. DO physical inspection to make sure all hoses and tubes are connected.

Air is easy. Make sure the filter and its path are unrestricted.

Fuel: A new fuel filter, no crimped or bent lines, good pressure at the carb

Spark: You can buy a small in line tester to make sure you have consistent good spark at each plug.

Diagnose before you replace parts.

 

PK1 is correct
also check the carb make sure the base plate gasket is good and the carb is tight not loos on the manifold

 

It ran fine for a while with part throttle, but now goes bad with all throttle. Idle is Good.
I was gonna change that fuel filther but theres a 2 line filter and this new is the same kind but has 3 lines.
Can i plug the 3rd line without causing any problems?

 

s -

Lets think about this for a second. If you're back firing through the carb, it's almost always a timing/spark problem. While a sticking valve or bad spring could be at fault, it's less likely, but certainly not impossible. One way or another, an intake valve is open when the fuel is igniting.

Not sure what you mean by part and full throttle (rpm numbers would help), but you may have insufficient total advance on the timing.

If you think you're missing in a cylinder, get a laser thermometer (about $30) and take a reading from each exhaust port on the manifold or header. They should all be pretty close in temp.

There's nothing wrong with the Mopar ECUs, the last one that failed on me was 30 years old.

Archer

 

To answer your ??? the third port on the fuel filter is a return and yes it can be pluged off. I think your on the right track it called a lean backfire. Do the filter before you change anything else. Keep us posted but I think you will be good

 

Does the distributor have a vacuum canister on it ?? If no ? it may still have the lean burn dist. I would start by replacing the vacuum lines 30 year old lines are probably rotting & check the ign timing with a timing light

 

I would say it is a fuel problem Vehicles dont just have a timing problems all of a sudden. Unless it jumped time or the distributor is loose neither is likely. So change the fuel filter and let us know that it is fine/fixed. The problem here is there is to much thinking going on. And the obvious is overlooked. And amagine if you took it to a shop to be fixed it would cost you hundreds of dollars to get you car misdiagnosed when all it needed was a fuel filter. trust me.

 

Thanks for thinking and answering!
I changed the fuel filter and guess what it worked! no more jerking or backfiring, works nice, BUT now i got a new problem.
While starting the engine, i have to press gas about ½way down and crank it for a while before it starts, before the filter change i just had to turn the key and it fired right up,
its not that big deal, but of course it would be nice to work properly, so what next?

 

Needs a tune up and check the wearable parts. If you drove it until the filter was clogged consider that the other items are past their service life too.

 

More than likely a piece of dirt is allowing gas to get passed the needle an seat causing it to flood when sitting. To check this look in the carb. throat and see if you can see gas dripping or if it is wet. The needle and seat is real easy change on a 318 with a carter carb. It just screws into the front of the carb after the fuel line is removed.

 

Ok it worked fine about 2days but now the backfire / jerkin is worse than ever.

 

s -

Really??? Actually I was kinda expecting. You have a timing problem, not a carb problem. (Sorry, just can't see how a carb issue would cause a backfire through the carb, mechanics just don't work that way. There has to be a spark getting to the atomized fuel in the manifold or carb.)

If you have the stock timing chain with plastic gears, you could have slipped a tooth. Your timing light readings will be right, but the crank and cam will be out of sequence. Could be cross-fires between wires, anything, kinda hard to diagnose over the net. May just have to be trail and error. Start with the simplest things things, even if they have a low probability, and work your way to the harder and more expensive.

What the other guys are saying is correct and can explain your symptoms, EXCEPT for the backfires.

Archer

 

could be possible the Dist cap is cracked or the rotor has gone bad. or maybe it just needs a good old fashion tune up.

 

How long did this car sit before you bought it??? I guess no one has heard of a lean condition causing a buck or jerking. What about when a bad accelerator pump?? Its called a lean backfire. It can also cause the engine to skip. MAYBE just MAYBE the fuel filter is plugged again because there is water or stale gas or just plain dirt in the tank. Take the fuel filter off again and blow through it if you can. Or blow backwards through the filter capturing the fuel in a container to see what is in it. Put a see through filter on so you can see the gas,dirt & water if any. It is the quickest way to check for your problem, Think for a minute it ran good for 2 days why would timing or plugs run good for 2 days then run poorly again. It makes no sense at all. Keep me posted

 

My ten cents.

Carb has crap in it. Fuel filter was toast and junk got thru. Its now going ultra lean and back firing due to lack of fuel, not premature spark. Premature combustion. Lean back fire.

Although two things could go bad at the same time. I wouldn't take timing out yet as it would just be masking the symptom.

 

PK1, You are the only one on here that actually thinks and agrees with what I have been saying all along. You must have been born and bred on carburated cars. On todays cars this symptom is a little more complexed but with a carburated car it is simple mechanics. I too would rebuild the carb. and clean the fuel system if the fuel filter is dirty again after just replacing it

 

O man.. Things were so much easier then! In the time it takes to read this thread we could have throw on an old transplant carb and fired it up to confirm contamination, rebuilt it and still caught today's race

I would throw another filter on there. Worse case scenario you have a spare and spent 10 bucks if it isnt that. If she is clogged again the tank has crud in it.

If not grab a rebuild kit and a pizza... Hell, she is 36 years old, she's gonna need some TLC. It would get a carb rebuild for piece of mind if I were running her daily.

 

I'm still waiting for him to pop the top off the carb and find black and grey stuff in there along with green and brown.

 

10/4 PK If it were a 360 with a Holley 2 barrel I would send him one that came on the engine I bought for the block to build for my Street Duster

 

I will check the filter again soon and then open carbs top, but its too cold to do anything outside now (-20 c) and i lack an inside place, but i post the results soon.

Btw how does that self releasing parking brake work? After putting gear in N or P it makes vacuum hissing noise and then i can put the brake on, and when selecting any driving gear it released, but sometimes it takes pretty long time to make that sound, and sometimes it cant be used at all.
Never seen that kind of brake system.

 

i'm just throwing idea's out here....
what about worn points and or distributor bushings?... what about a crossed plug wire maybe a defective coil maybe bad coil wire and or plug wires?...maybe a sticky valve/lifter?... maybe a lean back fire maybe a leaking vacuum line? bad leaky fuel lines?
a lot too check

 

I opened the carb and it had some brown/greyish stuff in there, so i cleaned the whole carb and used rebuild kit and made the adjustments. Choke pulloff was broken so i changed it too.
I put it back and it fired up nice and idle ok, but still backfiring, plus it makes a strange sound now that i cant describe, i tried to put a video on youtube but its slow.
Gonna go back tomorrow and try to check if i failed something

 

please tell me you didn't connect the plastic line from the passenger side of car to the tube on the top of carb yet.

 

Yes i did put everything back in place. I didint know that i should leave something out :/

 

the plastic line coming from the charcoal canister should have been left off for now. Chances are the canister is shot and is putting stuff into your carb.

Take the top off again and look inside the carb does it look like there is grey stuff in it again?

 

It was still clean.
I got the backfiring stop by turning metering rod to richer mix, but i havent got it running good yet. Idle is good but when pressing little gas while cruising it just slows down.
So the backfire issue is solved, now i just have to try tune it right.

 

With everything that has been said ??? Have you ever put a timing light on it to check the mechanical timing ??????

 

Checked the ignition timing. It was 12 on idle vacuum line disconnected and 14 at 2000rpm

 

Check the timing at say 3000 rpm, you may have a stuck or sticking secondary mechanical advance inside the distributor.