Engine Running Rough and Backfiring

[coolhuh]

1984 CJ7 with a 2.5L 4cyl.

Engine runs rough, backfires and has very little power. I changed the plugs, rotor, cap and wires, set the timing and it ran fine. I parked it in the garage, today I started it up and it is running rough, backfiring and low on power.
It has done this several times, I get it running good and after it sits for a day or 2 it runs rough and backfires.

Any suggestions, it seems like a timing problem.

 

[lqdtrance]

When this happened to me it was my cat. blocked up.

 

[coolhuh]

Mine only has a muffler no cat.
It runs good, then it runs like crap, then it runs good.
It feels like a timing issue, but the distributor stays in the same place.
Would a loose timing chain do this?

 

[xt master]

timing chain could cause the problem,but you may want to check out the carb also..I am assuming you have a carb.could be sticking after sitting.

 

[coolhuh]

I took the carb apart and cleaned it good, it should be good. I am in the process of looking at it again.

 

[xt master]

check the vacuum lines going to the carb also if one has a leak some where can cause some problems.

 

[SteelHeadz]

I'm thinking the carburator as well. If it's the timing chain, it would do it all the time. I could see a possible vac. leak as XT has mentioned but i would suspect it to be a gasket instead of a line since it only does it after sitting and seals up after the engine is heated up. Just a thoery. A bad catalytic converter usually does the opposite as Lqdtrance has mentioned. If the cat. is not 100% plugged yet, it will run fine when cold and progressively will cause the engine to loose power at around 2000 rpm as the engine warms up.

 

[coolhuh]

I noticed the shaft for the butterfly near the base is leaking gas. It is a Carter 1bbl carb, can this be repaired or does it need replaced?
If needing replaced what is a good 1bbl replacement

 

[SteelHeadz]

Depending on how worn that carburator is would be contingent if its a rebuildable unit or not..Weber has a replacement unit for that but i dont know if there is any other alternative sources out there..

 

[sweetpeet]

1984 CJ7 with a 2.5L 4cyl.

Engine runs rough, backfires and has very little power. I changed the plugs, rotor, cap and wires, set the timing and it ran fine. I parked it in the garage, today I started it up and it is running rough, backfiring and low on power.
It has done this several times, I get it running good and after it sits for a day or 2 it runs rough and backfires.

Any suggestions, it seems like a timing problem.

you should check and make sure that the firing order is set up right becouse that happened to me. I got my jeep then it started to ride rough then I set the order right then it ran gerat. so give it a shot.

 

[denisg]

1984 CJ7 with a 2.5L 4cyl.

Engine runs rough, backfires and has very little power. I changed the plugs, rotor, cap and wires, set the timing and it ran fine. I parked it in the garage, today I started it up and it is running rough, backfiring and low on power.
It has done this several times, I get it running good and after it sits for a day or 2 it runs rough and backfires.

Any suggestions, it seems like a timing problem.

I've the exactly the same problem in a jeep racecar with an allis chalmers engine
I'm on my 4th carburetor, this one seems much better than the others. little backfiring and more power.
3rd heatrange of plugs.
set the valves
checked timing
cant find it...yet.
dennis

 

[coolhuh]

I found a good deal on a Weber carb, it gets here on Tuesday.
Hopefully that will fix the issue.

 

[coolhuh]

I put the Weber on and it still runs rough.
It is very rough at idle and clears up a little with higher RPM but is still rough.
When I pull a plug wire on 2 of the cylinders the engine gets rougher, the other 2 their is no change?

 

[SteelHeadz]

I put the Weber on and it still runs rough.
It is very rough at idle and clears up a little with higher RPM but is still rough.
When I pull a plug wire on 2 of the cylinders the engine gets rougher, the other 2 their is no change?

If the other 2 ignition wires you pulled didnt make a difference on the engine idle, that indicates a Misfire condition. Check for spark on those 2 wires. Recheck the wires for their proper cylinders, you might have swapped 2 wires by accident.

 

[denisg]

I put the Weber on and it still runs rough.
It is very rough at idle and clears up a little with higher RPM but is still rough.
When I pull a plug wire on 2 of the cylinders the engine gets rougher, the other 2 their is no change?

mine cleared up with a different carb. [I ran hotter plugs too].

 

[coolhuh]

I replaced the fuel filter and no difference.
When it starts when cold it runs very rough at idle. If I drive it, it spits and spudders down the road. After about 3-4 miles it all of a sudden runs perfect.
It does this every time and it does not gradually get better, it is like turning on a switch. After it cools for a while the same thing until you drive it for a bit.

I am totally confused.

 

[denisg]

Normally, spitting out the carb is said to be due to a lean mixture and popping out the exhaust takes place when the mixture is too rich.
It is easier to understand the exhaust popping as that takes place when unburned fuel ignites in the exhaust. [ Made worse when there is a leak which can admit oxygen that helps things burn]
Now the other half that takes place in the intake is backfiring. It ranges from minor spitting out the intake to really loud hard backfires. Mine was ok at low speed but it sounded like gunfire when I got it on the road..it was undriveable so I only ran it far enough to turn around [1 mile]. It did it for me at low speed also until I changed to richer jets. Carbs have several ways of adjusting the fuel to air ratio:
1. for an autolite[motocraft] carb
idle..set by a screw adjustment.
Midrange.... determined by the mainjets.
high power... determined by a vaccum operated erichening valve [the power valve]. the power valve determines WHEN to open extra passages and the AMOUNT added is determined by the passage size]
acceleration: extra-rich for acceleration needs supplied by a single shot pump
Fuel mixture ratio problems were at the root of it for me.
[Power valves have a rubber diaphram which is destroyed by one good backfire.]

2, Weber carbs are a little different. It is easy to change jets on them as on my webber the jets can be changed from outside the carb. The weber company is good at suppplying jets. It is not hard to plug up a Webber. To clean mine I had to drill out the lead plugs and run a small drill down the passages to clean them. Then I replaced the plugs, tapping lead fishing weights in where plugs were needed. Cleaning made a huge difference in how well it worked.
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You had backfiring until it warmed up. A very good clue. Wires to the wrong sparkplug are eliminated as that does not change with temperature. Crossfiring could cause your trouble. I think it is not the cause but to be safe, move the plug leads well apart from eachother, if they have to cross do so at 90 degrees, but do not let them be parallel and close.
As the carb has different circuits, identify which one is giving trouble. I think it is a mixture problem in your case. Sounds like what would happen if a choke was not working as the trouble departs once your engine is warm. When it is warm a leaner mixture can be used, but when it is cold fuel vaporization is not as good and more fuel must be supplied.
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I was making up a system from scratch. What I had was worse than yours as mine never got better. When scratch building a manifold, it is good to use an oxygen sensor in the system [connected to a digital voltmeter, ideal voltage is between .4 volt and .6 volt]
and a vaccum gauge so you know the carb circuit in operation

 

[coolhuh]

I understand where you are coming from but why would it be like a switch was turn on and it runs better. it is not gradual, it goes from bad to good in a second.

 

[yo momma yj]

I'd check the compression for intermittent sticky valve stems in the guides.

it sounds like the valves aren't seating with backfire thru both the intake and exhaust...assuming the cam is staying in time.

do a compression check when running right and also when the fault surfaces...and see if the numbers change.

could be carbon migrating or even a loose valve seat in the head that occassionally gets dislodged.

 

[carnuck]

Could be sticky valve (a quart of synthetic oil or CD2 engine detergent in the motor tends to help clear that up) or cam walk (sloppy chain will smooth out after warmup) brake booster sucking air or another vacuum leak? (intake gaskets are common) Timing too far retarded.