Intermittent misfiring problem and black smoke from the exhaust

[Cowhorns]

I have a 79 4LF4 R2109. I had a problem with the car stalling over the summer here in France. Whipped out the plugs last week which were black( I had to keep putting on the choke to stop it stalling) and then cleaned them put them back and adjusted the idle speed. Car was running fine but then started to misfire and lose power for a 10 secs or so. Yesterday ran fine, today wouldn't hardly run at all this morning, misfiring, very ragged and shakey and even backfired (which is super loud in a 4L!) and bad again this afternoon then this evening all fine again. I did however notice that even when running fine the exhaust was pumping out black smoke and soot. Also fuel consumption has gone up. Looking initially at the misfiring, I took the cap off and the rotor looked worn. Was planning on replacing condenser, points, rotor and distributor cap but I'm told problems there might not necessarily account for black smoke. Reading on here could it be a carb problem? Or a combination of both? The 28IF carb was replaced earlier this year with a brand new one. Any guidance about either issue gladly received.

Peter

 

[Cowhorns]

And on a related point.....hoe do I tell the brand/manufacturer of the starter?

 

[Andy McGhee]

And on a related point.....hoe do I tell the brand/manufacturer of the starter?

The make will be stamped into the body of the starter - difficult to see, especially on a LHD vehicle!

 

[Andy McGhee]

I have a 79 4LF4 R2109. I had a problem with the car stalling over the summer here in France. Whipped out the plugs last week which were black( I had to keep putting on the choke to stop it stalling) and then cleaned them put them back and adjusted the idle speed. Car was running fine but then started to misfire and lose power for a 10 secs or so. Yesterday ran fine, today wouldn't hardly run at all this morning, misfiring, very ragged and shakey and even backfired (which is super loud in a 4L!) and bad again this afternoon then this evening all fine again. I did however notice that even when running fine the exhaust was pumping out black smoke and soot. Also fuel consumption has gone up. Looking initially at the misfiring, I took the cap off and the rotor looked worn. Was planning on replacing condenser, points, rotor and distributor cap but I'm told problems there might not necessarily account for black smoke. Reading on here could it be a carb problem? Or a combination of both? The 28IF carb was replaced earlier this year with a brand new one. Any guidance about either issue gladly received.

Peter

Maybe you've already looked at these, but it'd be worth checking the following:
- Is the choke linkage working properly?
- Has the pipe that goes to the manifold (under the carb, on the engine side) fallen off?
- Have the points closed up? If they have (which they often do), it'll retard the timing and make the mixture too rich.
- Condenser okay?
- Dirty air filter?
It could be a carb issue, but it'd be worth checking the ignition system first - ideally, one thing at a time.
Good luck!

 

[André4Renaults]

CONDENSER! You can't normally repair or test them, unless you've both a degree in electronics and a load of sophisticated electronic equipment, so change it and see if things improve. A faulty condenser will cause the points to burn out, so examination of them will prove instructive, but I would bet my reputation that the condenser is at the bottom of this.

 

[angel]

The 28IF carb was replaced earlier this year with a brand new one.

This makes me suspect the carburettor, these offered nowadays as "brand new" are poorly made copies. Check the float and float valve, it seems to me that the carburettor is overflowing or the fuel level is too high.

 

[Cowhorns]

Maybe you've already looked at these, but it'd be worth checking the following:
- Is the choke linkage working properly?
- Has the pipe that goes to the manifold (under the carb, on the engine side) fallen off?
- Have the points closed up? If they have (which they often do), it'll retard the timing and make the mixture too rich.
- Condenser okay?
- Dirty air filter?
It could be a carb issue, but it'd be worth checking the ignition system first - ideally, one thing at a time.
Good luck!

Sorry for the delay responding. I had to pop back to Blighty. Choke seems to be working fine although not quite going fully in( a couple of mm of play) , condenser replaced, rotor arm replaced, points replaced- still need to reset with a feeler gauge but looked ok vs the photo I took before. Air filter fine. Engine seemed to be running better but.....it was always a bit hit and miss and it might misbehave again if I go for a drive. Still the black smoke and soot though especially when you rev it. Next stop, after the points reset is the carb.

 

[Cowhorns]

CONDENSER! You can't normally repair or test them, unless you've both a degree in electronics and a load of sophisticated electronic equipment, so change it and see if things improve. A faulty condenser will cause the points to burn out, so examination of them will prove instructive, but I would bet my reputation that the condenser is at the bottom of this.

It may be at the bottom of this but replacing it hasn't had the desired effect that I can see. Its still pumping out the smoke etc. Although the points were very pitted and rough.

 

[Cowhorns]

This makes me suspect the carburettor, these offered nowadays as "brand new" are poorly made copies. Check the float and float valve, it seems to me that the carburettor is overflowing or the fuel level is too high.

Thats the next step I feel. Anything immediately apparent to look for while it is in situ? Ie after air filter etc and the top of the carb is removed?

 

[André4Renaults]

It may be at the bottom of this but replacing it hasn't had the desired effect that I can see. Its still pumping out the smoke etc. Although the points were very pitted and rough.

The points being very pitted is indicative of a failed condenser, since the pitting means too much current is passing through the points, because the condenser isn't "cushioning" the load. I would check the new points are both clean and correctly set before deciding the condenser's not at the bottom of this. it's also possible that the new condenser you have fitted isn't all it's cracked up to be......

 

[angel]

Thats the next step I feel. Anything immediately apparent to look for while it is in situ? Ie after air filter etc and the top of the carb is removed?

Have a look inside the carburettor throat with choke flap open. With engine running at idle, you should not see fuel puddling on the throttle butterfly (the one that is located at the bottom of the carburettor), nor fuel dripping from the diffuser.

 

[Cowhorns]

Have finally got to the bottom of this. I've changed the condenser and the points. That may have helped or may not but it didnt fix the black smoke. So attention turned to the carb, looked for an airleak but didnt find one although replaced the pipes in any case. The petrol was kind of pooling in the bottom of the carb. Took it off its a 28IF and took it apart. One of the brass screws ( not sure if this was a jet) was loose so we tightnened it. The brass needle was stuck- whether this was a cause or a symptom not sure but we replaced it in any case and then finally the brass disc that sits inside the carb had fallen off and was sitting under the float. We "peened" this back on ( an new word for me but made little punch holes around the side so it is held in (the french verb for this is sertir btw) cleaned everything changed the gaskets both in the carb and under it as well as under the supporting bracket and then put it all together again. Work perfectly. All this expert assistance from a retired mechanic cost me a couple of bottles of nice wine . Now I have to change the oil as it has a bit of a petrol smell and I'm good to go. There are some advantages to living in France. THanks to everyone for their help and suggestions on here.

 

[Agb]

Had an intermittent misfire as above. Changed the condenser but it persisted. Turns out the new condenser was slightly loose in the strap bracket that attaches it to the distributor body so it wasn’t earthing properly.
Have swapped for a condenser with an integral bracket and all is now fine.

 

[Lou]

Our 83 R4 1108cc has started getting a similar problem. Been good all summer but then poor at starting this autumn when it's turned colder and wetter, eventually with 1/2 choke it does start and once going suffering flat spots when accelerating even when warmed up. Today when driving back home it lost power and cut out completely. Waited a few minutes and it restarted, but had to use some choke and keep the revs up to keep it running to get home. If I put the choke in it started nearly stalling again.

It was all restored in 2018 but then sat about unused for years until we got it this summer so have gradually been replacing stuff - fresh fuel, tyres, brakes and fluid, oil, coolant, air filter, plugs, HT leads, and soon to do rotor arm, coil, condenser, points etc but am thinking it could be a fuelling problem causing the recent running problems. It has a Zenith 28 carb, see pic, I noticed a clamp missing off the fuel line so I'll replace that. Perhaps this carb needs a refurb and look at the filters or any air leaks? Maybe some gunge in the float chamber or jets from when it was stood for ages. Just seems odd as it was all okay in the summer months. Can do most stuff myself and have an old school good mechanic friend to help too when needed. We'll get there....Any thoughts appreciated. Cheers L

 

[Andy McGhee]

If it's not gunge in the fuel system (quite likely) or an ignition problem, have you checked the air filter hose position? I remember you said that the hose was still pointing forward. It might be worth putting the hose on the winter setting to see if it makes a difference.

 

[Lou]

Yep I'll try moving that too, cheers