Hot Engine dies on idling

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kyamon

kyamon

Active Member
Posts
114
Location
Lausanne, Switzerland
Hello again
as described in a previous post, I recently had power-loss issues with my 6-pot engine on a 1974 S3. I replaced the distributor, cleaned the carburettor, replaced the head gasket and gave the cylinders and valves a bit of a cleaning. Yesterday I changed the oil... Everything was fine, the power was back, and the sudden power-loss issues from before were solved (because the flame trap in the fuel line had been clogged, actually). But now today, after driving about 50 km, the engine suddenly stalled, from one second to the next. I could immediately start it again, without problems, but then a couple of minutes later it happened again. Both times it happened when the engine was idling or near-idling.

What could this be? As always, your help is greatly appreciated!
 
+1 on idle jet, can you keep it running on the accelerator pump? ie press the pedal quickly just as its dieing? If yes then its probably a dirty jet, if no then it could be ignition, probably not fuel starvation as this would be worse under load. Clean the jets, check the adavnce / retard is working (and oil it) and speed up the idle a bit.
 
Hello back - I would like to reactivate this since the problem has come back (probably has never been solved...).
In the meantime I have practically redone the entire fuel delivery up to the carb (I forgot to specify that this is not a diesel, see below), so fuel starvation definitely is not the issue. It runs really well and seems to produce quite the power it should while driving. But when I drive for a while and everything is heated up, some times the engine stalls when idling - this never happens when the clutch is engaged, but when I depress the pedal the engine shuts off. So far it has always fired right back up, so it is not a serious issue, more of an annoyance.
I can keep the engine running either by slightly pressing the gas pedal, or by slightly pulling the choke.

What I have tried is to adjust the timing while the engine was hot, and retard as much as possible, but that did not help.
I am not sure what the idle jet is - might that be something specific to a diesel, so could some of the comments above come from the fact that I did not specify I had a petrol engine?
I did readjust the tappets when the engine was hot, but of course it could be that those are not perfect - would that lead to this symptom?
Increasing idling speed would, of course, remove the symptom. But I prefer to use this only as a last resort if there indeed might be other issues.

Thanks!
 
tottot said:
The idle jet is just that,a jet in the carb that feeds just enough fuel to keep the engine ticking over.
Click to expand...
Aha! (me be noob ;) )
So to add potentially silly nomenclature-related questions: in the carb I have the needle that points down into the reservoir - is that the jet, or is the jet formed through that needle?

My carb is a Stromberg 175. I will send a picture when I get a chance.

One other thing that may or may not be related - when the engine runs there is a clicking sound that is either at the rate of the rpm or for each tappet/valve (I can not measure the rpm, so I can not really decide which it is). It is a rather faint high-pitch (like when you softly hit wooden desk with your finger nail) tick that is there all the time (obviously faster when the rpm increase), but I am not certain if it is new or has always been there (I bought the car a year ago). Does this sound normal or could it be related to the stalling issue?
 
Turns out I have a couple of photos of my carb on my work-pc...
One thing I forgot to mention - when I pull the choke completely, I can feel (and hear) that the mechanism picks up the screw from the accelerator and almost gets stuck. At that point the engine revs up a bit (and stays), enough to generate quite noticeable torque on the wheels when I slowly release the clutch (I hope this description is clear...). From a purely mechanical point of view this might indicate that indeed the screw that sets the idling speed is too high (so not enough idling speed), which in turn would push the other set screw closer to the choke mechanism. If this is the case, then maybe I should really just adjust the idling speed mechanically...

What this does not explain, though, is why the problem only shows when the engine is hot.
 

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Aha a Stromberg carb.Look up how to tune a Stromburg carburetor, lots of info on line. [ Not fitted to many Landrovers but found on many older British cars.]
 
tottot said:
Aha a Stromberg carb.Look up how to tune a Stromburg carburetor, lots of info on line. [ Not fitted to many Landrovers but found on many older British cars.]
Click to expand...

:) Your "Aha" does not exactly sound encouraging. I have tried to figure out how to tune it, and tried a bit (as little as necessary, so far) - but the weird thing is that I dont have all the adjustment points that should be there. For example, there should be a screw below that regulates the fuel flow. On mine It is simply capped off with no possibility for adjustment. There is the plunger on the top that sets the spring force inside (?), but rotating that has no effect. I can change the floater level by slightly bending the wing that presses on the valve, but beyond that I dont see many possibilities to adjust.
 
kyamon said:
Turns out I have a couple of photos of my carb on my work-pc...
One thing I forgot to mention - when I pull the choke completely, I can feel (and hear) that the mechanism picks up the screw from the accelerator and almost gets stuck. At that point the engine revs up a bit (and stays), enough to generate quite noticeable torque on the wheels when I slowly release the clutch (I hope this description is clear...). From a purely mechanical point of view this might indicate that indeed the screw that sets the idling speed is too high (so not enough idling speed), which in turn would push the other set screw closer to the choke mechanism. If this is the case, then maybe I should really just adjust the idling speed mechanically...

What this does not explain, though, is why the problem only shows when the engine is hot.
Click to expand...
The CD Stromberg is a rather simple efficient device but can be a complex carburetor to set up for someone inexperienced, your initial post said you dismantled the carburetor as part of the original fault finding, in doing this you may have inadvertently upset the relationship between the needle and jet, the jet, in the main body of the carburetor needs to be perfectly centred to the needle, located in the dashpot piston. If the needle is dragging against the side of the jet, it will stop the dashpot piston from dropping down and rising as it is meant to do with variations of the throttle butterfly valve opening. Also check that the rubber diaphragm on the dashpot piston is in good condition, (no holes), and it is mounted correctly in the chamber cap and onto the top of the carburetor body. Be sure to put the required quantity of oil in the dashpot damper rod, (under the top screw cap, centre of the piston chamber).
I suggest you search out the complete setting procedure for the CD Stromberg and go back through setting the elements as per instruction. From what you have described it sounds as if you may have fixed the original problem and created another, but carefuly going back over the job you should be able to get things working well again.
 
Gazbo said:
The CD Stromberg is a rather simple efficient device but can be a complex carburetor to set up for someone inexperienced, your initial post said you dismantled the carburetor as part of the original fault finding, in doing this you may have inadvertently upset the relationship between the needle and jet, the jet, in the main body of the carburetor needs to be perfectly centred to the needle, located in the dashpot piston. If the needle is dragging against the side of the jet, it will stop the dashpot piston from dropping down and rising as it is meant to do with variations of the throttle butterfly valve opening. Also check that the rubber diaphragm on the dashpot piston is in good condition, (no holes), and it is mounted correctly in the chamber cap and onto the top of the carburetor body. Be sure to put the required quantity of oil in the dashpot damper rod, (under the top screw cap, centre of the piston chamber).
I suggest you search out the complete setting procedure for the CD Stromberg and go back through setting the elements as per instruction. From what you have described it sounds as if you may have fixed the original problem and created another, but carefuly going back over the job you should be able to get things working well again.
Click to expand...


Thank you (and everybody, in fact) for your help!
You are probably right in saying that I fixed one problem and created a new one (or more than one, in fact). The price I pay for doing something that I am absolutely no expert in - but that is how I am learning. I will certainly go back and have a much closer look at the carb, and use more specific instructions (thanks, Hat man, for the link!) to adjust it - I was not aware, for example, that one had to add oil to the dashpot damper rod!

There are still a few things that fundamentally confuse me, though:
1. In all instructions, including the ones linked above, it says that the mixture-adjusting screw (or self-adjusting screw) had to be set. I dont have that screw at all, there is simply a cap.
2. The dashpot piston has been stuck all the way up at some point, but now is in the right place. When it was stuck, the engine would not start unless I sprayed petrol directly into the carb (through the air intake). Once running like that it was idling fine for a while, but as soon as the accelerator was depressed, it would die. This is not all that surprising, and I found and solved that issue.
3. The problem I am having now is no longer the same as what I described at the very beginning of this post. That was, in fact, caused by the stuck dashpot piston, in combination with a faulty fuel pump - I believe. By now the engine in principle is running fine (sounds good (almost quiet ;) ), nearly no misfires, good power, normal fuel consumption as far as I can tell, no coloured smoke from the exhaust). But when it is hot, it stalls when idling. Do the required settings on the carb depend on the engine temperature? Or should they be set when the engine is hot? Or could the problem still be a combination of imperfect settings on distributor, carb, valves, etc.?

In any case, the thing for me to do indeed seems to be to double check the carb and set it up as instructed.
Again, thank you all for your patience and help!
 
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