Engine cuts out when hot

PeterF

Member
Hi all,
I've had my S2 P6B 3500 Auto (1972) for a few months now. The car had been laid up for some years, so i've been fixing various problems that have arisen since using it. The forum has been a great source of help, what a great bunch of expert contributors!

I have often had a problem with the engine stalling when coming to a stop, but it has always started again. However, now it will not start until the engine has cooled down a lot. It starts on first turn when cold and will idle OK (a bit rough though) and i can leave it to idle until it gets hot (when the thermostat opens), but then the revs start to drop and it cuts out.

Some symptoms are:
  • fuel coming out of LH carb vent and breather pipe after it stalls. I think i've stopped this now by cleaning the suction chambers, pistons and replacing seats & needle valves in float chambers.
  • all plugs are very sooty; and will get sooty again very quickly after being cleaned up
  • I've fitted a colour tune to No.1 cylinder; it seems to get more yellow (richer mixture) as the engine runs and gets hotter.
I've done a major service after i got the car, so i've changed: condensor, coil, points (mechanical ignition), fuel filter, plugs, ignition leads. Dwell and timing are on spec.

I'm suspecting the carbs, which are HS6. The engine serial number commences 451 with D suffix, and has HIF6 stamped on the tower, so not sure if this is a problem or not?

I'd appreciate any thoughts on what could be the cause before i go to my next step of reburb'ing the carbs.

thanks in anticipation,
Peter
 
A common problem with failing to hot start is that the coolant outlet on the carb tower gets blocked, leading to fuel vaporisation. Pull the tube off where it returns to the rad and check there is a good flow. If there is not, then remove tube at tower end and get stuck in clearing out the hole....
 
Hi Peter,

Fuel coming from the overflow usually means the float is either incorrectly set or in need of replacement. I have never worked on HS6 carburettors, but the HIF6 have plastics floats that eventually take in fuel.

I am afraid I disagree with the suggestion that a blocked tower leads to fuel vaporisation. The reason for having the coolant flowing through the tower is two fold. To minimise air building up within the tower, and to aid fuel atomisation. The problem that your Rover is having is most likely carburettor related, as stalling when coming to a halt is a typical symptom.

Ron.
 
Ron, I'm only stealing words from Chris York............
"The hose from the tower between the carburrettors may possibly assist in preventing carburrettor icing in really cold climates. But it's principle function is to COOL the carbs. Without a decent flow from this hose you are almost certain to suffer from fuel vaporisation...."
 
My friend bought a 3500 auto and had the same faults, this car had also been laid up for years.
It required the fuel tank removing and cleaning out with a descaler as was full of white powdery mess / blocked fuel lines/ fuel pump diaphragm perished and the carbs ( HIF) fully overhauled complete with new needles and jets due to the corrosion.
This seems a bit overboard but that's what happens when you leave motors a long time without use.
Stale petrol is one thing, corrosion is something else.
Clive.
 
My friend bought a 3500 auto and had the same faults, this car had also been laid up for years.
It required the fuel tank removing and cleaning out with a descaler as was full of white powdery mess / blocked fuel lines/ fuel pump diaphragm perished and the carbs ( HIF) fully overhauled complete with new needles and jets due to the corrosion.
This seems a bit overboard but that's what happens when you leave motors a long time without use.
Stale petrol is one thing, corrosion is something else.
Clive.
I've had the fuel tank out and de-rusted it, sealed it and cleared out all fuel lines. There was plenty of rust and crud coming through initially, but it all seems clear in the feed now. Of course, the carbs may have suffered with all that crud in them. The mechanical fuel pump diaphragm doesn't look too good, so i'll probably refurb the pump as well, but i can't see how that might cause the problem as fuel flow doesn't seem to be an issue.

Peter
 
What happens is that the main jet builds up a scale inside and with the needle which also can corrode ( check needle with magnifying glass) effects the fuelling.
Clive.
 
been there. even now it can cut out when pulling up at lights or on drive. grrrr. had both carbs checked new seals etc . found i was suffering fuel vapour issues as the newer fuels are high in ethanol and will 'boil' easily in hot areas. so the gassing we get causes cutting out. do check for air leaks? wd 40 etc sprayed around inlets areas etc . even vacuum line to dizzy! any air leaks cause imbalance. have we check carb balance ? used lifting pins ? burn in cylinders ought to be blue if memory serves ! I have fitted new filters .carbs refurb. balanced . new full electronic dizzy . leads. plugs etc still get cutting out issues and poor .idling ( checked cam =ok)I have found an electric lift pump has reduced cutting out by a huge margin!
 
There is one other item on HIFS that can give fuelling issues ( not to common) and that is the temperature bi metallic device, this can cause excessive weak mixture when hot/ stalling.
Clive.
 
I'm suspecting the carbs, which are HS6. The engine serial number commences 451 with D suffix, and has HIF6 stamped on the tower, so not sure if this is a problem or not?

If the manifold is for HIF6, and you have HS6, throw the HS6 in the skip, get a pair of HIF6 from a P6B, fit them and start again.
 
Ron, I'm only stealing words from Chris York............
"The hose from the tower between the carburrettors may possibly assist in preventing carburrettor icing in really cold climates. But it's principle function is to COOL the carbs. Without a decent flow from this hose you are almost certain to suffer from fuel vaporisation...."

No worries Pete :)
 
Hi Peter,

Fuel coming from the overflow usually means the float is either incorrectly set or in need of replacement. I have never worked on HS6 carburettors, but the HIF6 have plastics floats that eventually take in fuel.

I am afraid I disagree with the suggestion that a blocked tower leads to fuel vaporisation. The reason for having the coolant flowing through the tower is two fold. To minimise air building up within the tower, and to aid fuel atomisation. The problem that your Rover is having is most likely carburettor related, as stalling when coming to a halt is a typical symptom.

Ron.

Blocked tower definitely leads to hot spots and air locks... That definitely one of the faults I had when I first got mine. Probably not fuel vapourisation but definitely very erratic behaviour....
 
If the manifold is for HIF6, and you have HS6, throw the HS6 in the skip, get a pair of HIF6 from a P6B, fit them and start again.
Is that because HS6 are definitely incompatible and will never work properly with my manfold/engine, or are they just better carbs?
 
Is that because HS6 are definitely incompatible and will never work properly with my manfold/engine, or are they just better carbs?

The HS6 is an earlier design where the float chamber is placed forward of the dashpot axis. The HIF6 is a later fully integrated design that is considerably better.
Almost certainly the problem that you are seeing with your Rover is carburettor related.

Ron.
 
The advantage of hs6 carbs is that they're easier to work on and tune. Disadvantage is that you have to work on them and tune them more often....
 
The advantage of hs6 carbs is that they're easier to work on and tune. Disadvantage is that you have to work on them and tune them more often....

I'd have to disagree with that, the HIF6 linkage is easier to set up initially, and when it's done, it doesn't have to be done again, and after that, altering the mixture couldn't be easier than it is on the HIF6, no struggling to wind the HS6 jet tube up or down, and as for the idle adjustment, there's no difference between them.
I wouldn't say overhauling an HIF6 is any more difficult either.
 
Blocked tower definitely leads to hot spots and air locks... That definitely one of the faults I had when I first got mine. Probably not fuel vapourisation but definitely very erratic behaviour....
Checked for water flow out of the tower - not even a dribble! So, I'll add that to the list of jobs.
Thanks, all, for the suggestions. I think i'd prefer to have HIF6 carbs, so will maybe go down that route if I can find a decent pair.
Peter
 
Checked for water flow out of the tower - not even a dribble! So, I'll add that to the list of jobs.
Thanks, all, for the suggestions. I think i'd prefer to have HIF6 carbs, so will maybe go down that route if I can find a decent pair.
Peter
Where abouts are you Peter? I have a set of HIFs on an inlet manifold if you are close to SE London.
They will need a rebuild kit as they have been in the garage for at least 20 years

Also Chris York posted this on a P6 Facebook group ju now, and it might be of interest .

"
Chris York It shouldn't vapour lock....... Fixing a symptom won't fix that problem...........

Most likely problem is a blocked coolant outlet fom the "tower" between the carburrettors.... When this doesn't flow it is well known to cause fuel starvation/vapour lock. And pinking....

So have the radiator cap off and check that, with the engine running, you can see a strong flow of coolant entering the radiator from the hose that comes from the "tower".

If you can't see flow there, you have either an internally collapsed hose or the outlet from the tower is blocked. If the latter that is likely to need vigorous attack with a large hammer and jewellery screwdriver until flow is restored.

Even then, extreme cases have been known to need the inlet manifold to be removed and chemically dip cleaned.

A final flourish is to flush the entire cooling system using a chemical cleaner - the sort for cleaning out dishwashers is fine, two supermarket bottles should do the trick.....

In a very well ventillated space, run the engine up to temperture so that you are sure the thermostat has opened. Add the cleaner. Continue to run for around 20 minutes or until the foaming stops - with the rad cap OFF. Topping up as you go.....

Note also that the P6B radiator is undersized. The engine much prefers a three row rad instead of a two row. Any radiator repair shop should be able to change the core. This is irrespective of what temperature you see on the temperature gauge in the car. It's not the outlet temperature that benefits - that's controlled by the thermostat. It's the inlet temperature that the engine prefers to be cooler than usually achieved by the standard radiator.

All this sorted and it is most unlikely you will suffer from vaporisation - or pinking - again.
Ignore this feature of the engine and you are well on the way to a cracked block and slipped liners.....
"
 
I've got the inlet manifold off now and am applying the various techniques posted on the forum to clean out the tower chamber and tubes.
I had a very interesting conversation with a very nice man at Burlen today, about the respective merits of finding a pair of HIF6 carbs to refurb, or whether I should refurb the HS6's that are currently fitted. He pointed out that not all levers and cams are available for the HIF6, which could be a problem should I find a pair and they have bits missing. Whereas he said HS6 are still in production and all parts are available, and he saw no reason why I shouldn't refurb the HS6s. That would certainly be easier and cheaper. So decisions, decisions !
 
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