Cutting out when hot

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Bermondseylandy

Member
Posts
10
Location
London
Hi all

I'm new to the forum, and to Defenders in general, so forgive me if I talk any nonsense.

I've got a problem with my 1986 2.5 petrol 110, that's been baffling a few mechanics over the past couple of months.

It started when I had the head gasket changed, which seems to have got the engine running a little warmer than usual.

It runs nicely at lower temperatures, but if I'm driving at 50 or so for any prolonged period (usually an hour or so), with the engine running a little over it's usual temperature, all of a sudden I'll hit the throttle and the revs won't do anything. A few seconds later the engine will cut out altogether and I'll be over to the side of the road.

When I fire her back up, there's a rough idle which stabilises when I put my hand over the air intake (so a fueling issue presumably?). I've noticed vapor leaking out of the carb a couple of times at this point. I can limp off with the choke way out, leave it to cool for half an hour and it runs again fine.

I put a new coil on just in case, and the rest of the ignition stuff is all new and fine. Fuel pump sounds alright.

Am I right in thinking it might be a carb thing? It's a weber carb, and I've heard that one of the solenoids can fail when hot, but I'm not sure what affect that would have on the running.

Any help would be much appreciated with this. I've never managed to replicate this state in front of a mechanic, and I've been spending quite a lot of quality time with the hard shoulder.

Cheers

Harry
 
Bermondseylandy said:
I've noticed vapor leaking out of the carb a couple of times at this point
Click to expand...
There are only two possible faults with carburation - running weak or running rich. Petrol spraying out of the carb air intake is a sign of over rich mixture. Petrol spitting out of the air intake is a sign of a weak mixture. Putting your hand over the intake to settle it down indicates the mixture is weak (shutting off air supply enriches it at idle). But lots of other things can mask the fault (eg ignition timing out). A good indicator is the colour of the spark plugs - black or wet core indicates richness and white / blistered core indicates weakness. (the outer ring will be normally black, its the central electrode area you need to look at). An experienced old school mechanic will know all this but I suspect modern mechanics (technicians) are trained to plug into diagnostics which tell them what the fault is, not possible on older stuff.
 
The spacer looks like a bit of black plastic between the carb and the manifold. make sure that the through bolts are nipped up.
Do you have a Weber, SU or Zenith carb, as there can be different as well as common issues with each
 
Also check breather on filler cap, had similar on a fiesta many many years ago caused by a blockage in breather pipe
 
Thanks everyone - It's a weber carb. I'll check the spacing and will see if that works. Only trouble is that the problem is so sporadic that it's hard to really test and see what's working. Cheers
 
I had similar issues with mine for a while, can't remember what carb we had, but it turned out to be a combination of three things to get it running properly.

First thing was a blocked fuel tank pick-up filter gauze, actually the gauze was completely blocked and crumbled when we found it! This presented as good running at tickover and round town or steady driving, wouldn't handle full throttle or towing, or anything that put the engine under load and needing fuel.

Crap in the carb float bowl .. I mean, don't actually do a No2, but there's something in the float bowl or the jets are blocked .. On mine it was the jets, a good airline blow-through cleared that. We reckon this followed from above ..

At the same time, which took longer to find, was a rotor cap with a crack in the body. Worked fine at tickover, low and high revs for a short while, but if the engine went a bit hotter, say pulling hard uphill, it spluttered and struggled a lot. Changed rotor and all good. Mate reckoned the crack widened and shorted the sparks, I dunno but it worked when changed, whatever the actual reason.

... And of course a good service getting the timing spot on, filters, fuel lines, air inlet pipes sealed and cleaned, oil changes etc etc.
 
Cheers Paul.

What's interesting is that it does run quite nicely at 55-60, sometimes for a hour or two - then all of a sudden it dies without any warning.

I'll certainly give the carb a good service - thanks for your advice.
 
Bermondseylandy said:
Cheers Paul.

What's interesting is that it does run quite nicely at 55-60, sometimes for a hour or two - then all of a sudden it dies without any warning.

I'll certainly give the carb a good service - thanks for your advice.
Click to expand...
+1 with Paul
30 yrs ago I had a petrol car that got about 10 miles down the road and then would cut out. If I took a different route it cut out at a different time. Turned out to be a small inline fuel filter that was blocked and starved the carb. Depended on the route/speed I was travelling away from home as to how far I got. There was still some fuel getting through, but under particular conditions (travelling fast for a while or going up hill) supply couldn't keep up with demand and it cut out.
 
No it just means you have a constant fuel level going to the Weber carb. It's in the right place on the bulkhead.
Check carb filter
Coil is screwed down well & not getting hot
Check cap & rotor arm

When you feel it cutting out is it sudden like turning off power or slowly like fuel been restricted?
 
Hicap phill said:
No it just means you have a constant fuel level going to the Weber carb. It's in the right place on the bulkhead.
Check carb filter
Coil is screwed down well & not getting hot
Check cap & rotor arm

When you feel it cutting out is it sudden like turning off power or slowly like fuel been restricted?
Click to expand...
It feels like fuel starvation - initially refusing to rev and then cutting a while later. if I fire it straight back up it has a rough idle that stabilises when I block the air intake, so presumably a fuel issue. The cap and rotor arm are new - had it serviced and checked by a landy specialist and no problems were made apparent. as I say, it's a tricky one because it only happens after an hour or two at higher speed.

Cheers, Harry j
 
As said before check the jets.
There may be a bit of crud in there.
Also check the base of the carb is tight to to the inlet.
Check solonids to the carb are fine.
 
Hi all

Bit of an update.

So I stripped the carb, cleaned it, checked all the lines into it and sorted the fuel filter. Had it tuned by a mechanic and It all seemed to be running well.

I took it down the M4 for a couple of hours and it was fine - but on the way back the next day the problem reoccurred. It was driving fine at 50, and the I gave it some throttle and there was a sudden loss of power. It felt like fuel starvation, but before it stalled I pulled the choke all the way out, that helped and kept it running (badly) until I could get it off the motorway. Then I stopped, gave it a 20 minute break, and fired it back up. It was still running very lean, but with the choke pulled out a little I could get it home (about an hours drive). If I put the choke back in it stalled, and hard started before i could get it running again.

It's a weird one - because I'd assume if it was a normal source of fuel starvation (dodgy fuel pump etc) the choke would be of no use.

Has anyone got any idea, because I'm baffled by this.

Cheers

Harry
 
I own a 110 2.5 petrol.
I had exactly the same issues you have got and it took me nearly 3 years to cure it!
The webber dmtl carb is a fussy bugger, the tiniest bit of crap and it will run rough.
Mine would run fine for months then do what yours is doing, start cutting out on the motorway or under load up hill.
I had my carb rebuilt by a webber expert and she ran fine for about a year(I only do about 2-3000 miles a year) then started playing up again.

I took the carb back to the carb expert to have it checked/cleaned, and he said he could not find anything obvious wrong with it.

Yours sounds like there is crap getting in the carb somehow, and when under load its blocking a jet, when you stop and cool down, crap the settles back to the bottom of the float chamber.

The fact that it will run on choke shows its not a fuel supply issue, mine was the same.
This is what you need to do. imo.
Check the corragated pipe that runs from air filter to carb, they are made of a sort of canvas/rubber, and mine was rotting underneath where I could not see it, this allowed tiny bits of crap to enter the carb.
Make sure you have an extra fuel filter before the carb, this will stop any crap getting in via the fuel, allthough, in theory this should not be possible as the dmtl has a filter in the housing where fuel pipe enters carb.

Also, and this is what I did, there is a pipe comming from the top of the carb that goes into the oil cap, this pipe is T'd off and a smaller pipe runs to the bottom of the carb, I blocked both pipes off and fitted an oil catch can to the oil cap.
I also fitted a chinese copy K+N type air filter, carb guy said that alot of his customers use these air filters with no problems.

I went from essex to the dorset steam fair via the motorway and had 1 slight misfire for about 10 minutes and it cleared itself and she has run fine ever since.
PM me your number and i'm happy to talk you through it in more detail.
 
landrover11019 said:
I own a 110 2.5 petrol.
I had exactly the same issues you have got and it took me nearly 3 years to cure it!
The webber dmtl carb is a fussy bugger, the tiniest bit of crap and it will run rough.
Mine would run fine for months then do what yours is doing, start cutting out on the motorway or under load up hill.
I had my carb rebuilt by a webber expert and she ran fine for about a year(I only do about 2-3000 miles a year) then started playing up again.

I took the carb back to the carb expert to have it checked/cleaned, and he said he could not find anything obvious wrong with it.

Yours sounds like there is crap getting in the carb somehow, and when under load its blocking a jet, when you stop and cool down, crap the settles back to the bottom of the float chamber.

The fact that it will run on choke shows its not a fuel supply issue, mine was the same.
This is what you need to do. imo.
Check the corragated pipe that runs from air filter to carb, they are made of a sort of canvas/rubber, and mine was rotting underneath where I could not see it, this allowed tiny bits of crap to enter the carb.
Make sure you have an extra fuel filter before the carb, this will stop any crap getting in via the fuel, allthough, in theory this should not be possible as the dmtl has a filter in the housing where fuel pipe enters carb.

Also, and this is what I did, there is a pipe comming from the top of the carb that goes into the oil cap, this pipe is T'd off and a smaller pipe runs to the bottom of the carb, I blocked both pipes off and fitted an oil catch can to the oil cap.
I also fitted a chinese copy K+N type air filter, carb guy said that alot of his customers use these air filters with no problems.

I went from essex to the dorset steam fair via the motorway and had 1 slight misfire for about 10 minutes and it cleared itself and she has run fine ever since.
PM me your number and i'm happy to talk you through it in more detail.
Click to expand...

Thanks very much for your advice, that sounds massively frustrating!

It's been at the mechanic's, and he seems to think that it's the coil that's failing. What I can't understand is how that would create a lean condition that the choke could help with. Does that sound plausible to you?

Fingers crossed though - it would be a simple fix.
 
Bermondseylandy said:
Thanks very much for your advice, that sounds massively frustrating!

It's been at the mechanic's, and he seems to think that it's the coil that's failing. What I can't understand is how that would create a lean condition that the choke could help with. Does that sound plausible to you?

Fingers crossed though - it would be a simple fix.
Click to expand...
Hmmmm, not sure. However, on a cold start, to help with combustion, you pull the choke out. If the voltage of the spark is dropping then it might be easier for the weaker spark to ignite the fuel if its a weaker/lighter/leaner mixture. ie the weak spark might be simulating a cold start condition.
 
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