III stalls and revs then dies

[NickDawson]

Hey y'all!
I've been pretty fortunate to have a rather stable and reliable III for the past few years. I try never to take the good days for granted 🤣

Recently I've had some problems and could use some thoughts about where to start. Here's the symptoms:

I'll be driving and out of the blue stepping on the gas produces the opposite of the expected effect. The engine starts to stall. If I floor it, it'll rev back up.

If I go into neutral and/or pull over, it is in some kind of rev/stall cycle. Like every 3-5 seconds it'll almost stall and then rev back up.

Having the choke engaged helps a little and can often get me home.

Occasionally, when I do get home, it will "Diesel" and chug for 30 seconds before finally shutting down.

When I go to re-start it, it won't start again for some period of time (I usually give it a day). When it does start again, it runs fine like nothing happened.

It may be reliable again for a week (100 miles) or only a day (5 miles).

I assumed it was a dying fuel pump and ordered one. But now that I've spent some time under the truck with a flash light, I can see that the inline filter (after the pump) is full and remains full. The manual pump also works just fine.

So now I'm at a loss. I can't imagine it is an ignition issue - but maybe? Could it be the carb? This truck has the rare 2.5L petrol and that carb is strange. The one on it is only a few hundred miles old.

The only other consideration is ambient temperature. We're in the hot sunny days of summer here in Montana. But that was true last summer and I didn't have any problems then.

Thanks for sharing any thoughts or tips you may have for troubleshooting!

[roverp480]

Is the carb. by any chance a twin choke Weber , this would be standard on a 2.5 Litre out of a Ninety or One Ten ?

[NickDawson]

I'm embarrassed to say that it has been running so well so long that I've since forgotten a lot of the painful and intimate details of this truck. For the life of me I cannot remember what the carb is... I know it is a strange and rare one. And I recall, for a long time at least, our hosts didn't have it. I searched my old posts because I recall having this issue 15 years ago, but I couldn't find anything helpful. That said, it was briefly in may dad's custody and he had someone looking at a brake line issue - that guy ended up replacing the carb ¯\_(ツ)_/¯ ... so that tells me 1. that it is quite new (less than 1000 mi) and 2. it is attainable

I'm attaching some pics.

I'm mostly curious what leads you to thinking it is carb, based on my description? Could it be the distributor (points or failing condenser?)
14048
14049
14050

[roverp480]

The fact operating the choke sometimes helps could point to fuelling. I had an early One Ten , about 1983, and the carburation was an issue from new , part of which was gas vapour locking . Land Rover dealer had it back numerous times and fitted all sorts of new parts before it was eventually cured . A number of symptoms were similar to yours and your carb. looks like the correct Weber for that engine. It may be worth checking the two electrical solenoids are working correctly. One is to stop the running on, " dieseling" you experienced and the other is to help with hot starting by changing the air venting. I wouldn't discount a faulty condenser and that is an easy thing to change , even if it just eliminates it as the problem. Pic is of a new carb which I think matches yours.
14051

[jimrr]

carb! engine rpm changes you are not initiating ....... gotta be carb!

[charles1943]

You say your carb is only a few 100 miles old. There are lots of Chinese knockoff out there and they are 99% GARBAGE!! B absolutely sure it is Genuine WEBER!!! You may have a vapour lock situation and there are also MANY junk fuel pumps out there!! I recommend checking your fuel pressure....esp. when hot. S.B. between 1.75 & 2.5 # p.s.i. Post your results please so we can continue helping. When a client was having problems with his carb I sent this to him: I'm wondering if there might B something else lurking in the bushes....failing fuel pump ?? Leaking inlet manifold or other air/fuel induction system issue. Faulty ignition timing/advance...failing points, fouled plugs [remove and inspect, starting w/cylinder #s 3 & 4] nasty plug wires, poor or incorrect spark plugs, failing coil, failing condenser in the distributor, burned distributor points, low compression, leaking head gasket. Any of the above-mentioned candidates could even B an 'emerging problem'....1 not full-blown yet but problematic enough to make your engine run poorly. Also I tend 2 agree with the chap whose thoughts point to a carb problem but it's not unheard of that 1 kind of issue will mimic another 1 and that the actual issue is EXACTLY what we were absolutely certain it couldn't possibly be!!

[jimrr]

You say your carb is only a few 100 miles old. There are lots of Chinese knockoff out there and they are 99% GARBAGE!! B absolutely sure it is Genuine WEBER!!! You may have a vapour lock situation and there are also MANY junk fuel pumps out there!! I recommend checking your fuel pressure....esp. when hot. S.B. between 1.75 & 2.5 # p.s.i. Post your results please so we can continue helping. When a client was having problems with his carb I sent this to him: I'm wondering if there might B something else lurking in the bushes....failing fuel pump ?? Leaking inlet manifold or other air/fuel induction system issue. Faulty ignition timing/advance...failing points, fouled plugs [remove and inspect, starting w/cylinder #s 3 & 4] nasty plug wires, poor or incorrect spark plugs, failing coil, failing condenser in the distributor, burned distributor points, low compression, leaking head gasket. Any of the above-mentioned candidates could even B an 'emerging problem'....1 not full-blown yet but problematic enough to make your engine run poorly. Also I tend 2 agree with the chap whose thoughts point to a carb problem but it's not unheard of that 1 kind of issue will mimic another 1 and that the actual issue is EXACTLY what we were absolutely certain it couldn't possibly be!!

wow, my Series 3 has ALL of that! but runs good anyway. don't forget broken motor mounts ........ ok, don't get me started!!

[mearstrae]

Wow! That's a lot of stuff. Since it works sometimes with the choke engaged, try putting a vacuum gauge on it. Maybe a vac. leak or a stuck intake valve? An air/fuel exhaust tester might tell a story also. Do some testing first, throwing parts at it might mask the real problem(s).

[jimrr]

a intake leak is ez to find with a can of starting fluid ............... i'm still suspecting some part in the carb but a timing advance plate moving when it's not suppose to could be a culprit also .............. didn't see that one here yet !!!!!!!!!!!!!!

[NickDawson]

Thanks yall!
I've been moving into a new house which means that my Rover is both my workhorse and that I haven't had any time to dig in to the issues. It has made for a little bit of a stressful week driving back and forth between houses and hoping this thing keeps running.

I fiddled with the timing a bit and —perhaps coincidently —the rev/stall cycle has gone away.

I still have the most persisting issue which is when I first depress the gas, the engine wants to stall. I have to floor it and get the engine revving to keep it from stalling out. I took the air filter off and opened the throttle manually at the carb. At that early moment (when the gas would be initially depressed), I hear a massive sucking sound and the engine tries to die. If I go past that point, it revs back up.

I have a mostly useless vacuum gauge on my dash and it seems to be living in the "poor" range on the dial rather than the normal drive or idle. That said, I'm not sure we should take that to mean anything.

Lastly, I remember this happening 10-15 years ago and I'm fairly sure the culprit was points and condenser. I'm inclined to start there since it is the cheapest thing to test :)

If I go the route of checking fuel pressure and vacuum, what's the best approach? Assume those are separate instruments?

[mearstrae]

I have a gauge that tests both vacuum and fuel pressure (Sears), but it's probably at least 55 years old (got it when I was 15 for working on my '57 Buick hot rod). Perhaps they still make such a thing.

[jimrr]

Thanks yall!
I've been moving into a new house which means that my Rover is both my workhorse and that I haven't had any time to dig in to the issues. It has made for a little bit of a stressful week driving back and forth between houses and hoping this thing keeps running.

I fiddled with the timing a bit and —perhaps coincidently —the rev/stall cycle has gone away.

I still have the most persisting issue which is when I first depress the gas, the engine wants to stall. I have to floor it and get the engine revving to keep it from stalling out. I took the air filter off and opened the throttle manually at the carb. At that early moment (when the gas would be initially depressed), I hear a massive sucking sound and the engine tries to die. If I go past that point, it revs back up.

I have a mostly useless vacuum gauge on my dash and it seems to be living in the "poor" range on the dial rather than the normal drive or idle. That said, I'm not sure we should take that to mean anything.

Lastly, I remember this happening 10-15 years ago and I'm fairly sure the culprit was points and condenser. I'm inclined to start there since it is the cheapest thing to test :)

If I go the route of checking fuel pressure and vacuum, what's the best approach? Assume those are separate instruments?

again, unaccounted for rpm changes can usually be attributed to carb issues. As previously mentioned timing advance/retard can do this quite effectivly !!. . trust your guages ..... if your vacume indicates low figure that one out !! ...... especially if it's verified or a good guage like a smiths or something.
keep us informed

[erik88lr]

Look down the throat of your carb while the engine is running and blip the throttle linkage. Does the carb's accelerator pump squirt some fuel or does it not and as a result the engine RPM drops and/or it backfires in your face?

My original Zenith carb had this problem, and the replacement Chinese Zenith knockoff developed it too. Installing the single bore Weber cured the problem and the truck no longer stalls when I try to pull into the intersection from a red light turning green.

[roverp480]

Thanks yall!
I've been moving into a new house which means that my Rover is both my workhorse and that I haven't had any time to dig in to the issues. It has made for a little bit of a stressful week driving back and forth between houses and hoping this thing keeps running.

I fiddled with the timing a bit and —perhaps coincidently —the rev/stall cycle has gone away.

I still have the most persisting issue which is when I first depress the gas, the engine wants to stall. I have to floor it and get the engine revving to keep it from stalling out. I took the air filter off and opened the throttle manually at the carb. At that early moment (when the gas would be initially depressed), I hear a massive sucking sound and the engine tries to die. If I go past that point, it revs back up.

I have a mostly useless vacuum gauge on my dash and it seems to be living in the "poor" range on the dial rather than the normal drive or idle. That said, I'm not sure we should take that to mean anything.

Lastly, I remember this happening 10-15 years ago and I'm fairly sure the culprit was points and condenser. I'm inclined to start there since it is the cheapest thing to test :)

If I go the route of checking fuel pressure and vacuum, what's the best approach? Assume those are separate instruments?

I had very similar symptoms with faulty fuel. I spent ages checking carb. distributer etc. then had to fill with fresh fuel, problem solved . Does it continue the same after fill ups?

[NickDawson]

Quick update on this thread....
I can't believe I missed it, but I finally (with some help of a 2nd set of eyes) noticed a pretty massive fuel leak coming from the outlet of the pump. A few turns of a wrench and it went away. That really helped the reving symptoms. I also discovered a hole in the boot that connects the vacuum advance to the carb and I repaired it with Sugru. The engine needs to be timed before it will run well... but the starter died during all that cranking when it died. So now I'm waiting on a replacement.

[jimrr]

stabbing the gas and having a duuhhhh moment is usually the power piston (aka accelerator pump) ........... followed by timing.
good you spotted the fuel leak but the power piston will initalize the rpm jump and whats in the float bowl will run it till a lack of supply catches up ..... IE' your leaking fuel line from the pump.
sounds like you have a handle on it?