Poor running when warmed up

Happy New Year to all,

It's been a while since I was on here. My '75 SIII (Lenny) has had little use for a couple of years since we were renting in town. Now back in our own place in the country and Lenny is back at work lugging trailer fulls of wood, etc.



I've not done much other than an oil and filter change and a carb tune. Generally it starts well and runs well for maybe 30 mins but then, if I stop, it struggles to start again and when it eventually does it won't rev properly when under load. If I nurse it along on very light throttle it gets me home.

I thought the coil was the problem but I've put in a replacement and it hasn't solved the problem. I don't think it's fuel related since there is a strong smell of petrol when it's trying to start.

Distributer is clean and dry, plugs are new last summer, leads are newish. I guess my next port of call might be the points/condenser but surely if they were bad it wouldn't run well for 30 mins? Tempted to put in some electronics, the Accuspark setup worked well on my 1500 Spitfire.

Before I do that, any other suggestions? I was reading that a head that has not been reworked for unleaded and where owner hasn't used additive can eventually have running issues when warmed up. I've used treatment since I bought the landy in 2016 but who knows before that.

Thoughts appreciated!

Al

Dodgy condenser can give weird issues like this. Easy and cheap to replace.

Flat 6 said:

Happy New Year to all,

It's been a while since I was on here. My '75 SIII (Lenny) has had little use for a couple of years since we were renting in town. Now back in our own place in the country and Lenny is back at work lugging trailer fulls of wood, etc.

View attachment 307638

I've not done much other than an oil and filter change and a carb tune. Generally it starts well and runs well for maybe 30 mins but then, if I stop, it struggles to start again and when it eventually does it won't rev properly when under load. If I nurse it along on very light throttle it gets me home.

I thought the coil was the problem but I've put in a replacement and it hasn't solved the problem. I don't think it's fuel related since there is a strong smell of petrol when it's trying to start.

Distributer is clean and dry, plugs are new last summer, leads are newish. I guess my next port of call might be the points/condenser but surely if they were bad it wouldn't run well for 30 mins? Tempted to put in some electronics, the Accuspark setup worked well on my 1500 Spitfire.

Before I do that, any other suggestions? I was reading that a head that has not been reworked for unleaded and where owner hasn't used additive can eventually have running issues when warmed up. I've used treatment since I bought the landy in 2016 but who knows before that.

Thoughts appreciated!

Al

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Try the points and condenser. Condensers can give weird faults, and modern condensers aren't thought to be very good.
Accuspark is good if you don't mind spending the money.
Checking the valve clearances can't do any harm.
Not hear of the head issue, but is sounds plausible, but try the ignition stuff first, it will be cheaper than dealing with a head that has valve recession.

If the valve seats were worn out would be bad all the time?

kermit_rr said:

If the valve seats were worn out would be bad all the time?

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Not sure. Never heard the theory before. But different expansion of the metals might make a difference when the engine was hot.

Still reckon the ignition is a better option for immediate attention, though.

Thanks gents, could be a cheap fix then.

Not sure exactly where I read about the valve seat issue. I had a quick browse there and there are clearly plenty of opinions on whether it is a thing or not.

I'm now using two additives per fill, one for lead, one for ethanol.

Cheers,

Al

Flat 6 said:

Thanks gents, could be a cheap fix then.

Not sure exactly where I read about the valve seat issue. I had a quick browse there and there are clearly plenty of opinions on whether it is a thing or not.

I'm now using two additives per fill, one for lead, one for ethanol.

Cheers,

Al

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The lead replacement additive is supposed to be better than lead for your engine.
But if the valve seats have already receded, it won't restore them, just prevent further damage.
But try the ignition and valve clearances first, then worry about the head if the problem doesn't improve.

Turboman said:

But if the valve seats have already receded, it won't restore them, just prevent further damage.

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Not so sure, if a valve isn't sealing 100% then blow by will damage/burn further, regardless of any additive. In my opinion.

Flat 6 said:

Thanks gents, could be a cheap fix then.


I'm now using two additives per fill, one for lead, one for ethanol.

Cheers,

Al

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I wouldn't worry about the ethanol if you're using it daily/weekly.
Also have you worked out the cost/convenience vs using super/E5? Which has better octane rating anyways

kermit_rr said:

Not so sure, if a valve isn't sealing 100% then blow by will damage/burn further, regardless of any additive. In my opinion.

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It won't prevent blow by, but if it hardens the seats, it may prevent further wear.

I'm only 10 years from retirement...soo many things to check when I get there...!

Flat 6 said:

I'm only 10 years from retirement...soo many things to check when I get there...!

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Changing a condenser and setting the valves take about an hour.

Turboman said:

It won't prevent blow by, but if it hardens the seats, it may prevent further wear.

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Lead replacement additives add lubricant and usually add octane too.
Lubricates the valve so it doesn't stick/weld itself to the seat, causing damage when it opens again

There's is an arguement it's most effective in high rpm engines with heavy valve springs which hammer the valves shut.
The landy engine isn't high revving or high power, so probably won't suffer like a more sporty car

Oh I know, just thinking ahead to which engine to rebuild first! The landy's oil pressure light comes on very briefly when I stop at lights but my Spitfire's oil pressure has been marginal for 40 years. I'd love to get stuck into one of them but between day job and having just bought an old stone built farmhouse that needs work, I'm well short of time. I'd retire tomorrow if I could afford it!

kermit_rr said:

Lead replacement additives add lubricant and usually add octane too.
Lubricates the valve so it doesn't stick/weld itself to the seat, causing damage when it opens again

There's is an arguement it's most effective in high rpm engines with heavy valve springs which hammer the valves shut.
The landy engine isn't high revving or high power, so probably won't suffer like a more sporty car

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Sure all that is right, I was under the impression that lead used to deposit itself on surfaces as well, act as a physical shield.
But really not sure about this, not looked into it much, as I have never seen an engine with valve seat recession as far as I can remember.

Flat 6 said:

Oh I know, just thinking ahead to which engine to rebuild first! The landy's oil pressure light comes on very briefly when I stop at lights but my Spitfire's oil pressure has been marginal for 40 years. I'd love to get stuck into one of them but between day job and having just bought an old stone built farmhouse that needs work, I'm well short of time. I'd retire tomorrow if I could afford it!

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Probably just the oil pressure sensor, they fail for a pastime. Another one costs about a tenner.

Turboman said:

Sure all that is right, I was under the impression that lead used to deposit itself on surfaces as well, act as a physical shield.
But really not sure about this, not looked into it much, as I have never seen an engine with valve seat recession as far as I can remember.

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Yes it did that's also why you'd get a light grey coating on the inside of the exhaust when the engine was running well.

They do say the modern replacements are 'better' than TEL, but they would say that

kermit_rr said:

Yes it did that's also why you'd get a light grey coating on the inside of the exhaust when the engine was running well.

They do say the modern replacements are 'better' than TEL, but they would say that

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It is probably good stuff.

But what they don't say is that it is probably even worse for the environment than lead!

Turboman said:

It is probably good stuff.

But what they don't say is that it is probably even worse for the environment than lead!

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Yes but it's not lead and the new stuff doesn't count!! Because it's not lead. Which is bad

kermit_rr said:

Yes but it's not lead and the new stuff doesn't count!! Because it's not lead. Which is bad

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I think lead was banned because of it's impact on yooman health, but it wasn't too bad for the wider environment.
Being heavy, it didn't get far from roads before falling to earth.
The studies that led to lead being removed from petrol in Britain, were done on primary school kids in schools that were almost underneath the M4 flyover in West London. Unsurprisingly, high concentrations of lead were found in the kids.