Head gasket or not?

[johny]

8 minutes ago, Puglet1 said:

My car ran ok when cold but I guess the fuel bowls were full at that point- it seemed to loose power but after stopping for a while it would start and run again for another few miles.

But if the bowls have run dry I cant see how the carb bowls can refill after the engine has stopped so that it restarts and runs a bit more...

[Puglet1]

19 minutes ago, johny said:

But if the bowls have run dry I cant see how the carb bowls can refill after the engine has stopped so that it restarts and runs a bit more...

Probably refilled at a very slow pace as we sat in the lay-by for about half an hour and I cranked the engine several individual times without flattening the battery. It eventually started and drove for another few miles before losing power again.

However, I’m only trying to help Roger by offering the symptoms I experienced at that time.

[johny]

I suppose they could fill by gravity but the fuel needed on tick over is minimal so that any blockage would have to be pretty complete. The usual thing is to get the rubbish in the float valve so it cant close properly and the carb overflows but that doesnt seem to be happening here🤔 

[Pete Lewis]

two chances with the float valves

blocked so you get starvation 

or blocked and you get flooding 

pesky things  and chuck in nasty rubber slivers every time you mess with the hoses 

means you conk out in your best shirt when its dark and raining 

Pete

[Roger]

Thanks for all your comments, it helps a lot to get feedback. As mentioned above, it seems unlikely that the engine would stop completely if only one cylinder is the problem. It should continue to run on five cylinders. Or even four. Your comments made me think of fuel starvation, I have to check that again. The backfiring is gone! The valve clearence was under spec on some valves, so maybe they did not close properly when warm, but I fixed that by increasing the clearance.

[Roger]

1 hour ago, Puglet1 said:

Can you isolate the misfire to a particular cylinder by pulling the plug leads off with the engine running?

Backfiring is gone now, see post above.

[Iain T]

I don't think any of the carb suggestions can cause the blow back at the carb. Bad ignition timing, but as reported it's been checked, or sticky valves or over tight valve clearances are to my mind the only way that much cylinder compression can be blown back through the carb. 

I assume you are still using the mechanical fuel pump. You could try running the engine with the fuel line to the carb disconnected (use something to catch the pumped fuel) to see if the pump is working properly. The engine will run for a while using the fuel in the float chamber. 

Are you still getting the blow back from the carb? 

Iain 

PS

I had problems with my mechanical pump and changed to a low pressure Huco sited next to the battery. I did fix it on rubber mounts where the mechanical pump was but it suffered from fuel evaporation. 

 

Edited August 4, 2023 by Iain T

[DanMi]

With that amount of oil on the valve head, could the valves not always be seating properly due to excessive valve stem/guide wear? just a thought

[Iain T]

I don't think it's the valve seat as that would be shown in the compression test. 

[Roger]

1 hour ago, Iain T said:

I assume you are still using the mechanical fuel pump. You could try running the engine with the fuel line to the carb disconnected (use something to catch the pumped fuel) to see if the pump is working properly.

No, I actually have a Huco pump. I replaced all hoses and after that I disconnected the hose to the carbs and pumped out almost one liter of petrol just to make sure I removed any rubber slivers that might be in the pipes. It did not take long for the pump to fill the bottle, it looks to me like the flow is ok. No vacuum in the tank, I'm sure air can enter the tank.

Edited August 4, 2023 by Roger

[Iain T]

So do you still get the blow back through the carb when increasing throttle as per your video? 

Where have you mounted the Huco? 

Iain 

Edited August 4, 2023 by Iain T

[Roger]

11 minutes ago, Iain T said:

So do you still get the blow back through the carb when increasing throttle as per your video?

No, that seems to have been cured (valve not closing properly then maybe). This is how it sounds just before it dies. It runs for 10minutes, won't rev, looses power and finally dies. This drives me nuts.

[Iain T]

So there is pressurised fuel coming out of the Huco and it's mounted away from the heat of the block?

Then it can only be a sticky float valve letting fuel in but not enough to keep the engine running? 

Does the engine start after stopping ie no fuel in the float chambers? Try testing by turning the ignition on for a minute to activate the pump and prime the float chambers then start the engine. Or when the engine dies have you taken the carbs off to see how much fuel there is in the float chamber? 

Edited August 4, 2023 by Iain T

[Roger]

16 minutes ago, Iain T said:

it's mounted away from the heat of the block?

Yes, it is mounted according to picture. I know the pressure regulator is a bit overkill since the huco only deliver low pressure, but it makes the flow more even (at least thats how it looks when I fill the bottle). Regarding heat, I could also mention that our wonderful scandinavian climate helps a lot in that case. It is 18 degrees C outdoors, about 65 F I think. This island is a lot cooler than Rhodes.

 

Edited August 4, 2023 by Roger

[Roger]

20 minutes ago, Iain T said:

Does the engine start after stopping ie no fuel in the float chambers?

It does (barely) start again (most of the times I try) but it runs really rough and dies again.

[Ian Foster]

34 minutes ago, Roger said:

This is how it sounds just before it dies. It runs for 10minutes, won't rev, looses power and finally dies.

Roger

Can you please take a video looking into the mouth of the carbs, so we can see what the slides are doing.

I have a Huco on my GT6. Good bit of kit. I can clearly hear the pump filling the float chambers before a first start. After yours has conked, when you turn the ignition back on does the pump run to fill the bowls?

Ian

[Roger]

2 minutes ago, Ian Foster said:

I have a Huco on my GT6. Good bit of kit. I can clearly hear the pump filling the float chambers before a first start. After yours has conked, when you turn the ignition back on does the pump run to fill the bowls?

Same here. The Huco is ticking for a few seconds when starting from cold. It does not have to work a lot after it conked, just one or two "ticking". Good idea to look in to the carbs. I had a Volvo 240 with strombergs with similar symptoms and it was a hole in the diaphragm. I did check for holes when cleaning the carbs, but maybe they leak some other way, I don't know

[Iain T]

To eliminate heat can you confirm the engine runs from cold then stops. I know the temperature where you are is 'milder' than Rhodes but changing the position of the Huco from where you have it to horizontal mounted on the 'shelf' next to the battery solved all my fuel supply problems. It could also be the Huco doesn't like engine vibrations? Whatever it now works. 

[Iain T]

32 minutes ago, Roger said:

I did check for holes when cleaning the carbs, but maybe they leak some other way, I don't know

A hole in the diaphragm won't stop the engine. 

Edited August 4, 2023 by Iain T

[Roger]

18 minutes ago, Ian Foster said:

Can you please take a video looking into the mouth of the carbs, so we can see what the slides are doing.

Now it spits out fuel again. Right in my face while filming 🙄

 

Edited August 4, 2023 by Roger

[Pete Lewis]

you can ramble of to get knowhere    spitting out  the throat is compression in the wrong place with absolutely nowt to do with air leaks pumps or any other myth 

air going the wrong way is compression in the wrong place 

the oil of top of the valve is a good tell tale that something is  not happy there 

how does oil get on the back of the valve  .......down the valve guides    i asked are they secure or is No6 going up and down with the valve ?????

Pete

[Roger]

1 minute ago, Pete Lewis said:

you can ramble of to get knowhere    spitting out  the throat is compression in the wrong place with absolutely nowt to do with air leaks pumps or any other myth 

air going the wrong way is compression in the wrong place 

I'm sure your right Pete but this comes and goes, so I just want to look at all possible causes before removing the cylinder head. The oil on the valve could also (at least some of it) come from the carbs, I filled them up, a bit more than needed.

[Iain T]

Oil from the carbs can't really feed into the intake system. Certainly not to that extent. It really is delaying the inevitable which is head off. 

Iain 

[Roger]

7 minutes ago, Pete Lewis said:

i asked are they secure or is No6 going up and down with the valve ?????

Not sure what you mean with this comment. I assume something could be wrong with the valves, but it is a mystery for me how valves could be stuck, worn or burned and I still have very good results on my compression tests, also on a warm engine.

[Roger]

2 minutes ago, Iain T said:

It really is delaying the inevitable which is head off. 

Yes, I think that will be the next move... I wish this was mine 🙂

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