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Thu Jun 12, 2025 11:05 am

My 72 Fastback that I have spent over 5 years restoring gives out a big cloud of smoke when starting up and within 5 minutes no smoke. The engine was rebuilt last year with new barrel, pistons and rings. Some people have suggested that it will be OK after the new piston rings have bedded in.

Just a thought, would a faulty oil pressure relief valve cause the smoking problem? I'm sure my engine has two.

Thu Jun 12, 2025 11:43 am

short answer NO, oil pressure relief valve has no bearing on smoke out the tale pipe. as you stated it has new P+C's and rings, need time to seat in, when you run the Engine and then stop it. the oil will pool down to the bottom and can leak into the combustion chamber, if the ring gaps were not done right it will aggerate the problem.

Thu Jun 12, 2025 11:51 am

Photos of the engine bay may help us.
Carbs or FI?
What breather setup (one cap or two)?

Thu Jun 12, 2025 12:35 pm

[

quote="KTPhil"]Photos of the engine bay may help us.
Carbs or FI?
What breather setup (one cap or two)?[/quote]

Thu Jun 12, 2025 1:11 pm

Nothing jumps out at me here.
Do these carbs have chokes? Are they adjusted properly?
Have you checked fuel pump pressure?
Early cars with carbs had a fuel valve that prevented flooding while sitting, something like these:
https://www.thesamba.com/vw/forum/viewtopic.php?t=671540

Thu Jun 12, 2025 1:23 pm

halfassleatherworks wrote: short answer NO, oil pressure relief valve has no bearing on smoke out the tale pipe. as you stated it has new P+C's and rings, need time to seat in, when you run the Engine and then stop it. the oil will pool down to the bottom and can leak into the combustion chamber, if the ring gaps were not done right it will aggerate the problem.

Yup, once the rings have seated, the oil smoke should go away. If it doesn't then the rings probably weren't set right at assembly, and the oil is just passing by the rings thru the end gaps.

Fri Jun 13, 2025 11:32 am

KTPhil wrote: Nothing jumps out at me here.
Do these carbs have chokes? Are they adjusted properly?
Have you checked fuel pump pressure?
Early cars with carbs had a fuel valve that prevented flooding while sitting, something like these:
https://www.thesamba.com/vw/forum/viewtopic.php?t=671540

The carbs don't have chokes but they were set up by and old school mechanic friend and the car is running really quite well and after a few minutes there is no smoke. I have never seen one of those fuel valves in any of the many air cooled VWs I've ever had.

Fri Jun 13, 2025 11:40 am

Bobnotch wrote: halfassleatherworks wrote: short answer NO, oil pressure relief valve has no bearing on smoke out the tale pipe. as you stated it has new P+C's and rings, need time to seat in, when you run the Engine and then stop it. the oil will pool down to the bottom and can leak into the combustion chamber, if the ring gaps were not done right it will aggerate the problem.

Yup, once the rings have seated, the oil smoke should go away. If it doesn't then the rings probably weren't set right at assembly, and the oil is just passing by the rings thru the end gaps.

So, if the smoke doesn't stop it looks like an engine out and heads off, cylinders off and re-align the piston rings job?

Fri Jun 13, 2025 12:54 pm

Trekker182 wrote: The carbs don't have chokes but they were set up by and old school mechanic friend and the car is running really quite well and after a few minutes there is no smoke. I have never seen one of those fuel valves in any of the many air cooled VWs I've ever had.

They were only used for a couple of years. Later an anti-flow valve was incorporated into the fuel pump itself, so the separate valve was discontinued.

Fri Jun 13, 2025 12:55 pm

Can you smell the smoke; more like unburned fuel, or like oil? Sometimes hard to tell...

Fri Jun 13, 2025 1:55 pm

KTPhil wrote: Can you smell the smoke; more like unburned fuel, or like oil? Sometimes hard to tell...

I will have a sniff tomorrow. Late evening here in the North East of Scotland.

Fri Jun 13, 2025 2:29 pm

Trekker182 wrote: Bobnotch wrote: halfassleatherworks wrote: short answer NO, oil pressure relief valve has no bearing on smoke out the tale pipe. as you stated it has new P+C's and rings, need time to seat in, when you run the Engine and then stop it. the oil will pool down to the bottom and can leak into the combustion chamber, if the ring gaps were not done right it will aggerate the problem.

Yup, once the rings have seated, the oil smoke should go away. If it doesn't then the rings probably weren't set right at assembly, and the oil is just passing by the rings thru the end gaps.

So, if the smoke doesn't stop it looks like an engine out and heads off, cylinders off and re-align the piston rings job?

Yeah basically. Another thing might be that the oil is draining from the heads into the cylinders and causing the oil smoke until it's burned off on start up.