Left pot sputtering and popping, air leak... but where?

I'm on my second composite head gasket since top end refresh, I've eliminated ignition as a possible culprit, carbs are tuned and synced. But the left pot sputter, pops and spits back through carb and is smoking. Timing has been triple checked. Compression test on the unbroken-in rings shows 150 on both cylinders, so I'm thinking possible intake guide leak (seals have bee replaced), but the new head gasket can be seen leaking on the intake side of that cylinder. Before I installed this new gasket (the first blew out by the pushrods), I made certain to skim the head flat and check cylinder deck flatness, I also checked for valve leakage with fuel in the hemispheres of the upturned head, all was good.

Any thoughts are appreciated

p.s. Ran cylinder head dry and smoking stopped.

acadian said:

but the new head gasket can be seen leaking on the intake side of that cylinder.

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We think you have answered your own question ?!

What gasket did you use ?
Obviously, it needs to be redone, again ?

What did you torque the various fasteners to ?
And what did the follow-uo retorques show ??

Time to try a different type of head gasket.

I have "never" had issues with annealed copper and have always had higher than stock compression.

pete.v said:

Time to try a different type of head gasket.

I have "never" had issues with annealed copper and have always had higher than stock compression.

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I may do that, the composites I've used on my triumph and beezer have been great. Thought the same about the andover version. another possible culprit, the stainless headbolts I've got... I suspect they are not providing full torque/giving false readings.

acadian said:

I may do that, the composites I've used on my triumph and beezer have been great. Thought the same about the andover version. another possible culprit, the stainless headbolts I've got... I suspect they are not providing full torque/giving false readings.

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Yes, they can be screwy. Sorry for that. They need to be lubed for proper torqueing. Galling can be a real killer.

pete.v said:

They need to be lubed for proper torqueing.

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Lubed fasteners need a whole new set of values to torque them to.
Or they can be seriously overtorqued, compared to the dry values that are (almost) always provided.
Its not like you are doing stainless into stainless, after all.

What do the suppliers say ?

There is only one type of composite head gasket I trust to use on a Commando and that is the Victor Reinz brand. They work, unbranded gaskets are a problem waiting to happen.

On the head bolt holes - did you clean them out before screwing in the bolts? Any debris or fluid trapped inside will bottom out the bolts giving false torque reading. Also do the 3 torque ups routine to settle the head and you should be OK.

Update: while waiting on a new head gasket I've determined:

- the inlet valve guides/seals are not leaking at all
- the stainless head bolts I have were too long and most likely bottoming out
- the composite head gasket I had installed did not blow, but was letting oil past the head side (most likely due to the bolts not torquing)