Another lean on one cylinder question - Harley VL

[Buster]

My 1931 VL suddenly started having lean condition with no color on sparkplug on one cylinder 1,500 miles after rebuild. Still runs great, but compression on lean cylinder is now 35 lbs and leak down at 20 lbs pressure is about 25%. Almost all leak down is at intake valve, very little at exhaust. I have done 15 lbs pressure test with Snoop and/or soapy water on intake manifold, intake nipples, head gasket, and flange between carb and manifold. No leaks. Found leaks on both heads at bosses where sparkplug plug gaskets seal. had bosses milled and no leakage now. Removed both primer cups and plugged holes. Intake valve is only leak I can find, and it is significant. Getting ready to tear back down again. Would an intake leak cause the cylinder to run lean. I have been told that a leaking intake valve would not affect the lean condition and only a leaking exhaust valve would make cylinder run lean. Is this correct or if not, anybody have any other ideas so I will know what to look for? Thanks.

[T. Cotten]

Just to make it complicated, Buster,...

No two vacuum leaks behave the same (except those that prevent the motor from running at all!)

And reading plugs is futile with modern 'anti-deposit' additive fuels: Any "color" at all is over-rich.

"Would an intake leak cause the cylinder to run lean. " What else?

"I have been told that a leaking intake valve would not affect the lean condition and only a leaking exhaust valve would make cylinder run lean."

Spoken like a true arm-chair engineer. Tell him I said so.

....Cotten

[dukekleman]

Buster,
Absolutely, positively with certainty a leaking intake valve will cause the cylinder to run lean.
Question is, why is it not sealing properly after 1500 miles on the new rebuild?
Have you checked the clearance at the tappet?
Has this clearance been checked during service intervals after the rebuild?
If there are any oil control issues in that cylinder or if it ran to rich, it's possible that excessive carbon is causing the leak down issue.

Either way, it shouldn't a worn valve guide, valve or valve seat issue this early on after rebuild.
This means lack of clearance at the tappet or carbon is most likely the cause of your leaking at the valve seat.

Duke

[T. Cotten]

...Still runs great, but ..

But .. ..

...I have done 15 lbs pressure test with Snoop and/or soapy water on intake manifold, intake nipples, head gasket, and flange between carb and manifold. No leaks..

The bubble-test is performed with the carb removed; Please review http://virtualindian.org/11techleaktest.html.

Testing the manifold-to-carb interface ain't so easy,

...Cotten

[Steve Slocombe]

Dear Buster, is it front ot rear cylinder? Any problems are usually on the hotter running front cylinder.

[Buster]

It's the front cylinder. I'm guessing it is carbon maybe since there was no problem before, I will report back with findings after disassembly. Thanks for info on intake valve leak. Going to road run next week, so might be a couple of weeks on report back.