Air Leak at Carb Holder, 550 seca

I have an xj550r seca that has an air leak on the engine side of #2 carb holder. I can’t seem to fix it. This is what i have tried:


Bought new set of carb holders and paper gaskets, installed with Hylomar to 100 inch-pounds (~9 n-m) torque. Fail.


Replaced vacuum hose---no change.


Removed and cut a new gasket from sheet of (somewhat thicker) gasket paper. Again Hylomar, used per instructions. Intake flange lightly sanded by hand with 320 grit paper before assembling. Fail.


Tried reusing old carb holder with Hylomar. Fail.


Cut another gasket (i’m getting pretty good at this) and tried high temp RTV (at lower torque) with the new holder. Fail.


Any ideas?

 

How are you detecting a 'fail' ?

 

When idling, spray carb/brake cleaner around the engine side of the #2 carb holder; revs increase. Doesn't happen with other 3 holders. Also, won't hold idle.

 

Hmm. Is the bike fully warm when doing this ? Idle can be fickle when cold. I would try repairing old #2 with RTV, old inner tube or what have you, then one more gasket - no hylomar, but maybe some silicone grease if you have some.

 

You may have bad seals at the butterfly shaft. Have you cleaned the carbs.

 

Both cold and warm. Hylomar is claimed good to 250C, silicone grease to around 200C---why do you prefer silicone?

 

Have run into that in the past, but this is leaking from the engine/carb holder joint.

 

Good question, I don't really know.. I would use Hylomar at an oil interface and normally use nothing at the gas mixture interface other than the gasket. I guess in my mind the grease is softening for the gasket and it's rubber compatible.. Temperature is not an issue on the inlet.

 

Can you pinpoint the leak more closely? Is is possible that the leak is at the YICS o-ring between the head and cylinder instead of at the intake?

 

No idea---i don't know beans about yics and have never had the yics access bolts off. How could you tell?