Yamaha TRX850 Enthusiasts Forum

Morning from a surprisingly sunny England.

Went to take my tank off last night to change the ignition switch and found the foam around the outside of the airbox in pretty poor condition.

Have seen on here people have removed it and raised the tank, how do you achieve that and drilling holes in the airbox lid? Any point and if so where please?

Cheers me dears

Under the front tank mount you can place a 10-20mm spacer that raises the tank at the front to gain a little more airflow to the airbox.
Pointless drilling holes in the airbox as it’s tuned to the resonate at cam overlap to neutralise the pressure wave from the exhaust and stop any exhaust blowing past the inlet valves and corrupting the air/fuel intake. The only thing drill holes does is place a 3 hp hole in the torque curve .
That pesky foam can be a restriction once it begins to degrade and fall apart tho especially if not seated in the correct position. I had 1 motor I did work on and when the foam degraded, it was drawn into the inlet manifolds and left tiny sticky balls of shit in the inlet tract.

Hi cobba!

cobbadiggabuddyblooo wrote: ...
That pesky foam can be a restriction once it begins to degrade and fall apart tho especially if not seated in the correct position. I had 1 motor I did work on and when the foam degraded, it was drawn into the inlet manifolds and left tiny sticky balls of shit in the inlet tract.

In case the "sticky balls" in the carburettor look like this:



then they quite surely originate from the degrading filters of the carburettor:


and not from the foam surrounding the tank.

Anyway, the foam is odd and can (should) be removed but the filters of the carbs should be replaced.

Been there done that greets from Munich!

Edit:
This is what a degraded filter looks like (cut open):



Pictures taken from the German TRX forum in this thread:
https://supertwin850.de/forum/index.php ... #post51190

Yes that’s another issue and involves the chamber and diaphragm of std trx Constant velocity carburettors.The sticky foam balls I found where all inside the inlet manifold all the way to the inlet valve. I found the airbox had been fitted with a K&N hi flow filter and if the filter is not positioned correctly would not give a complete seal so air could flow around and bypass going through the filter and how the tiny particles of the degrading foam between the tank and airbox could enter the inlet tract.