YS Engines Support Direct support from YS Performance Engines by Dave Shadel

Is it manditory to use a gas ported piston?

Old 06-28-2020, 05:56 AM
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Default Is it manditory to use a gas ported piston?

I haven't seen a post from Dave in a while so whoever wants to respond is fine with me.

I recently purchased a 91AC that is actually an FZ by all rights. Tore it down due to rusty bearings and cleaned everything up. I have new gaskets, orings, front seal, diaphram and plunger for the overhaul. This is my first YS but by no means my first 4 stroke, I have rebuilt A LOT of Saitos, OS and similar engines.

Because this is my first YS I have read every thread in this forum regarding the 91AC/FZ and there seems to be a common issue with surging at midrange and top end as well as flooding at idle due to intermittent or poor piston ring sealing. The fix that Dave recommended many times was to send the engine in to have the piston gas ported. Makes perfect sense to me, having intermittant/excessive blowby would definitely cause regulator inconsistencies.

Apparently the old pistons were not gas ported whereas the new replacement pistons are, as well as the pistons in all engines from the 110 on. Early on Dave said he made a jig to modify the pistons with gas ports.

It's hard to understand the frequency of the problem regarding non-gas ported pistons just by reading these threads. Maybe everyone eventually has problems? maybe not? Were some of you able to run your non-gas ported piston engines gallon after gallon without issues related to piston ring sealing?



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