View Full Version : OS 91szh-ps mod
Heard from some people that some of OS 91 szh-ps running rough and need to do some mod to the carb. Is that sound right? I am about to switch from YS to OS (did 2 already).
Thanks,
x
It's not that the engine runs rough,
that would be tuning or a mechanical balance issue,
Some people feel that the low to midrange area is lean on the PS,
they perform the cat eye modification to address this...
DavidH
08-25-2006, 07:42 AM
Some people feel that the low to midrange area is lean on the PS,
That is interesting. Most of the pilots I know here that are using the OS 91 SZ Hyper(pumped) have the mid range needle completely closed. So they are definitely not having a lean issue in the mid range.
David
Jerry
08-25-2006, 11:35 AM
I think sometimes people get confused between the OS engines available. I've seen several instances where someone asks for help with an SZH-PS and someone offers them advice meant for the Cspec PS.
Two completely different engines.
The OS91 SXH Cspec PS was an engine that some people resorted to modifying to get satisfactory results. Cateye and 3rd needle mods primarily.
The OS91 SZH-PS does not have any common mods that I am aware of regarding carb work, cateyes, or needles.
Jerry
Whoops - I miss read the question - I had assumed SXH - my bad
Yes, we are running the SZ's with the middle needle closed also
Please educate me. Don't understand why some people closed middle needle. From my understanding. The more you close the needle, the more lean you will get. About seven tanks on my Stratus my high is 1.5, mid is 1.
Regards,
x
Jerry
09-12-2006, 10:20 AM
This particular carb has so much flow through the primary metering channel, that the midrange is already on the rich side.
Remember - the mid-range needle on the 60 series carb is a 'supplement.' It provides fuel when demanded via the midrange cateye on the carb rotor. The amount available is proportional to how much you open the midrange needle.
Since the fuel flow through the hi needle - mixture control valve - spraybar path is already adequate across the entire throttle range - this 'supplement' is not in demand or needed in many cases.
So in this case - with the midrange needle, the more you close the needle doesnt necessarily mean it gets more lean in the midrange. An OS carb is way different than a YS carb.
Jerry