View Full Version : Question about my OS 91SZ, backplate pressure fitting vs muffler pressure for tank
CoronaL
06-25-2008, 01:35 PM
I bought a lightly used OS 91SZ from a guy and it has the backplate tapped with a fitting. I was wondering if I should use this to pressurize the fuel tank, or should I block this and use the muffler pressure for the tank. I will be running this motor in a TREX700 when it arrives. I'm probably going to run a carbsmart as well. Was considering a Cline but am undecided at this point.
John
DavidH
06-25-2008, 08:39 PM
Well the only reason it would have a fitting in the backplate is for two things.
IT had a Cline regulator on the carb and the fitting was used to pressurize the fuel tank
Or
It had a fuel pump on it and the fitting was use to power the pump.
Sounds to me like you didn't get the complete setup for the motor.
David
CoronaL
06-25-2008, 10:18 PM
I agree. Motor is like new though. I've torn it apart and looks almost new, very clean etc...
Wondering which way i should go :)
LAMAR COOLEY
06-25-2008, 11:29 PM
CoronaL,
These engines run extremely well when tuned properly. Depending on the fuel you use you may or may not need to add a head shim or two.
Without the pump you will need to plug one or the other.
Since your are considering the cline.
Try the muffler pressure first then when you get the cline you'll then be able to determine
which set-up you prefer.
Regards
CoronaL
06-26-2008, 08:33 AM
CoronaL,
These engines run extremely well when tuned properly. Depending on the fuel you use you may or may not need to add a head shim or two.
Without the pump you will need to plug one or the other.
Since your are considering the cline.
Try the muffler pressure first then when you get the cline you'll then be able to determine
which set-up you prefer.
Regards
thanks :)
I'm going to run a mix of 50% CY 30% heli and 50% 2/4cycle Wildcat for a 22.5% nitro blend and ~20% oil give or take. I think the 2/4 cycle is 18% oil and the CY is 22 or 23% oil. Anywho, I think I may get away w/out shimming the head, but if it proves difficult to tune I'll put one in. I'll probably close off the crank vent at this time and if when I get the cline use it at that point. Going to run a FunTech muffler as well if that makes a diff.
Other motor I have is a YS91ST with Hatori SB16FH, not sure which one I want to use first on the TREX700 I'm waiting on :)