Tuning the Cspec PS

[claysmith]

My new PS wants to run lean on the low end. I have the screw set as rich as it will go and it is still running lean. Is there any secret to tuning these motors? I thought the pump was supposed to make these motors easy to tune. I'm running a MP2, magmun 30% fuel, and an OS #8 plug. The engine is installed on a raptor 90 with 8.27 gearing.

[WillJames]

I am not sure about the low end, never had a problem with that, but you will probably need to run an extra .004 to .008 of shims under the PS Hyper Head with the Magnum to get very consistent runs and no predetenation. It only takes a few minutes to install the shims and you will be happy with the top end and torque results. :)

Low end... I don't have that problem with either of my C-SPECS. Have you checked the tubing that connects to the pump. (Remove the pump from the backplate?

[claysmith]

Thanks for te help. I added the .004 shim and got the mixture set so it was running perfect and guess what happened next. I crashed because the collective link popped off while doing low flips. The crashed damaged the pump, so I gotta get a new one and start over trying to tune it again.

[WillJames]

AWWWWW BUMMER!! SOunds like something I would do. Those shims really make a difference on the C-SPEC.

[VBarrett]

I have a new OS 91 ps engine and it ran so lean that I thought that I had damaged it. The engine ran fine When I first got it so what had changed?This is what I found makes this engine work properly. This engine even with a pump needs sufficient muffler pressure in order to supply enough fuel to the engine. The new OS 91/ps has a very fine mixture control valve that needs to be under pressure in order to supply the right amount of fuel. I compared an old SXH mixture control valve to the new one and it is much larger. The point here is that due to the size difference muffler pressure is more important now that the mixture control valve is smaller. In the past small muffler pressure leaks would not cause a problem because the mixture control valve openings were large. Now heres why we need high pressure from the muffler in order to make the engine work properly. Fuel pressure is high from the pump to the carb. The carb has a check valve that opens when the pressure is lower on the back side of the check valve. The back side of the check valve is connected to the tank or the front side of the pump. If sufficient muffler pressure isn't maintained the check valve will open up and allow fuel to bypass the carb. The higher the muffler pressure the harder it is for the check valve to open and allow fuel to bypass the engine. Higher muffler pressure results in a richer running engine. If the muffler pressure fittings are leaky enough it will cause over heating problems all around. I've had my needle 3 turns out and I still got a lean run until I addressed the leaky tank fittings.

[dunbare]

VBarrett,

I'm having the same problem. When I first got my C-Spec-PS no problem. Now, when the tank is full it seems to do okay, but as the fuel goes down it begins to lean. I have the low end wide open, and like you opened up the high end three turns and nothing.

What did you do to cure your muffler pressure problem. I'll check mine tonight.

[VBarrett]

I'm currently flying a Fury and this is what I did to insure that the tank fittings would hold muffler pressure. I put a nylon washer and rubber washer on each tank fitting to seal the leaks that I had. I also noticed that the check valve if it is screwed in too tightly it will open very easily which is something that you don't want. I also take a small piece of fuel tube about 5mm in length and slip it over the end of each fuel line connections for an extra tight fit. The check valve is now connected to the tank with it's own fitting instead of the Tee connection. Basically you have to prepare your tank to as if you were going to run a YS even though it won't be under constant pressure. If you preparing your tank that well it will insure that you won't get any lean runs.

[VBarrett]

Well it looks as O.S will finally address the lean problem with the P.S engine. Part number 29081910( Return needle set). This item limits the flow of fuel away from the carb through the check valve.

[sumonzu]

Well it looks as O.S will finally address the lean problem with the P.S engine. Part number 29081910( Return needle set). This item limits the flow of fuel away from the carb through the check valve.

Hi,
did you try to put this new part on your OS 91 PS? How it works? Does it really solve all the setting problems of this engine?
Please let me know since I'm looking for the right solutions!

Marcello

[WillJames]

Put a crushed eyelit or something like a filter that is soldered up with only a tiny hole in it in the return line and see how it effects your motor. I know people flying servo eyelits for over a year with good results.