I just bought an os 120 ax to replace the previous engine on my showtime. I have a xoar 16 x 6 and 17 x 6. I want to leave the tank on my cg like with my previous engine. what pump will i need to do this? I do not want to move the tank up. I hate cg shift in flight. i like it slightly tail heavy all the time for 3d flight. having it nose heavy at first and tail heavy later sucks.

how far is too far away with this motor?

how much fuel tubing can safely be between the motor and tank without fuel delivery problems.

If i want to pump it, what will i use? will it get me the length i want?

If the perry pump you got works anything like how YS engines work then you should be able to place the tank anywhere in the plane (just like the YS). If I wanted for the CG not to shift then I would advise getting a YS110 or YS120 off eBay.

I have a Perry V20 pump on my 120AX with the tank on the C of G and it never misses during 3D or pattern (U-can-do 60). I also have a YS110. It has shaken two good airframes to bits (magnetic balanced prop) and I will never buy another.

I had a ys 110. i replaced it. i did not like it at all, it needed at least 25% nitro for a reliable idle and to generate good enough power for what i want. the os 120ax has much more power and i do not mind buying a pump to make it run perfect. thanks for your input.

I have 2-120 ax's running fuel tanks at the cg without pumps and have never missed a beat. One is a Harrier 90 and the other is on a 25% Cermark Pitts Special. I have Pitts mufflers on them both. O.S. 120's are very good with pulling fuel and the pressure from the pitts muffler must be pretty good also.

My vote goes for the cline regulator. I have had two, one on a 120ax, and they were both flawless.

is this the cline regulator>? http://www.greathobbies.com/productinfo/?prod_id=PERP30

will it work the same?

I have great luck using the Perry V 30 pump on my OS 46, OS 50, OS 91 FX and OS 160 FX. You can move the tank back as far as you want. Have had no problems even in the cold. I use Morgan fuel "MV Type" 15% nitro.

I also have the VP30 on my 120 AX works great love the throttle response[sm=thumbs_up.gif]

I agree with piroflip2 about the YS110 jackhammer. I am a convert back to 2-strokes, at least for light 3d airframes.

My 120ax runs good with a conventional Perry setup, terrible with the perry "bypass" arrangement so often discussed.

I have been working with commercial pumping systems for 25 years now and the bypass makes no sense to me. If anyone says their bypassed pump works great, then I'll bet it runs just as good with no pump at all. With the bypass, mine is very pitch sensitive. Without the bypass its perfect. The only way it runs good though is to really back out the pump pressure screw. Mine is screwed in only 3 or 4 tuns from the "oops I lost the spring" position.

My only complaint is the fuel metering curve is off a tad. It's too lean through midrange, which is indicated by the detonation "rattle" everyone hears. If you simply open up the idle needle during this midrange knock, it goes away completely and smooths out. However, this makes it too rich at idle.

The only (60 year old) hot rod trick that I know of to fix this is to open a small hole (or in our case a small notch) in the throttle barrel so that the throttle barrel must be rotated further closed than before to get the same idle speed. This lets the idle needle seat even deeper and leans the flow, but does not affect other throttle positions appreciably. As the throttle opens, the little notch becomes a smaller percentage of effect on airflow, and does not greatly affect midrange or full throttle mixtures. This is how you can reshape the fuel curve for richer midrange with lean idle. Interestingly, YS did this very process on the latest 110 throttle.