Kirilian

My Feedback: (4)

I have been having trouble tuning my new OS 1.20AX. It is installed in a Seagull PC-9 1.20 where it is inverted and the carb is about 1" or so below the tank centerline, using a JTec wrap-around Pitts, #8 plug, 10% fuel, and a MA 15x7 3-blade prop (I have tried a 2-blade with the same problems). The tanks is pretty much impossible to move without major modification...I really want to use the wrap-around pitts...and I really want to keep the motor inverted. Others fly this model/engine/muffler with no trouble.

Here is what all I have tried...

1.) Iron Bay regulator located ~1.5" from carb inlet using crankcase pressure
No fuel dripping from carb with engine off (very nice). Cranks up pretty good and idles pretty good. Good tank pressure as I can see the tanks walls bulging slightly. If I remove the fill line, the tank pressure relieves. I am able to get the low-end mixture set so when I pinch the line it revs up only slightly then begins to quit. This is with needle valve at about 4 turns out.

When throttled slowly up to WOT, the engine doesn't really hesitate and revs well. It will only run for about a second upon reaching WOT before immediately dying. If I stay just off WOT, it will stay at high RPM, but all the way to WOT it quits. Any slight pinch of the line causes it to quit immediately (even if I release the line). Tried backing the needle valve nearly all the way out with no improvement. Screwing needle valve in (~2 turns from all the way in), it won't rev and dies immediately when trying. When throttling back to idle from near WOT, the engine takes a while to slow down.

2.) Perry VP-30 pump
Very very rich. Fuel pours out of carb when engine off, fuel sprays out of exhaust when running. Won't rev. Engine floods easily and has to be drained after every couple of starts.

3.) Only muffler pressure into the tank (no pump or regulator)
Fuel continuously drips from the carb with engine off. At WOT, I could not get the mixture rich enough. It idled pretty good and had good acceleration, but too lean at WOT and begins to quit like in #1, but not as bad. In this config, it flew for about 30 seconds before quitting at 1/2 throttle. Too little tank pressure?

4.) Muffler pressure with check valve in pressure line (no pump or regulator)
This caused excessive fuel pressure at the carb inlet. Engine runs for a few seconds and then quits (floods). Fuel then 'flows' out of the carb until pressure is relieved from the tank. This is what I would expect to happen.

5.) Crankcase pressure with check valve in pressure line (no pump or regulator)
Same as #2 results but much worse.

In all combinations, the engine 'bangs' and vibrates violently at idle...so bad that it vibrates screws out of the wood (servo screws, canopy screws, etc) and the whole airplane sounds like a drum. I have taken apart the carb and cleaned and inspected everything. Has anyone else ever had these symptoms?

Thanks!

jaka

Hi!
It's an easy fix!
First you have to fix the tank position! Remember the tank mounting rule?! Thats the most important thing to do if you want to have the engine run well.

Second: Get rid of the pump and regulator! It's not necessary if you fix the tank position.

Third: Set the tank up with Uni-Flow! That means using two clunks, one to silencer pressure, one to carb! This gives a more even fuel distribution.

Forth: Use fuel containing 5-15% nitro. 5% is all it takes to have a dead reliable engine!

Fifth: Use a OS 8 or Enya 3 glow plug.

Sixth: Bench run the engine with the J-tec silencer so you are sure that it functions as well as the OS silencer!

Kirilian

My Feedback: (4)

Thanks Jan. Unfortunately, the only fix for the fuel tank location is to put it in the tail. There is no where else to move it. I would imagine if I did that, I would be needing a pump to get enough fuel pressure back to the engine.

jaka

Hi!
The tail! Why? Is the forward landing gear interfering?

I would mount the engine sideways, that way the tank would be placed better compared to the tank centerline!