I have been running my AMT Mercury on a test stand and have been using my retract air pump to prime the fuel pump through the vent line. I just put pressure on the tank and watch all the air bubbles head toward the turbine and shut off the valve before fuel starts entering the engine. This works fine but now that i have the engine mounted it is hard to see the fuel line going into the enigine, also the closest spot for the shut off valve is about 14 inches from the engine. Just wondering how you guys take care of the air bubbles in the lines without filling the engine with fuel. Everytime I try to start it without priming I get a "rpm low error". I am trying to aviod a BIG flame out the back due to a wet start.

Thanks for your ideas
Bill

Bill,
I can't speak for the AMT but on my original RAM 750F I power up the RX and move the throttle stick to full on the TX and turn it on. Then the red button on the start box will activate the pump for a second for each push. I use this for the first start of the day on my Roo and it works great.

I wonder if the AMT has a feature like this?

Sorry I can't help further,

Randy

Not sure why you have to prime every run. I don`t run AMT but a friend does and I do not recall seeing him prime the pump ever. I am running Jetcat and never prime the pump, except on a new installation. Maybe its the way you fuel and de-fuel, there should be enough kero in the lines for the next startup?? A few air bubbles for sure but they clear out during the spool up and do not create any problems.

Vin...

Bill,

You shouldn't have any air in the lines at all after the first initial set up..How are you fueling the airplane?? If you are breaking the fuel line between the hopper or final tank & the pump you will indeed get air in the system. You need to put a third line into the hopper for fueling only & use a festo shut off valve on it. That way when you fuel the plane, no air gets in you system. works great.. I had mine set up the other way for a while, always had problems that you are describing, it would be wet from over prime or time out on the start cause the kerosene would not ramp quick enough because of air in the lines. Hope this helps!!


Regards,

Dan M.

bonanza driver,

hey bro', you don't need to prime the pump prior to light off. Vincent was correct, you may have a few bubbles at initial start up but the Merk will power through them with ease.

Reference Danno's message regarding fueling the system. this may be where you're injecting air into the system. although, I flew for a year w/o a UAT in a 145oz fuel system and never had a problem. I merely placed the clear festo filter included with the engine just prior to the pump and filled my tanks there. I had a few insignificant bubbles at startup but that was it. The key obviously is to have an air tight fuel system. Just watch the fuel transferring from the tank through the UAT to the pump or whatever system you are using. you will find the tank injecting air into your system. remember, no sharp turns from tank nipples to connecting lines.

If you are continuing to get the low rpm error then the problem may be with the engine mounting system. Couple places to check: 1. air in system ( fix this first ) 2. you may have a crimped o-ring in the fuel inlet nipple on the engine ( not likely if you didn't have any trouble on the bench ) 3. check the engine mounting straps.

#3 was giving me the low rpm error when I ran my first Merk. It was mounted on a kangaroo with a pair of hose clamps. what I discovered was the hose clamp deformed the outer casing just enough to create a gap between the face of the engine and the outer casing. ( result, you guessed it low rpm error ) I was able to correct this problem by placing a small sheet of high temp gasket material between the clamp and the engine casing.

just a guess, but if you're using a bypass set up, problem #3 is not your likely culprit but worth checking.

the manual states your not getting a minimum of 26,000 rpm so just ensure you have a good air source. the best situation is to keep the air lines from the scuba bottle to the engine a short distance without compromising safety. You may be losing some air pressure to spin the compressor if the lines are excessive. Have your regulator set to 150psi and ensure none of your lines are kinked. You never know.

feel free to e-mail with any other questions or problems. I'd be happy to help.

good luck

buck

Dan I read into that also but did not want to say anything. If the system is truly sealed there should be no air in it. Hmmmmmm. If I was him I think I would start looking for that pin hole, split tube, or loose fitting. And I really don't see any reason not to replace all the fuel tubing at least once a year and the fuel tank pickup line twice. Bkf

Thanks for all the advice guys. On the test stand I was breaking the fuel line between the tank and the pump. Once I get it in the plane I will be using a third line in the hopper to fill. I hope this will solve my problems. So even after it sits on the selve for a couple weeks it still should not need prime??

Thanks agian,
Bill

a good thing to get is a bvm air trap...

Bill,

Just fired up my Pegusus last sunday for the first time since mid november... fired right off, no bubbles either.. Sound like you are on the right track!!!

Good luck!!!

Dan M.

Bill,

I've got Danno beat by 2 months. I put my Pegasus away for a long summer nap last year but when I wanted to fly, she started up as if it had been flown the day prior.

The JPO website has a how-to article on making a homemade UAT. I built one according to their instructions and it works great. Ofcourse, BVs is also an excellent choice. The beauty of making your own UAT is the ability to increase the size of the hopper tank.

have fun,

buck

thanks agian guys, It is great getting advice and ideas from people who have done this before. YOu brought up another question though. What should I do if i am not going to be flying it for awhile?? Lube it oil it or store it in any speacial way??
Thanks for all you help
Bill

Bill,

there is a section in the manual that has the specifics behind storing it for a long time. I think it's 5cc of straight turbine oil, spin it by hand, hold vertically to let the oil drain, replace inlet and outlet covers and store.

good luck,

buck

Buck
You would know better than me, but when I went to our buddy Joe G.'s house for my ground school on the Merc. I remember him priming the fuel pump for it's initial run. I mean the system was freshly assembled and completly dry.
Scott

Scott,

I suppose priming the fuel pump helps the gears on a new pump but can lead to trouble if the fuel is allowed to get to the engine. I've never pre-primed the fuel pump on any of my engines.

Haven't had any trouble yet ( knock on wood ). I don't recall any mention of this technique in the engine manual but Joe has been running AMTs a little bit longer than I have. He would have a better experience base to draw from.

the key feature is not allowing any fuel to get to the engine.

c'ya

Buck