GMS .47 Running Problem?
 

Hello,

Ok this might of been covered many times but I thought I would run this past the experts. I installed a GMS .47 into a Sportster type airplane and am having a bit of a problem getting it to run right, I'm pretty new to this hobby so please don't flame me. The engine starts up great, Idles perfectly but when I go to throttle it, it dies, OK so this is lean so in order for it to run at wide open throttle I have to let the needle out like 6-7 turns, I don't think this is right but after I do that it runs great till I tip the nose up to the air and it wants to die again. Please help me out, that last thing I need is this heavy plane to dead stick on me when I'm just trying to learn how to fly a tail dragger. I have included a pic of it for reference.

Ski..

RE: GMS .47 Running Problem?
 

Ski...

If you have to open the HS needle that far...something is funky....yes?

Is your pressure line from the muffler to the tank attached?

Are the fuel/pressure lines free-flowing? (no kinks, sharp bends,etc)

Has the carb been flushed to rule out a blockage of some sort?

The pictures of the plane are great, but not terribly helpful in determining where
your problem is.

You're right...something is "lean". The idea now is to find out why.

Attend to the basics. Fuel tank level with carb....fuel lines as short as possible and
absolutely leak free, etc.

Do some more detective work, and get back to us all.

'Race

RE: GMS .47 Running Problem?
 

I might be able to help on this one. I too have a GMS 47, just bought two more of them. I had the same problem with mine until I figured out that it ain't lean. The low end is too rich. I wound up with the HI needle out about 1 1/2 turns and the LO needle open only about 1/2 turn. If your LO needle is any further out than that, SCREW IT IN. I still have a slight hesitation in mine but not too bad. I think I'll be able to correct it tomorrow.
Oh, and BTW, do the smart thing and seal the carb to engine with blue silicone, the back plate to engine likewise, and the muffler likewise. I have also heard about sealing the front bearing but haven't done it yet.
One other thing, this engine is a fuel hog, it puts out like crazy but it likes the 15% fuel. Use as large of a tank as you can get in the plane..

Holler at me if any of this helps.

RE: GMS .47 Running Problem?
 

The other tips you received from 'jimross' and 'race' are good ones.

I noticed the muffler you're using is the "Pitts" type, with twin outlet pipes. These mufflers don't supply the amount of tank pressure the stock muffler does, and may cause a lean condition.

If all else fails, try blocking one of the muffler outlet pipes, or temporarily mount the stock muffler to increase the tank pressure.

Ski

RE: GMS .47 Running Problem?
 

3d_ski,

I was having the same problem(just yesterday!!! [&:]).... Look further down this forum. The advice I received about muffler pressure ended up being my problem.

After I went thru the entire fuel system I discovered a pin hole in the fuel line from clunk to the brass fitting in the rubber stopper of the fuel tank.

replaced this peice of fuel line, and now she screams at wide open throttle..... :D

RE: GMS .47 Running Problem?
 

WOW,

This is the best help I have ever had on this forum, thanks alot guys I noticed that my makeshift gasket for the pitts slid out, I'm sure this is not helping anything but I'm going to take all your suggestions and tear it apart again. I have a P40 ready to go and there is no way I'm taking that out before I get tail dragger time. I hope to be posting vids of the maiden flight of this thing. This plane was designed to take a .35 I think so this should be a demon. When I did have it running good for a little while and held it verticle I let it go for a second and it wanted to take off like a rocket!!! Thanks again for your help guys..... Hope I don't have to go to Iraq anytime soon.

Here is another pic of some fuel routing....
Ski....

RE: GMS .47 Running Problem?
 

Oh Ya,

I thought about the pitts being the problem. The two outlets are huge compared to the stock muffler but OMG have you seen the size of the muffler that comes with the GMS .47. It's ouragously huge.

Ski....