Thumper1

We had our two day yearly fun fly contest this weekend. After the first day, I was solidly in second place. On day two, I had the engine quit on thorttling up in the air two times, putting me solidly in last place. I have been using the same combination for about four years, this has never happened. After the first time, I changed plugs and checked the idle mixture. I couldn't get it to fail on the ground, but it insists on dying in the air. Before I tear into the carb, does anyone have any words of wisdom. There are no air leaks, (first thing I checked for). The plane is a Smith Super Special with a mousse can equiped Webra 32. (well used). 15% Powermaster fuel, 10X4 rev up prop. 2oz Hays fuel tank. Hopefully, it's just dirt in the carb, but like I said, I have never had this happen before.
Thanks
Bill

Sometimes you get to be the windshield, sometimes you have to be the bug. Yesterday, I was the bug.

miderror

In my case it turned out to be a pin hole in the pick up inside
the fuel tank. Wouldn't show with the plane held nose high
but kept showing up on pull ups to vert. Guess it was the G's
on the tank pulling down on the line. Anyway changed the line,
after trying plugs, needle settings,fuel,head shims,etc.
Problem solved.
Maybe you have the same problem?

Thumper1

I changed the line from the tank to the carb, I'll check the lines inside the tank.
Thanks
Bill

Kevins_RC

My Feedback: (1)

I have had the same issues with Webra 50's. I didn't think that it was an air leak at first, especially after I changed all of the lines, resealed the back plate, checked the O-ring at the base of the carb, etc. I found once that it was the O-ring on my low speed needle by removing the carb, sealing it off, and pressurizing the carb (by mouth). Another time I found that the air was leaking between the piston sleeve and the casing (I have yet to fix this one. I now have 2 Webra 50s doing this)

Thumper1

Kevin
That sure would explain a lot. How did you determine that it was leaking between the liner and the case? I seal the carb base with a very thin bead of Silicone, that may be useful on the liner??
Thanks
Bill

Kevins_RC

My Feedback: (1)

Believe me, it wasn't easy. I got desperate, and pulled the sleeve. The evidence was on the outside of the liner. I am going to try some hign temperature RTV between the liner and the casing to see if that won't work. I refuse to give up on the Webra, so much power to weight ratio I tried everything else and the engine was still loosing pressure when presurrized. That is when I decided to tear it down completely.

Thumper1

I have three .32's One of them is a real dog. Sent it back to Horizon, they returned it "No problem found" but it won't stay running for any length of time and it is really down on power. I am going to make a plug to pressureize it and check for air leaks around the cylinder. Let you know what I find out
Later
Bill

miderror

We have used locktite on the cyl/case fit in the past with good
results. I think it was the green type. Its thin and seals quite
well and handles the heat.
Makes removing a bit of fun. Heat in oven @250 to remove.
I was't to sure about it but it made a unrealiable eng
into a good runner with about an extra 500rpm.

Just a thought

Thumper1

I am going to make a block off plate for the exhast port, then a cap that will slip over the carb intake with a nipple on it. (I have a lathe). Next, I will plug the fuel inlet line and hook up an air source to the engine and pressureize it and look for air leaks. (could probably get away with putting it in water to check for bubbles. It sure wouldn't take much in the way of an air leak to make the engine run like doggy do-do.

Kevins_RC

My Feedback: (1)

All I did was cap off the exhaust port with my thumb, finger to cover the fuel nipple, and blow into the carb. Then you listen for an airleak. If air is leaking around or through the carb, you'll hear it and / or feel it real quick. I had to remove the back plate and seal it off with the palm of my hand to verify that air was leaking between the cylinder sleeve and casing. Once the sleeve is removed, it was verified without a doubt.