Last week I posted some problems about my evolution 40. It seems to have an air leak somewhere and I was going over everything and found NO LEAKS anywhere. All lines are new. All bolts are tight. Tried an old and a new glow plug. RTV'd the carb and back plate. I tore the engine down and checked the bearings. They seemed ok as they were smooth feeling and didn't have any noticeable play. Well tonight I got the engine back together....after RTVing everything and fired her up, hoping that the air leak had been cured. NOPE still acting up!!!!!!!!

I pulled the fuel line that runs between the carb and the needle valve off, and placed my fingers over the venturi and the fuel inlet. Then I gently rocked the piston in and out of compression and heard a sucking sound. Listening carefully I decided that it was coming from the bottom of the carb....or behind the prop. I went and got some soapy water and discovered bubbles were coming out from behind the prop. I HOPE I JUST DISCOVERED MY PROBLEM AND CAN REMEDY THIS!

So engine gurus, Do you think this is my problem? Or is it acceptable to have a little air come out of there? Will a new bearing cure this?

Or are there any other solutions you might have besides the obvious leaky fuel lines or loose bolts?

This engine has gotten on my last nerve and I really only want to have to take this turd apart one more time.

Thanks for all the help!! You guys are awesome.

dumb question...but are you sure you are connecting the lines properly? not interchanging the clunk and pressure line? or that the tank is properly assembled?

That was one of the first things I checked when I started this whole thing. And that's not a dumb question, I've seen people do that before and ended up with similar problems to mine.

Problems are from carb.Mostly o rings.

Some blow by on the front bearing is to be expected. That isn't your problem.

Don

A few things:

Make sure the carb is tightly down. Look at the carb o ring.

Pull the hs needle out and look at it with a magnifying glass. I had to replace mine a few months ago.

Did you disassemble the carb when you removed it?

What are the running symptoms of the leak? I'm no expert but have dealt with leaks causing two different problems- one, lower compression and two, fuel draw or idling problem. And like your engine, I've heard the leak but had to couple it with the running symptom to find the root problem. Lately, I'm amazed at how badly the seals are on the needle valves of these chinese engines. Brand new out of the box and I've got to put fuel line or different orings on the needle valves to get them to run and idle right.

I agree.

I had an os45fsr that was driving Me crazy, doing the same thing, I also had sealed the carb, back plate, new fuel lines, tank and checked the "o" ring on the high speed needle, it ended up being the "o" ring on the slow speed needle ( which isn't really a needle ) but replacing that "o" ring solved the problem.
Just pointing out an other place to check.
Hope this helps.
Here is the link to Your original post
Jeff

Thanks guys! I have the new o rings coming in tomorrow. I'll put them in and see how it goes. The funny thing is that this will just about be the last to be sealed or replaced. When I started I initially replaced the highspeed needle and needle valve. Hopefully the low speed needle o-rings take care of business!

DING DING DING!!!!!! WE HAVE A WINNER!!!!
Low speed needle valve O-Rings. All of those problems due to two tiny little flipping rings. Next time I will check those first!!!!! Thanks to everyone for your help. Now I can't wait for the weather to settle down so I can go knock the dust off this Tribute 36.
THANKS AGAIN!!!!

Glad you found the problem.