Sucking Air = Air Leak? How to find? (Full Version)

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Zephirus79 -> Sucking Air = Air Leak? How to find? (12/11/2006 8:24:10 PM)

My engine isn't running right. It dies and it wont adjust right. We noticed that it wont stop even when the carb is closed all the way. it runs very VERY slowly (in fact I can stop it by touching the spinner with 1 finger). But he said that was an air leak. I took the carb off and reseated it along with the muffler. Now the engine shuts off normally. But its still not running quite right and the guy at the field says is "sucking air" now I didn't want to look like an idiot and ask him what that meant. But if it means i still have an air leak, how do I find it? There has to be some way to find a leak...

Oh its a Tower Hobbies .46. Despite what you have heard, its a good engine. Starts and runs good. I just think I have an air leak or something out of adjustment. It ran fine and then I crashed it. Havne't been able to get it just perfect since. No cracks or anything like that and the engine runs, but its just having little quirks...




w8ye -> RE: Sucking Air = Air Leak? How to find? (12/11/2006 9:37:59 PM)

It's better for it to not stop when you want it to than to stop when you don't want it to?

Tower's seem to have air leak problems.

    Area's for air leaks
  • Carb to engine
  • Carb barrel to carb
  • Front bearing area seal
  • Back plate to crankcase



Flyboy Dave -> RE: Sucking Air = Air Leak? How to find? (12/12/2006 6:58:51 AM)

If you really want to pressure check the engine....take an old glow plug, and drill it out
from the bottom with about a 3/16" drill....drill the top of the plug right off.

J-B Weld....or epoxy a length of tubing into the hole in the glow plug. Fit the glow plug
to the engine by hand, with a gasket. Now....submerge the engine into a coffee can, with
about 2 or 3 cups of kerosine....and blow into the tubing/glow plug.

Watch for the air leaks....don't worry if the glow plug is leaking at the gasket. The most likely
leaks will be at the carb base, and the front bearing. The others areas to look for are the
head gasket, and the back plate.

If the leak is at the front bearing, you can use a bearing with a rubber seal on the front of
the bearing. [;)]

FBD. [:D]




BillS -> RE: Sucking Air = Air Leak? How to find? (12/12/2006 10:51:32 AM)

Spraying WD 40 on the suspected leak with the engine running will often identify the problem.

Bill



Checklst -> RE: Sucking Air = Air Leak? How to find? (12/13/2006 1:26:59 AM)

Agree with Bill, I use(car)starter spray on auto carbs or manifolds to find leaks. Its ether based so it should rev up when you hit the leak, my brain tells me wd 40 would plug the leak and kill the engine,or it's possible wd40 could burn and speed up also?????????????????some sprays use propane as the propellant, either way you find the leak.......Just use the long spray tube to keep fingers clear of the prop.........Please.[8D]



BillS -> RE: Sucking Air = Air Leak? How to find? (12/13/2006 3:11:00 AM)

The propellant in WD 40 will burn.

Bill



w8ye -> RE: Sucking Air = Air Leak? How to find? (12/13/2006 3:48:05 AM)

A fellow brought a McCulloch 28 weed whacker to work that the carb was broken off. We ran it on WD 40. As long as the can held out that is. Just spray it into the cylinder where the carb used to be.

He gave the engine to me and I made a 32 out of it with another cylinder from one with a bad crankcase. Runs good as a model airplane engine. 18-8 at 7600



Newc -> RE: Sucking Air = Air Leak? How to find? (12/13/2006 1:33:53 PM)

A way to check for leaks is to use a length of fuel tubing in the same way that we used to balance dual SU carburetors on race cars. Put one end next to your ear and the other at various points around the suspected leak. With the engine running you will hear air rushing past the fuel tubing where the leak is. For the carburetor balancing we used the old airtube headsets from airplanes and knew we had them balanced when the sounds from the carburetor intake at idle in both ears were the same.

Best to do this from behind the engine!! [:)]



Sport_Pilot -> RE: Sucking Air = Air Leak? How to find? (12/13/2006 1:46:47 PM)

Just tighten the backplate and be done with it. Most engines will run fine when the air leak prevents the engine from stopping when the throttle is closed. They just don't stop. If your engine will now quit when the throttle is closed then any other leaks are likely too minor to bother with. Most likely you need to tune the engine, possibly change plugs, etc.



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